What effect do aliphatic phenothiazines have on blood pressure?

Aliphatic phenothiazines, which include medications like chlorpromazine, primarily act as antipsychotic agents by blocking dopamine receptors in the central nervous system. One of their side effects can be orthostatic hypotension, a condition where blood pressure drops significantly upon standing up. This occurs due to the drug's ability to antagonize alpha-adrenergic receptors, which are responsible for maintaining vascular tone and blood pressure when a person changes positions.

When a patient takes aliphatic phenothiazines, especially during initial treatment or dose adjustments, they may experience a drop in blood pressure upon standing. This can lead to dizziness, light-headedness, or even fainting. The risk of orthostatic hypotension is particularly pertinent in elderly patients or those on other medications that also affect blood pressure.

This mechanism of action not only explains why orthostatic hypotension is a common side effect of aliphatic phenothiazines but also why monitoring blood pressure is crucial when these medications are prescribed.