Vitamin deficient is most commonly seen in a pregnant mother who is on phenytoin therapy for epilepsy?: (A) Vitamin B6, (B) Vitamin B12, (C) Vitamin A, (D) Folic acid
Answer is D. Phenytoin interferes with metabolism of folate and patients taking phenytoin may become deficient in folic acid. Phenytoin decreases absorption of folic acid and increases its excretion. Ref: Advanced Therapy in Epilepsy By Wheless, James W. Wheless, James Willmore, Roger A. Brumback, 2009, Page 259.