Extemporaneous Compounding of Low-strength Aspirin Capsules for Desensitization Protocols

Aspirin is a non-steroidal, anti-inflammatory drug used for a range of indications. For patients with aspirin hypersensitivities, a desensitization procedure may be prescribed, and the initial low doses of <81 mg need to be provided by compounded preparations. Compounding with aspirin is associated with stability challenges due to its poor chemical stability. Additionally, low-strength preparations often exhibit dosage accuracy and uniformity issues. This study was designed to assess the feasibility of compounding low-strength aspirin capsules for the use in desensitization protocols. Aspirin capsules of 40-mg, 10-mg, 3-mg, and 1-mg strengths were prepared by manual filling of dry powders. Formulations were kept as simple as possible for ease of compounding, and the ingredients and compounding procedures were carefully selected to minimize the moisture content and to optimize the dosage accuracy. For the 40-mg and 10-mg capsules, two formulations were tested, using pure drug or crushed tablet powder. For the 3-mg and 1-mg capsules, only one formulation was tested, using a 5% mixture of pure drug and cellulose. All formulations were filled into hydroxypropyl methylcellulose capsule shells and stored at room temperature for 90 days. A  stability indicating, high-performance liquid chromatography method was used to analyze the quality of the capsules. The initial potency results of all capsule formulations were within 100% to 105% of the label claim, and the standard deviation was <3% for all formulations except the 1-mg strength (7%). The use of crushed tablet powder over pure drug powder appeared to reduce the potency variability, probably due to the larger fill weight per capsule. Upon storage at room temperature, the 40-mg and 10-mg formulations retained >90% of the label claim for up to 90 days, but the 3-mg and 1-mg formulations retained >90% of the label claim for up to only 31 days. Low-strength aspirin capsules were prepared successfully by compounding with a beyond-use date of at least 31 days at room temperature. However, the overall trend confirmed the challenges of achieving dosage uniformity and aspirin stability at 3-mg and 1-mg strengths. For general application in compounding pharmacies, trial batches are recommended with proper analytical testing.