Effect of Medium pH on In Vitro Dissolution of Marketed Tetracyclines (Tetracycline and Doxycycline) Solid Oral Dosage Forms in Bahia, Brazil

Tetracyclines are widely used for the treatment of infections of the lower respiratory tract and other systems. In Brazil, tetracyclines are available as generic and similar products. The aim of this study was to evaluate the in vitro release of tetracycline capsules (500 mg) and doxycycline tablets (100 mg) in different reaction media, from dissolution profiles, using sensitive and rapid ultraviolet spectrophotometric methods. The dissolution test was used to obtain and compare dissolution profiles and establish similarities of pharmaceutical formulations in compliance with the Brazilian (for tetracycline hydrochloride capsules) and United States (USP) (for doxycycline hydrochloride tablets) pharmacopoeia. For both drugs, the dissolution studies were conducted using an USP type 2 apparatus at 75 rpm with 1000 mL distilled water at 37.0 ± 0.5 oC for 90 minutes, to evaluate the influence of pH (1.0–8.0) on the release of drugs. The methods were validated, showing precision, linearity, and accuracy. All the products satisfactorily released tetracycline and doxycycline, with at least 80% of the drug dissolved within 30 minutes. Tetracycline and doxycycline are weak acids, which favors their dissolution in acid media (pH range 1.0–6.0). This research contributes to studies that guarantee the quality control of tetracyclines and to the expansion of the novel methodologies established by the Brazilian Pharmacopoeia for doxycycline.