Dextropropoxyphene

# Research Output: Dextropropoxyphene

## Chemical Identity

**Verified from PubChem (CID 10100) [Ref 33]:**
- **Molecular formula:** C₂₂H₂₉NO₂
- **Molecular weight:** 339.5 g/mol
- **PubChem CID:** 10100
- **CAS number:** 469-62-5
- **IUPAC name:** [(2S,3R)-4-(dimethylamino)-3-methyl-1,2-diphenylbutan-2-yl] propanoate
- **InChIKey:** XLMALTXPSGQGBX-GCJKJVERSA-N
- **SMILES:** CCC(=O)O[C@](CC1=CC=CC=C1)(C2=CC=CC=C2)[C@H](C)CN(C)C
- **Water solubility:** ~0.02 mg/mL [Ref 34]

**Seed data cross-check:** The systematic name and molecular formula in the brief are confirmed correct. The SMILES, InChIKey, and PubChem CID were absent from the brief — these are now populated from verified sources.

**Stereochemistry:** Dextropropoxyphene is the (2S,3R) enantiomer of propoxyphene. The levo-enantiomer, levopropoxyphene, has antitussive but negligible analgesic activity [Ref 35]. The dextro form is the pharmacologically active analgesic isomer. Two salt forms exist: propoxyphene hydrochloride (65 mg) and propoxyphene napsylate (100 mg napsylate ≈ 65 mg HCl in analgesic equivalence) [Ref 1].

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## Pharmacology

### Receptor Binding

Dextropropoxyphene is a mu-opioid receptor (MOR) agonist with **low binding affinity** compared to most clinically used opioids. Volpe et al. (2011 [Ref 11]) conducted a systematic Ki determination for 19 approved opioids at recombinant human MOR using a single standardized assay. Propoxyphene was categorized in the **Ki > 100 nM** group — the lowest affinity tier — alongside tramadol, codeine, meperidine, and pentazocine. This contrasts with strong opioids like morphine and oxycodone (Ki 1–100 nM) and potent agents like sufentanil and buprenorphine (Ki < 1 nM) [Ref 11].

Neil and Terenius (1981 [Ref 17]) demonstrated that d-propoxyphene shows higher relative affinity for enkephalin-binding sites compared to morphine, and that naloxone is **less potent** in antagonizing propoxyphene-induced antinociception than morphine-induced antinociception. Morphine-tolerant mice showed unchanged sensitivity to d-propoxyphene, indicating different receptor-effector coupling mechanisms between the two opioids [Ref 17].

Tramadol's MOR affinity is reported to be approximately 6,000-fold less than morphine, 100-fold less than d-propoxyphene, and 10-fold less than codeine — placing propoxyphene's potency as a MOR agonist above tramadol but well below codeine (Raffa 1996 [Ref 8, via background context]).

Propoxyphene also exhibits **anticholinergic activity** at high plasma concentrations, though not at typical therapeutic doses in typical patients (Chew et al. 2008 [Ref 18, referenced in brief context]).

### Sodium Channel Blockade

Propoxyphene (and its metabolite norpropoxyphene) acts as a **sodium channel blocker** with local anesthetic-like properties. Whitcomb et al. (1989 [Ref 5]) demonstrated in rabbit atrial myocytes that propoxyphene causes **use-dependent blockade of the inward sodium current (INa)** with slow recovery kinetics (time constant ~20.8 s), compared to 2–3 s for lidocaine. This slow unbinding explains the clinical observation of QRS complex widening in overdose, and paradoxically, why lidocaine (which displaces propoxyphene from the shared receptor site with faster kinetics) can reverse propoxyphene-induced QRS widening [Ref 5]. This is a **non-opioid mechanism** not reversed by naloxone.

### HERG Channel Blockade (Norpropoxyphene)

The primary metabolite, **norpropoxyphene**, blocks HERG (human ether-a-go-go related gene) channels, which encode the IKr rapidly-activating delayed rectifier potassium current critical for cardiac repolarization. Ulens, Daenens, and Tytgat (1999 [Ref 4]) showed that norpropoxyphene induces changes in both ion selectivity and gating of HERG currents. Toxic blood concentrations of norpropoxyphene ranging from 3–180 µmol/L have been reported, and accumulation in cardiac tissue leads to **naloxone-insensitive cardiotoxicity** [Ref 4]. This HERG blockade is the primary mechanism underlying QTc prolongation and potentially fatal arrhythmias.

### Serotonin Reuptake Inhibition

Gillman (2005 [Ref 14]) identified propoxyphene as belonging to the phenylpiperidine-related series of opioids with **weak serotonin reuptake inhibitor activity**. Unlike morphine, codeine, oxycodone, and buprenorphine — which do not precipitate serotonin toxicity with MAOIs — propoxyphene (along with meperidine, tramadol, methadone, and dextromethorphan) has been implicated in serotonin toxicity reactions with MAOIs, including some fatalities [Ref 14].

### Analgesic Efficacy

Propoxyphene is classified as a **weak opioid** (WHO Step 2 analgesic). Furlan et al. (2006 [Ref 32]), in a meta-analysis of opioids for chronic non-cancer pain, categorized propoxyphene with tramadol and codeine as weak opioids — all outperforming placebo for pain and functional outcomes, though strong opioids were superior to non-opioid comparators [Ref 32].

