Methadone Pathway


Methadone exerts its analgesic by acting on the mu-opioid receptor of sensory neurons. Binding to the mu-opioid receptor activates associated G(i) proteins. These subsequently act to inhibit adenylate cyclase, reducing the level of intracellular cAMP. G(i) also activates potassium channels and inactivates calcium channels causing the neuron to hyperpolarize. The end result is decreased nerve conduction and reduced neurotransmitter release, which blocks the perception of pain signals. Methadone further acts as an antagonist at the NMDA receptor, reducting calcium influx and neuronal excitability.

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References

  1. Fredheim, O.M., Moksnes, K., Borchgrevink, P.C., Kaasa, S., and Dale, O. (2008). Clinical pharmacology of methadone for pain. Acta Anaesthesiologica Scandinavica, 52, 879-889. PMID: 18331375
  2. Opioids. (2009). [Electronic version]. e-CPS. Retrieved October 25, 2009.