Which drugs are known to potentially alter the efficacy of B-12?

Cimetidine and neomycin are known to potentially impact vitamin B-12 absorption and efficacy. Cimetidine is an H2-receptor antagonist used to reduce stomach acid. Long-term use of this medication can alter the stomach environment and may lead to reduced gastric acid secretion, which is essential for the proper release of vitamin B-12 from food sources. Decreased gastric acid can impair the protein digestion necessary for B-12 absorption in the intestines.

Neomycin is an antibiotic that can disrupt the normal gut bacteria, which in turn can affect the absorption of several nutrients, including vitamin B-12. The disturbance of gut flora not only can hinder the absorption of B-12 but also affect other critical vitamins and minerals due to its role in gut health.

The other options listed involve drugs that have other mechanisms of action and are less directly linked to the alteration of B-12 absorption or effectiveness. While some medications may impact vitamin levels over time or in specific populations, the direct impact of cimetidine and neomycin on B-12 absorption is well-documented and established, which supports the assertion that they are significant in altering the efficacy of vitamin B-12.