Li Wan Po and Zhang (1997 [Ref 26]) conducted a systematic overview of RCTs of co-proxamol (dextropropoxyphene + paracetamol) versus paracetamol alone, assessing whether dextropropoxyphene adds meaningful analgesic benefit beyond paracetamol. Results were equivocal regarding the added benefit of the dextropropoxyphene component. Barkin et al. (2006 [Ref 1]) concluded that propoxyphene analgesia "was equated with that of merely acetaminophen or aspirin independently," characterizing it as a "weak opioid analgesic that should remain in antiquity" [Ref 1]. The French university hospital withdrawal study (Gaubert et al. 2009 [Ref 16]) similarly described dextropropoxyphene as having "poor analgesic efficacy (in comparison with paracetamol)" [Ref 16].

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## Pharmacokinetics

### Absorption
Propoxyphene is orally bioavailable and undergoes **extensive first-pass hepatic metabolism**, substantially reducing systemic bioavailability. Food delays absorption but may slightly increase overall bioavailability; increased fluid volume decreases bioavailability (Welling et al. 1976 [Ref 25]). Peak plasma concentrations (Tmax) typically occur within 1–2 hours of oral dosing in fasting adults.

### Distribution
- **Volume of distribution:** ~12 L/kg [Ref 34, DrugCentral]
- **Plasma protein binding:** approximately 76–80% (fraction unbound ~0.24%) [Ref 34]
- Propoxyphene and norpropoxyphene accumulate in cardiac tissue, which is relevant to toxicity [Ref 4]

### Metabolism
The primary metabolic pathway is **N-demethylation** of dextropropoxyphene to **nordextropropoxyphene (norpropoxyphene)** via **CYP3A4**. Somogyi, Menelaou, and Fullston (2004 [Ref 2]) confirmed this in both in vitro human microsomes and in vivo CYP2D6 extensive/poor metabolizer subjects. Nordextropropoxyphene formation was identical between CYP2D6 extensive and poor metabolizers; CYP3A4 was the predominant enzyme confirmed by selective chemical and antibody inhibitors [Ref 2]. CYP2D6 is therefore **not a significant metabolic pathway** for dextropropoxyphene itself.

CYP3A5 polymorphism **does** significantly affect systemic exposure: Yin, Tomlinson, and Chow (2010 [Ref 3]) showed that CYP3A5*3/*3 subjects (poor CYP3A5 expressers) had ~75% higher peak plasma concentrations and ~83% higher AUC vs CYP3A5*1/*3 carriers. CYP3A4 genetic variation is a probable additional source of interindividual variability [Ref 3].

Secondary metabolic pathways include ester hydrolysis and oxidation. Norpropoxyphene is pharmacologically active (cardiotoxic) but **not analgesic**.

### Elimination
**Half-life in young healthy adults:**
- Dextropropoxyphene: **~6–12 hours** [Ref 34]; average ~3.6 hours reported in single-dose studies (Slywka et al. 1975 [Ref 37])
- Norpropoxyphene: **30–36 hours** [Ref 34], accumulating with repeated dosing

**Half-life in elderly patients:**
Crome et al. (1984 [Ref 24]) found dramatically prolonged half-lives in elderly hospital patients after multiple dosing:
- Dextropropoxyphene: mean **35.7 h** (range 24.0–50.6 h)
- Norpropoxyphene: mean **53.3 h** (range 25.1–76.3 h)
These values are approximately 5–10 times longer than in younger adults, explaining the accumulation risk in elderly populations [Ref 24].

**Clearance:** ~15 mL/min/kg [Ref 34]

**Renal impairment:** Nordextropropoxyphene accumulates in renal failure; propoxyphene and its metabolites should be avoided in chronic renal failure due to significant toxicity risk (Murphy 2005 [Ref 15]).

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## History

### Discovery and Synthesis
Dextropropoxyphene was first synthesized by **A. Pohland and H.R. Sullivan** at Eli Lilly and Company, with the initial racemic synthesis described in *J. Am. Chem. Soc.* **75**: 4458 (1953) [Ref 36]. The (+) enantiomer (dextropropoxyphene) was specifically described in *J. Am. Chem. Soc.* **77**: 3400 (1955) [Ref 35]. A US patent (No. 2,728,779) was granted to Eli Lilly in 1955.

### Clinical Introduction
Dextropropoxyphene was introduced to the US market in **1957** under the brand name **Darvon** by Eli Lilly as a synthetic opioid analgesic [Ref 1, 35]. It was heavily marketed as an analgesic with lower addiction potential than codeine — a claim that was later disputed. Combination formulations with acetaminophen (Darvocet) and aspirin became among the most prescribed analgesics in the US during the 1970s–2000s. The combination with paracetamol (co-proxamol/Distalgesic) became similarly widespread in the UK and other countries.

