Serum Concentrations and ex vivo Inhibitory/Bactericidal Activity of Clindamycin after Administration of Two Oral Dosages

Two dosages of clindamycin, 300 and 600 mg, were given orally to 10 patients each. The patients were admitted for minor elective surgery. Their mean age was 39.3 years; mean weight was 67.5 kg. None of them had taken antibiotics for at least 1 month. After administration of a single dose, blood samples were obtained at 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10 and 12 h after dosing. Drug levels were determined by the bioassay method using Micrococcus luteus as test organism. Serum inhibitory and bactericidal activities against five isolates each of Staphylococcus aureus and Streptococcus pyogenes were determined by the microdilution method according to the National Committee for Clinical Laboratory Standards guidelines. The mean peak serum level was 3.4 mg/l for the 300-mg dose and 4.8 mg/l for the 600-mg dose. The mean reciprocal peak inhibitory titers for the 300-/600-mg doses were 13.7/23.8 and 15.2/ 34.7 against S. aureus and S. pyogenes, respectively. Most serum samples did not show bactericidal activity against S. aureus.