Naltrexone is not metabolised by CYP enzymes. Side effects such as nausea, vomiting, diarrhoea and insomnia may be potentially porphyrinogenic.

Cyclopropylmethyl epoxydihydromorphinan M=341. Freely soluble in water.

Naltrexone is a competitive antagonist at opioid receptors and is indicated as an adjunctive prophylactic therapy in the maintenance of detoxified, formerly opioid-dependent patients. It is also used within a treatment programme against abstinence symptoms in alcohol abuses. Very common side effects that can be confused with an acute porphyria attack are abdominal pain, nausea and vomiting. Other common side effects are diarrhoea, constipation, insomnia, tachycardia, arthralgia and myalgia. Some of the side effects have probably an association with abstinence reactions after an uncompleted opioid weaning.

Irrelevant

In vitro studies have shown that neither naltrexone nor its main metabolite 6-β-naltrexol is metabolised via human CYP450 enzymes. Therefore it is unlikely that the pharmacokinetics of naltrexone is affected by cytochrome P450 enzyme inhibiting drugs (SPC). One in vivo study showed that naltrexone does not appear to induce or inhibit metabolic activity of CYP2C9 or CYP3A4 (Adams 2005).