Stability Assessment of Amoxicillin Capsules Stored Under Tropical Climatic Conditions in Port Harcourt, Rivers State

Amoxicillin is among the most frequently prescribed antibiotics in Nigeria and is listed on the country's Essential Medicines List. In the South South geopolitical zone, high ambient temperature and humidity characteristic of the tropical coastal climate of Rivers State may accelerate drug degradation, particularly for moisture-sensitive beta-lactam antibiotics. This study assessed the stability of three commercially available brands of amoxicillin 500 mg capsules stored under actual ambient conditions in Port Harcourt over a twelve-week period. Temperature and relative humidity were monitored continuously using calibrated data loggers. At predetermined intervals, samples were analysed for physical appearance, moisture content, dissolution profile, and active pharmaceutical ingredient content by HPLC. All three brands showed progressive decline in API content over the storage period, with one brand showing a reduction to below 90% of the declared content by week eight, falling outside pharmacopoeial acceptance limits. Moisture content increased significantly for samples not stored in airtight secondary packaging. Drug dissolution was significantly affected in the brand with highest moisture uptake. These findings confirm that tropical storage conditions in Rivers State accelerate amoxicillin degradation when adequate secondary packaging is not used. Improved dispensing practices and patient counselling on storage conditions are recommended. Keywords: amoxicillin, stability, tropical storage, HPLC, Port Harcourt.