Methyldopa can cause sodium and fluid retention, and tolerance can develop during long-term therapy. Serum prolactin levels can increase during administration. Methyldopa appears to cross the blood- brain barrier as well as the placenta. The drug distributes in breast milk, but the quantity is probably not clinically significant. Antihypertensive effects last 12-24 hours.
Unabsorbed drug is excreted in the feces.
Because of the risk of hemolytic anemia, patients receiving methyldopa should have a hemoglobin, hematocrit, or red blood cell count assessed before and during therapy. If there is evidence of anemia or a positive Coombs' test during therapy, hemolysis should be ruled out. Methyldopa should be used with caution in patients with a history of hemolytic anemia or autoimmune disease. If hemolytic anemia is present, the drug should be discontinued. Hepatic function also should be determined periodically to detect methyldopa-induced hepatic changes.