Opioid antagonists

Opioid antagonists

Opioid antagonists have a greater attraction for opiate receptors than opioids do; however, they don’t stimulate those receptors. As a result, opioid antagonists block the effects of opioid drugs, enkephalins, and endorphins.Opioid antagonists include:

• naloxone

• naltrexone.

Pharmacokinetics

Naloxone is administered I.M., subQ, or I.V. Naltrexone is administered orally in tablet or liquid form. Both drugs are metabolized by the liver and excreted by the kidneys.

Pharmacodynamics

Opioid antagonists act by occupying opiate receptor sites, displacing opioids attached to opiate receptors, and preventing opioids from binding at these sites. This process, known as competitive inhibition, effectively blocks the effects of opioids.

Pharmacotherapeutics

Naloxone is the drug of choice for managing an opioid overdose. It reverses respiratory depression and sedation and helps stabilize the patient’s vital signs within seconds after administration.Naloxone also reverses the analgesic effects of opioids. There-fore, after naloxone administration, the patient may complain of pain or even experience withdrawal symptoms.

Kicking the habit

Naltrexone is used along with psychotherapy or counseling to treat drug abuse; however, the recipient must first have gone through a detoxification program. Otherwise, if the patient re-ceives naltrexone while he still has opioids in his body, acute with-drawal symptoms may occur. (See Managing naltrexone therapyfor drug addiction.)

Drug interactions

Naloxone produces no significant drug interactions. Naltrexone will cause withdrawal symptoms if given to a patient receiving an opioid agonist or to an opioid addict. (See Adverse reactions tonaloxone and naltrexone.)