Stability testing of extemporaneous preparation of methyl salicylate ointment

Background: Pharmacist in community pharmacy, hospital or nursing home may be left with only option of preparing extemporaneous formulation using traditional compounding techniques when none of the available commercial dosage forms is appropriate to meet the special needs of some special patients. It is essential to make available safe, effective and stable drug formulation that is well-tolerated by the patient of particular age and condition, but the biggest concern is quality, particularly the stability of extemporaneous preparations which are not subjected to testing like a product approved for market. Unavailability of stability data limits the availability of many medicines for special patients. Aim: The dermatological formulations constitute a large proportion of extemporaneously compounded drugs and condition at which such extemporaneous products shall be stored to maintain the quality of product until use needs to be determined. This research was undertaken to carry out the stability testing of extemporaneous methyl salicylate ointment to determine the shelf life. Materials and Methods: Methyl salicylate analgesic ointment prepared extemporaneously as per extemporaneous preparation manual of King Fahad Central Hospital, Jazan, was subjected to stability study at 25°C ± 5°C and 2°C–8°C for 120 days. Results: The shelf life (t90%) of extemporaneously prepared methyl salicylate ointment was found to be 131 days at room temperature (25°C ± 5°C) and 176 days in the refrigerator (2°C–8°C). Conclusion: The methyl salicylate present in extemporaneous ointment preparation is fairly stable at cool temperatures but shows faster degradation at higher temperature conditions. Therefore, it is recommended that an expiry date of 4 months can be safely mentioned when stored in cool.