Naltrexone implants five effective blood levels and can completely prevent early (one month) relapse after opiate detoxification: a report on two cohorts totalling 101 patients with a note on naltrexone blood levels.

Early relapse is common after opiate withdrawal and deprives addicts of important opportunities to develop new, opiate-free cognitive-behavioural habits. The oral opiate antagonist naltrexone (NTX) significantly reduces relapse only when rigorously supervised and/or probation-linked. Simple but effective NTX implants, containing 1G NTX and giving an average blockade of 6–7 weeks, have been available since 1997. We present outcome data for two cohorts. Group 1 were the first 55 consecutive implanted British patients (76% male, 51% unemployed, 64% in social classes III–V). Group 2 were a second consecutive group of 46. Implants were inserted subcutaneously mainly during rapid opiate detoxification under general anaesthesia or sedation. The follow-up rate for group 1 was 100%. At 12 weeks after first implantation, 21% of group 1 patients and 26% of group 2 patients had apparently resumed opiate use. Thirty per cent of patients tested-out the blockade in the first week. None reported any opiate effects at less than 5 weeks after insertion. In other patients, typical blood NTX levels 4–5 weeks post-insertion were in the range 3–5 ng/ml, which is evidently enough to block 500 mg of pure diamorphine. NTX implants provide considerable protection against early relapse and may increase the likelihood of therapeutically useful periods of abstinence after opiate withdrawal. Troublesome tissue reactions were infrequent. Improvements in implant technology and duration are already occurring. We stress that implants strengthen rather than replace the therapeutic alliance.