Article Title

Naltrexone implant and blood naltrexone levels over pregnancy


Approximately 80–90% of all women using intravenous heroin are of reproductive age. Although heroin use can cause menstrual irregularities such as amenorrhoea, oligomenorrhea and suppression of ovulation, pregnancy is not uncommon. (1) Maternal heroin use during pregnancy is associated with an increased risk of a number of adverse maternal and neonatal outcomes, including low birthweight (LBW) and reduced birthweight neonates, ante-partum haemorrhage and increased neonatal mortality.(2–4)

The currently accepted management of the pregnant heroin user involves methadone maintenance treatment (MMT). Importantly, no serious foetal toxicity has been associated with methadone. (5,6) Naltrexone, a long-acting opiate antagonist that can be administered to persons who have detoxified completely from heroin (7) and which is effective in completely blocking the effects of heroin, (8) has also been used in a depot preparation in the management of the heroin dependent pregnant women.

In this form of maintenance, naltrexone is delivered by a surgically inserted sustained release preparation. Recently, a number of case studies have described positive obstetric and neonatal outcomes associated with the management of pregnant women with implant naltrexone; (9) however, no data on blood naltrexone concentration with time has been provided to date.

The present case study provides profiles of blood concentrations of naltrexone and 6-beta naltrexol following naltrexone implant over pregnancy. It uses data from blood samples collected over pregnancy by the treating clinic (Australian Medical Research Procedures Foundation (AMPRF), Perth, Western Australia) as part of routine clinical management to investigate the length of time naltrexone blood levels are sustained above 2 ng/mL following implant. Bloods were analysed for naltrexone by the Forensic Science Laboratory, Chemistry Centre (WA) by liquid chromatography and mass spectrophotometry using an adaptation of the method described by Bugge et al. (10) These methods are able to quantify naltrexone and its active metabolite 6-beta-naltrexol in human blood with a limit of detection of 0.5 ng/mL for both compounds.



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