DIFFERENT EFFECTS OF NIFEDIPINE AND AMLODIPINE ON CIRCULATING CATECHOLAMINE LEVELS IN ESSENTIAL HYPERTENSIVE PATIENTS

Objective To compare the acute and chronic effects of nifedipine retar d (NPA), nifedipine gastrointestinal therapeutic system (NGITS) and am lodipine at trough and peak plasma concentrations of drug on blood pre ssure and heart rate, and on plasma norepinephrine and epinephrine lev els in patients with mild-to-moderate hypertension (diastolic blood pr essure 95-115 mmHg). Design and methods After 3-4 weeks' placebo treat ment, patients of both sexes were randomly allocated to be administere d 10 or 20 mg NPA twice a day, 30 or 60 mg NGITS once a day, and 5 or 10 mg amlodipine once a day for 6 weeks. Initially, for the first 2 we eks, the lowest dose of each drug was used, but higher doses were admi nistered after 2 weeks if sitting diastolic blood pressure was > 90 mm Hg. Patients were evaluated after administration of the first dose and after 6 weeks' therapy in a hospital setting, Blood samples were take n for high-performance liquid chromatography measurement of catecholam ine and drug levels at various intervals for a period covering trough to peak drug level ranges. Results Administration of all three drugs r educed clinic blood pressure to the same level after 6 weeks' therapy, but heart rate was increased slightly only with amlodipine (P< 0.05), Administration of NPA reduced blood pressure more abruptly whereas ad ministrations of NGITS and amlodipine induced smoother falls after acu te and chronic treatments: a significant increase in heart rate was ob served with amlodipine after chronic treatment. Both acute and chronic treatments with NPA (n = 19) increased norepinephrine levels (P< 0.01 ) transiently (2-4 h), In contrast, administration of NGITS (n = 22) d id not increase norepinephrine levels and even induced a slight but si gnificant decrease in norepinephrine levels 5-6 h after chronic treatm ents. Although administration of amlodipine (n = 22) did not increase norepinephrine levels transiently either after acute or after chronic administration, it did induce a sustained rise in basal norepinephrine levels by more than 50% after chronic therapy (P < 0.01). Plasma epin ephrine levels were not increased by any of the treatments and even a slight decrease was observed 4 h after administration of a dose follow ing chronic treatments with NGITS and amlodipine (P < 0.05). Conclusio ns The transient increase in norepinephrine levels observed with NPA a nd the sustained increases in norepinephrine levels observed after chr onic treatment with amlodipine suggest that sympathetic activation occ urs with those two drugs. The lack of increase in norepinephrine level s after administration of NGITS suggests that this formulation does no t activate the sympathetic system. The lowering of epinephrine levels after administrations of NGITS and amlodipine suggests that inhibition of release of epinephrine by the adrenal medulla occurs with longer-a cting dihydropyridine formulations. J Hypertens 16:1357-1369 (C) 1998 Lippincott Williams & Wilkins.