Thiamine is usually nontoxic even following administration of large doses; however, feelings of warmth, tingling, pruritus, pain, urticaria, weakness, sweating, nausea, restlessness, tightness of the throat, angioedema, respiratory distress, cyanosis, pulmonary edema, GI bleeding, transient vasodilation and hypotension, vascular collapse and death have occurred occasionally, mainly following IV administration of the drug. In animals, very large parenteral doses of Thiamine have produced neuromuscular and ganglionic blockade.
Pyridoxine is usually nontoxic; however, chronic administration of large doses of Pyridoxine has been associated adverse effects. Nausea, headache, paresthesia, somnolence, and increased serum AST (SGOT) and decreased serum folic acid concentrations have been reported.
Cyanocobalamin is usually nontoxic even in large doses, however, mild transient diarrhea, peripheral vascular thrombosis, itching, transitory exanthema, urticaria, feeling of swelling of the entire body, anaphylaxis, and death have been reported.
Although allergic reactions to cyanocobalamin have generally been attributed to impurities in the preparation, a few patients have reacted positively to skin testing with purified cyanocobalamin of hydroxocobalamin.