Pharmacodynamic studies on mianserin and its interaction with clonidine

There is evidence that clonidine's hypotensive effect is reduced by the concurrent administration of tricyclic antidepressants. It has been proposed that this results from an interaction at alpha 2-receptors in the brain stem where clonidine acts as a relatively selective agonist and the tricyclic antidepressants as antagonists. Mianserin is an antidepressant with a tetracyclic structure and, although it has been reported to cause less cardiovascular disturbance, there is evidence that it also has alpha-adrenoceptor blocking effects. This study in 6 normotensive healthy male volunteers was designed to investigate a possible interaction between clonidine and the antidepressant mianserin. Administration of the first dose of 20 mg mianserin was associated with acute cardiovascular effects, notably transient postural hypotension, but no significant disturbance of heart rate or blood pressure was detected after 3 days continuous treatment with mianserin 20 mg tid. Following pre-treatment with mianserin or placebo the responses to a single oral dose of 300 micrograms clonidine were then assessed. The combination of mianserin and clonidine was not associated with any attenuation of clonidine's hypotensive effect, erect or supine, but there was significant attenuation of clonidine's supine bradycardic effect. There was no evidence that mianserin interfered with the ability of clonidine to diminish salivary flow, cause sedation, and reduce catecholamine output, but it was noted that mianserin itself had a very pronounced sedative effect. Mianserin alone had no significant effect on salivary flow. This short term study demonstrates that mianserin does not significantly interfere with the responses to a single oral dose of clonidine.