Pharmacokinetics and hypotensive effect of diltiazem in rabbits after a single intravenous administration: effect of phenobarbital.
Metabolism of the widely used calcium antagonist diltiazem (DTZ) is an important contributing factor to its therapeutic effects. In order to study the effects of CYP3A induction on the pharmacokinetics and haemodynamic effect of DTZ, it was administered as a single 5 mg/kg dose i.v. to two groups of New Zealand white rabbits (n = 6 in each group). Prior to the injection, one of the groups received phenobarbital 20 mg/kg s.c. two times a day for 3 days to ensure CYP3A induction, and the other received normal saline. A third group of animals (n = 6) received neither phenobarbital nor DTZ, and served as the control. Blood samples, systolic and diastolic blood pressure (SBP and DBP), and heart rate (HR) recordings were obtained from each rabbit up to 7 h, and urine samples for 48 h post-dose. Plasma concentrations of DTZ and its metabolites were determined by HPLC. The results showed that phenobarbital increased the Cl and Vdss of DTZ from 24 +/- 14 to 51 +/- 4.9 ml/min/kg and from 1.9 +/- 1.2 to 3.8 +/- 0.7 l/kg, respectively (p < 0.05). It also decreased the plasma concentrations of DTZ and all the measured metabolites in this study. Both phenobarbital and DTZ decreased SBP and DBP significantly without affecting the HR.
Yeung
P K
PK
Pharmacokinetics and Metabolism Laboratory, College of Pharmacy, Dalhousie University, Halifax, Nova Scotia, Canada.
Feng
J D
JD
Buckley
S J
SJ
D000818:Animals; D000959:Antihypertensive Agents / Q000097:blood / Q000494:pharmacology*; D001189:Aryl Hydrocarbon Hydroxylases; D001794:Blood Pressure / Q000187:drug effects*; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D004110:Diltiazem / Q000097:blood / Q000494:pharmacology*; D004347:Drug Interactions; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D007275:Injections, Intravenous; D010089:Oxidoreductases, N-Demethylating / Q000502:physiology; D010634:Phenobarbital / Q000008:administration & dosage / Q000494:pharmacology*; D011817:Rabbits
D000959:Antihypertensive Agents; D002121:Calcium Channel Blockers; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D004110:Diltiazem; D010634:Phenobarbital