Validated spectrophotometric methods for simultaneous determination of oxytetracycline associated with diclofenac sodium or with piroxicam in veterinary pharmaceutical dosage form

Two simple, precise, accurate and robust UV zero and first derivative orders spectrophometric methods have been developed and validated for the simultaneous determination of oxytetracycline (OTC) associated either with diclofenac sodium (DICLO) or with piroxicam (PIRO) in veterinary pharmaceuticals, without prior separation of the drugs. These proposed methods are also suitable for individual estimation of each drug in pharmaceutical products for human use. The first method is a zero order spectrophotometry for estimation of OTC at 360 nm in the association with DICLO. The second one employs a first derivative at 339 nm, using a zero-crossing technique to measure the OTC content in the association with PIRO. Both nonsteroidal anti-inflammatory drugs (DICLO and PIRO) were analyzed by first derivative spectrophometric at 298.5 nm (OTC zero-crossing point) in their respective associations. All measurements were carried out in acetronitrile:water (50:50, v/v; pH 2.5) and at room temperature (25 ± 2 °C). Analytical curves were linear (r > 0.9996) in the concentration range of 10.0–80.0 μg mL−1 for OTC, 1.5–25.0 μg mL−1 for DICLO and 2.5–30.0 μg mL−1 for PIRO. The limits of quantification were lower than 1.50 μg mL−1 and the mean of recoveries were within the acceptable limits of 98–102% for all three drugs. The developed methods can be successfully applied in the quality control routine for the simultaneous or individual determination of OTC, DICLO and PIRO in pharmaceutical dosage forms.