Preservation of magistral formulas
The type of base used to make magistral formulas has a considerable impact on their preservation. For instance, making a hydrocortisone 2.5% magistral formula using an oil base rather than a water base will significantly extend its expiry date and effectiveness.
To this end, the Ordre des pharmaciens du Québec has set the best before date (DLU)** for non-aqueous preparations at six months.
A study conducted by researchers at Université de Montréal in conjunction with a pharmacist named Philip Morgan showed that oil-based products degraded by less than 4% after twelve months.
It is therefore feasible to record an expiration date of 12 months on the formula at the time of delivery to the patient, which would result in significant savings for the later.
The analyses also focused on the container in which Nitroglycerin formulas are contained.
The attached graph shows that neither the amber glass container nor the plastic container affects the stability of the product in any significant way.
Using a plastic container for oil-based preparations is therefore perfectly suitable.
As far as claims go, it is important to indicate “white soft paraffin” to help ensure that the formula is covered by private insurance or government insurance.
Details on this particular study can be found in the November 2016 edition of Québec Pharmacie.
* Percentage of residual active elements in the topical formula after storage at 25 Celsius/60% RH
** DLU: date limite d’utilisation