Objective Capsule compounding is common for paediatric patients. In Europe, pharmacists often use a volume-based method whereas, in the USA, the weight-based method prevails. These two methods should be compared in order to help hospital pharmacists to make their choice.

Methods We evaluated the difference between the volume-based method and the weight-based method with 10 mg spironolactone capsules. Six independent batches were made with each technique and their conformity was evaluated with a high-performance liquid chromatography assay.

Results The weight-based method showed superiority over the volume-based method for the following parameters: spironolactone content homogeneity, total weight content homogeneity, batch reproducibility and batch conformity. No differences were seen in spironolactone content between the two methods, but an overall trend towards underweighing the excipient was found with the volume-based method.

Conclusions Capsule compounding with the weight-based method increases the quality of the resulting formulation. The weight-based method requires knowledge of the galenic parameters of the active pharmaceutical ingredient and excipients, but should be preferred to the volume-based method.