1 A new osmotic pressure mediated delivery system for metoprolol (Lopresor Oros) has been evaluated by measuring the haemodynamic effects and pharmacokinetics after single and multiple oral dosing in young healthy volunteers. 2 Similar studies have been carried out in the same group using equivalent single and multiple oral doses of the commercial slow‐release preparation (Slow Lopresor). 3 The new osmotic delivery system produces a more uniform haemodynamic response: a plateau metoprolol concentration in plasma is reached about 6 h after dosing and is maintained for 10 h.
This double-blind, cross-over study in healthy male subjects evaluated the pharmacokinetics of felodipine and metoprolol given both separately and in combination. During three, five-day study periods, felodipine 10 mg b.d., metoprolol 100 mg b.d. and a combination of the two, were given in random order. There was at least a 7-day washout period between each pharmacokinetic study day. Plasma levels of unchanged felodipine and metoprolol were measured for 24 h after the last dose, on the 5th day of each treatment period. Eight subjects, aged 19-22 years, completed the study. Both felodipine and metoprolol, given alone and in combination, were well tolerated. None of the felodipine pharmacokinetic variables (tmax, Cmax, Cmin, AUC (0-12) and t1/2) changed significantly when felodipine and metoprolol were given in combination. Cmax and AUC (0-12) for metoprolol increased significantly when metoprolol and felodipine were combined, although tmax, Cmin and t1/2 for metoprolol remained unchanged. The changes in metoprolol pharmacokinetics induced by felodipine are small and unlikely to be clinically important.
Nifedipine, metoprolol and atenolol were administered orally to young, healthy volunteers. Each drug was given alone and nifedipine was also given with both beta‐adrenoceptor blockers. Each drug was given for 3 days immediately before the study days. Plasma and urine drug concentrations were measured and the relevant pharmacokinetic parameters calculated. No pharmacokinetic interaction between nifedipine and the beta‐adrenoceptor blockers was revealed.
In a placebo controlled exercise protocol using healthy volunteers the effects of nadolol 80 mg and 160 mg orally and of nadolol 80 mg during treatment with nifedipine 20 mg 8 hourly were compared. Resting systolic and diastolic blood pressures were reduced by both nifedipine (p less than 0.05) and nadolol (p less than 0.01) acting alone. An unexpected finding was that nifedipine alone significantly inhibited exercise tachycardia (p less than 0.01) (8 to 12 h post dose). Predictably both doses of nadolol produced significant reduction in exercise tachycardia which was still apparent at 24 h. There was a linear relationship between log10 plasma nadolol concentration and reduction in exercise heart rate. The combined inhibitory effects of nifedipine and nadolol 80 mg on exercise heart rate showed partial additivity but did not summate. There was no pharmacokinetic interaction between the 2 drugs. The inhibition of exercise tachycardia by nifedipine, not previously documented, is consistent with an effect of the drug on the sinus node, as has been reported in in-vitro studies, and may contribute to the drugs efficacy in angina.
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