Fentanyl

Fentanyl is absolutely contraindicated in individuals with significant respiratory depression, severe bronchial asthma in unmonitored settings, or any condition characterized by hypoxia or hypercapnia. MOR agonism at brainstem respiratory centers further depresses already compromised ventilatory function.

Hepatic impairment reduces fentanyl clearance due to decreased hepatic blood flow. Because fentanyl is a high-extraction drug, its clearance is flow-dependent rather than enzyme-dependent. Dose reduction required; monitoring for prolonged respiratory depression essential.

Fentanyl crosses the placental barrier and can produce respiratory depression in the neonate. Chronic use during pregnancy leads to neonatal abstinence syndrome requiring medical management.

Elderly patients show substantially prolonged fentanyl elimination (half-life up to 15 hours vs 1.5-6 hours in younger adults). Dose reduction and extended monitoring intervals are required.

Concurrent use of any CNS depressant substantially increases the risk of fatal respiratory depression. Benzodiazepine-opioid co-exposure is a well-documented risk factor for overdose death.

Gabapentinoids enhance fentanyl's respiratory depressant effects while simultaneously reducing naloxone's reversal potency, creating a uniquely dangerous combination where overdose is both more likely and harder to reverse.

Strong CYP3A4 inhibitors (ketoconazole, ritonavir, itraconazole, clarithromycin) increase fentanyl exposure, potentially shifting plasma concentrations from therapeutic to toxic range. Dose adjustment required.

Fentanyl is absolutely contraindicated in paralytic ileus or suspected gastrointestinal obstruction. MOR agonism in the enteric nervous system suppresses propulsive peristalsis and increases intestinal fluid absorption, exacerbating obstruction.