Vitamin B12 (Cobalamin)
  Supplements with Similar Uses
View List by Use
  Drugs that Interact
Phenobarbital-containing Medications
Phenytoin-containing Medications
Tetracycline-containing Medications
  Drugs that Deplete this Substance
View List
  Learn More About
Look Up > Supplements > Vitamin B12 (Cobalamin) > Interactions
Interactions with Vitamin B12 (Cobalamin)
Phenobarbital; Phenytoin

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.


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.


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

Copyright © 2000 Integrative Medicine Communications

This publication contains information relating to general principles of medical care that should not in any event be construed as specific instructions for individual patients. The publisher does not accept any responsibility for the accuracy of the information or the consequences arising from the application, use, or misuse of any of the information contained herein, including any injury and/or damage to any person or property as a matter of product liability, negligence, or otherwise. No warranty, expressed or implied, is made in regard to the contents of this material. No claims or endorsements are made for any drugs or compounds currently marketed or in investigative use. The reader is advised to check product information (including package inserts) for changes and new information regarding dosage, precautions, warnings, interactions, and contraindications before administering any drug, herb, or supplement discussed herein.