TAMBOCOR ^TM (flecainide acetate) is an antiarrhythmic drug available in tablets of 50, 100 or 150 mg for oral administration.

Flecainide acetate is benzamide, N-(2-piperidinylmethyl) -2,5-bis(2,2,2- trifluoroethoxy)-monoacetate.  The structural formula is given below.

Flecainide acetate is a white crystalline substance with a pK _a of 9.3. It has an aqueous solubility of 48.4 mg/mL at 37°C.

TAMBOCOR tablets also contain: croscarmellose sodium, hydrogenated vegetable oil, magnesium stearate, microcrystalline cellulose and starch.

In patients without structural heart disease, TAMBOCOR is indicated for the prevention of

• paroxysmal supraventricular tachycardias (PSVT), including atrioventricular nodal reentrant tachycardia, atrioventricular reentrant tachycardia and other supraventricular tachycardias of unspecified mechanism associated with disabling symptoms
• paroxysmal atrial fibrillation/flutter (PAF) associated with disabling symptoms
  TAMBOCOR is also indicated for the prevention of
• documented ventricular arrhythmias, such as sustained ventricular tachycardia ( sustained VT), that in the judgment of the physician are life-threatening.

Use of TAMBOCOR for the treatment of sustained VT, like other antiarrhythmics, should be initiated in the hospital. The use of TAMBOCOR is not recommended in patients with less severe ventricular arrhythmias even if the patients are symptomatic.

Because of the proarrhythmic effects of TAMBOCOR, its use should be reserved for patients in whom, in the opinion of the physician, the benefits of treatment outweigh the risks.

TAMBOCOR should not be used in patients with recent myocardial infarction. (See Boxed Warnings .)

Use of TAMBOCOR in chronic atrial fibrillation has not been adequately studied and is not recommended. (See Boxed Warnings .)

As is the case for other antiarrhythmic agents, there is no evidence from controlled trials that the use of TAMBOCOR favorably affects survival or the incidence of sudden death.

For patients with sustained VT, no matter what their cardiac status, TAMBOCOR, like other antiarrhythmics, should be initiated in-hospital with rhythm monitoring.

Flecainide has a long half-life (12 to 27 hours in patients). Steady-state plasma levels, in patients with normal renal and hepatic function, may not be achieved until the patient has received 3 to 5 days of therapy at a given dose. Therefore, increases in dosage should be made no more frequently than once every four days, since during the first 2 to 3 days of therapy the optimal effect of a given dose may not be achieved.

For patients with PSVT and patients with PAF the recommended starting dose is 50 mg every 12 hours. TAMBOCOR doses may be increased in increments of 50 mg bid every four days until efficacy is achieved. For PAF patients, a substantial increase in efficacy without a substantial increase in discontinuations for adverse experiences may be achieved by increasing the TAMBOCOR dose from 50 mg to 100 mg bid. The maximum recommended dose for patients with paroxysmal supraventricular arrhythmias is 300 mg/day.

For sustained VT the recommended starting dose is 100 mg every 12 hours. This dose may be increased in increments of 50 mg bid every four days until efficacy is achieved. Most patients with sustained VT do not require more than 150 mg every 12 hours (300 mg/day), and the maximum dose recommended is 400 mg/day.

In patients with sustained VT, use of higher initial doses and more rapid dosage adjustments have resulted in an increased incidence of proarrhythmic events and CHF, particularly during the first few days of dosing (see WARNINGS ). Therefore, a loading dose is not recommended.

Intravenous lidocaine has been used occasionally with TAMBOCOR while awaiting the therapeutic effect of TAMBOCOR. No adverse drug interactions were apparent. However, no formal studies have been performed to demonstrate the usefulness of this regimen.

An occasional patient not adequately controlled by (or intolerant to) a dose given at 12-hour intervals may be dosed at eight-hour intervals.

Once adequate control of the arrhythmia has been achieved, it may be possible in some patients to reduce the dose as necessary to minimize side effects or effects on conduction. In such patients, efficacy at the lower dose should be evaluated.

TAMBOCOR should be used cautiously in patients with a history of CHF or myocardial dysfunction (see WARNINGS ).

Any use of TAMBOCOR in children should be directly supervised by a cardiologist skilled in the treatment of arrhythmias in children. Because of the evolving nature of information in this area, specialized literature should be consulted. Under six months of age, the initial starting dose of TAMBOCOR in children is approximately 50 mg/M ² body surface area daily, divided into two or three equally spaced doses. Over six months of age, the initial starting dose may be increased to 100 mg/M ² per day. The maximum recommended dose is 200 mg/M ² per day. This dose should not be exceeded. In some children on higher doses, despite previously low plasma levels, the level has increased rapidly to far above therapeutic values while taking the same dose. Small changes in dose may also lead to disproportionate increases in plasma levels. Plasma trough (less than one hour pre-dose) flecainide levels and electrocardiograms should be obtained at presumed steady state (after at least five doses) either after initiation or change in TAMBOCOR dose, whether the dose was increased for lack of effectiveness, or increased growth of the patient. For the first year on therapy, whenever the patient is seen for reasons of clinical follow-up, it is suggested that a 12-lead electrocardiogram and plasma trough flecainide level are obtained. The usual therapeutic level of flecainide in children is 200-500 ng/mL. In some cases, levels as high as 800 ng/mL may be required for control.

