Antifolates and MTHFR. 
We describe a patient who developed symptoms of headache, fatigue, and dizziness after administration of terbinafine (Lamisil).  Laboratory tests revealed that he is heterozygous for the C677T variation of the methylenetetrahydrofolate reductase genetic mutation.  The prescription of Deplin (L-methylfolate) greatly reduced the symptoms.  It was later noted that Lamisil's mechanism of action interferes with cells' methylation cycle, which we suspect compromises cellular function in people with the methylenetetrahydrofolate reductase genetic mutation.