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LONG-ACTING NALTREXONE IMPLANTS FOR OPIATE ADDICTION


1. Naltrexone Implant. Wedgewood Model

We started using naltrexone implants in 1997, a few months after the first commercially available models became available in the USA. Since that time, there have been important developments in implant technology and three main types are now available. However, what follows largely applies to all three types but first, a bit of background. The need for implants, or long-acting injections, was noted when oral naltrexone was first used to treat opiate addicts back in the early 1970s. Naltrexone tablets worked well but - like any other medication - only if patients took them regularly. Not surprisingly, many addicts were tempted to stop the tablets so that they could use heroin 'just the once'and then most of them relapsed and couldn't resume naltrexone without another detox. It was obvious that implants would by-pass the daily decision about taking a tablet and would also make supervision of tablet-taking - the key to success with oral naltrexone - unnecessary. The first experimental implants were made by US university or government labs in the early 1980s but no commercial pharmacy took them on until 1996. Even now, no implant has an official product licence (see also latersection on 'off-label use' of medication) and the first long-acting ('depot') injection only received a US product licence in April 2006.



Implants can be inserted initially subcutaneously (ie just under the skin) using local anaesthesia, at the time of an in-patient detox or as soon as possible after any other sort of detox. Subsequent implants should normally be inserted before the current implant starts to lose its effect. The new depot injections are injected into a muscle (eg the buttock or shoulder) and do not need local anaesthetic.


Implants are usually inserted through a half inch (1cm) incision in the lower abdomen or, occasionally, elsewhere.

ADVANTAGES
  • make relapse almost impossible, especially the first month or two when the risk is highest
  • avoid the need to supervise naltrexone and the arguments it can cause
  • make it impossible to 'forget' to take naltrexone
  • probably reduce craving even more than oral naltrexone because there is no point in craving for what you can't have


DISADVANTAGES
  • involve (minor) surgery and a small scar with temporary
    tenderness and bruising
  • occasional local infection or inflammation of implant site, usually responding to antibiotics or anti-inflamatory drugs
  • much more expensive than oral naltrexone. Sometimes available on a NHS prescription, but not easily.
  • risk of turning to non-opiate drugs - including alcohol - as a substitute but this also applies to oral naltrexone.


None of the implants have been produced by a major drug company. They are imported officially but have no product licence and should still be regarded as experimental. However, in recent years, several implant studies have been published and it is clear that they do what is claimed for them. Naltrexone itself is a very safe drug and the implants contain nothing which is known to have significant toxic effects. They are particularly useful for patients who have nobody to supervise their oral naltrexone or who think they will be tempted to cheat. We know of nobody who has overcome the blockade with an adequate blood naltrexone level. However,. attempts to do so with large amounts of opiates could obviously be dangerous, especially if the effect of an implant has almost worn off and the blood naltrexone level is low.

1. THE O'NEILL LONGER-ACTING AUSTRALIAN NALTREXONE IMPLANT

Your O'Neill naltrexone implant is intended to protect you against relapse to heroin use for many months. Obviously, you should use this time to get a 'life', if you don't already have one, or to change some aspects of your life so as to make relapse less likely when the naltrexone in the implant wears off. Incidentally, you will be able to feel the absorbable, biodegradable plastic, in which the naltrexone is embedded, for over a year before it starts to disappear.

Tissue Reactions
Any implant can cause reactions in the surrounding tissue. The O'Neill implants seem to cause fewer reactions than the American six-week implants but reactions can still occur. Sometimes medical treatment or, very occasionally, surgical removal may be necessary. Infection can complicate any surgical procedure but it should be rare, especially since we give you antibiotic cover. If it happens, it will nearly always be within the first few days. Fortunately, true allergy to naltrexone seems to be very unusual but if you get any swelling, soreness, redness or other change in skin colour, particularly when the initial post-implant bruising and discomfort have settled, please telephone us immediately. We will do our best to provide advice and treatment over the telephone but we may need to see you in person or advise you to see a local doctor so that they can describe the appearance of the implant site to us.

Length of Action
The six-week implants provide naltrexone at levels which are often far higher than is necessary to block heroin. Daily naltrexone tablets provide even higher levels. The O'Neil implants, which are designed to make the most efficient use of the naltrexone in them. provide a lower level for a much longer period. They do not suddenly stop pushing out naltrexone at six months and naltrexone levels are often measurable for nine months or more. We know that typical levels will usually block large amounts of heroin for up to six months. However,, as with six-week implants, the blockade may last for a bit more or a bit less that the average period in some cases. Patients who are much heavier than average, may need a booster. Since the O'Neil implants are very expensive, an additional charge may be necessary in such cases. If there is any sign that the implant is beginning to wear off prematurely, we will do our best to get you back onto higher naltrexone levels, including a free six-week implant booster.

Naltrexone Blood Levels
A leading NHS laboratory is now able to measure naltrexone blood levels quickly enough for routine use. This will help us to identify people whose implants are lasting a bit longer or a bit shorter than average and to advise them about the most appropriate and economical time for re-implantation.

Long Term Outcome
Common sense suggests that the longer you stay clean, the longer you are likely to stay clean in the the long run. Evidence is now emerging that even the six-week implants really make a big difference compared with oral naltrexone in the number of patients who are still clean 12 months after detox. this is probably because most relapses occur during the first two or three weeks but the few months after that are still a danger zone and the O'Neil implants protect during that period. However, if you start using other non-opiate drugs heavily during that time, the benefits may be lost. We don't believe that everyone necessarily has to be drug-free for the rest of their life but during this crucial period, you really should try to clean up your act. (Though, you may still need some sleeping tablets if persistent insomnia is not to drive you crazy and undermine your recovery)

Finally, a word about Dr George O'Neil, the developer of these implants and a respected obstetrician and gynaecologist in Perth, Western Australia. He became knowledgeable about plastics as a missionary surgeon in Africa, where he had to improvise medical equipment in primitive surroundings. Subsequently, he established a company for manufacturing ingenious low-cost plastic medical devices. He has made Perth probably the only city in the world where even the taxi drivers have heard of naltrexone.