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Theo-24

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Theo-24

WARNINGS

Concurrent Illness

Theophylline should be used with extreme caution in patients with the following clinical conditions due to the increased risk of exacerbation of the concurrent condition:

Active peptic ulcer disease
Seizure disorders
Cardiac arrhythmias (not including bradyarrhythmias)

Conditions That Reduce Theophylline Clearance

There are several readily identifiable causes of reduced theophylline clearance. If the total daily dose is not appropriately reduced in the presence of these risk factors, severe and potentially fatal theophylline toxicity can occur. Careful consideration must be given to the benefits and risks of theophylline use and the need for more intensive monitoring of serum theophylline concentrations in patients with the following risk factors:

Age

Neonates (term and premature)
Children < 1 year
Elderly ( > 60 years)

Concurrent Diseases

Acute pulmonary edema
Congestive heart failure
Cor-pulmonale
Fever; ≥ 102° F for 24 hours or more; or lesser temperature elevations for longer periods
Hypothyroidism
Liver disease; cirrhosis, acute hepatitis
Reduced renal function in infants < 3 months of age
Sepsis with multi-organ failure
Shock

Cessation of Smoking

Drug Interactions

Adding a drug that inhibits theophylline metabolism (e.g., cimetidine, erythromycin, tacrine) or stopping a concurrently administered drug that enhances theophylline metabolism (e.g., carbamazepine, rifampin) (see PRECAUTIONS: DRUG INTERACTIONS, Table II).

When Signs or Symptoms of Theophylline Toxicity Are Present

Whenever a patient receiving theophylline develops nausea or vomiting, particularly repetitive vomiting, or other signs or symptoms consistent with theophylline toxicity (even if another cause may be suspected), additional doses of theophylline should be withheld and a serum theophylline concentration measured immediately. Patients should be instructed not to continue any dosage that causes adverse effects and to withhold subsequent doses until the symptoms have resolved, at which time the healthcare professional may instruct the patient to resume the drug at a lower dosage (see DOSAGE AND ADMINISTRATION, Dosing Guidelines, Table VI).

Dosage Increases

Increases in the dose of theophylline should not be made in response to an acute exacerbation of symptoms of chronic lung disease since theophylline provides little added benefit to inhaled Beta2 -selective agonists and systemically administered corticosteroids in this circumstance and increases the risk of adverse effects. A peak steady-state serum theophylline concentration should be measured before increasing the dose in response to persistent chronic symptoms to ascertain whether an increase in dose is safe. Before increasing the theophylline dose on the basis of a low serum concentration, the healthcare professional should consider whether the blood sample was obtained at an appropriate time in relationship to the dose and whether the patient has adhered to the prescribed regimen (see PRECAUTIONS, Laboratory Tests).

As the rate of theophylline clearance may be dose-dependent (i.e., steady-state serum concentrations may increase disproportionately to the increase in dose), an increase in dose based upon a sub-therapeutic serum concentration measurement should be conservative. In general, limiting dose increases to about 25% of the previous total daily dose will reduce the risk of unintended excessive increases in serum theophylline concentration (see DOSAGE AND ADMINISTRATION, Table VI).

PRECAUTIONS

General

Careful consideration of the various interacting drugs and physiologic conditions that can alter theophylline clearance and require dosage adjustment should occur prior to initiation of theophylline therapy, prior to increases in theophylline dose, and during follow up (see WARNINGS). The dose of theophylline selected for initiation of therapy should be low and, if tolerated, increased slowly over a period of a week or longer with the final dose guided by monitoring serum theophylline concentrations and the patient's clinical response (see DOSAGE AND ADMINISTRATION, Table V).

