Naloxone: uses and side effects of this drug

Naloxone is an opioid antagonist which is used to treat opioid poisoning or overdose (especially heroin). It also has among its indications for treating respiratory depressions or depressions of the CNS (central nervous system).

In this article, we will know its characteristics, routes of administration, mechanism of action, side effects, indications and precautions to be taken regarding its use.

    Naloxone: characteristics

    Naloxone 1 is an opioid antagonist, which is indicated to treat opioid poisoning and respiratory depression. The fact that it is an opioid antagonist means that it “slows down” or blocks the effect of this substance. It is usually given as a solution for injection.

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


    To understand how naloxone works, you also need to know what an opioid is.

    Opiates are analgesic substances, that is, pain relievers. These are natural substances (from seeds called “debris”), but they can also be synthesized; Outraged, they can be used as drugs or as drugs (According to its use, its characteristics, …). Morphine, heroin, hydrocodone, codeine, etc. are opiates. These molecules work by binding to opioid receptors (a type of protein), minimize the person’s perception of pain.

    Routes of administration

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

    However, it is important to note that in acute cases (especially due to an overdose of opiates such as heroin), the most recommended route of administration will be intravenous (IV), as the effect occurs faster; more precisely, the effect becomes apparent after about 2 minutes. The duration of effects will always depend on the dose; however, it is usually between 1 and 4 hours.

    Whether you need a second or third dose, it will always depend on the opioid you want to upset (or the patient’s type of respiratory or CNS depression); more precisely, of its type, its amount and the route of administration used, among others.

    Action mechanism

    Naloxone in fact is composed of naloxone hydrochloride, which is a semi-synthetic derivative of morphine (A natural opiate). Its mechanism of action involves specifically antagonistic opioids; more specifically, it works by competing with opioid receptors.

    This drug has a very high affinity for these types of receptors (that is, it integrates very well with them). What it does with this is that it displaces the opioid antagonists and agonists.

    Composition and dosage

    At the chemical level, is derived from oxymorphone, a very strong semi-synthetic opioid pain reliever. The drug is composed of naloxone hydrochloride. Specifically, each 1 ml vial of naloxone contains 0.4 mg of naloxone hydrochloride.

    The recommended doses for adults are generally 0.4 to 20 mg intravenously. If no improvement in respiratory depression is obtained after administration by this route, it can be re-administered at intervals of 2 to 3 minutes (always by a healthcare professional). Of course, its use should be indicated and guided by physicians.


    Naloxone it is frequently known for its use in acute poisoning or opioid overdose. The main natural opiate is morphine. Another opiate drug is heroin, a drug made from morphine.

    Other indications for naloxone are: to treat respiratory depression or CNS (central nervous system) depression. The respiratory depression that we mention usually results from the consumption of opiates, natural or synthetic. It is also indicated for newborns, whose mothers take opiates.

    Another interesting fact is that when naloxone is given for opioid addiction, what happens is that increase the symptoms of physical dependence on it.

    pharmacokinetic properties

    Pharmacokinetics have to do with the time of absorption of drugs, the duration of their effect, etc. In other words, it encompasses the processes that the drug goes through once it is delivered into the body. Naloxone (naloxone hydrochloride) it is rapidly absorbed from the gastrointestinal tract.

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


    Particular attention should be paid to patients who are physically dependent on narcotics (narcotics are analgesics and / or anesthetics), or who have been intoxicated by such substances; this is due to the fact that the use of naloxone it can induce an acute withdrawal syndrome. In contrast, naloxone is not effective when respiratory depression is due to factors other than opiates.

    Naloxone should also be used with caution in elderly patients, especially in people with a history of cardiovascular disease. This is because there are known cases where naloxone has caused serious cardiovascular side effects in the elderly.

    In addition, it is not recommended to take naloxone in large doses during surgery after consuming opiates. Special care or caution should be exercised in patients with cardiovascular disease or in patients taking cardiotoxic drugs which may cause heart problems.

    Pregnancy and breast feeding

    If you are pregnant, you should consider the relationship between the risks and benefits of taking naloxone. consult your general practitioner or psychiatrist. Little data is available from taking naloxone during pregnancy, but it is known to cause withdrawal symptoms in babies.

    As for breastfeeding, it is not known whether or not naloxone can pass into breast milk. It has also not been established whether breastfed infants have any effects from naloxone.

    Side effects

    Like all medicines, naloxone can also cause a number of side effects in the patient, such as: nausea, vomiting, tachycardia, hiccups / hypertension, headache, postoperative pain and fainting, Others.

    Other side effects that naloxone can cause, and which have been reported especially in the postoperative period, are hypotension, hypertension, pulmonary edema, fibrillation and ventricular tachycardia. In addition, these side effects have been observed in particular in people with cardiovascular diseases or who have taken similar medicines.

    Bibliographical 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 brief: naloxone. 1 to 8.
    • Stahl, SM (2002). Essential psychopharmacology. Neuroscientific bases and clinical applications. Barcelona: Ariel.
    • Vade mecum. (2016). Naloxone.

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