In patients with severe renal impairment (creatinine clearance of 35 mL/min/1.73 square meters or less), the initial dosage should be 100 mg once daily (or 50 mg bid); when used in such patients, frequent plasma level monitoring is required to guide dosage adjustments (see Plasma Level Monitoring). In patients with less severe renal disease, the initial dosage should be 100 mg every 12 hours; plasma level monitoring may also be useful in these patients during dosage adjustment. In both groups of patients, dosage increases should be made very cautiously when plasma levels have plateaued (after more than four days), observing the patient closely for signs of adverse cardiac effects or other toxicity. It should be borne in mind that in these patients it may take longer than four days before a new steady-state plasma level is reached following a dosage change.

Based on theoretical considerations, rather than experimental data, the following suggestion is made: when transferring patients from another antiarrhythmic drug to TAMBOCOR allow at least two to four plasma half-lives to elapse for the drug being discontinued before starting TAMBOCOR at the usual dosage. In patients where withdrawal of a previous antiarrhythmic agent is likely to produce life-threatening arrhythmias, the physician should consider hospitalizing the patient.

When flecainide is given in the presence of amiodarone, reduce the usual flecainide dose by 50% and monitor the patient closely for adverse effects. Plasma level monitoring is strongly recommended to guide dosage with such combination therapy (see below).

Plasma Level Monitoring.   The large majority of patients successfully treated with TAMBOCOR were found to have trough plasma levels between 0.2 and 1.0 µg/mL. The probability of adverse experiences, especially cardiac, may increase with higher trough plasma levels, especially when these exceed 1.0 µg/mL. Periodic monitoring of trough plasma levels may be useful in patient management. Plasma level monitoring is required in patients with severe renal failure or severe hepatic disease, since elimination of flecainide from plasma may be markedly slower. Monitoring of plasma levels is strongly recommended in patients on concurrent amiodarone therapy and may also be helpful in patients with CHF and in patients with moderate renal disease.

All tablets are embossed with 3M on one side and TR 50, TR 100 or TR 150 on the other side.

Tambocor, 50 mg per white, round tablet, is available in

Bottles of 100 NDC #0089-0305-10.

Boxes of 100 in unit dose blister strips NDC #0089-0305-16.

Tambocor, 100 mg per white, round, scored tablet, is available in

Bottles of 100 NDC #0089-0307-10.

Boxes of 100 in unit dose blister strips NDC #0089-0307-16.

Tambocor, 150 mg per white, oval, scored tablet, is available in

Bottles of 100 NDC #0089-0314-10.

Store at controlled room temperature 15°-30°C (59°-86°F) in a tight, light-resistant container.

Rx only

Jun 1998

Manufactured by

3M Pharmaceuticals

Northridge, CA 91324

In post-myocardial infarction patients with asymptomatic PVCs and non-sustained ventricular tachycardia, TAMBOCOR therapy was found to be associated with a 5.1% rate of death and non-fatal cardiac arrest, compared with a 2.3% rate in a matched placebo group. (See WARNINGS .)

Adverse effects reported for TAMBOCOR, described in detail in the Warnings section, were new or worsened arrhythmias which occurred in 1% of 108 patients with PSVT and in 7% of 117 patients with PAF; and new or exacerbated ventricular arrhythmias which occurred in 7% of 1330 patients with PVCs, non-sustained or sustained VT. In patients treated with flecainide for sustained VT, 80% (51/64) of proarrhythmic events occurred within 14 days of the onset of therapy. 198 patients with sustained VT experienced a 13% incidence of new or exacerbated ventricular arrhythmias when dosage was initiated at 200 mg/day with slow upward titration, and did not exceed 300 mg/day in most patients. In some patients, TAMBOCOR treatment has been associated with episodes of unresuscitatable VT or ventricular fibrillation (cardiac arrest). (See WARNINGS .) New or worsened CHF occurred in 6.3% of 1046 patients with PVCs, non-sustained or sustained VT. Of 297 patients with sustained VT, 9.1% experienced new or worsened CHF. New or worsened CHF was reported in 0.4% of 225 patients with supraventricular arrhythmias. There have also been instances of second- (0.5%) or third-degree (0.4%) AV block. Patients have developed sinus bradycardia, sinus pause, or sinus arrest, about 1.2% altogether (see WARNINGS ). The frequency of most of these serious adverse events probably increases with higher trough plasma levels, especially when these trough levels exceed 1.0 µg/mL.

There have been rare reports of isolated elevations of serum alkaline phosphatase and isolated elevations of serum transaminase levels. These elevations have been asymptomatic and no cause and effect relationship with TAMBOCOR has been established. In foreign postmarketing surveillance studies, there have been rare reports of hepatic dysfunction including reports of cholestasis and hepatic failure, and extremely rare reports of blood dyscrasias. Although no cause and effect relationship has been established, it is advisable to discontinue TAMBOCOR in patients who develop unexplained jaundice or signs of hepatic dysfunction or blood dyscrasias in order to eliminate TAMBOCOR as the possible causative agent.

