Quantitation of Cimetidine and Cimetidine Sulfoxide in Serum by Solid-Phase Extraction and Solvent-Recycled Liquid Chromatography

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Abstract
A high performance liquid chromatographic method for the simultaneous determination of cimetidine and its major metabolite, cimetidine sulfoxide, was developed. These compounds and the internal standard, ornidazole, were extracted from 0.5 mL of serum using a solid phase Bond Elut® C18 analytical column with detection at 229 nm. Absolute recoveries were 94 to 103%, 93 to 104%, and 95 to 105% for cimetidine, cimetidine sulfoxide, and ornidazole, respectively. The minimum detection limit for cimetidine was 0.1 mg/L and for cimetidine sulfoxide was 0.05 mg/L when the concentrating step was used. Cimetidine and cimetidine sulfoxide demonstrated linearity up to 10 mg/L and 7.5 mg/L respectively, with the between-run precision of less than a 5% coefficient of variation for both compounds. Interferences from other drugs tested or endogenous substances in serum were not detected. The mobile phase was recycled to maintain better long term column stability and to minimize solvent cost. The instability of the drugs in solution was circumvented with a reduced-pressure drying process that produced working standards possessing long-term stability. The problem of drug interconversion observed during sample storage and with concentrating steps was controlled also. In addition, a resolution test mixture was chromatographed daily to control chromatographic quality.