The relative bioavailability of metoprolol following oral and rectal administration to volunteers and patients

The pharmacokinetics, efficacy and safety of metoprolol tartrate 25 mg fatt y suppositories were studied in 5 healthy volunteers and in 8 patients suff ering from instable angina pectoris. Metoprolol 25 mg capsules were used as a control oral dosage form. Metoprolol showed a considerable rectal bioava ilability (AUC, C max) and was absorbed quickly from the rectum (T max). In both groups rectal bioavailability was comparable. However, oral bioavaila bility was much lower in the volunteer group than in the patient group. Fur thermore, ratios of metoprolol/alpha-OH-metoprolol concentrations in plasma and urine gave an indication for a partial avoidance of the first pass eff ect after rectal administration. Further research is necessary to define an exact rectal dosage of metoprolol. In all patients, a substantial drop in heart rate, systolic and diastolic blood pressure was seen after administra tion of the first suppository. Metoprolol suppositories appear to be an eff ective, safe and suitable alternative for patients who are in need for beta blocking medication and who are unable to take oral medication for a certa in amount of time.