Sensitive and Rapid HPLC Method for Determination of Memantine in Human Plasma Using OPA Derivatization and Fluorescence Detection: Application to Pharmacokinetic Studies

A rapid, sensitive and reproducible HPLC method was developed and validated for the analysis of memantine in human plasma after derivatization with o-phthaldialdehyde (OPA) and fluorescence detection. Amantadine was used as internal standard. The derivatized memantine and amantadine were eluted in less than 10 min with no interference from endogenous plasma peaks. The analysis was carried out on a monolithic silica column (Chromolith Performance RP-18e, 100×4.6 mm). The mobile phase was composed of a mixture of acetonitrile and 0.025 M phosphate buffer (50:50, v/v, pH=4.6) with a flow rate of 2.5 mLmin⁻¹. The excitation and emission wavelengths were set at 335 nm and 440 nm respectively. The assay enables the measurement of memantine for therapeutic drug monitoring with a lower quantification limit of 2 ngmL⁻¹. The method involves simple extraction procedure and analytical recovery was 82.8± 0.9%. The calibration curve was linear over the concentration range 2–80 ngmL⁻¹. The coefficients of variation for inter-day and intra-day assay were found to be less than 8%. The method was successfully applied to pharmacokinetic studies in humans.