Mode Of Action Of Opioid Analgesics
The treatment of pain has been the subject of constant research throughout history. Opiate pain relievers were used naturally a long time ago, obtained from the opium plant. In 1806, morphine was first isolated as a principal element of opium. Since then, the development of this group of drugs has grown.
So what are opioid pain relievers? Opioid analgesics are drugs which have great analgesic power and which owe their pharmacological action to the union with the opioid receptors of the central nervous system. There are natural opiates derived from opium such as morphine and synthetic ones such as fentanyl.
They are characterized by an analgesic power without a ceiling effect. In other words, the higher the dose, the greater the analgesic effect. However, this comes with many side effects, as we will see later in the article.
They are mainly used in the treatment of severe and acute pain, as well as in terminally ill patients, especially in cancer. Prior to initiating treatment with opioid analgesics, a prior assessment should be performed. It must be severe pain for which other types of medication are unnecessary.
How do opioid analgesics work for pain relief?
Opioid pain relievers, as we have mentioned, unite with opioid receptors in the central nervous system. Although there are mainly 4 types of receptors, only 3 of them act on pain: μ, κ, y δ (mu, kappa and delta). Depending on the affinity with the receptor and the action they exert on it, opioid drugs have different effects.
According to their affinity with the receptors and their clinical utility, we classify them as follows:
- Pure agonists at μ receptors: for example, morphine, fentanyl, metadone or oxycodone. They have an analgesic action and also an important euphoric action
- Agonists on the κ receptors and partial agonists or antagonists on the μ receptors: such as nalbuphine or butorphanol. If administered with a pure agonist, they can negate its effect and thus suppress its effectiveness.
- Partial agonists, such as buspirone. They have an analgesic effect when administered alone
- Pure antagonists: they have the ability to nullify or reverse the effects of the rest of the opiates
Other uses of opioid pain relievers and side effects
Besides their use in the analgesic treatment of pain, opioid drugs are also used in other areas, such as anesthesia. In this case, a combination of a numbing drug and a neuromuscular blocker is often used. They can also be used to obtain sedation of a patient or to suppress independent breathing in the case of necessary mechanical ventilation.
The main problem with the use of these opioid analgesic drugs is the risk of addiction. This is why they are only used in short-term treatments for acute pain or in terminally ill patients. The most common side effects in treatment with these drugs are:
- Constipation: These drugs reduce gastrointestinal mobility and gastric, biliary and pancreatic secretions
- Nausea
- Drowsiness
- Confusion
Other side effects that may also appear are, for example:
- Headache
- Dizziness
- Sweat
- Mood swings
- Difficulty urinating
- Dry mouth
- Muscle stiffness
- Respiratory depression
Chronic use of opioid analgesics has also been observed to have a depressant effect on the immune system. Thus, its ability to produce antibodies is reduced. In addition, it increases the possibility of suffering from infections. Other possible cardiovascular effects are bradycardia and hypotension.
When prescribed long-term treatment with opioid analgesics, tolerance often occurs. In other words: the dose must always be higher to obtain an identical therapeutic effect. We can say that the body gets used to the drug.
Physical or even psychological dependence
In addition, they can generate physical dependence by causing withdrawal syndrome upon discontinuation of treatment or reduction of the dose significantly. This can be prevented if the reduction is gradual by following the advice of the specialist.
Another type of addiction would be psychological dependence, which is also called addiction. In this case, the patient seeks the psychic effects of this type of medication beyond its analgesic and pain treatment objective.
Our thoughts The opioid epidemic causes more deaths than guns and car crashes in the United States. Find out more about this situation.
