Chronic adverse effects may include bleeding, tender and enlarged gums, muscle pain, enlargement of facial features, swelling of breasts in males, excessive hair growth on body and face, and insomnia. Formate and phosphate metabolites of fosphenytoin may contribute to overdose toxicity. Formate toxicity is associated with severe anion-gap metabolic acidosis. Hypocalcemia may result from large increases in phosphate concentrations