What indicates a physical incompatibility when combining drugs?

A change in solution temperature can indicate a physical incompatibility when combining drugs because it often suggests that a chemical reaction or physical change is occurring between the substances. When two drugs are mixed, an exothermic or endothermic reaction might take place, leading to a noticeable change in the temperature of the solution. This temperature change is a direct indicator of interactions occurring at a molecular level, such as precipitation, dissolution, or other physical changes that may compromise the efficacy or safety of the combined formulation.

Other options do not reliably indicate physical incompatibility. A decrease in solution viscosity might suggest certain interactions but doesn't necessarily confirm incompatibility. An increase in drug potency typically signals an enhancement of drug effects rather than incompatibility. The formation of acid-base pairs may occur in drug combinations but is more related to chemical interactions than to physical incompatibility.