Tarka (Trandolapril / Verapamil Hydrochloride Extended Release) - Drug Interactions, Contraindications, Overdosage

DRUG INTERACTIONS

Digitalis

Clinical use of verapamil in digitalized patients has shown the combination to be well tolerated if digoxin doses are properly adjusted. Chronic verapamil treatment can increase serum digoxin levels by 50 to 75% during the first week of therapy, and this can result in digoxintoxicity. In patients with hepatic cirrhosis, the influence of verapamil on digoxin kinetics is magnified. Verapamil may reduce total body clearance and extrarenal clearance of digitoxin by 27% and 29%, respectively. Maintenance digoxin doses should be reduced when verapamil is administered, and the patient should be carefully monitored to avoid over- or under-digitalization. Whenever overdigitalization is suspected, the daily dose of digoxin should be reduced or temporarily discontinued. Upon discontinuation of any verapamil-containing regime including TARKA (trandolapril/verapamil hydrochloride ER), the patient should be reassessed to avoid underdigitalization. Neither trandolapril nor its metabolites have been found to interact with digoxin.

Lithium

Increased sensitivity to the effects of lithium (neurotoxicity) has been reported during concomitant verapamil-lithium therapy with either no change or an increase in serum lithium levels. Increased serum lithium levels and symptoms of lithium toxicity have been reported in patients receiving concomitant lithium and ACE inhibitor therapy. TARKA and lithium should be coadministered with caution, and frequent monitoring of serum lithium levels is recommended. If a diuretic is also used, the risk of lithium toxicity may be increased.

Cimetidine

The interaction between cimetidine and chronically administered verapamil has not been studied. Variable results on clearance have been obtained in acute studies of healthy volunteers; clearance of verapamil was either reduced or unchanged. Neither trandolapril nor its metabolites have been found to interact with cimetidine.

Beta Blockers

Verapamil Component

Concomitant therapy with beta-adrenergic blockers and verapamil may result in additive negative effects on heart rate, atrioventricular conduction, and/or cardiac contractility. The use of verapamil in combination with a beta-blocker should be used only with caution, and close monitoring.

Asymptomatic bradycardia (36 beats/min) with a wandering atrial pacemaker has been observed in a patient receiving concomitant timolol (a beta-adrenergic blocker) eyedrops and oral verapamil.

OVERDOSAGE

No specific information is available on the treatment of overdosage with TARKA.

Verapamil Component

Overdose with verapamil may lead to pronounced hypotension, bradycardia, and conduction system abnormalities (e.g., junctional rhythm with AV dissociation and high degree AV block, including asystole). Other symptoms secondary to hypoperfusion (e.g., metabolic acidosis, hyperglycemia, hyperkalemia, renal dysfunction, and convulsions) may be evident.

Treat all verapamil overdoses as serious and maintain observation for at least 48 hours, preferably under continuous hospital care. Delayed pharmacodynamic consequences may occur with the sustained release formulation. Verapamil is known to decrease gastrointestinal transit time. In cases of overdose, tablets of ISOPTIN SR have occasionally been reported to form concretions within the stomach or intestines. These concretions have not been visible on plain radiographs of the abdomen, and no medical means of gastrointestinal emptying is of proven efficacy in removing them. Endoscopy might reasonably be considered in cases of overdose when symptoms are unusually prolonged. Verapamil cannot be removed by hemodialysis.

Treatment of overdosage should be supportive. Beta adrenergic stimulation or parenteral administration of calcium solutions may increase calcium ion flux across the slow channel, and have been used effectively in treatment of deliberate overdosage with verapamil. The following measures may be considered:

Bradycardia and Conduction System Abnormalities

Atropine, isoproterenol, and cardiac pacing.

Hypotension

Intravenous fluids, vasopressors (e.g., dopamine, dobutamine), calcium solutions (e.g., 10% calcium chloride solution).

Cardiac Failures

Inotropic agents (e.g., isoproterenol, dopamine, dobutamine), diuretics. Asystole should be handled by the usual measures including cardiopulmonary resuscitation.

Trandolapril Component

The oral LD₅₀ of trandolapril in mice was 4875 mg/kg in males and 3990 mg/kg in females. In rats, an oral dose of 5000 mg/kg caused low mortality (1 male out of 5; 0 females). In dogs, an oral dose of 1000 mg/kg did not cause mortality and abnormal clinical signs were not observed.

In humans, the most likely clinical manifestation would be symptoms attributable to severe hypotension. Laboratory determinations of serum levels of trandolapril and its metabolites are not widely available, and such determinations have, in any event, no established role in the management of trandolapril overdose. No data are available to suggest that physiological maneuvers (e.g., maneuvers to change pH of the urine) might accelerate elimination of trandolapril and its metabolites. It is not known if trandolapril or trandolaprilat can be usefully removed from the body by hemodialysis.

Angiotensin II could presumably serve as a specific antagonist antidote in the setting of trandolapril overdose, but angiotensin II is essentially unavailable outside of scattered research facilities. Because the hypotensive effect of trandolapril is achieved through vasodilation and effective hypovolemia, it is reasonable to treat trandolapril overdose by infusion of normal saline solution.

Contraindications

TARKA is contraindicated in patients who are hypersensitive to any ACE inhibitor or verapamil.

Because of the verapamil component, TARKA is contraindicated in:

1. Severe left ventricular dysfunction (see WARNINGS).
2. Hypotension (systolic pressure less than 90 mmHg) or cardiogenic shock.
3. Sick sinus syndrome (except in patients with a functioning artificial ventricular pacemaker).
4. Second- or third-degree AV block (except in patients with a functioning artificial ventricular pacemaker).
5. Patients with atrial flutter or atrial fibrillation and an accessory bypass tract (e.g. Wolff-Parkinson-White, Lown-Ganong-Levine syndromes) (see  WARNINGS).

Because of the trandolapril component, TARKA is contraindicated in patients with a history of angioedema related to previous treatment with an angiotensin converting enzyme (ACE) inhibitor.