Comparative ultraviolet spectrophotometric assay and post-marketing potency evaluation of available brands of doxycycline hyclate capsules in Nigeria

Introduction: Doxycycline is a semi-synthetic tetracycline antibiotic in which a hydroxy group replaces the 5?-hydrogen, while the 6?-hydroxy group is replaced by hydrogen. It is used to inhibit bacterial protein synthesis and treat non-gonococcal urethritis and cervicitis, as well as exacerbations of bronchitis in patients with chronic obstructive pulmonary disease, and adult periodontitis. This study developed and validated an ultraviolet (UV) spectrophotometric method for the assay of doxycycline capsule formulations using 0.1N NaOH as the solvent and compared it with the previously developed and validated method, using 0.1N HCl. Methods: The UV methods were applied to evaluate the quality of marketed formulations by assessing identity, weight variation, and strength. Results and Discussion: Besides the detection wavelength of 265 nm versus 268 nm, the optical and validation parameters of the method using 0.1N NaOH as the assay solvent did not differ from the method using 0.1N HCl, as shown by the limits of detection [(µg/mL): 0.3200 versus 0.3219], limits of quantification [(µg/mL): 0.9698 versus 0.9755], and Sandell's sensitivity [(µg·cm-2): 0.0311 versus 0.0255]. Of the six available brands of doxycycline tested, all passed the identity test, but only 66.67% met the USP specifications for dosage uniformity and doxycycline content. Conclusion: The new method proved to be simple, rapid, precise, accurate, and cost-effective, and compared favourably with the previously reported method using 0.1N HCl as the assay solvent. It was successfully used to assay the doxycycline content in capsule formulations.