Final answer:
Erythromycin and cimetidine inhibit liver microsomal enzymes, leading to increased plasma concentrations and prolonged actions of other drugs metabolized by the same enzymes, potentially increasing the risk of side effects.
Step-by-step explanation:
Erythromycin and cimetidine are examples of drugs that can inhibit the metabolism of other drugs. These drugs are known to inhibit microsomal enzymes in the liver, such as cytochrome P450 isoenzymes, which are involved in the metabolic processing of many medications. The effect of this inhibition is an increase in the plasma concentration of the other drugs that are metabolized by the same pathway. For instance, erythromycin is a protein synthesis inhibitor that binds to the 50S ribosomal subunit of bacteria, thereby inhibiting bacterial growth. If erythromycin inhibits the metabolism of another drug, it could prolong the drug's action and increase the risk of side effects due to higher drug levels in the system.