Introduction: in spite of significant risks, as well as non-clinical importance due to loss of potency, stiff penalties against administration of expired medications are still not appropriately enforced by health policy makers in many developing countries, possibly because of little evidence to support that expired medications are hazardous. The purpose of this study therefore, was to investigate the effect of expiration dates on in vitro bacteriostatic potentials of oral paediatric antibiotics.

Methods: comparative bacteriostatic potentials of 31 expired and seven corresponding unexpired oral paediatric antibiotics were determined on infantile diarrhoeagenic bacteria, using a modification of agar well-diffusion method.

Results: verall total percentage in vitro resistance rates against expired and unexpired paediatric antibiotics respectively were - E. coli (≤100% vs. ≤15.9%), Klebsiella pneumoniae (≤100% vs. ≤31.3%), Proteus mirabilis (≤91.7% vs. ≤41.7%) and Staphylococcus aureus (≤100% vs. ≤18.2%). Resistance rates of 45.5-55.8% (sulfamethoxazole + trimethoprim 5), 39.5-63.6% (amoxycillin 6), 46.5-54.5% (cotrimoxazole 7), 37.5-63.6% (ampicillin + cloxacillin 18), and higher resistance rates of ≥75.0-100% were exhibited towards remaining expired antibiotics. Higher total resistance and multiple antibiotic resistance (MAR) rates were also recorded against expired antibiotics (45.2-93.5%) compared to unexpired antibiotics (28.6-57.2%), except for few strains of E. coli and Proteus mirabilis. Furthermore, unexpired paediatric antibiotics exhibited wider zones of inhibition towards the test diarrhoeagenic bacteria (≥25.0 mm diameter).

Conclusion: this study provided preliminary microbiological results on the appreciable reduction in in vitro bacteriostatic potentials, as well as higher resistance and multiple antibiotic resistance rates among expired oral paediatric antibiotics on infantile diarrhoeagenic bacteria. Apart from less-efficacy, administration of expired antibiotics can lead to increased antibiotic resistance and clinical treatment failure, as well as adverse drug reactions.