A simple and rapid liquid chromatographic assay for evaluation of potentially counterfeit Tamiflu®

A simple and rapid liquid chromatographic assay for the evaluation of potentially counterfeit oseltamivir (Tamiflu®) has been developed and assessed. The assay uses approximately 1 mg Tamiflu® powder when used for authentication and content estimate. The procedure was validated using 50 replicates analysed during five independent series with a total R.S.D. of 11.2%. The assay can also be used to monitor the exact content of oseltamivir in Tamiflu® capsules. One Tamiflu® capsule was transferred to a 250 mL volumetric flask and 150 mL water was added. The flask was placed in an ultrasonic bath at 40 °C for 20 min to dissolve the capsule. The solution was allowed to cool to room temperature before the flask was filled up to the mark (250 mL). A small aliquot was centrifuged and then directly injected into the LC-system for quantification. Oseltamivir was analysed by liquid chromatography with UV detection on a Hypersil Gold column (150 mm × 4.6 mm) using a mobile phase containing methanol–phosphate buffer (pH 2.5; 0.1 M) (50:50, v/v) at a flow rate of 1.0 mL/min. The assay was implemented for the analysis of Tamiflu® purchased over the Internet and at local pharmacies in Thailand and Vietnam.