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Pharmacology: Clindamycin exhibits its action by binding to the 50S subunit of the bacterial ribosome and thereby suppressing protein synthesis. On parenteral administration, the phosphate ester is rapidly hydrolyzed to the active parent compound. Following intramuscular injection, peak plasma concentrations are only attained after 3 hours in adults and 1 hour in children. The peak plasma concentrations obtained following intramuscular administration are 6 μg/mL with a 300 mg dose and 9 μg/mL with a 600 mg dose in adults. Immediately after a 20-45 minute intravenous infusion of 600 mg, the plasma concentrations is approximately 10 μg/mL. The half-life of clindamycin is about 2.7 hours and modest accumulation is thus expected to occur if it is given every 6 hours. The half-life may be lengthened in patients with impaired renal function, and dosage in these patients should he adjusted according to plasma concentrations. Accumulation may also occur in patients with hepatic failure. Clindamycin is 90% plasma protein bound. It is widely distributed in many fluids and tissues including bone, but not in sufficient concentrations in the cerebrospinal fluid. It does however cross the placental barrier. It accumulates in polymorphonuclear leukocytes and alveolar macrophages and is also concentrated in abscesses in experimental animals. About 10% of clindamycin is excreted unaltered in the urine and small quantities are to be found in the faeces. Clindamycin has been shown to have in vitro activity against isolates of the following organisms (in vitro sensitivity does not necessarily imply in vivo efficacy): Gram positive cocci: Staphylococcus aureus; Streptococcus (anaerobic species); Streptococcus pneurnoniae. Gram negative cocci: Clostridium perfringens. Gram negative bacilli: Campylobacter jejuni, Bacteroides species; Fusobacterium nucleatum. Susceptibility test should be performed.
Pharmacokinetics: General characteristics of active substance: Following parenteral administration, the biologically inactive clindamycin phosphate hydrolysed to clindamycin. When the equivalent of 300 mg of clindamycin is injected intramuscularly, a mean peak plasma concentration of 6 microgram/mL is achieved within three hours; 600 mg gives peak concentration of 9 microgram/mL. In children, peak concentration may be reached within one hour. When the same doses are infused intravenously, peak concentrations of 7 and 10 micrograms per mL respectively are achieved by the end of infusion. Clindamycin is widely distributed in body fluids and tissues, including bone, but it does not reach the cerebrospinal fluid in significant concentrations. It diffuses across the placenta into the foetal circulation and appears in breast milk. High concentrations occur in bile. It accumulates in leucocytes and macrophages. Over 90% of clindamycin in the circulation is bound to plasma proteins. The half-life is 2 to 3 hours, although this may be prolonged in pre-term neonates and patients with severe renal impairment, Clindamycin undergoes metabolism, to the active-demethyl and sulphoxide metabolites and also some inactive metabolites. About 10% of the drug is excreted in the urine as active drug or metabolites and about 4% in the faeces; the remainder is excreted as inactive metabolites. Excretion is slow and takes place over several days. It is not effectively removed from the blood by dialysis.
