When preparing suspensions there are a number of sources from which you can access the active pharmaceutical ingredient or API. Raw materials are always the preferred source for compounding, however, this is not always possible (e.g. patented drugs). In these instances, a compounding pharmacist may be required to crush or open a commercially available tablet or capsule. Although this may appear to be an easy option, there are many pitfalls which need to be considered.
The Australian Don’t Rush to Crush handbook states that delayed-release, extended-release, cytotoxic or immunosuppressant, and buccal or sublingual formulations should not be crushed. Altering these formulations by crushing can alter the intended activity of the API or even render the API redundant by changing the route of administration leading to under-dosing of a therapy.
A good suspension relies on small particles for even distribution. Crushing tablets or capsule contents is not a reliable or effective way to micronize a powder. When compounding with enterically-coated or modified release commercial products, there is a risk of dose-dumping. Dose dumping is the rapid release of the entire amount or a significant fraction of an API from its dose form. This can mean that patients may get dosed with toxic levels of their treatment due to binders holding together clumps of the API after not being crushed enough.
These extra excipients, binders and coatings create more work for the compounder as the API weight does not correspond with the actual powder weight from a crushed tablet. Further calculations need to be completed to know how much of the crushed powder is required for the concentration required and adds an extra step for errors to occur. The manual crushing of a tablet in a mortar and pestle also means that 5-10% of the powder is lost.
Chemically, these extra excipients can interfere with the stability of a compounded formulation. Unless tested with the exact commercial product, any reactions between the compounding formulation and the commercial product are unknown and can lead to more rapid degradation. For example, if an ingredient in a commercial omeprazole capsule decreases the pH of a compounded omeprazole suspension, this can lead to rapid degradation of the omeprazole.
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References:
The Society of Hospital Pharmacists (2015). Reasons not to crush, Australian Don’t Rush to Crush Handbook, second edition, pg.13
Thong et al (2018). Drug loss while crushing tablets: Comparison of 24 tablet crushing devices. https://doi.org/10.1371/journal.pone.0193683
