Metered dose inhalers III: Metaproterenol sulphate; particle size distribution and dose uniformity.

Three American products and one Canadian product were examined for content uniformity and particle size distribution. The results showed that not all products performed equally well. Some of the products exhibited high sprays early in the canister lifetime and all products demonstrated loss of prime. The particle size distributions were determined using the Andersen cascade impactor (USP Induction Port) and the fine particle fraction was determined using the twin impinger. The results showed that three of the four products had similar particle size distribution profiles. Both the Andersen cascade impactor and the twin impinger yielded the same trends in the amount of drug substance delivered to the fine particle fraction.