Mass Balance Criteria (Uniformity of Dosage Units)

• Where possible, all laboratory measurements are validated in terms of establishing mass recovery to within ±20% either of the label claim (pMDIs) or the mass of formulation inserted in the reservoir (nebulizers). 
• If the result falls outside of these limits the test is repeated. 
• The label claim is the total mass per actuation specified by the manufacturer of the pMDI. 
• For those formulations for sale in the USA, label claim dose is specified ex-actuator mouthpiece. 
• Whereas, for pMDIs currently offered for sale in Europe and Canada, label claim is specified as ex-metering valve, and therefore includes that portion of the dose retained on the metering valve stem and within the actuator mouthpiece.

United States Pharmacopeia
European Pharmacopeia