Norpace (Disopyramide Phosphate) Drug Information: Overdosage and Contraindications

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May 27, 2012

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Arrhythmia »

Introduction to Arrhythmia

An irregular heartbeat is an arrhythmia (also called dysrhythmia). Heart rates can also be irregular. A normal heart rate is 50 to 100 beats per minute. Arrhythmias and abnormal heart rates don't necessarily occur together. Arrhythmias can occur with a normal heart rate, or with heart rates that are slow (called bradyarrhythmias -- less than 50 beats per minute). Arrhythmias can also occur with rapid heart rates (called tachyarrhythmias -- faster than 100 beats per minute). In the United States, more than 850,000 people are hospitalized for an arrhythmia each year.

What causes an arrhythmia?

Arrhythmias may be caused by many different factors, including:

Coronary artery disease.
Electrolyte imbalances in your blood (such as sodium or potassium).
Changes in your heart muscle.
Injury from a heart attack.
Healing process after heart surgery.
Irregula...

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OVERDOSE

Symptoms

Deliberate or accidental overdosage of oral diso-pyramide may be followed by apnea, loss of consciousness, cardiac arrhythmias, and loss of spontaneous respiration. Death has occurred following overdosage.

Toxic plasma levels of disopyramide produce excessive widening of the QRS complex and Q-T interval, worsening of congestive heart failure, hypo-tension, varying kinds and degrees of conduction disturbance, bradycardia, and finally asystole. Obvious anticholinergic effects are also observed.

The approximate oral LD₅₀ of disopyramide phosphate is 580 and 700 mg/kg for rats and mice, respectively.

Treatment

Experience indicates that prompt and vigorous treatment of overdosage is necessary, even in the absence of symptoms. Such treatment may be lifesaving. No specific antidote for disopyramide phosphate has been identified. Treatment should be symptomatic and may include induction of emesis or gastric lavage, administration of a cathartic followed by activated charcoal by mouth or stomach tube, intravenous administration of isoproterenol and dopamine, insertion of an intra-aortic balloon for counterpulsation, and mechanically assisted ventilation. Hemodialysis or, preferably, hemoper-fusion with charcoal may be employed to lower serum concentration of the drug.

The electrocardiogram should be monitored, and supportive therapy with cardiac glycosides and diuretics should be given as required.

If progressive AV block should develop, endocar-dial pacing should be implemented. In case of any impaired renal function, measures to increase the glomerular filtration rate may reduce the toxicity (disopyramide is excreted primarily by the kidney).

The anticholinergic effects can be reversed with neostigmine at the discretion of the physician.

Altering the urinary pH in humans does not affect the plasma half-life or the amount of disopyramide excreted in the urine.

CONTRAINDICATIONS

Norpace (disopyramide phosphate) and Norpace (disopyramide phosphate) CR are contraindicated in the presence of cardiogenic shock, preexisting second-or third-degree AV block (if no pacemaker is present), congenital Q-T prolongation, or known hypersensitivity to the drug.

Last reviewed on RxList: 7/17/2008
This monograph has been modified to include the generic and brand name in many instances.