Use cautiously in patients with coronary disease, advanced renal damage, and cerebrovascular accidents. In the rare patient with marked reduction of blood pressure, withdraw hydralazine gradually in order to avoid a possible sudden rise in pressure. In patients with more severe forms of hypertension and with uremia, too rapid an increase of dosage may produce a marked fall in blood pressure. In these cases, certain cerebral symptoms, from mild anxiety or depression to acute anxiety or severe depression and coma, may appear. Although hydralazine alone does not have a sedative or hypnotic effect, extreme drowsiness has occurred in patients taking it and a barbiturate. Similarly, the narcotic effect of alcohol has been potentiated by hydralazine. Periodic blood counts and liver function tests are advised during prolonged therapy.
Hydralazine HCl should not be used during the first trimester of pregnancy unless the potential benefits outweigh the possible risks.
Hydralazine is metabolized primarily by acetylation and dehydrazination. The rate of acetylation is genetically determined. Approximately 50% of Negroes and Caucasians are "slow inactivators"; the majority of Eskimos and Orientals are "rapid inactivators".
The rate of acetylation can significantly alter the effectiveness of hydralazine. Slow acetylation may lead to higher blood concentrations of the drug and, thus, to an increase in toxic reactions.