Compatibility definitions

Definition of observational compatibility data

Observational data gives an indication of the likely physical compatibility of the combination in use, i.e. no obvious physical change in appearance, e.g. discoloration, clouding, the precipitation of particles or crystals. It is subjective, limited and imprecise and generally, only major incompatibilities will be identified in this way.

Definition of physical laboratory compatibility data

Laboratory data is generally derived from microscopic examination of a drug mixture under polarised light at specified concentrations and several time points when kept under controlled conditions. It may include other laboratory tests to determine whether any physical changes have taken place. It is more robust than observational data, but is still not definitive as a solution may remain physically clear even when there is chemical incompatibility.

Definition of chemical compatibility data

If mixing two or more drugs does not result in a chemical change leading to loss or degradation of one or more of the drugs, the mixture is said to be chemically compatible. Chemical compatibility data are generally obtained by analyzing the drug mixture by high-performance liquid chromatography (HPLC) at specified concentrations and several time points when kept under controlled conditions
Occasionally a drug combination has been shown to be chemically compatible but physically incompatible. Thus, physical compatibility should be checked before proceeding to chemical analysis.