Incidence figures for other adverse effects in patients with ventricular arrhythmias are based on a multicenter efficacy study, utilizing starting doses of 200 mg/day with gradual upward titration to 400 mg/day. Patients were treated for an average of 4.7 months, with some receiving up to 22 months of therapy. In this trial, 5.4% of patients discontinued due to non-cardiac adverse effects.

The following additional adverse experiences, possibly related to TAMBOCOR therapy and occurring in 1% to less than 3% of patients, have been reported in acute and chronic studies: Body as a Whole  malaise, fever; Cardiovascular tachycardia, sinus pause or arrest; Gastrointestinal  vomiting, diarrhea, dyspepsia, anorexia; Skin  rash; Visual diplopia; Nervous System  hypoesthesia, paresthesia, paresis, ataxia, flushing, increased sweating, vertigo, syncope, somnolence, tinnitus; Psychiatric  anxiety, insomnia, depression.

The following additional adverse experiences, possibly related to TAMBOCOR, have been reported in less than 1% of patients: Body as a Whole  swollen lips, tongue and mouth; arthralgia, bronchospasm, myalgia; Cardiovascular  angina pectoris, second-degree and third-degree AV block, bradycardia, hypertension, hypotension; Gastrointestinal  flatulence; Urinary System  polyuria, urinary retention; Hematologic  leukopenia, granulocytopenia, thrombocytopenia; Skin  urticaria, exfoliative dermatitis, pruritus, alopecia; Visual  eye pain or irritation, photophobia, nystagmus; Nervous System  twitching, weakness, change in taste, dry mouth, convulsions, impotence, speech disorder, stupor, neuropathy; Respiratory  pneumonitis/pulmonary infiltration possibly due to chronic flecainide treatment: Psychiatric amnesia, confusion, decreased libido, depersonalization, euphoria, morbid dreams, apathy.

For patients with supraventricular arrhythmias, the most commonly reported noncardiac adverse experiences remain consistent with those known for patients treated with TAMBOCOR for ventricular arrhythmias. Dizziness is possibly more frequent in PAF patients.

Drug Interactions.   TAMBOCOR has been administered to patients receiving digitalis preparations or beta-adrenergic blocking agents without adverse effects. During administration of multiple oral doses of TAMBOCOR to healthy subjects stabilized on a maintenance dose of digoxin, a 13%-19% increase in plasma digoxin levels occurred at six hours postdose.

In a study involving healthy subjects receiving TAMBOCOR and propranolol concurrently, plasma flecainide levels were increased about 20% and propranolol levels were increased about 30% compared to control values. In this formal interaction study, TAMBOCOR and propranolol were each found to have negative inotropic effects; when the drugs were administered together, the effects were additive. The effects of concomitant administration of TAMBOCOR and propranolol on the PR interval were less than additive. In TAMBOCOR clinical trials, patients who were receiving beta blockers concurrently did not experience an increased incidence of side effects. Nevertheless, the possibility of additive negative inotropic effects of beta blockers and flecainide should be recognized.

Flecainide is not extensively bound to plasma proteins. In vitro studies with several drugs which may be administered concomitantly showed that the extent of flecainide binding to human plasma proteins is either unchanged or only slightly less. Consequently, interactions with other drugs which are highly protein bound (e.g., anticoagulants ) would not be expected. TAMBOCOR has been used in a large number of patients receiving diuretics without apparent interaction. Limited data in patients receiving known enzyme inducers ( phenytoin, phenobarbital, carbamazepine ) indicate only a 30% increase in the rate of flecainide elimination. In healthy subjects receiving cimetidine (1 gm daily) for one week, plasma flecainide levels increased by about 30% and half-life increased by about 10%.

When amiodarone is added to flecainide therapy, plasma flecainide levels may increase two-fold or more in some patients, if flecainide dosage is not reduced. (See Dosage and Administration.)

Drugs that inhibit cytochrome P450IID6, such as quinidine , might increase the plasma concentrations of flecainide in patients that are on chronic flecainide therapy; especially if these patients are extensive metabolizers.

There has been little experience with the coadministration of TAMBOCOR and either disopyramide or verapamil. Because both of these drugs have negative inotropic properties and the effects of coadministration with TAMBOCOR are unknown, neither disopyramide nor verapamil should be administered concurrently with TAMBOCOR unless, in the judgment of the physician, the benefits of this combination outweigh the risks. There has been too little experience with the coadministration of TAMBOCOR with nifedipine or diltiazem to recommend concomitant use.

