Naloxone – An Opioid Antagonist

Naloxone – An Opioid Antagonist

Naloxone is used as an antidote for opioid overdose.

What are Opioids?

Opioids are substances that affect the opioids receptors and produce morphine-like effects. These drugs are used to relieve severe pain. These include morphine, codeine, heroin, and fentanyl.


Naloxone is an opioid antagonist. It reverses the effects of opioids immediately within five to ten minutes of use. The drug was patented in 1961, and it was approved by the Food and Drug Authority, the USA, in 1971. It is available in intravenous, intramuscular, subcutaneous, and nasal dosage forms. It is not available in an oral dosage form as the oral route does not readily absorb it. It is, sometimes, added to a pill with an opioid to discourage drug abuse.

When given intravenously, it takes two minutes. When given intramuscularly, it takes five minutes for the drug to start its effects. This drug has been added to emergency drugs kits for people who struggle with opioid abuse and misuse. It is interesting to note that this drug does not affect a person who does not have any opioids in his system.

Opioid Withdrawal

Side effects of naloxone include opioid withdrawal symptoms. It produces the same symptoms one might have in case of withdrawal. These include itching, restlessness, agitation, nausea, vomiting, sweating, and a slow heart rate. Another fact about naloxone is that it might not show efficacy after only one dose. One might have to increase dosage up to 10 mg before any effect is shown.


The pharmacokinetics and pharmacodynamics of naloxone are as follow:


Pharmacodynamics is the branch in which we study the effects of drugs and their mechanism of action.

Naloxone is a lipophilic drug that means it can cross the blood-brain barrier and directly affect the central nervous system. Naloxone is a competitive antagonist of opioid receptors. It binds to the receptors where opioids bind and thus lowers the efficacy of other opioids.

Suppose this drug is administered when there is no opioids are present within the body. In that case, there will be no pharmacological effect produced. However, it will take away the body’s ability to combat any pain by lowering the pain tolerance. When given in the presence of an opioid, it will compete with the opioid for a spot at the CNS receptors and render the opioid incapable.


Naloxone is most efficacious when given parenterally either by a vein or muscular route. It will be rapidly dissolved. The half-life of naloxone is shorter than many opioids. It has very low efficacy when given by mouth and only blocks the opioids receptors found in the intestines. The nasal spray is also available now in the market. The spray has a delayed response but has a high bioavailability.

How is Naloxone Administered?

Naloxone is either given by an injection (intravenously, intramuscularly, subcutaneously) or via a spray. The spray was introduced to make it easier for the families and first responders to administer in case of an overdose. The FDA-approved dosage form is recommended as it is more efficacious than a non-FDA-approved dosage form. In some states of the USA, naloxone is available only via prescription. In other, the pharmacist can also write a naloxone prescription in case of an emergency.

It is also advised that the families, who have members battling with opioid addiction, should have an emergency naloxone kit nearby in case of an overdose. Some states also provide training to families on the administration of naloxone.

Precautions during Naloxone Administration

One should take precautions during the administration of naloxone. The drug only works for 30-90 minutes. Many opioids have a longer half-life, so they might remain in the body even after naloxone is no longer in the system. Many opioids are very strong so that they will need more than one dose of naloxone. A layman or a family member might not know the proper dosage. Therefore, they should immediately call the emergency services in case of an overdose so that the professionals might advise them on the correct usage.

This drug is under a category B or C drug that means it can be given in pregnancy when the situation calls for it. It can cross the placenta, so more research is required before making it a safe drug during pregnancy. There is no evidence of this drug being in breast milk.

Uses of Naloxone

The main use of naloxone is in opioid overdose.

Opioid Overdose

The main reason for opioid overdose is addiction. The addict will increase the dose to feel euphoria till the moment of overdose. Naloxone is used to treat overdose of opioids. It can also be used in alcohol overdose. The dosing is done till the dose reaches 10mg. Even if this does not have any effect, an alternative treatment should be used. Patient having naloxone is their symptoms should be monitored for heart rate, respiratory rate, blood pressure, and level of consciousness because they are at a greater risk of respiratory depression.

Clonidine Overdose

Clonidine is an antihypertensive drug. Naloxone can also be used in case of a clonidine overdose. Clonidine overdose is of special importance in children because even small doses can cause disturbances of significant value. However, more research is required before making naloxone the official antidote to clonidine.

Recreational Use

As discussed previously, naloxone is added to opioid pills to discourage misuse and abuse. This combination also prevents the non-medical use of opioids.

Side Effects

Following are the side effects:

  • Restlessness
  • Agitation
  • Itching
  • Lowers Pain tolerance
  • Vomiting
  • Nausea
  • Seizures
  • Pulmonary Edema
  • Respiratory Depression
  • Coma

This drug is also contraindicated in people who are allergic and develop hypersensitivity reactions. It is also important to monitor the person who is taking naloxone.

Bottom Line

Naloxone is a very good antagonist of opioids, but an experienced and trained person should administer it. The emergency kits are now being distributed among the families of addicts to prevent overdose.










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