Pharmacokinetics and hemodynamic effects of tiapamil: exercise performance, thallium stress scintigraphy, and...

The pharmacokinetic behavior and hemodynamic effects of tiapamil, a calcium antagonist, were studied in 16 cardiac patients during an eight-day treatment course, giving oral doses of 600 mg daily. The hemodynamic effects were investigated using exercise performance tests, thallium stress scintigraphy, and radionuclide ventriculography. The areas under the plasma concentration-time curve after the final dose were greater than after the first dose for both tiapamil (+53 per cent) and its metabolite (+24 per cent). One possible explanation is that tiapamil undergoes saturable intestinal wall metabolism. Alternatively, like verapamil, it may undergo a saturable hepatic elimination process. The hemodynamic test series showed that, despite increasing the exercise tolerance, tiapamil significantly reduced the rate-pressure product, an index of myocardial oxygen requirement. Regional myocardial perfusion clearly improved. Ventriculography showed a significant increase in ejection fraction (+18 per cent), cardiac index (+12 per cent), and stroke volume index (+19 per cent). At the same time, the measured mean arterial pressure decreased significantly by about 10 per cent and the calculated peripheral vascular resistance, by about 19 per cent.