PROARRHYTHMIC EFFECTS

TAMBOCOR, like other antiarrhythmic agents, can cause new or worsened supraventricular or ventricular arrhythmias. Ventricular proarrhythmic effects range from an increase in frequency of PVCs to the development of more severe ventricular tachycardia, e.g., tachycardia that is more sustained or more resistant to conversion to sinus rhythm, with potentially fatal consequences. In studies of ventricular arrhythmia patients treated with TAMBOCOR, three-fourths of proarrhythmic events were new or worsened ventricular tachyarrhythmias, the remainder being increased frequency of PVCs or new supraventricular arrhythmias. In patients treated with flecainide for sustained ventricular tachycardia, 80% (51/64) of proarrhythmic events occurred within 14 days of the onset of therapy. In studies of 225 patients with supraventricular arrhythmia (108 with paroxysmal supraventricular tachycardia and 117 with paroxysmal atrial fibrillation), there were 9 (4%) proarrhythmic events, 8 of them in patients with paroxysmal atrial fibrillation. Of the 9, 7 (including the one in a PSVT patient) were exacerbations of supraventricular arrhythmias (longer duration, more rapid rate, harder to reverse) while 2 were ventricular arrhythmias, including one fatal case of VT/VF and one wide complex VT (the patient showed inducible VT, however, after withdrawal of flecainide), both in patients with paroxysmal atrial fibrillation and known coronary artery disease.

It is uncertain if TAMBOCOR's risk of proarrhythmia is exaggerated in patients with chronic atrial fibrillation (CAF), high ventricular rate, and/or exercise. Wide complex tachycardia and ventricular fibrillation have been reported in two of 12 CAF patients undergoing maximal exercise tolerance testing.

In patients with complex ventricular arrhythmias, it is often difficult to distinguish a spontaneous variation in the patient's underlying rhythm disorder from drug-induced worsening, so that the following occurrence rates must be considered approximations. Their frequency appears to be related to dose and to the underlying cardiac disease.

Among patients treated for sustained VT (who frequently also had CHF, a low ejection fraction, a history of myocardial infarction and/or an episode of cardiac arrest), the incidence of proarrhythmic events was 13% when dosage was initiated at 200 mg/day with slow upward titration, and did not exceed 300 mg/day in most patients. In early studies in patients with sustained VT utilizing a higher initial dose (400 mg/day) the incidence of proarrhythmic events was 26%; moreover, in about 10% of the patients treated proarrhythmic events resulted in death, despite prompt medical attention. With lower initial doses, the incidence of proarrhythmic events resulting in death decreased to 0.5% of these patients. Accordingly, it is extremely important to follow the recommended dosage schedule. (See Dosage and Administration .)

The relatively high frequency of proarrhythmic events in patients with sustained VT and serious underlying heart disease, and the need for careful titration and monitoring, requires that therapy of patients with sustained VT be started in the hospital. (See Dosage and Administration .)

HEART FAILURE

TAMBOCOR has a negative inotropic effect and may cause or worsen CHF, particularly in patients with cardiomyopathy, preexisting severe heart failure (NYHA functional class III or IV) or low ejection fractions (less than 30%). In patients with supraventricular arrhythmias new or worsened CHF developed in 0.4% (1/225) of patients. In patients with sustained ventricular tachycardia during a mean duration of 7.9 months of TAMBOCOR therapy, 6.3% (20/317) developed new CHF. In patients with sustained ventricular tachycardia and a history of CHF, during a mean duration of 5.4 months of TAMBOCOR therapy, 25.7% (78/304) developed worsened CHF. Exacerbation of preexisting CHF occurred more commonly in studies which included patients with class III or IV failure than in studies which excluded such patients. TAMBOCOR should be used cautiously in patients who are known to have a history of CHF or myocardial dysfunction. The initial dosage in such patients should be no more than 100 mg bid (see Dosage and Administration ) and patients should be monitored carefully. Close attention must be given to maintenance of cardiac function, including optimization of digitalis, diuretic, or other therapy. In cases where CHF has developed or worsened during treatment with TAMBOCOR, the time of onset has ranged from a few hours to several months after starting therapy. Some patients who develop evidence of reduced myocardial function while on TAMBOCOR can continue on TAMBOCOR with adjustment of digitalis or diuretics, others may require dosage reduction or discontinuation of TAMBOCOR. When feasible, it is recommended that plasma flecainide levels be monitored. Attempts should be made to keep trough plasma levels below 0.7 to 1.0 µg/mL.

Effects on Cardiac Conduction .  TAMBOCOR slows cardiac conduction in most patients to produce dose-related increases in PR, QRS, and QT intervals.

PR interval increases on average about 25% (0.04 seconds) and as much as 118% in some patients. Approximately one-third of patients may develop new first-degree AV heart block (PR interval ≥ 0.20 seconds). The QRS complex increases on average about 25% (0.02 seconds) and as much as 150% in some patients. Many patients develop QRS complexes with a duration of 0.12 seconds or more. In one study, 4% of patients developed new bundle branch block while on TAMBOCOR. The degree of lengthening of PR and QRS intervals does not predict either efficacy or the development of cardiac adverse effects. In clinical trials, it was unusual for PR intervals to increase to 0.30 seconds or more, or for QRS intervals to increase to 0.18 seconds or more. Thus, caution should be used when such intervals occur, and dose reductions may be considered. The QT interval widens about 8%, but most of this widening (about 60% to 90%) is due to widening of the QRS duration. The JT interval (QT minus QRS) only widens about 4% on the average. Significant JT prolongation occurs in less than 2% of patients. There have been rare cases of Torsade de Pointes-type arrhythmia associated with TAMBOCOR therapy.

