When the opioids bind to mu receptors, it leads to K+ outflux and hyperpolarization of cell membrane. Thus, it decreases neuron firing and excitability. Ca influx is also decreased which inhibits the release of neurotransmitter from the cells. This also blocks the transmission of pain signals.
Binding of opioids on kappa receptors closes Ca channels and therefore, there is no Ca influx into the cells which results in inhibition of release of neurotransmitter and transmission of pain signals.
Narcotics bind to delta receptors and activate the G-proteins which inhibit the production of cAMP. This leads to inhibition of transmission of pain signals.
Codeine, hydrocodone and oxycodone are widely used narcotic agents in dentistry for many purposes.
Codeine is used for pain relief in toothache and also after dental surgeries. It can also be used for chronic pain relief, for e.g. pain of temporomandibular joint. It is usually combined with other analgesics like aspirin and paracetamol. The usual dosage of codeine is two tablets of 30 mg, 4-6 hourly as required for pain relief in combination with non-narcotic analgesics (Codeine).
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