Quantification of an antiviral drug (stavudine) by three procedures based on redox and complex formation using N-bromosuccinimide

Abstract

Three simple, sensitive and rapid methods are described for the determination of stavudine (STV) in bulk drug and in formulations using N-bromosuccinimide (NBS) as the oxidimetric reagent. In titrimetry, an aqueous solution of STV is titrated directly in HCl medium with NBS using methyl orange as indicator. Spectrophotometric methods involve the addition of a known excess of NBS to STV in HCl medium followed by estimation of the unreacted oxidant by two reaction schemes involving the use of iron(II) and thiocyanate (method A) or tiron (method B). In all the methods, quantification is based on the amount of NBS reacting with STV. Calculations in titrimetry are based on a 1:2 (STV:NBS) reaction stoichiometry and the method is applicable over 1-9 mg range. In spectrophotometric methods, the absorbance is found to decrease linearly with STV concentration. Beer’s law is obeyed over the ranges 0.5-4.0 and 1.5-18 µg mL⁻¹ for method A and method B, respectively. The calculated molar absorptivity values are 6.5×10⁴ and 1.1×10⁴ L mol⁻¹cm⁻¹ for method A and method B, respectively. The limits of detection (LOD) and quantification (LOQ) are also reported for both methods. The RSD values for intra-day and inter-day precision studies were <2.5 and 3.0%, respectively. The procedures were successfully applied for the determination of STV in pharmaceutical formulations with good recovery, good accuracy and precision, and without measurable interference by the excipients.