Dextropropoxyphene

prolonged QTc, bundle branch block, arrhythmia history

Pre-existing prolonged QTc, bundle branch block, or arrhythmia history are absolute contraindications. Both the parent compound and its metabolite produce naloxone-insensitive cardiac ion channel blockade that compounds pre-existing conduction abnormalities.

antipsychotics, certain antibiotics, class III antiarrhythmics

Co-administration with QTc-prolonging medications (antipsychotics, certain antibiotics, class III antiarrhythmics) carries additive risk of QTc prolongation and torsades de pointes via norpropoxyphene's HERG channel blockade.

COPD, obstructive sleep apnea

Patients with COPD, obstructive sleep apnea, or other respiratory disease face compounded respiratory depression risk. Opioid-mediated central respiratory depression adds to pre-existing ventilatory compromise.

phenelzine, tranylcypromine, linezolid, moclobemide

MAOIs (phenelzine, tranylcypromine, linezolid, moclobemide) are absolutely contraindicated due to risk of fatal serotonin toxicity. Propoxyphene belongs to the phenylpiperidine-related opioid series with weak SRI activity, unlike morphine or codeine which lack this risk.

Hepatic impairment reduces CYP3A4-mediated N-demethylation of dextropropoxyphene, delaying parent drug elimination. This may increase systemic exposure and alter the ratio of parent compound to norpropoxyphene.

Dextropropoxyphene is contraindicated in chronic renal failure. The primary metabolite norpropoxyphene undergoes renal elimination and accumulates in renal impairment, reaching cardiotoxic concentrations that cause QRS widening and QTc prolongation not reversible by naloxone.

Individuals homozygous for CYP3A5*3 (non-expressers, common in Caucasian populations) demonstrate approximately 75% higher peak plasma concentrations and 83% higher AUC compared to CYP3A5*1/*3 carriers at identical doses, approaching a two-fold difference in systemic exposure.

Elderly patients show dramatically prolonged half-lives: mean 35.7 hours for dextropropoxyphene and 53.3 hours for norpropoxyphene, compared to approximately 6-12 hours and 30-36 hours respectively in younger adults. This produces accumulation of both the parent drug and its cardiotoxic metabolite even at standard dosing regimens.

alcohol, benzodiazepines, other opioids, GHB, GBL, barbiturates

Co-administration with alcohol, benzodiazepines, other opioids, GHB/GBL, or barbiturates is absolutely contraindicated. The synergistic respiratory depression and cardiac toxicity create unacceptable risk. Alcohol co-ingestion lowers the fatal dose to concentrations that would otherwise be survivable.

metoprolol, tricyclic antidepressants, codeine

Dextropropoxyphene potently inhibits CYP2D6 despite not being a CYP2D6 substrate. Co-administration with CYP2D6-metabolized drugs including metoprolol, tricyclic antidepressants, and codeine can elevate their plasma levels to toxic concentrations. Life-threatening bradycardia has been documented with metoprolol co-administration.