Serum magnesium levles in patients treated with phenytoin. 
Phenytoin and magnesium levels were measured in eighty epileptics and seventy-one control subjects in an investigation into possible effects of phenytoin on serum magnesium levels.  Phenytoin levels were measured using GLC and magnesium levels by atomic absorption spectrophotometry.  The study showed no significant effect of phenytoin on serum mangesium concentration.