Propranolol combined with dopamine has a synergistic action in intensifying and prolonging cutaneous analgesia in rats

BackgroundThe purpose of the experiment was to assess interactions of dopamine with propranolol as an infiltrative anesthetic.MethodsAfter injecting the rats with four doses of drugs subcutaneously, the cutaneous analgesic effect of propranolol was compared with dopamine through the blockade of cutaneous trunci muscle reflex (CTMR) in response to local skin pinprick. Drug–drug interactions were examined via an isobolographic analysis.ResultsWe demonstrated that the action of propranolol and dopamine was dose dependent to skin infiltrative analgesia. On the ED50 (50% effective dose) basis, the rank of drug potency was propranolol (11.3 [10.6–12.2] μmol) > dopamine (195 [188–205] μmol) (p < 0.001). At the equi-anesthetic doses (ED25, ED50, ED75), the block duration caused by dopamine was equal to that caused by propranolol. Coadministration of dopamine and propranolol exhibited a synergistic effect on infiltrative cutaneous analgesia.ConclusionsThe preclinical data showed that dopamine produced a lesser potency but a comparable duration of cutaneous analgesia compared to propranolol. Adding dopamine to propranolol potentiated and prolonged propranolol's cutaneous analgesic effect.