Journal of Clinical & Experimental Pharmacology

Abstract

The Occurrence of Spontaneous Lymphomas but Not Adenomas or Sarcomas in Rats Treated With Sustained Release Naltrexone

Erin Kelty, Philip K. Nicholls, George O’Neil, Zoe Harrison, Chin-Tark Chan, Peter Symons, Albert Stuart Reece and Gary Hulse

Naltrexone has been observed to have both a stimulatory and inhibitory effect on the development of tumours in rodents, potentially mediated by changes to the neuroendocrine system as a result of blockade of the opiate receptors, with the period of blockade and the tumour type thought to be influential. This study examined the occurrence of spontaneous tumours in rats treated with a sustained release naltrexone preparation. Materials and methods: 27 male and 27 female rats were randomized into three equal treatment groups (A, B and C). Rats in group A were implanted with a single naltrexone implant tablet, rats in group B were implanted with a single polymer implant tablet (placebo) and rats in group C underwent a sham procedure (control). Three different groups of spontaneous tumours were observed; lymphomas, adenomas and sarcomas. Lymphomas (4 tumours/3 rats) were observed solely in naltrexone treated rats, while adenomas (9 tumours/5 rats) and sarcomas (4 tumours/3 rats) were only observed in the placebo and the control groups. The data suggests that the association of naltrexone on the development of tumours maybe dependent on tumour type. Long term exposure to naltrexone appears to have both a stimulatory and inhibitory effect on tumours in rats, dependent on tumour type.