Naloxone: Uses and Side Effects of This Medicine

Naloxone is an opioid antagonist used to treat opiate poisoning or overdose (especially heroin). It also has among its indications to treat respiratory depressions or depressions of the CNS (Central Nervous System).

In this article we will learn about its characteristics, routes of administration, mechanism of action, adverse reactions, indications and precautions that should be taken regarding its use.

• Related article: "Types of psychotropic drugs: uses and side effects"

Naloxone: characteristics

Naloxone is an opioid antagonist drug, which is indicated to treat opioid poisoning and respiratory depression. The fact that it is an opiate antagonist means that it "slows down" or blocks the effect of this substance. It is usually given as an injectable solution.

The main contraindication to naloxone is hypersensitivity to it, or hypersensitivity to its main compound, naloxone hydrochloride (or to any of its excipients).

Opiates

To understand how naloxone works, it is also useful to know what an opiate is.

Opioids are substances that reduce pain, that is, analgesic substances. These are natural substances (from seeds called "poppies"), but they can also be synthesized; what's more, can be used as drugs or as drugs (according to its use, characteristics, ...). Are opiates morphine, the heroin, hydrocodone, codeine, etc. These molecules work by binding to opioid receptors (a type of protein), minimizing the person's perception of pain.

Administration routes

Continuing with naloxone, this is usually given intravenously (IV) through an injectable solution. It can also be given intramuscularly (IM), or it can be given through an intravenous infusion. This last route of administration, less known, consists of introducing an intravenous solution into the bloodstream continuously; It is done through a catheter inserted into a peripheral or central vein.

However, it is important to note that in acute cases (especially from opioid overdose such as heroin), the most recommended route of administration will be the intravenous (IV) route, since the effect occurs more quickly; specifically, the effect becomes apparent at approximately 2 minutes. The duration of the effects will always depend on the dose; however, it is generally between 1 and 4 hours.

If a second or third dose is needed, this will always depend on the opioid to be antagonized (or on the type of respiratory or CNS depression that the patient presents); specifically, of whatever type, its quantity and the route of administration used, among others.

Mechanism of action

Naloxone actually is made up of naloxone hydrochloride, which is a semi-synthetic derivative of morphine (a natural opiate). Its mechanism of action involves specifically antagonizing opioids; specifically, it acts by competing at opiate receptors.

This drug has a very high affinity for these types of receptors (that is, it fits very well with them). What it does thanks to this is to displace opiate antagonists and agonists.

Composition and dosage

At the chemical level, is derived from oxymorphone, a very potent semisynthetic opioid pain reliever. The drug is made up of naloxone hydrochloride. Specifically, each 1 ml ampoule of naloxone contains 0.4 mg of naloxone hydrochloride.

The recommended doses in adults are generally 0.4 to 20 mg through the IV. In the event that an improvement in respiratory depression is not obtained after its administration by this route, it can be re-administered at intervals of 2 to 3 minutes (always by a medical professional). Of course, its use must be indicated and prescribed by doctors.

Indications

Naloxone is frequently known for its use during acute intoxication or opioid overdose. The main natural opiate is morphine. Another opiate drug is heroin, a drug synthesized from morphine.

Other indications for naloxone are: to treat respiratory depression or CNS (Central Nervous System) depression. The respiratory depression that we mentioned is usually caused by the consumption of opiates, either natural or synthetic. It is also indicated for babies who have just been born, with mothers who have been taking opioids.

Another interesting fact is that when naloxone is administered in cases of opiate dependence, what happens is that symptoms of physical dependence increase.

Pharmacokinetic properties

Pharmacokinetics has to do with the absorption time of drugs, the duration of their effect, etc. That is, it encompasses the processes through which the drug passes once it is administered in the body. Naloxone (naloxone hydrochloride) is rapidly absorbed from the gastrointestinal tract.

But why is naloxone usually not given by mouth? It is also effective, but in order for it to produce the same effect as from the other routes, they would be much higher doses necessary to allow opioid antagonism (in case of overdose). That is why it is administered intravenously and intramuscularly.

Precautions

Special caution should be exercised with patients who have a physical dependence on narcotics. (narcotics are analgesic and / or anesthetic drugs), or who have been intoxicated by this type of substances; this is because the use of naloxone can induce an acute withdrawal syndrome. On the other hand, naloxone is not effective when respiratory depression is due to factors other than opiates.

In elderly patients, naloxone should also be used with caution, especially in those with some previous cardiovascular disease. This is because there are known cases where naloxone has caused serious adverse cardiovascular effects in the elderly.

Also, taking high-dose naloxone during surgery after taking opioids is not recommended. Special care or precaution should be taken in cases of patients with cardiovascular diseases, or patients taking cardiotoxic drugs that can cause heart disorders.

Pregnancy and breastfeeding

In the case of being pregnant, the relationship between risks and benefits of taking naloxone should be evaluated. consulting the family doctor or psychiatrist. There is not much data on taking naloxone during pregnancy, but it is known that it can cause withdrawal symptoms in the baby.

Regarding breastfeeding, it is not known whether or not naloxone can pass into breast milk. It has also not been established whether children who are breastfed have the effects of naloxone.

Side effects

Like any drug, naloxone can also cause a series of adverse reactions in the patient, such as: nausea, vomiting, tachycardia, hypo / hypertension, headache, postoperative pain, and fainting, among others.

Other adverse reactions that naloxone may cause, and which have been reported especially in periods postoperative, are states of hypotension, hypertension, pulmonary edema, fibrillation and tachycardia ventricular. In addition, these adverse reactions have been seen especially in people with cardiovascular diseases or who have been taking similar drugs.

Bibliographic references:

• Ferrandis, V. (2013). Professional Association of Physiotherapists of Castilla y León. Pharmacokinetics and pharmacodynamics. Pharmacology Course for Physiotherapists.
• Gregorio Marañón University Hospital. (2014). Continuous intravenous infusion. Nursing documentation: 2 - 10.
• Ministry of Health, Social Policy and Equality. (2018) Technical data sheet: naloxone. 1 - 8.
• Stahl, S.M. (2002). Essential psychopharmacology. Neuroscientific bases and clinical applications. Barcelona: Ariel.
• Vademecum. (2016). Naloxone.