Clinically significant conduction changes have been observed at these rates: sinus node dysfunction such as sinus pause, sinus arrest and symptomatic bradycardia (1.2%), second-degree AV block (0.5%) and third-degree AV block (0.4%). An attempt should be made to manage the patient on the lowest effective dose in an effort to minimize these effects. (See Dosage and Administration .) If second- or third-degree AV block, or right bundle branch block associated with a left hemiblock occur, TAMBOCOR therapy should be discontinued unless a temporary or implanted ventricular pacemaker is in place to ensure an adequate ventricular rate.

Sick Sinus Syndrome (Bradycardia-Tachycardia Syndrome). TAMBOCOR should be used only with extreme caution in patients with sick sinus syndrome because it may cause sinus bradycardia, sinus pause, or sinus arrest.

Effects on Pacemaker Thresholds.   TAMBOCOR is known to increase endocardial pacing thresholds and may suppress ventricular escape rhythms. These effects are reversible if flecainide is discontinued. It should be used with caution in patients with permanent pacemakers or temporary pacing electrodes and should not be administered to patients with existing poor thresholds or nonprogrammable pacemakers unless suitable pacing rescue is available.

The pacing threshold in patients with pacemakers should be determined prior to instituting therapy with TAMBOCOR, again after one week of administration and at regular intervals thereafter. Generally threshold changes are within the range of multiprogrammable pacemakers and, when these occur, a doubling of either voltage or pulse width is usually sufficient to regain capture.

Electrolyte Disturbances.   Hypokalemia or hyperkalemia may alter the effects of Class I antiarrhythmic drugs. Preexisting hypokalemia or hyperkalemia should be corrected before administration of TAMBOCOR.

Pediatric Use.   The safety and efficacy of TAMBOCOR in the fetus, infant, or child have not been established in double-blind, randomized, placebo-controlled trials. The proarrhythmic effects of TAMBOCOR, as described previously, apply also to children. In pediatric patients with structural heart disease, TAMBOCOR has been associated with cardiac arrest and sudden death. TAMBOCOR should be started in the hospital with rhythm monitoring. Any use of TAMBOCOR in children should be directly supervised by a cardiologist skilled in the treatment of arrhythmias in children.

Carcinogenesis, Mutagenesis, Impairment of Fertility. Long-term studies with flecainide in rats and mice at doses up to 60 mg/kg/day have not revealed any compound-related carcinogenic effects. Mutagenicity studies (Ames test, mouse lymphoma and in vivo cytogenetics) did not reveal any mutagenic effects. A rat reproduction study at doses up to 50 mg/kg/day (seven times the usual human dose) did not reveal any adverse effect on male or female fertility.

Pregnancy. Pregnancy Category C.  Flecainide has been shown to have teratogenic effects (club paws, sternebrae and vertebrae abnormalities, pale hearts with contracted ventricular septum) and an embryotoxic effect (increased resorptions) in one breed of rabbit (New Zealand White) when given doses of 30 and 35 mg/kg/day, but not in another breed of rabbit (Dutch Belted) when given doses up to 30 mg/kg/day. No teratogenic effects were observed in rats and mice given doses up to 50 and 80 mg/kg/day, respectively; however, delayed sternebral and vertebral ossification was observed at the high dose in rats. Because there are no adequate and well-controlled studies in pregnant women, TAMBOCOR should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Labor and Delivery.   It is not known whether the use of TAMBOCOR during labor or delivery has immediate or delayed adverse effects on the mother or fetus, affects the duration of labor or delivery, or increases the possibility of forceps delivery or other obstetrical intervention.

Nursing Mothers.   Results from a multiple dose study conducted in mothers soon after delivery indicates that flecainide is excreted in human breast milk in concentrations as high as 4 times (with average levels about 2.5 times) corresponsing plasma levels; assuming a maternal plasma level at the top of the therapeutic range (1 µg/mL), the calculated daily dose to a nursing infant (assuming about 700 mL breast milk over 24 hours) would be less than 3 mg.

Pediatric Use.   The safety and efficacy of TAMBOCOR in the fetus, infant, or child have not been established in double-blind, randomized, placebo-controlled trials (see CLINICAL PHARMACOLOGY, WARNINGS, and DOSAGE AND ADMINISTRATION).

Hepatic Impairment.   Since flecainide elimination from plasma can be markedly slower in patients with significant hepatic impairment, TAMBOCOR should not be used in such patients unless the potential benefits clearly outweigh the risks. If used, frequent and early plasma level monitoring is required to guide dosage (see Plasma Level Monitoring); dosage increases should be made very cautiously when plasma levels have plateaued (after more than four days).

