SummaryThe action of the antihypertensive agent, debrisoquin (Declinax®) is, both in pharmacological studies on animals and in its clinical use, similar to guanethidine (Ismelin®). They have the following characteristics in common : they inhibit the adrenergic neuromuscular transmission; they provoke a transient release of norepinefrine and a short lasting blood pressure rise after the first intravenous injection; their blood pressure lowering effect is more pronounced in the standing than in the recumbent position, which frequently leads to orthostatic hypotension; in acute experiments the blood pressure decrease is due mainly to a decrease of the cardiac output, the changes in total peripherial resistance being variable; their blood pressure lowering effect is antagonised by imipramine (Tofranil®); their side-effects are similar in nature : orthostatic hypotension, diarrhoea, muscle weakness.Debrisoquin differs from guanethidine. The antihypertensive action of debrisoquin has a quicker onset and is shorter lasting : the drug should therefore be given at least three times a day and is considered by certain workers as more easy to handle; debrisoquin does not inhibit the uptake of norepinephrine from the extracellular fluid; debrisoquin does not lower the norepinephrine concentration in the heart or brain of the experimental animal; debrisoquin inhibits in vitro the mono-amino-oxydase of platelets, probably also in the neurones, but not in the wall of the duodenum. It is not definitely excluded that the ingestion of certain cheeses or wines could provoke a hypertensive attack in debrisoquin treated patients.A controled clinical trial comparing debrisoquin to other inhibitors of the adrenergic neuromuscular transmission, such as guanethidine, or bethanidine is upto now not available; it is therefore not proven that debrisoquin is superior in the chronic antihypertensive treatment.