O’Neil, George; Hulse, Gary, K.; Chan, Chin-Tark; Parsons, Zoe University of Western Australia/ University of Western Australia, Australia/ Go Medical Industries Pty. Ltd., Australia
A total of 1,575 patients were treated with naltrexone implants over a 5-year period (August 2000 to December 2005). These sustained-release implants (Go Medical Implants) have previously been described by Hulse and O’Neil (Addiction Biology 2004) and deliver naltrexone for approximately twelve months with blood levels maintained above 1 ng/mL for 272 days. Forty percent of the patients presented for a repeat implant but this figure rose to 42 percent when the estimated 180 new patients who received their first implant recently and had not yet returned for follow up treatment were included. Patients returned for a second implant treatment a mean of 353 days after their first implant. In addition, 263 of 623 patients (42 percent) presented for further implants after their second implant. Approximately 40 percent presented again for their 4th implant, and 40 percent of that group for their 5th implant. This trend of approximately 40-50 percent returning for subsequent implants is consistent with some of the treatment programs using short acting implants. The naltrexone levels recorded are usually above 4ng/mL for the first 180 days and above 1ng/mL for the first 270 days. Abstinence from opiates is virtually complete in the first 90 days (3/830 urines were positive) with opiate use usually delayed until the blood level falls below 2ng/mL and often until it falls below 1ng/mL. It is common to see opiate use recommence for a short time (usually less than 3 weeks) prior to the second implant. Most patients re-present for their second implant with a history of being drug free for 6-9 months, with many having a short relapse almost electively prior to their second implant.