No specific antidote has been identified for the treatment of TAMBOCOR overdosage. Overdoses ranging up to 8000 mg have been survived, with peak plasma flecainide concentrations as high as 5.3 µg/mL. Untoward effects in these cases included nausea and vomiting, convulsions, hypotension, bradycardia, syncope, extreme widening of the QRS complex, widening of the QT interval, widening of the PR interval, ventricular tachycardia, AV nodal block, asystole, bundle branch block, cardiac failure, and cardiac arrest. The spectrum of events observed in fatal cases was much the same as that seen in the non-fatal cases. Death has resulted following ingestion of as little as 1000 mg; concomitant overdose of other drugs and/or alcohol in many instances undoubtedly contributed to the fatal outcome. Treatment of overdosage should be supportive and may include the following: removal of unabsorbed drug from the gastrointestinal tract, administration of inotropic agents or cardiac stimulants such as dopamine, dobutamine or isoproterenol; mechanically assisted respiration; circulatory assists such as intra-aortic balloon pumping; and transvenous pacing in the event of conduction block. Because of the long plasma half-life of flecainide (12 to 27 hours in patients receiving usual doses), and the possibility of markedly non-linear elimination kinetics at very high doses, these supportive treatments may need to be continued for extended periods of time.

Hemodialysis is not an effective means of removing flecainide from the body. Since flecainide elimination is much slower when urine is very alkaline (pH 8 or higher), theoretically, acidification of urine to promote drug excretion may be beneficial in overdose cases with very alkaline urine. There is no evidence that acidification from normal urinary pH increases excretion.

TAMBOCOR is contraindicated in patients with pre-existing second- or third-degree AV block, or with right bundle branch block when associated with a left hemiblock (bifascicular block), unless a pacemaker is present to sustain the cardiac rhythm should complete heart block occur. TAMBOCOR is also contraindicated in the presence of cardiogenic shock or known hypersensitivity to the drug.

TAMBOCOR has local anesthetic activity and belongs to the membrane stabilizing (Class 1) group of antiarrhythmic agents; it has electrophysiologic effects characteristic of the IC class of antiarrhythmics.

Electrophysiology.   In man, TAMBOCOR produces a dose-related decrease in intracardiac conduction in all parts of the heart with the greatest effect on the His-Purkinje system (H-V conduction). Effects upon atrioventricular (AV) nodal conduction time and intra-atrial conduction times, although present, are less pronounced than those on ventricular conduction velocity. Significant effects on refractory periods were observed only in the ventricle. Sinus node recovery times (corrected) following pacing and spontaneous cycle lengths are somewhat increased. This latter effect may become significant in patients with sinus node dysfunction. (See WARNINGS .)

TAMBOCOR causes a dose-related and plasma-level related decrease in single and multiple PVCs and can suppress recurrence of ventricular tachycardia. In limited studies of patients with a history of ventricular tachycardia, TAMBOCOR has been successful 30-40% of the time in fully suppressing the inducibility of arrhythmias by programmed electrical stimulation. Based on PVC suppression, it appears that plasma levels of 0.2 to 1.0 µg/mL may be needed to obtain the maximal therapeutic effect. It is more difficult to assess the dose needed to suppress serious arrhythmias, but trough plasma levels in patients successfully treated for recurrent ventricular tachycardia were between 0.2 and 1.0 µg/mL. Plasma levels above 0.7-1.0 µg/mL are associated with a higher rate of cardiac adverse experiences such as conduction defects or bradycardia. The relation of plasma levels to proarrhythmic events is not established, but dose reduction in clinical trials of patients with ventricular tachycardia appears to have led to a reduced frequency and severity of such events.

Hemodynamics.   TAMBOCOR does not usually alter heart rate, although bradycardia and tachycardia have been reported occasionally.

In animals and isolated myocardium, a negative inotropic effect of flecainide has been demonstrated. Decreases in ejection fraction, consistent with a negative inotropic effect, have been observed after single administration of 200 to 250 mg of the drug in man; both increases and decreases in ejection fraction have been encountered during multidose therapy in patients at usual therapeutic doses. (See WARNINGS .)

Metabolism in Humans.   Following oral administration, the absorption of TAMBOCOR is nearly complete. Peak plasma levels are attained at about three hours in most individuals (range, 1 to 6 hours). Flecainide does not undergo any consequential presystemic biotransformation (first-pass effect). Food or antacid do not affect absorption. Milk, however, may inhibit absorption in infants. A reduction in TAMBOCOR dosage should be considered when milk is removed from the diet of infants.

The apparent plasma half-life averages about 20 hours and is quite variable (range, 12 to 27 hours) after multiple oral doses in patients with premature ventricular contractions (PVCs). With multiple dosing, plasma levels increase because of its long half-life with steady-state levels approached in 3 to 5 days; once at steady-state, no additional (or unexpected) accumulation of drug in plasma occurs during chronic therapy. Over the usual therapeutic range, data suggest that plasma levels in an individual are approximately proportional to dose, deviating upwards from linearity only slightly (about 10 to 15% per 100 mg on average).

In healthy subjects, about 30% of a single oral dose (range, 10 to 50%) is excreted in urine as unchanged drug. The two major urinary metabolites are meta-O-dealkylated flecainide (active, but about one-fifth as potent) and the meta-O-dealkylated lactam of flecainide (non-active metabolite). These two metabolites (primarily conjugated) account for most of the remaining portion of the dose. Several minor metabolites (3% of the dose or less) are also found in urine; only 5% of an oral dose is excreted in feces. In patients, free (unconjugated) plasma levels of the two major metabolites are very low (less than 0.05 µg/mL).

