What this test measures
Propoxyphene is a synthetic opioid analgesic that was widely prescribed under brand names like Darvon and Darvocet for mild to moderate pain. The US FDA withdrew propoxyphene from the market in 2010 because of cardiac toxicity (QT prolongation and arrhythmias), and it has been progressively de-listed in many countries including India. The test quantifies propoxyphene and its long-lived metabolite norpropoxyphene, the latter being more cardiotoxic than the parent drug.
The assay is by LC-MS/MS for accuracy. Propoxyphene is not detected by routine opiate immunoassays — a specific test is required.
Why it matters
Although prescribing has fallen sharply, propoxyphene still occasionally turns up in Indian toxicology — through old stock, smuggled imports, and combination analgesics in some legacy formulations. In suspected overdose, the picture combines opioid features (respiratory depression, miosis, decreased consciousness) with cardiac effects (widened QRS, prolonged QT, ventricular arrhythmias, seizures). The level confirms the diagnosis and guides ICU-level monitoring.
Forensic and medico-legal labs also use the test in unexplained sudden cardiac death investigations, particularly when an analgesic was found at the scene. A high norpropoxyphene level can persist for days after the parent drug becomes undetectable, extending the diagnostic window.
How to prepare
No fasting needed. Sample is drawn on presentation in suspected overdose, with timing recorded relative to the last suspected dose. For forensic submissions chain-of-custody documentation is essential. Disclose all medications — methadone and diphenhydramine can occasionally interfere with older immunoassays.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Propoxyphene (ng/mL)[1][2] | Not detected (no current legitimate use in most countries) | Not detected: rules out recent propoxyphene exposure. | 100 – 400 ng/mL: therapeutic range when historically used. > 500 ng/mL: associated with toxicity. > 1000 ng/mL: severe overdose — risk of cardiac arrhythmia, seizures, coma, death. The norpropoxyphene metabolite is often higher than the parent and persists longer. |
Propoxyphene serum interpretation
| Level (ng/mL) | Category | Clinical context |
|---|---|---|
| Not detected | Negative | No recent exposure |
| 100 – 400 | Historical therapeutic | Analgesic range (when used) |
| 400 – 1000 | Toxic | Sedation, cardiac conduction effects |
| > 1000 | Severe overdose | Arrhythmia, seizures, coma — ICU |
Frequently asked questions
Is propoxyphene still available?
No — the US FDA withdrew it in November 2010, and most countries have followed. India has progressively de-listed it. The drug occasionally turns up via old stocks or illicit channels.
Why was propoxyphene withdrawn?
It causes dose-related cardiac toxicity even at therapeutic doses — QT prolongation, QRS widening, and arrhythmia risk. Clinical-trial data showed risks outweighed the modest analgesic benefit over safer alternatives like paracetamol or codeine.
Does routine opioid screening detect propoxyphene?
No. Routine opiate immunoassays target morphine and codeine-like opioids. Propoxyphene needs a specific assay, typically LC-MS/MS.
What happens in propoxyphene overdose?
A dangerous combination of opioid (respiratory depression, pinpoint pupils, sedation) and cardiac effects (widened QRS, prolonged QT, ventricular arrhythmia, seizures). Naloxone reverses the opioid component but not the sodium-channel blocking cardiac toxicity, which is managed with sodium bicarbonate and supportive ICU care.
Why is norpropoxyphene important?
Norpropoxyphene is the main metabolite, has a longer half-life (~30 hours) than the parent (~6 hours), and is more cardiotoxic. It can be detected for days after parent drug is gone, extending the diagnostic window in suspected overdose.
When is the test used in 2026?
Forensic post-mortem analysis, unexplained sudden cardiac death where an analgesic was found, occasional overdose presentations, and comprehensive toxicology panels in emergency rooms when the cause is unclear.
Related Drugs / Therapeutic Monitoring tests
Tests commonly ordered alongside PROPOXYPHENE, or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Propoxyphene Toxicity · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Propoxyphene Overdose · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Propoxyphene, Serum · accessed 2026-05-30T00:00:00.000Z
- FDA — Propoxyphene Withdrawal Announcement (2010) · accessed 2026-05-30T00:00:00.000Z
Book with Zelnoo
Get your PROPOXYPHENE test done at home — transparent prices, NABL-accredited labs.
Zelnoo lets you compare diagnostic test prices across NABL-accredited labs in Mumbai & Thane, book a free home phlebotomist visit, and receive digital reports in 24–48 hours into a consent-first report vault. No subscriptions, no membership fees — pay only for the test you book.
Book PROPOXYPHENE now