Naltreksoni

Naltreksoni, known in English as naltrexone, is a synthetic opioid receptor antagonist used to treat opioid dependence and, in some settings, alcohol use disorder. It is a competitive antagonist at mu-, kappa-, and delta-opioid receptors, which blocks the effects of opioid agonists and dampens endogenous opioid–mediated reinforcement. Because it blocks opioids, starting naltrexone can precipitate withdrawal in individuals who are currently opioid dependent, so treatment is usually preceded by a period of opioid abstinence.

Naltrexone is available in oral tablet form and as an extended-release intramuscular injection. Oral tablets are commonly given in 25–50 mg daily doses, while the depot formulation is administered as a 380 mg intramuscular injection every four weeks, providing long-acting receptor blockade. The oral form has variable adherence due to daily dosing, whereas the depot form improves persistence with treatment.

Pharmacokinetically, naltrexone has relatively low oral bioavailability due to first-pass metabolism, producing an active metabolite, 6β-naltrexol, that also contributes to receptor antagonism. The drug’s effects depend on sustained receptor blockade, and the depot formulation maintains therapeutic levels for about a month.

Safety and monitoring considerations include the risk of hepatotoxicity at high doses, so liver function should be monitored. It is contraindicated in individuals currently dependent on opioids or those presenting with acute withdrawal. Common adverse effects include nausea, headache, dizziness, and injection-site reactions for the depot form. Pregnancy category C is often cited; dosing decisions should consider potential interactions with other central nervous system depressants and the need for ongoing psychosocial support alongside pharmacotherapy.

Naltreksoni is marketed under various names, including generic formulations and brand names such as Revia (oral) and Vivitrol (depot).