Hydrazinophthalazines are a class of antihypertensive drugs characterized by a phthalazine ring system with a hydrazine group attached.

[1] The most notable member of this class is hydralazine, a medication used to treat high blood pressure and heart failure.

Hydrazinophthalazines act as direct-acting smooth muscle relaxants, primarily affecting resistance arterioles to cause vasodilation.

[2] This pharmacological action results in decreased peripheral resistance and lowered blood pressure.

While hydralazine is the most well-known compound in this class, other related drugs such as dihydralazine also belong to the hydrazinophthalazine family and exhibit similar antihypertensive properties.