In vitro metabolic studies have confirmed that cytochrome P450IID6 is involved in the metabolism of flecainide.

When urinary pH is very alkaline (8 or higher), as may occur in rare conditions (e.g., renal tubular acidosis, strict vegetarian diet), flecainide elimination from plasma is much slower.

The elimination of flecainide from the body depends on renal function (i.e., 10 to 50% appears in urine as unchanged drug). With increasing renal impairment, the extent of unchanged drug excretion in urine is reduced and the plasma half-life of flecainide is prolonged. Since flecainide is also extensively metabolized, there is no simple relationship between creatinine clearance and the rate of flecanide elimination from plasma. (See Dosage and Administration .)

In patients with NYHA class III congestive heart failure (CHF), the rate of flecainide elimination from plasma (mean half-life, 19 hours) is moderately slower than for healthy subjects (mean half-life, 14 hours), but similar to the rate for patients with PVCs without CHF. The extent of excretion of unchanged drug in urine is also similar. (See Dosage and Administration .)

Under one year of age, currently available data are limited but suggest that the half-life at birth may be as long as 29 hours, decreasing to 11-12 hours by three months of age and 6 hours by one year of age. The pharmacokinetics in hydropic infants have not been studied, but case reports suggest prolonged elimination. In children aged 1 year to 12 years the half-life is approximately 8 hours. In adolescents (age 12 to 15) the plasma elimination half-life is approximately 11-12 hours. Since milk may inhibit absorption in infants, a reduction in TAMBOCOR dosage should be considered when milk is removed from the diet (e.g., gastroenteritis, weaning). Plasma trough flecainide levels should be monitored during major changes in dietary milk intake.

From age 20 to 80, plasma levels are only slightly higher with advancing age; flecainide elimination from plasma is somewhat slower in elderly subjects than in younger subjects. Patients up to age 80+ have been safely treated with usual dosages.

The extent of flecainide binding to human plasma proteins is about 40% and is independent of plasma drug level over the range of 0.015 to about 3.4 µg/mL. Thus, clinically significant drug interactions based on protein binding effects would not be expected.

Hemodialysis removes only about 1% of an oral dose as unchanged flecainide.

Small increases in plasma digoxin levels are seen during coadministration of TAMBOCOR with digoxin. Small increases in both flecainide and propranolol plasma levels are seen during coadministration of these two drugs. (See Precautions , Drug Interactions.)

Clinical Trials.   In two randomized, crossover, placebo-controlled clinical trials of 16 weeks double-blind duration, 79% of patients with paroxysmal supraventricular tachycardia (PSVT) receiving flecainide were attack free, whereas 15% of patients receiving placebo remained attack free. The median time-before-recurrence of PSVT in patients receiving placebo was 11 to 12 days, whereas over 85% of patients receiving flecainide had no recurrence at 60 days.

In two randomized, crossover, placebo-controlled clinical trials of 16 weeks double-blind duration, 31% of patients with paroxysmal atrial fibrillation/flutter (PAF) receiving flecainide were attack free, whereas 8% receiving placebo remained attack free. The median time-before-recurrence of PAF in patients receiving placebo was about 2 to 3 days, whereas for those receiving flecainide the median time-before-recurrence was 15 days.

No Information Provided.

IMPORTANT NOTE: This is a summary and does not contain all possible information about this product. For complete information about this product or your specific health needs, ask your health care professional. Always seek the advice of your health care professional if you have any questions about this product or your medical condition. This information is not intended as individual medical advice and does not substitute for the knowledge and judgment of your health care professional. This information does not contain any assurances that this product is safe, effective, or appropriate for you.

FLECAINIDE - ORAL

(fleck-UH-nide)

COMMON BRAND NAME(S): Tambocor

WARNING: Although this medication and others like it are used to treat certain kinds of abnormal heartbeats, they may rarely cause serious (sometimes fatal) irregular heartbeats. Therefore, flecainide should be used carefully only in selected patients. Flecainide should not be used in patients with persistent atrial fibrillation/flutter or those who have recently had a heart attack. Consult your doctor or pharmacist for more information.

USES: This medication is used to treat a certain serious (possibly life-threatening), persistent, abnormally fast heartbeat (sustained ventricular tachycardia). It is also used to treat occasional, disabling, abnormally fast heartbeats (e.g., paroxysmal supraventricular tachycardias, paroxysmal atrial fibrillation/flutter). Flecainide belongs to a class of drugs known as antidysrhythmics. It works by blocking the abnormal electrical activity of an irregular heartbeat so that the normal heartbeat can occur.

HOW TO USE: This medication may be started at a low dose in the hospital so that your doctor can determine the best dose, increase it gradually as needed, and monitor you closely for side effects.

Take this medication by mouth with or without food, usually twice daily or as directed by your doctor. If your abnormal heartbeat is not easily controlled, your doctor may prescribe this medication 3 times daily.

Milk may partly block the absorption of this medication into the bloodstream of infants. Contact your infants doctor if you plan to add or remove milk from the diet.

Dosage is based on your age, kidney and liver function, medical condition, other medications you may be taking, and response to therapy.

