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Naltrexone implants success rate

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- How Naltrexone implant was developed?

- Clinical experience with Naltrexone

- About Naltrexone's toxicity

       Dr. Victor Shubaev on heroin blockers

Naltrexone was synthesized in the 1960s. Scientists had first used Naltrexone clinically in the early 1970s. It soon became evident that its therapeutic potential was undermined by poor compliance. Therefore the first studies of depot Naltrexone date from the mid 70s. Human studies took place in the early 1980s, and most of the basic science was known by then.

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Naltrexone is a pure opiate antagonist with low oral bioavailability of around 40%. Clinical data has indicated that poor medication compliance occurs with daily naltrexone tablets treatment for opioid dependence. Naltrexone’s lack of agonist activity causes no withdrawal-related side-effects. There are no negative consequences when patient stops taking it.

Better Naltrexone compliance has been observed when a responsible adult is available to supervise daily Naltrexone dosing.  There are reports that the method of daily Naltrexone tablets intake is not very efficient. Experienced doctors specialized in the filed recommend another solution. Long-term sustained release of Naltrexone would be more appropriate in drug addiction treatment.

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Wise (1984) developed a naltrexone (70%)-poly(D,L-lactide-co-glycolide) copolymer (30%) which was the first biodegradable drug delivery system.  It was approved by the Food and Drug Administration (FDA) for clinical testing, and was limited by “burst release” in human trials.  Previous findings also suggested that polymeric naltrexone sustained release systems are biocompatible formulations.

85% Naltrexone implants success rate reported in the USA

Naltrexone prices


First generation of Naltrexone blockers

The first Naltrexone implants for clinical as opposed to experimental use took place around 1997 by Lance L Gooberman (Pellet Technologies LLC, NJ), George Malmberg (Wedgewood Pharmacy, NJ) and Alan R Tripp. See the patent These ‘first generation’ models currently consist of a cigarette-butt size pellet of  compressed naltrexone powder with a small percentage of magnesium stearate. Magnesium stearate is apparently a normal component of implants but sometimes causes tissue irritation. At one time, they also contained 10mg of slow-release triamcinolone to reduce allergic reactions. These drug implants dissolve and disappear completely in about  5-7 weeks on average. Naltrexone implants success rate got improved significantly.

Pharmacy of a Berlin hospital has made similar drug implan for internal use by . Due to having no stearate component seems to have better tissue tolerability and was supposed to be available by the end of 2006. George Sherman at Towne Pharmacy, NJ has  manufactured the later implant. It is a 1g  pellet with 10mg of slow release triamcinolone. It is manufactured in a novel manner producing effective opioid blockage for 12 to 14 weeks.

The same product is now licensed in Russia as Prodetoxone. It is currently being used at three extensive trials. The trials are conducted at St.Petersburg Scientific-Research Center of Addictions and Psychopharmacology. Also at Pavlov Medical University, St.Petersburg,Russia in conjunction with the University of Pennsylvania, Department of Psychiatry, Philadelphia, USA. Naltrexone implants success rate in Russia is not known because of lack research.

Second generation of Naltrexone blockers

‘Second generation’ drug implants use another established implant technique because of embedding naltrexone in a matrix of biodegradable polymer microspheres. Dr George O’Neill of GO-Medical Industries in Perth, WA had made the first available implant of this type.  The polymer takes 1-2 years to break down and naltrexone is released for 5-12 months or more. Opiate blockade may be only partial after about 9-13 months though.

These drug implants are generally well-tolerated and there is no need to include a steroid. Both types of implants are usually inserted with antibiotic prophylaxis. They also can block very large amounts of heroin because of containing large quantity of Naltrexone. Basic composition of the O’Neill implant is approximately 50% naltrexone, 49% of biodegradable polymer and £1% magnesium stearate.  The polymer material is similar material to that used in biodegradable sutures and has the FDA's license.

