Narcotic (opioid) analgesics are very potent pain killers obtained from Opium poppy plants. They produce pain relief by depression of the central nervous system (CNS), especially cerebrum and medulla. They also act on glands and smooth muscles of the respiratory and gastrointestinal system which accounts for the side effects of these drugs. The main limitation of these analgesics is that their long term use leads to dependence and addiction (Narcotic Analgesic Drugs).
Site and mechanism of action of Narcotic Analgesics
There are different types of opiate receptors in the CNS which are responsible for the pharmacological actions of narcotic agents. Opiate receptors have three main parts: a flat portion which contains the aromatic part, a hollow portion which has the ethylene bridge and an ionic site with 30 nitrogen. These three parts from a specific spatial orientation of the receptors which is responsible for the specificity of these receptors for narcotic agents (Narcotic Analgesic Drugs).
There are three main types of opiate receptors, mu, kappa and delta. These receptors produce different effects on the body. Mu receptors produce analgesia, euphoria, respiratory depression and addiction. Kappa receptors produce dysphoria, euphoria and addiction. Delta receptors are linked to G-proteins.
When the opioids bind to mu receptors, it leads to K+ outflux and hyperpolarization of cell membranes. Thus, it decreases neuron firing and excitability. Ca influx is also decreased which inhibits the release of neurotransmitters 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 neurotransmitters 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.
Use of Narcotics in Dentistry
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).
Hydrocodone is the most commonly prescribed drug for relief of pain and is 6 times more powerful compared to codeine and thus requires lower dosages for pain relief. It is used for post-surgical pain relief and toothache. The usual dosage of hydrocodone is 5-7.5 mg, 4-6 hourly in combination with acetaminophen (500mg) (Hydrocodone).
Oxycodone is 12 times more powerful than codeine. It is used for the same indications as codeine and hydrocodone but requires much lower doses for its action. Usually, one to two tablets of 5 mg of oxycodone, 4-6 hourly are prescribed in combination with acetaminophen (325-500 mg) (Oxycodone).
The common side effects of these drugs are nausea, vomiting, constipation, drowsiness and dizziness. Therefore, the patients are instructed not to operate dangerous machines or consume large amounts of alcohol. As these drugs are used for short-term, efficient pain relief, it does not lead to dependence and addiction. Thus, they are a good option and can be safely used to relief dental pain.
References
- Codeine. (n.d.).
- Hydrocodone. (n.d.).
- Narcotic Analgesic Drugs. (n.d.). Web.
- Oxycodone. (n.d.).