Because dopamine is the chemical that normally inhibits prolactin secretion, doctors may treat prolactinoma with the dopamine agonists bromocriptine (Parlodel) or cabergoline (Dostinex). Agonists are drugs that act like a naturally occurring substance. These drugs shrink the tumor and return prolactin levels to normal in approximately 80 percent of patients. Both drugs have been approved by the U.S. Food and Drug Administration for the treatment of hyperprolactinemia. Bromocriptine is the only dopamine agonist approved for the treatment of infertility. This drug has been in use longer than cabergoline and has a well-established safety record. Nausea and dizziness are possible side effects of bromocriptine. To avoid these side effects, bromocriptine treatment must be started slowly. A typical starting dose is one-quarter to one-half of a 2.5 milligram (mg) tablet taken at bedtime with a snack. The dose is gradually increased every 3 to 7 days as needed and taken in divided doses with meals or at bedtime with a snack. Most people are successfully treated with 7.5 mg a day or less, although some people need 15 mg or more each day. Because bromocriptine is short acting, it should be taken either twice or three times daily. Bromocriptine treatment should not be stopped without consulting a qualified endocrinologist—a doctor specializing in disorders of the hormone-producing glands. Prolactin levels rise again in most people when the drug is discontinued. In some, however, prolactin levels remain normal, so the doctor may suggest reducing or discontinuing treatment every 2 years on a trial basis. Cabergoline is a newer drug that may be more effective than bromocriptine in normalizing prolactin levels and shrinking tumor size. Cabergoline also has less frequent and less severe side effects. Cabergoline is more expensive than bromocriptine and, being newer on the market, its long-term safety record is less well defined. As with bromocriptine therapy,...
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