Monitoring Serum Theophylline Concentrations

Serum theophylline concentration measurements are readily available and should be used to determine whether the dosage is appropriate. Specifically, the serum theophylline concentration should be measured as follows:

  1. When initiating therapy to guide final dosage adjustment after titration.
  2. Before making a dose increase to determine whether the serum concentration is sub-therapeutic in a patient who continues to be symptomatic.
  3. Whenever signs or symptoms of theophylline toxicity are present.
  4. Whenever there is a new illness, worsening of a chronic illness or a change in the patient's treatment regimen that may alter theophylline clearance (e.g., fever > 102°F sustained for ≥ 24 hours, hepatitis, or drugs listed in Table II are added or discontinued).

To guide a dose increase, the blood sample should be obtained at the time of the expected peak serum theophylline concentration; 12 hours after a dose at steady-state (expected peak serum theophylline concentration range is between 5 –15 mcg/mL). For most patients, steady-state will be reached after 3 days of dosing when no doses have been missed, no extra doses have been added, and none of the doses have been taken at unequal intervals. A trough concentration (i.e., at the end of the dosing interval) provides no additional useful information and may lead to an inappropriate dose increase since the peak serum theophylline concentration can be two or more times greater than the trough concentration with an extended-release formulation. If the serum sample is drawn more or less than twelve (12) hours after the dose, the results must be interpreted with caution since the concentration may not be reflective of the peak concentration. In contrast, when signs or symptoms of theophylline toxicity are present, the serum sample should be obtained as soon as possible, analyzed immediately, and the result reported to the healthcare professional without delay. In patients in whom decreased serum protein binding is suspected (e.g., cirrhosis, women during the third trimester of pregnancy), the concentration of unbound theophylline should be measured and the dosage adjusted to achieve an unbound concentration of 6-12 mcg/mL Saliva concentrations of theophylline cannot be used reliably to adjust dosage without special techniques.

Effects on Laboratory Tests

As a result of its pharmacological effects, theophylline at serum concentrations within the 10-20 mcg/mL range modestly increases plasma glucose (from a mean of 88 mg% to 98 mg%), uric acid (from a mean of 4 mg/dL to 6 mg/dL), free fatty acids (from a mean of 451 µEq/L to 800 µEq/L, total cholesterol (from a mean of 140 vs 160 mg/dL), HDL (from a mean of 36 to 50 mg/dL), HDL/LDL ratio (from a mean of 0.5 to 0.7), and urinary free cortisol excretion (from a mean of 44 to 63 mcg/24 hr). Theophylline at serum concentrations within the 10-20 mcg/mL range may also transiently decrease serum concentrations of tri-iodothyronine (144 before, 131 after one week and 142 ng/dL after 4 weeks of theophylline). The clinical importance of these changes should be weighed against the potential therapeutic benefit of theophylline in individual patients.

Carcinogenesis, Mutagenesis, and Impairment of Fertility

Long term carcinogenicity studies have been carried out in mice (oral doses 30-150 mg/kg) and rats (oral doses 5-75 mg/kg). Results are pending.

Theophylline has been studied in Ames salmonella, in vivo and in vitro cytogenetics, micronucleus and Chinese hamster ovary test systems and has not been shown to be genotoxic.

In a 14 week continuous breeding study, theophylline, administered to mating pairs of B6C3F1 mice at oral doses of 120, 270 and 500 mg/kg (approximately 1.0-3.0 times the human dose on a mg/m2 basis) impaired fertility, as evidenced by decreases in the number of live pups per litter, decreases in the mean number of litters per fertile pair, and increases in the gestation period at the high dose as well as decreases in the proportion of pups born alive at the mid and high dose. In 13 week toxicity studies, theophylline was administered to F344 rats and B6C3F1 mice at oral doses of 40-300 mg/kg (approximately 2.0 times the human dose on a mg/m2 basis). At the high dose, systemic toxicity was observed in both species including decreases in testicular weight.

Pregnancy

Category C

In studies in which pregnant mice, rats and rabbits were dosed during the period of organogenesis, theophylline produced teratogenic effects.

