Analysis of the antinociceptive properties of marrubiin isolated from Marrubium vulgare.

We have shown previously that Marrubium vulgare, a medicinal plant employed frequently in folk medicine to treat a variety of ailments, exhibits antispasmodic and antinociceptive effects in different experimental models. This work describes the antinociceptive profile of marrubiin, the main constituent of this plant, which was analysed in some models of nociception in mice. The results showed that marrubiin exhibits potent and dose-related antinociceptive effects, whose calculated ID50 values (micromol/kg, i.p.) were the following: 2.2 in the writhing test, 6.6 (first phase) and 6.3 (second phase) in the formalin-induced pain test and 28.8 when evaluated in the capsaicin test. It was more potent than some well-known analgesic drugs. The antinociception produced by the marrubiin was not reversed by naloxone when analyzed against the writhing test. In the hot-plate test, marrubiin did not increase the latency period of pain induced by the thermal stimuli. Its exact mechanism of action remains to be determined, but the results suggest that marrubiin, like hydroalcoholic extract of M. vulgare, does not interact with opioid systems.