Oral vs. Intramuscular Vitamin B12 for Treating Vitamin B12 Deficiency

(Strength of Recommendation [SOR]: C, disease-oriented evidence, systematic review of two randomized controlled trials [RCTs], and two additional RCTs.) For increasing vitamin B12 levels, oral supplementation at 2,000 mcg per day is more effective than intramuscular supplementation at 1,000 mcg per day; however, 1,000 mcg per day orally is equivalent to 1,000 mcg per day intramuscularly. A 2017 prospective, nonblinded, randomized trial from Switzerland, excluded from the 2018 Cochrane review, compared oral cyanocobalamin therapy with intramuscular hydroxo -cobalamin therapy in 37 patients (mean age = 49.5 years; 60.5% women) with vitamin B12 deficiency (less than 200 pg per mL).3 The oral group received 1,000 mcg of cyanocobalamin per day through an electronically monitored punch card (99.6% adherence by pill count), and the intramuscular group received 1,000 mcg of hydroxocobalamin weekly for four weeks. Serum vitamin B12 levels at the start of oral therapy (median = 410 pg per mL [302.50 pmol per L]) increased and then plateaued at three months (median = 1,164 pg per mL [858.80 pmol per L]), with no patients meeting criteria to restart intramuscular supplementation.