A study to investigate the chemical potency, physical stability, and efficacy of analgesic agents over a period of two years post their expiry date.

Background: As per regulations, drugs have to be used within their shelf life and must be discarded after their expiry date. The present study was conducted in commonly used analgesic agents to investigate the change in the physical, chemical, and efficacy parameters of the drugs over a period of two years after their expiry date.
Methods: The drugs studied were Tab Ibuprofen, Tab Diclofenac, Tab Piroxicam, Inj Diclofenac, and Inj Piroxicam. The parameters investigated were chemical potency, physical stability, and analgesic efficacy. Testing for these parameters was carried out once before expiry to establish the baseline followed by at expiry, and then every six months for two years post expiry date.
Results: The active ingredient in all the drugs were within the accepted range as per IP during the study period indicating that they retained their potency up to a period of two years post expiry. The analgesic efficacy as determined by the "Radiant Heat Tail flick" and "Acetic acid-induced writhing" model also showed no significant difference in the Maximum Possible Efficacy and Percent protection, indicating that the drugs retained their efficacy. There was a slight difference in the dissolution times at expiry as compared to different time periods in the case of Ibuprofen and Diclofenac, while there are was no statistical difference in the disintegration times during the study period.
Conclusion: The analgesic drugs in our study retained their chemical potency, physical stability and analgesic efficacy up to a period of two years after expiry. The expiry date of a drug, as estimated currently, is not an accurate reflection of its actual shelf life.