Long-term of phenytoin: Effects on whole blood and red cell folate and haematological parameters.

Patients treated when phenytoin for periods of several months or years have slightly, but significantly lower whole blood and red cell folate values than comparable controls. This holds true irrespective of whether folate is determined microbiologically with Lactobacillus casei or by a radioligand method using the bovine milk binder. Haematological parameters including Hb, MCH, MCV and red blood cell counts did not show any alterations and no patient developed any signs of anaemia. This indicates that long-term use of phenytoin does not cause a clinically significant state of folate deficiency, unless some other contributing factors are present.