Determination of clindamycin in plasma or serum by high-performance liquid chromatography with ultraviolet detection.

A simple, sensitive high-performance liquid chromatographic assay for the determination of clindamycin in human plasma or serum has long been hampered by inability to separate it from endogenous compounds. We describe here such an assay. Proteins from a 200-microliters sample were precipitated by addition of acetonitrile containing the internal standard, triazolam. The sample was then vortex-mixed and centrifuged at approximately 3000 g for 10 min. The supernatant was evaporated to about 250 microliters under nitrogen, and 10-30 microliters were analyzed using an autoinjector. An octadecylsilane column with acetonitrile-water-phosphoric acid-tetramethylammonium chloride as mobile phase and ultraviolet detection at 198 nm provided a reproducibly quantifiable peak corresponding to 0.17 micrograms/ml. Retention times for clindamycin and triazolam averaged 8 and 11.8 min, respectively. Replicate standard curves run over a 36-h period showed no loss of integrity; r2 values generally exceeded 0.999. The method has successfully been applied to the analysis of samples taken up to 12 h after administration of intravenous infusions of 600-1200 mg in healthy volunteers.