High Performance Liquid Chromatoqraphic Method for the Simultaneous Determination of Labetalol and Hydrochlorothiazide in Tablets and Spiked Human Plasma

A reversed-phase HPLC method with spectrophotometric detection was developed for the simultaneous determination of labetalol (LBT) and hydrochloro-thiazide (HCD). The chromatographic separation was performed using a Microbondapak C₁₈ column (4.6 i.d. x 250 nm) and paracetamol as internal standard. A mobile phase consisting of 0.05 M phosphate buffer/acetonitrile of pH 4 (7:3) at a flow rate of 0.7 ml/min was used. The detection was affected spectrophotornetrically at 302 nm. The working concentration range was 0.3–10 µg/ml with detection limits of 0.05 µg/ml for both drugs. The lower quantitation limit was 0.25 µg/ml in the two cases. The method was successfully applied to tablets, the % recoveries were 99.45 ± 0.68 for LBT and 99.79 ± 0.75 for HCD. The method was extended to the in-vitro determination in spiked human plasma. The % recoveries were 91.12 ± 0.33 for LBT and 91.37 ± 0.40 for HCD. The interday and intraday precision and accuracy were evaluated in plasma by calculating the % RSD (n=5) and the % error and were found to be in the ranges of 1.18–4.1% and 0.38–0.36% for both drugs, respectively.