Interactions with Vitamin B12 (Cobalamin)

In one study, 27 patients aged 15 to 54 treated with phenobarbitone (90 mg/day phenobarbital) and diphenylhydantion (300 mg/day phenytoin) regularly for 3 to 32 years had serum levels of vitamin B6 and B12 that were increased significantly relative to controls (Dastur and Dave 1987). Increased vitamin B12 levels in serum may indicate hepatic damage from anticonvulsants and reflect an impairment in hepatic storage capacity for the vitamin. Studies in rats suggest that phenytoin sodium may reduce vitamin B12 uptake by certain cells, including hematopoietic and neural cells (Latham et al. 1990). It is not known if phenytoin depletes vitamin B12 levels.

Tetracycline

In one study, the bioavailability of tetracycline hydrochloride was reduced significantly by concomitant administration of vitamin B complex to healthy subjects (Omray 1981). Patients should be cautioned to take vitamin B complex supplements at different times from tetracycline.

References

Dastur D, Dave U. Effect of prolonged anticonvulsant medication in epileptic patients: serum lipids, vitamins B₆, B₁₂ and folic acid, proteins and fine structure of liver. Epilepsia. 1987;28:147-159.

Latham J, Gill DS, Wickramasinghe SN. Effects of phenytoin sodium on doubling time, deoxyuridine suppression, 3H-methotrexate uptake and 57C0-cyanocobalamin uptake in HL60 cells. Clin Lab Haematol. 1990;12(1):67-75.

Omray A. Evaluation of pharmacokinetic parameters of tetracylcine hydrochloride upon oral administration with vitamin C and vitamin B complex. Hindustan Antibiot Bull. 1981;23(VI):33-37

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