An inexpensive and sensitive method for the determination of quinidine in plasma by high-performance liquid chromatography with ultraviolet detection.

A sensitive, specific, and rapid high-performance liquid chromatographic method with ultraviolet detection for therapeutic drug monitoring of the cardioactive compound quinidine is described. The method uses only 50 microliters of serum, which is extracted into methyl-t-butylether at an alkaline pH and consequently reextracted into dilute hydrochloric acid. Quinidine is separated from quinine, the internal standard, and dihydroquinidine on a reversed phase C18 column. The minimum detectable amount is 1 ng injected on column. The method is both precise and accurate, as shown by the validation data presented, and can also be of use in pharmacokinetic investigations.