Analysis of oseltamivir active metabolite, oseltamivir carboxylate, in biological materials by HPLC-UV in a case of death following ingestion of Tamiflu®

An HPLC-UV method was established for determination of oseltamivir carboxylate, an active metabolite of oseltamivir, in biological materials. Oseltamivir carboxylate and floropipamide (internal standard) were extracted by using a mixed mode cation exchange extraction cartridge. The recovery yields of oseltamivir carboxylate from spiked blood at concentrations 0.1 μg/ml and 1.0 μg/ml were 103.8 ± 16.9% and 95.0 ± 4.3%, respectively. Linearity was obtained in the concentration from 0.1 to 3.0 μg/ml. The detection limit was 0.04 μg/ml (S/N = 3). This method was applied to a case of death from falling after ingestion of a Tamiflu® capsule containing 75 mg of oseltamivir. Concentration of oseltamivir carboxylate in the femoral blood was 0.4 μg/ml. The highest concentration in all specimens was in the liver at 18.3 μg/g. In all brain samples, the concentrations were not higher than the quantification limit (0.1 μg/g).