Determination of pramipexole (U-98,528) in human plasma and urine by high-performance liquid chromatography with electrochemical and ultraviolet detection

A sensitive and selective high-performance liquid chromatographic (HPLC) method was developed for the determination of pramipexole in human plasma and urine. Plasma/urine is made alkaline before pramipexole and BHT-920 (internal standard) are extracted by ethyl ether and back-extracted with a solution that contains heptanesulfonic acid. Separation is achieved by ion-pair chromatography on a Zorbax Rx C₈ column with electrochemical detection at 0.6 V for plasma and ultraviolet detection at 286 nm for urine. The retention times of pramipexole and internal standard are approximately 14.4 and 10.7 min, respectively. The assay is linear in concentration ranges of 50 to 15 000 pg/ml (plasma) and 10 to 10 000 ng/ml (urine). The correlation coefficients are greater than 0.9992 for all curves. For the plasma method, the analysis of pooled quality controls (300, 3000, and 10 000 pg/ml) demonstrates excellent precision with relative standard deviations (R.S.D.) (n=18) of 1.1%, 2.3%, and 6.8%, respectively. For the urine method, quality control pools prepared at 30, 300, and 3000 ng/ml had R.S.D. values (n=18) of 2.9%, 1.7%, and 3.0%, respectively. The plasma and urine controls were stable for more than nine and three months, respectively. The mean recoveries for pramipexole and internal standard from plasma were 97.7% and 98.2%, respectively. The mean recoveries for pramipexole and internal standard from urine were 89.8% and 95.1%, respectively. The method is accurate with all intra-day (n=6) and overall (n=18) mean values for the quality control samples being less than 6.4 and 5.8% from theoretical for plasma and urine, respectively.