In studies with mice, a single intraperitoneal dose at and above 100 mg/kg (approximately equal to the maximum recommended oral dose for adults on a mg/m2 basis) during organogenesis produced cleft palate and digital abnormalities. Micromelia, micrognathia, clubfoot, subcutaneous hematoma, open eyelids, and embryolethality were observed at doses that are approximately 2 times the maximum recommended oral dose for adults on a mg/m2 basis.

In a study with rats dosed from conception through organogenesis, an oral dose of 150 mg/kg/day (approximately 2 times the maximum recommended oral dose for adults on a mg/m2 basis) produced digital abnormalities. Embryolethality was observed with a subcutaneous dose of 200 mg/kg/day (approximately 4 times the maximum recommended oral dose for adults on a mg/m2 basis).

In a study in which pregnant rabbits were dosed throughout organogenesis, an intravenous dose of 60 mg/kg/day (approximately 2 times the maximum recommended oral dose for adults on a mg/m2 basis), which caused the death of one doe and clinical signs in others, produced cleft palate and was embryolethal. Doses at and above 15 mg/kg/day (less than the maximum recommended oral dose for adults on a mg/m2 basis) increased the incidence of skeletal variations.

There are no adequate and well-controlled studies in pregnant women. Theophylline should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

Theophylline is excreted into breast milk and may cause irritability or other signs of mild toxicity in nursing human infants. The concentration of theophylline in breast milk is about equivalent to the maternal serum concentration. An infant ingesting a liter of breast milk containing 10-20 mcg/mL of theophylline per day is likely to receive 10-20 mg of theophylline per day. Serious adverse effects in the infant are unlikely unless the mother has toxic serum theophylline concentrations.

Pediatric Use

Theophylline is safe and effective for the approved indications in pediatric patients (see INDICATIONS). The maintenance dose of theophylline must be selected with caution in pediatric patients since the rate of theophylline clearance is highly variable across the age range of neonates to adolescents (see CLINICAL PHARMACOLOGY, Table I, WARNINGS, and DOSAGE AND ADMINISTRATION, Table V). Due to the immaturity of theophylline metabolic pathways in infants under the age of one year, particular attention to dosage selection and frequent monitoring of serum theophylline concentrations are required when theophylline is prescribed to pediatric patients in this age group.

Geriatric Use

Elderly patients are at a significantly greater risk of experiencing serious toxicity from theophylline than younger patients due to pharmacokinetic and pharmacodynamic changes associated with aging. The clearance of theophylline is decreased by an average of 30% in healthy elderly adults ( > 60 yrs) compared to healthy young adults. Theophylline clearance may be further reduced by concomitant diseases prevalent in the elderly, which further impair clearance of this drug and have the potential to increase serum levels and potential toxicity. These conditions include impaired renal function, chronic obstructive pulmonary disease, congestive heart failure, hepatic disease and an increased prevalence of use of certain medications (see PRECAUTIONS: DRUG INTERACTIONS) with the potential for pharmacokinetic and pharmacodynamic interaction. Protein binding may be decreased in the elderly resulting in an increased proportion of the total serum theophylline concentration in the pharmacologically active unbound form. Elderly patients also appear to be more sensitive to the toxic effects of theophylline after chronic overdosage than younger patients. Careful attention to dose reduction and frequent monitoring of serum theophylline concentrations are required in elderly patients (see PRECAUTIONS, Monitoring Serum Theophylline Concentrations, and DOSAGE AND ADMINISTRATION). The maximum daily dose of theophylline in patients greater than 60 years of age ordinarily should not exceed 400 mg/day unless the patient continues to be symptomatic and the peak steady-state serum theophylline concentration is < 10 mcg/mL (see DOSAGE AND ADMINISTRATION). Theophylline doses greater than 400 mg/d should be prescribed with caution in elderly patients.

Last reviewed on RxList: 4/8/2009
This monograph has been modified to include the generic and brand name in many instances.

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