Which medication can result in a 'first dose effect' causing profound hypotension?

The term 'first dose effect' is particularly associated with ACE inhibitors, which can lead to significant hypotension when treatment is initiated. This phenomenon occurs because ACE inhibitors block the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, and this can cause a sudden drop in blood pressure, especially in patients who are volume-depleted or are on diuretic therapy. This initial drop in blood pressure can be so pronounced that it may lead to dizziness, fainting, or syncope immediately after the first dose is administered.

When starting treatment with an ACE inhibitor, it is crucial to monitor the patient closely for the first few doses to prevent adverse effects associated with this rapid decrease in blood pressure. This first dose phenomenon is less commonly seen with the other medication classes listed. For example, beta-blockers, calcium channel blockers, and diuretics are usually not associated with such a dramatic initial drop in blood pressure upon first use in the way ACE inhibitors are.