Abstract

Phenytoin: Our statement that the slow absorption of intramuscular phenytoin did not matter when substituting for the oral drug postoperatively was incorrect. Changing from oral to intramuscular administration risks a fall in plasma concentration because of the slow absorption from muscle. Changing back to oral administration would then risk toxicity as the drug was slowly released from muscle. Restarting with a smaller oral dose can prevent this. However, intramuscular phenytoin can cause muscle necrosis. These disadvantages of intramuscular phenytoin are not mentioned in the data sheet, but should be. Slow intravenous injection (50 mg or less/minute) once daily is a better alternative, but requires monitoring of the pulse, blood pressure and respiration.