Water potentiates the pressor effect of ephedra alkaloids

The use of ephedra alkaloids in over-the-counter preparations has been associated with potentially serious cerebrovascular events. Because of its potential association with hemorrhagic strokes, phenylpropanolamine has been largely substituted for by pseudoephedrine, but it is not clear whether this is indeed a safer alternative. It would be important to understand the cardiovascular effects of ephedra alkaloids, but these are normally masked by baroreflex buffering mechanisms. We therefore investigated the effects of ephedra alkaloids in patients with autonomic impairment and explored their potential interaction with water ingestion.

The cardiovascular effects of phenylpropanolamine or pseudoephedrine, alone and in combination with water, were determined in 13 subjects with impairment of baroreflex function due to autonomic failure. Phenylpropanolamine, 12.5 to 25 mg PO, increased systolic blood pressure (SBP) by 21+/-14 mm Hg after 90 minutes. However, when ingested with 16 oz of room temperature tap water, phenylpropanolamine increased SBP by 82+/-2 mm Hg. Pseudoephedrine, 30 mg PO, increased SBP on average 52+/-9 mm Hg when taken with 16 oz of water and by as much as 88 mm Hg.

Ephedra alkaloids increase blood pressure significantly in individuals with impaired baroreflex function. Concomitant ingestion of ephedra alkaloids and water produced a greater increase in blood pressure. If used cautiously, this interaction can be beneficial in the treatment of orthostatic hypotension. On the other hand, it could contribute to the cardiovascular complications associated with the use of ephedra alkaloids, given that baroreflex function varies widely in normal individuals and is impaired in several medical conditions.