The polymer has been used previously in implantable norethisterone formulations (Beck et al, 1981). The incidence of foreign body reactions with polylactide biodegradable polymers has been recently reviewed (Perrin et al., 1997). Go Medical estimate an incidence of foreign body reaction of 4.9%, from accumulated data from 412 patients. That made the success rate  even higher.

Types of second generation Naltrexone implants

There are  several "new" second generation implants. The most recent is the LI LA naltrexone implant from China, and is also based on the use of biodegradeable polymer. However, the LI LA naltrexone implant appears to give good blood levels and hence effective opiate blockage over 360 days.

Afterwords three American companies have developed blockers:

1. Addex naltrexone implants - Bartor Pharmacal Inc.

2. Trident naltrexone implants - Trident Inc.

3. Hydron naltrexone implants - Valera Pharma Inc. the implants are at various stages of development. The polymer can also be formulated as a liquid vehicle for a depot injection of naltrexone.

One Alkermes Inc. USA have been working on this for over 10 years. FDA had approved Vivitrol under special license  for use in the treatment of alcoholics. Because of its efficiency in alcohol addiction treatment, it is used in many countries.



Since Naltrexone is a relatively old drug, its properties are correspondingly well known. It appears to have no significant organ toxicity apart from very rare rashes. In particular, there are no reports of clinically significant liver toxicity.


Anderson, J.M., Wise, D.L., 1975. Lactic/Glycolic acid polymers as narcotic antagonist delivery systems. Life Sci. 17, 1877-1886 Beck, L.R., Ramos, R.A., Flowers, C.E., Lopez, G.Z., Lewis, D.H., Cowsar, D.R..

Clinical evaluation of injectable biodegradable contraceptive system.  Am. J. Obstet Gynaecol.  1981; 140: 799-806. Bell, J.R., Young, M.R., Masterman, S.C., Morris, A., Mattick, R.P., Bammer, G., A pilot study of naltrexone-accelerated detoxification in opioid dependence.Med. J. Austr.  1999; 171:  26-30. Brewer, C.  Naltrexone:  An "Antiabuse" for heroin addicts?  Pharm. J.  1987; 239: 182-183. Brewer, C.  Naltrexone implants for opiate addiction:  new life for a middle-aged drug because of Naltrexone.  Pharm. J.  2001; 267: 260. Brewer C. and Gastfriend DR. Rapid opioid detoxification. [Comment. Letter] JAMA. 1998; 279(23):1872. Bugge, C. J. L., Grun, I., Stanfor, K., Tan, M. S. & Garcia, D. B. Determination of Naltrexone and 6-b-Naltrexol in human plasma by LC-MS-MS. Determination of Naltrexone and 6-b-Naltrexol in human plasma by LC-MS-MS; 1996 . Chiang, C.N., Hollister, L.E., Kishimoto, A., Barnett, G., 1984. Kinetics of a naltrexone sustained-release preparation. Naltrexone implants success rate.

More resources

Clin. Pharm. Ther. 36, 704-708. Hulse, G. K., Basso, M. R.  The association between naltrexone compliance and daily supervision.  Drug Alcohol Rev. 2000; 19:  41-48. Maa Y F and Heller J. Controlled release of naltrexone pamoate from linear poly ortho esters. [Article] Journal of Controlled Release. 1990; 14(1): 21-28.

Perrin, D.E., English, J.P.   Polyglycolide and polylactide in Handbook of Biodegradable polymers.  Bombe, A.J.,  Kost, J., Wiseman,D.M. eds. Harwood 1997, pp3-27. Wall, M.E., Braine, R.D., Perez-Reyes, M.  Metabolism and disposition of naltrexone in man after oral and intravenous administration.  Drug Metab. Dispos.  1981; 9: 370-375. Yamaguchi, K., Anderson, J.M., 1993. Biocompatibility studies of naltrexone sustained release formulations. J. Control. Release. 19, 299-314. Yolles, S., Leafe, T.D., Woodland, J.H.R., Meyer, F.J., 1975. Long acting delivery systems for narcotic antagonists II: release rates of naltrexone from poly(lactic acid) composites. J. Pharm. Sci. 64, 348-349.

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