No specific information is available on the treatment of overdosage with quinapril and hydrochlorothiazide tablets or quinapril monotherapy; treatment should be symptomatic and supportive. Therapy with quinapril and hydrochlorothiazide tablets should be discontinued, and the patient should be observed. Dehydration, electrolyte imbalance, and hypotension should be treated by established procedures.
The oral median lethal dose of quinapril/hydrochlorothiazide in combination ranges from 1063/664 to 4640/2896 mg/kg in mice and rats. Doses of 1440 to 4280 mg/kg of quinapril cause significant lethality in mice and rats. In single-dose studies of hydrochlorothiazide, most rats survived doses up to 2.75 g/kg.
Data from human overdoses of ACE inhibitors are scanty; the most likely manifestation of human quinapril overdosage is hypotension. In human hydrochlorothiazide overdose, the most common signs and symptoms observed have been those of dehydration and electrolyte depletion (hypokalemia, hypochloremia, hyponatremia). If digitalis has also been administered, hypokalemia may accentuate cardiac arrhythmias.
Laboratory determinations of serum levels of quinapril and its metabolites are not widely available, and such determinations have, in any event, no established role in the management of quinapril overdose.
No data are available to suggest physiological maneuvers (e.g., maneuvers to change the pH of the urine) that might accelerate elimination of quinapril and its metabolites. Hemodialysis and peritoneal dialysis have little effect on the elimination of quinapril and quinaprilat.
Angiotensin II could presumably serve as a specific antagonist-antidote in the setting of quinapril overdose, but angiotensin II is essentially unavailable outside of scattered research facilities. Because the hypotensive effect of quinapril is achieved through vasodilation and effective hypovolemia, it is reasonable to treat quinapril overdose by infusion of normal saline solution.