IMAI, Y., ABE, K., SASAKI, S., NIHEI, M., SEKINO, H. and YOSHINAGA, K. Pharmacokinetics and Pharmacodynamics of Conventional and Slow Release Forms of Nifedipine in Essential Hypertensive Patients. Tohoku J. exp. Med., 1986, 148 (4), 421-438-In patients with essential hypertension, the pharmacokinetics of nifedipine in 2 forms (capsule, 10mg nifedipine dissolved in an organic solvent; slow release tablet, 20mg nifedipine) and their pharmacodynamic effectiveness on arterial pressure were studied. The maximum plasma concentration was higher and achieved more rapidly after application of the capsule than after the retard tablet (p<0.01). The plasma half-time of nifedipine in the capsule was shorter than that in the retard tablet (p<0.05). The absorption rate of nifedipine from the capsule tended to be larger than that from the retard tablet. Plasma concentrations of nifedipine, measured 12hr after the dosing of the retard tablet during chronic treatment, were not different from those after the acute administration of the retard tablet, suggesting that no accumulation of nifedipine occurs. The capsule of nifedipine elicited prompt and profound hypotension with short uration, while the retard tablet produced a hypotensive effect with relatively slow onset and long duration. Arterial pressure reduction was maintained throughout the day using 12 hourly dose of the retard tablet. During the chronic treatment the maximum hypotensive effect was observed 4 weeks after the start of treatment. Twelve hourly administration of the retard tablet is a convenient regimen for the long-term control of mild to severe essential hypertension.