Naltrexone implant promising for heroin dependence

In a study of heroin-dependent patients, hospitalizations due to opioid use decreased significantly following treatment with a naltrexone implant, while a similar decrease was not observed in another group of similar patients who received traditional methadone maintenance treatment.

“However, hospitalizations due to non-opioid drug use increased for naltrexone patients but remained relatively unchanged for methadone patients,” Dr. Hanh T. Ngo from the University of Western Australia, Crawley, told Reuters Health.

Ngo and colleagues evaluated the number of hospital visits related to overdose associated with opioid or other types of drugs at 6 months and 42 months after the start of naltrexone implant treatment in 314 heroin-dependent patients. These findings were compared with those of a similar group of 522 patients in a methadone maintenance program for the first time.

In Australia, naltrexone implants are available to heroin-dependent subjects under the Therapeutic Goods Administration’s Special Access Scheme. Naltrexone is a drug, normally available in tablet form, which blocks the effects of opioids and reduces drug cravings.

Because patient compliance can be a problem with the tablet formulation, naltrexone implants were offered to these patients. All of the study patients provided written consent before they received the implant.

With naltrexone implant treatment, the risk of opioid overdose decreased by 77 percent and opioid use without overdose by 36 percent after 42 months, Ngo and colleagues report in the Archives of General Psychiatry. “Such reductions were not observed after methadone treatment,” they note.

“We find the long-term opioid drug-related outcomes associated with the unregistered Australian naltrexone implant very encouraging,” Ngo said.

The findings “make theoretical sense” because naltrexone is a potent opioid blocker. The long-lasting formulation appears to be therapeutic for about 4 months, the investigator added.

However, with naltrexone and methadone treatment, there was a steep increase in the risk of non-opioid use and overdose during the study period.

“Although we are excited about the reduction in high-risk opioid use after naltrexone implant, both short- and long-term, the evidence that problematic non-opioid drug use increased for this cohort is concerning, which warrants further investigation,” Ngo said.

There were six drug-related deaths—five after methadone maintenance and one after naltrexone implantation.

Summing up, Ngo said: “It is important for clinicians to be aware of the differential risks and benefits of the novel naltrexone implant product and the traditional methadone maintenance,” Ngo added. Patients also need to be informed about these risk and benefits and each patient needs to be individually assessed before a treatment is selected.

“Since this is the first study of its kind, we believe that similar findings need to be replicated before a firm conclusion is reached,” he concluded.

SOURCE: Archives of General Psychiatry, April 2008.