Harm Reduction Victoria

Naltrexone

Naltrexone


Naltrexone is available as an opiate pharmacotherapy in Victoria both as an oral tablet and – to some degree – as an implant.​ ​Naltrexone is an an opioid antagonist. It binds strongly to the opioid receptors and blocks the effect of of any other opioid. Naltrexone has no opiate effect of its own. Before taking naltrexone, a client should have had no other opiates in their system for 7 to 10 days, as an acute withdrawal reaction could occur.

Naltrexone is not included in the Victorian pharmacotherapy guidelines and no special requirements govern its prescription.​ However, a set of ‘national clinical guidelines’ is available.

Naltrexone Tablets

OLYMPUS DIGITAL CAMERANaltrexone tablets come under the brand name Revia in one 50mg strength. To date, they are only covered by the Pharmaceutical Benefits Scheme for patients with alcoholism. A month’s supply will cost approximately $200 for a person using them for the purpose of opioid dependence..

Naltrexone tablets are taken daily each morning. They are prescribed much as any other medications.

RISKS/DANGERS – Drug Overdose, if a person stops taking their tablets and then uses other opioids, they no longer have any opioid tolerance which greatly increases the risk of accidental overdose.

Naltrexone Implants and Injections

Naltrexone implants & injections are not approved by the Therapeutic Goods Administration in Australia. They are only available through the same Special Access Scheme which usually is used to access unapproved medications for patients with no other option (for example new medicines in first stage trials for the treatment of ‘untreatable’ cancer). Therefore, naltrexone implants and injections continue to be considered an experimental therapy, due to a lack of supporting scientific evidence.​​

Due to their unproven nature, there are very few Victorian doctors who will use naltrexone implants. The cost of a naltrexone implant varies from $1500 to $6000 depending on the individual GP. Naltrexone injections cost approximately $200 per month. If the implant/injection is used in conjunction with rapid detoxification (using naltrexone under mild sedation) the cost is likely to be higher.

Naltrexone Pharmacology

Naltrexone is an opioid antagonist. This means it binds to the opioid receptors in the body, but unlike other full opioid agonists (methadone, heroin, morphine), it produces no opioid effect. The naltrexone effectively creates a seal around the receptor, preveinting any other opioid from binding (attaching itself) to the receptor. This means that if you are taking naltrexone and then go and use heroin or morphine, you will not feel any of the opiate effect from the heroin or morphine as the opioid drugs can’t bind to the receptor when the naltrexone is present. This works as long as you keep taking naltrexone (tablets or injections) or until the implant (usually six months or longer) wears off.

One interesting fact about naltrexone is that after a person has been taking it for a period of time (usually weeks to months) it strips the body’s tolerance to opioids back to zero. Hence, the increased danger of accidental overdose if a person goes and uses heroin or morphine once the naltrexone tablet/injection/implant has worn off (no longer active in the body).