Final answer:
Cimetidine is an H2 blocker with numerous side effects and drug interactions, notably affecting the liver's enzyme system and potentially causing issues with various other medications.
Step-by-step explanation:
The H2 blocker with the most side effects (SE) and drug interactions is cimetidine.
Cimetidine is an H2 blocker known for having numerous side effects and drug interactions compared to others.
H2 blockers, also known as histamine H2-receptor antagonists, are a class of medications used to decrease stomach acid production. Among these, cimetidine has been historically noted for its side effects and interactions. Side effects may include gynecomastia (breast enlargement in men), impotence, and central nervous system effects such as confusion, especially in the elderly or in patients with renal dysfunction.
Regarding drug interactions, cimetidine can inhibit certain enzymes in the liver (cytochrome P450 enzymes), which are responsible for metabolizing many medications. This inhibition can lead to increased blood levels of these other drugs, potentially causing toxicity or increased side effects. Other drugs metabolized by the cytochrome P450 enzyme system that can interact with cimetidine include warfarin, phenytoin, theophylline, and some benzodiazepines. Prescribers often consider an alternative H2 antagonist, such as ranitidine or famotidine, which have fewer side effects and drug interactions.