Drug Interactions between heroin and olanzapine / samidorphan

CONTRAINDICATED: Samidorphan is an opioid antagonist and can block the effects of opioids via competitive inhibition of opioid receptors. Opioid-containing medications may be less effective or ineffective during and shortly after discontinuing treatment with samidorphan, which has an elimination half-life of 7 to 11 hours. In patients who are dependent on opioids, samidorphan can precipitate withdrawal symptoms and opioid withdrawal syndrome that may require hospitalization. Attempts to overcome the opioid blockade with increased or repeated doses of exogenous opioids (e.g., because of ineffective analgesia or opioid withdrawal symptoms) could result in life-threatening or fatal opioid intoxication due to respiratory arrest and/or circulatory collapse, particularly if samidorphan therapy is interrupted or discontinued, subjecting the patient to high levels of unopposed opioid agonist as the samidorphan blockade wanes. Following use of samidorphan, patients may have increased sensitivity to opioids. Therefore, patients with a history of chronic opioid use prior to receiving samidorphan may have decreased opioid tolerance when samidorphan treatment is interrupted or discontinued, which may increase the risk of overdose if opioids are resumed at previously tolerated dosages.

MANAGEMENT: The use of samidorphan is considered contraindicated in patients who are using opioids or undergoing acute opioid withdrawal. Prior to initiating samidorphan-containing medications, there should be at least a 7-day opioid-free interval from the last use of short-acting opioids and at least a 14-day opioid-free interval from the last use of long-acting opioids. In emergency situations where opioid treatment is required for anesthesia or analgesia in a samidorphan-treated patient, it is recommended to discontinue samidorphan and have opioid therapy administered by clinicians trained in the use of anesthetic drugs and the management of the respiratory effects of opioids, specifically the establishment and maintenance of a patent airway and assisted ventilation. The patient should be closely monitored by appropriately trained personnel in a setting equipped and staffed for cardiopulmonary resuscitation. In non-emergency situations where a samidorphan-treated patient is expected to require opioid treatment (e.g., for analgesia during or after an elective surgical procedure), it is advisable to discontinue samidorphan at least 5 days before opioid treatment.

MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients. Sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Cautious dosage titration may be required, particularly at treatment initiation. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.