Mianserin: is the intraperitoneal route of administration the best?

A 1 h pretreatment with s.c. mianserin (0.5 mg kg-1) markedly blunted the oedema of the rat paw induced by the subplantar injection of 5-HT (5 micrograms). In contrast, i.p. mianserin (same dose) failed to modify 5-HT-induced oedema. However, pretreatment with SKF-525-A (40 mg kg-1) resulted in a profound potentiation of the action of i.p. mianserin, the effect of the combination of SKF-525-A and i.p. mianserin rivaling that of s.c. mianserin. It is concluded that i.p. mianserin is metabolized by the rat liver to compounds which possess a reduced propensity to block peripheral 5-HT receptors and that the i.p. route of administration is not to be recommended when mianserin is being studied as a 5-HT receptor antagonist in the rat.