naltrexone hydrochloride /naltrek″sōn/ , an oral opioid antagonist. ▪ INDICATIONS: It is prescribed to block the effects of opioid analgesics, including heroin, morphine, and methadone, in patients recovering from addiction and to treat ethanol dependence. ▪ CONTRAINDICATIONS: Acute hepatitis or liver failure prohibits its use. Periodic liver function tests are recommended for all patients. Patients must be completely free of opioids before taking naltrexone to prevent severe withdrawal symptoms. Patients must be educated that their tolerance to morphine disappears while they are on naltrexone and that they can be much more sensitive to opioids after discontinuing naltrexone; dosage levels of heroin, morphine, and similar drugs that were previously tolerated could now be fatal. ▪ ADVERSE EFFECTS: The most serious adverse effects are abdominal pain, cramps, nausea, vomiting, headache, sleep disorders, and joint and muscle pain. Some adverse effects may actually be withdrawal symptoms rather than reactions to naltrexone.
