Interactions with Medications

Vitamin B12 has the potential to interact with certain medications. In addition, several types of medications might adversely affect vitamin B12 levels. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin B12 status with their healthcare providers.

Chloramphenicol

Chloramphenicol (Chloromycetin®) is a bacteriostatic antibiotic. Limited evidence from case reports indicates that chloramphenicol can interfere with the red blood cell response to supplemental vitamin B12 in some patients [82].

Proton pump inhibitors

Proton pump inhibitors, such as omeprazole (Prilosec®) and lansoprazole (Prevacid®), are used to treat gastroesophageal reflux disease and peptic ulcer disease. These drugs can interfere with vitamin B12 absorption from food by slowing the release of gastric acid into the stomach [83-85]. However, the evidence is conflicting on whether proton pump inhibitor use affects vitamin B12 status [86-89]. As a precaution, health care providers should monitor vitamin B12 status in patients taking proton pump inhibitors for prolonged periods [82].

H2 receptor antagonists

Histamine H2 receptor antagonists, used to treat peptic ulcer disease, include cimetidine (Tagamet®), famotidine (Pepcid®), and ranitidine (Zantac®). These medications can interfere with the absorption of vitamin B12 from food by slowing the release of hydrochloric acid into the stomach. Although H2 receptor antagonists have the potential to cause vitamin B12 deficiency [90], no evidence indicates that they promote vitamin B12 deficiency, even after long-term use [89]. Clinically significant effects may be more likely in patients with inadequate vitamin B12 stores, especially those using H2 receptor antagonists continuously for more than 2 years [90].

Metformin

Metformin, a hypoglycemic agent used to treat diabetes, might reduce the absorption of vitamin B12 [91-93], possibly through alterations in intestinal mobility, increased bacterial overgrowth, or alterations in the calcium-dependent uptake by ileal cells of the vitamin B12-intrinsic factor complex [92,93]. Small studies and case reports suggest that 10%–30% of patients who take metformin have reduced vitamin B12 absorption [92,93]. In a randomized, placebo controlled trial in patients with type 2 diabetes, metformin treatment for 4.3 years significantly decreased vitamin B12 levels by 19% and raised the risk of vitamin B12 deficiency by 7.2% compared with placebo [94]. Some studies suggest that supplemental calcium might help improve the vitamin B12 malabsorption caused by metformin [92,93], but not all researchers agree [95].