This medication works best when the amount of drug in your body is kept at a constant level. Therefore, take this drug at evenly spaced intervals. To help you remember, take it at the same times each day.

Take this medication exactly as prescribed by your doctor. Do not take more or less of this drug than prescribed or stop taking it (or other heart medicines) even for a short time unless directed to do so by your doctor. Skipping or changing your dose without approval from your doctor may cause your abnormal heartbeat to return. Do not run out of this medication. Order your refills several days early to avoid running out of pills.

Contact your doctor immediately and seek emergency medical attention (e.g., call 911, have someone else drive you to a hospital emergency room) if your condition persists or worsens.

SIDE EFFECTS: See also Warning section.

Dizziness, vision problems (e.g., blurring, spots, problems focusing, double vision), shortness of breath, headache, nausea, tiredness, and weakness may occur. Less common side effects may include shakiness of hands/arms, constipation, stomach pain, heartburn, mild difficulty speaking, drowsiness, dry mouth. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: vomiting, unusual sweating, swelling, mental/mood changes (e.g., anxiety, depression, memory loss, confusion, hallucinations), numbness/tingling, problems walking (staggering), ringing in the ears, loss of appetite, sore throat, decreased sexual interest/ability, problems starting the flow of urine, worsening symptoms of heart failure (e.g., ankle/leg swelling, increased tiredness, increased shortness of breath when lying down).

Seek immediate medical attention if any of these unlikely but serious side effects occur: chest pain, severe dizziness, fainting, sudden change in heartbeat (unusually faster/slower/more irregular).

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching, swelling, severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

Contact your doctor for medical advice about side effects. The following numbers do not provide medical advice, but in the US you may report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088. In Canada, you may call Health Canada at 1-866-234-2345.

PRECAUTIONS: See also Warning and How to Use sections.

Before taking flecainide, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies.

This medication should generally not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: certain heartbeat problems (second- or third-degree atrioventricular block or right bundle branch block with left hemiblock unless you have a heart pacemaker), persistent atrial fibrillation/flutter, shock due to the heart not pumping well (e.g., very low blood pressure and loss of consciousness), recent heart attack (within the last 2 years).

Before using this medication, tell your doctor or pharmacist your medical history, especially of: kidney problems, liver problems, angina (chest pain), heart failure, certain irregular heartbeats (sick sinus syndrome, torsade de pointes), a certain heart problem (QT prolongation in the EKG), abnormal blood minerals (high or low potassium), a heart pacemaker, conditions that may make the urine more alkaline (e.g., strict vegetarian diet, renal tubular acidosis).

Contact your doctor immediately if you develop other illnesses/conditions such as prolonged or large quantities of diarrhea, excessive sweating, vomiting, prolonged loss of appetite or desire to drink water. These conditions could cause you to have serious changes in blood minerals leading to increased side effects from flecainide.

This drug may make you dizzy or drowsy. Use caution while driving, using machinery, or doing any activity that requires alertness. Limit alcoholic beverages.

Caution is advised when using this drug in the elderly because they may be more sensitive to the effects of the drug, especially dizziness.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

This medication passes into breast milk and may have undesirable effects on a nursing infant. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor or pharmacist first.

This drug should not be used with the following medications because very serious interactions may occur: disopyramide, dofetilide, halofantrine, lumefantrine, pimozide, arbutamine, saquinavir, cisapride, gadoxetate, mizolastine, lopinavir/ritonavir, tipranavir.

Other drugs besides flecainide and those listed above that may affect the heart rhythm (QTc prolongation in the EKG) include sotalol, procainamide, droperidol, ziprasidone, ranolazine, levofloxacin, and erythromycin, among others. QTc prolongation can infrequently result in a serious (rarely fatal) irregular heartbeat. Consult your doctor or pharmacist for more details and for instructions on how you may minimize the risk of this effect.

If you are currently using any of these medications listed above, tell your doctor or pharmacist before starting flecainide.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: amiodarone, cimetidine, clozapine, quinidine, digoxin, verapamil, beta blockers (e.g., propranolol, metoprolol), barbiturates (e.g., phenobarbital), carbamazepine, phenytoin, drugs that make the urine more acid (e.g., large doses of vitamin C, methionine, ammonium chloride), drugs that make the urine more alkaline (e.g., sodium bicarbonate).

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

OVERDOSE: If overdose is suspected, contact your local poison control center or emergency room immediately. US residents can call the US National Poison Hotline at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe nausea/vomiting, seizures, very slow heartbeat, severe dizziness, fainting.

NOTES: Do not share this medication with others.

Laboratory and/or medical tests (e.g., EKG, routine blood tests) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.

MISSED DOSE: If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

STORAGE: Store at room temperature between 59-86 degrees F (15-30 degrees C) away from light and moisture. Do not store in the bathroom. Keep all medicines away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

MEDICAL ALERT: Your condition can cause complications in a medical emergency. For information about enrolling in MedicAlert, call 1-800-854-1166 (USA) or 1-800-668-1507 (Canada).

Information last revised July 2008 Copyright(c) 2008 First DataBank, Inc.