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Interpretive Handbook

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Test 505345:
Drug of Abuse, Propoxyphene Screen with GC-MS Confirmation, Urine

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Propoxyphene (Darvon) is an analgesic used for the treatment of mild-to-moderate pain that is not adequately relieved by aspirin. It is a congener of the narcotic methadone but is classified as a non-narcotic. It produces analgesia by binding to u-opioid receptors in the central nervous system (CNS).

 

Propoxyphene undergoes hepatic N-demethylation to produce a major metabolite, norpropoxyphene, which has one-fourth to one-half the pharmacologic activity of the parent drug. The serum half-lives of propoxyphene and norpropoxyphene are 8 to 24 hours and 20 to 50 hours, respectively. Rapid tissue binding of propoxyphene occurs, resulting in the immediate and almost complete disappearance from the bloodstream and relatively high concentrations in the brain, lung, liver, and kidney.

 

Toxic manifestations are similar to those produced by codeine and include respiratory and CNS depression, cardiac arrhythmias, pulmonary edema, hypotension, hallucinations, convulsions, and coma. Accidental or intentional ingestion of large amounts of propoxyphene may cause death.

Useful For Suggests clinical disorders or settings where the test may be helpful

Detecting and confirming drug abuse involving propoxyphene

Interpretation Provides information to assist in interpretation of the test results

A positive result derived by this testing indicates that the patient has used propoxyphene in the recent past.

 

Random urine collection results are not clinically definitive but the following values may be used as guidelines:

Propoxyphene:

1,000-5,000 ng/mL; typical for therapeutic dosages

>10,000 ng/mL; may indicate toxic blood concentration

>80,000 ng/mL; may indicate potentially lethal blood concentration

Norpropoxyphene:

2,000-20,000 ng/mL; typical for therapeutic dosages

>30,000 ng/mL; may indicate toxic blood concentration

>80,000 ng/mL; may indicate potentially lethal blood concentration

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

EMIT cutoff concentration: 300 ng/mL

Positives are reported with a quantitative GC-MS result.

GC/MS cutoff concentrations

Propoxyphene: <300 ng/mL

Norpropoxyphene: <300 ng/mL

Clinical References Provides recommendations for further in-depth reading of a clinical nature

Baselt RC: In Disposition of Toxic Drugs and Chemicals in Man, Fifth edition. Chemical Toxicology Institute, Foster City, CA 2000