Comparison of two spectrofluormetric procedures for quinidine determination in biological fluids.

Different methods for the spectrofluorometric determination of quinidine in plasma and urine were studied. The alkaline washings of plasma and urine extracts remove fluorescent metabolites, as shown by TLC analysis of urine extracts, and do not lead to a significant loss of alkaloids. The spectrofluormetric assays without alkaline washings of the benzene extract averaged 18% higher than the assays with alkaline washings. Since unchanged quinidine and hydroquinidine are responsible for antiarrhythmic activity, the method with alkaline washing is more appropriate for the control of quinidinemia than are other methods. The therapeutic plasma concentration range becomes 0.8-2.5 microng/ml with this methods.