Dilantin Effect on Thyroid Function

Although the drug Dilantin (phenytoin) is effective in controlling epileptic and other types of seizures, its side-effects require that it be carefully administered with the individual patient in mind. Owing to its depressive effect on the thyroid, phenytoin can cause a generalized depressed mood due to interaction of thyroxene with essential neurotransmitters such as serotonin. Phenytoin has a favorable effect on blood lipid levels, but can cause sexual dysfunction and feminization in men as well as softening of the bones.

Seizure medication

• Dilantin (phenytoin) acts to stabilize the motor centers of the brain and to regulate the overstimulation that can lead to a seizure. It is effective in treating grand-mal, focal, myoclonic (involuntary muscle contractions) and psychomotor seizures. Dilantin also is used to alleviate seizures that result from brain injury.

  Physicians also prescribe the drug for preeclampsia (sudden increase in blood pressure during pregnancy) and eclampsia (convulsions during pregnancy), chronic pain syndrome and trigeminal myalgia (severe facial pain caused by irritation of a nerve cluster).

Side effects

• Dilantin has the potential to cause hypothyroidism (low output of the hormone thyroxine, important in metabolism) and to aggravate already-existing hypothyroidism. Hypothyroidism is also linked with depression chemically by reduction of an amino acid necessary for proper functioning of the thyroid gland as well as production of neurotransmitters that regulate mood and anxiety.

  Low thyroid output can deplete the body of serotonin and other neurotransmitters essential for maintenance of energy and a healthy mood. Because it is not clear whether depression affects thyroid activity, or the other way around, many physicians treat both low thyroid and depression simultaneously. Thus, any medication such as Dilantin that can affect both mood and thyroid levels needs to be carefully monitored.

Other effects

• People with diabetes may require a higher dose of Dilantin to control seizures because the disease is associated with lower concentrations of the drug as well as increased glucose intolerance. One welcome side-effect of Dilantin is improvement in blood lipids---higher levels of HDL ("good cholesterol") and lower levels of LDL ("bad cholesterol").

  Men treated with phenytoin sometimes experience sexual dysfunction due to elevated levels of serum estradiol (estrogen, the female hormone). In addition, some men experience enlargement of their breasts (gynecomastia) for the same reason. And there is evidence that the drug causes softening of the bones (osteomalacia) because of impaired calcium absorption.