Pharmacokinetics of azidocillin in healthy adults

Two cross-over studies with azidocillin-sodium were carried out on healthy volunteers. In the first, we gave single doses of 375 mg, 750 mg, 1500 mg as tablets, 750 mg as a suspensions, i.m. and i.v. injections of 799 mg, and a course of 750 mg tablets twice daily for 14 days. In the second study, two 750 mg tablet batches were compared with the same dose i.v. Mean peak concentrations after 750 mg as tablets were 6.5-8 microgram/ml, as suspension 12.4 microgram/ml, and i.m. 18.5 microgram/ml. The urinary recovery of active antibiotic was 37-40% of the dose after the tablets, and nearly 50% after i.v. dosage. Thus, urinary elimination after the tablets was 75-83% of the amount eliminated after i.v. dosage. Bioavailabilities stipulated on the basis of the area under serum concentration curves in comparison with i.v. dosage were 57-60% for the tablets and 64% for the suspension. The bioavailability of the i.m. dose was comparable to that of the i.v. injection. The relatively small difference between the tablets and the suspension indicates that the tablets had favourable biopharmaceutical properties. Serum half-life of azidocillin was 0.6-0.7 h after the i.v. doses. For the other dosage forms, the half-life values varied between 0.6 and 1.1 h. The distribution volume Vd,beta ws 27-34 l after i.v. administration.