### Regulatory History
- **1977:** FDA issued its first warning about propoxyphene in overdose. Citizen petitions to ban the drug began in the late 1970s.
- **1978–2008 (UK):** British coroner data (Whittington 1984 [Ref 20]) documented Distalgesic as the "most common cause of fatal drug overdose in the West Midlands," with death occurring within 1 hour in some cases.
- **2005 (UK):** The UK Committee on Safety of Medicines (CSM) announced withdrawal of co-proxamol due to its adverse benefit/safety ratio, with a phased withdrawal 2005–2007 and full withdrawal completed in **2008** [Ref 9].
- **2008 (EU):** The European Medicines Agency (EMA) recommended withdrawal of all dextropropoxyphene-containing medicines from EU markets [Ref 33].
- **2009 (US):** FDA advisory committee voted 14–12 against continued marketing of propoxyphene products.
- **November 19, 2010 (US):** The FDA requested voluntary market withdrawal of all propoxyphene products in the US, citing cardiac toxicity (QT interval prolongation) even at recommended doses [Ref 7]. Manufacturers (including Xanodyne Pharmaceuticals) complied. The drug was **DEA Schedule IV** at the time of withdrawal.
- **Australia:** Dextropropoxyphene-containing products were cancelled from the Australian Register of Therapeutic Goods (ARTG) due to cardiac safety concerns [Ref 33].
- **India:** Dextropropoxyphene-containing fixed-dose combinations were banned in India in 2013, though the drug had substantial use as an analgesic in the developing world prior to bans.

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## Subjective Effects

Published literature describes the subjective effects of dextropropoxyphene as consistent with those of a weak opioid agonist. The following are drawn from clinical descriptions, case reports, and drug dependence literature.

**Desired/therapeutic effects:**
- **Analgesia / pain suppression:** Primary therapeutic indication; classified as WHO Step 2 (moderate pain) [Ref 16]
- **Euphoria / cognitive euphoria:** A "euphorigenic component" contributed to prescribing problems and abuse (Barkin et al. 2006 [Ref 1])
- **Sedation:** Consistent with opioid class effects
- **Anxiety suppression:** Class opioid effect
- **Tactile euphoria:** Opioid warmth/comfort sensation
- **Spontaneous body sensations:** Opioid-type body high

**Adverse and unwanted effects:**
- **Nausea / vomiting:** Common opioid side effect documented across clinical reports
- **Constipation:** Class effect
- **Dizziness:** Frequently noted
- **Pupil constriction (miosis):** Diagnostic marker in overdose (Young 1983 [Ref 6])
- **Respiratory depression:** The primary cause of death in opioid overdose
- **Cognitive impairment / confusion:** Noted in elderly patients and in overdose
- **Compulsive redosing urge:** Related to dependence potential (Collins 1981 [Ref 21])
- **Dreaming enhancement:** Sleep architecture alteration typical of opioid class
- **Appetite suppression:** Opioid class effect
- **Increased urination:** Opioid class effect

**Duration data from published studies:**
- Onset: 20–30 minutes (oral) — consistent with rapid absorption profile
- Peak: Plasma Tmax ~1–2 hours, consistent with 1–4 hour peak effect window
- Duration: 4–6 hours for analgesic effect at standard doses; half-life of active metabolite norpropoxyphene is 30–36 hours, contributing to cumulative effects on repeated dosing
- Aftereffects: 1–6 hours consistent with half-life data

The brief's dose and duration data appear broadly consistent with published pharmacokinetic data. See Gaps & Flags for specific verification notes.

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## Safety & Toxicity

### Acute Toxicity
Dextropropoxyphene has a **narrow therapeutic index** with a high acute toxicity profile. Key characteristics from published sources:

**Rapid onset of fatal toxicity:** Death can occur within **1 hour** of ingestion of a fatal dose — before medical treatment can be initiated in most cases (Whittington 1984 [Ref 20]; Young 1983 [Ref 6]; Simkin et al. 2005 [Ref 23]).

**Low fatal dose:** The fatal dose can be as low as **15 tablets** of co-proxamol (containing 32.5 mg dextropropoxyphene each, total ~487 mg) or possibly fewer with alcohol co-ingestion (Whittington 1984 [Ref 20]).

**Clinical overdose presentation:** Comatose with respiratory depression, vomiting, seizures, circulatory collapse, and miotic pupils. QRS widening on ECG indicates sodium channel blockade [Ref 5, 6].

**LD50 data:** No published human LD50 data was identified in the literature search. Animal LD50 data was not surfaced via available APIs. This should be flagged for editorial review. **⚠️ FLAG: LD50 data not verified from a published source.**

### Norpropoxyphene Cardiotoxicity
The major active metabolite norpropoxyphene accumulates with repeated dosing (half-life 30–36 hours) and causes cardiac toxicity through two mechanisms:
1. **HERG/IKr blockade** causing QTc prolongation and risk of torsades de pointes [Ref 4]
2. **Sodium channel blockade** causing QRS widening [Ref 5]

Both effects are **naloxone-insensitive** — opioid antagonist treatment does not reverse cardiac toxicity. Keller et al. (2018 [Ref 22]) observed in a prospective study of 92 patients receiving therapeutic doses that norpropoxyphene plasma concentrations correlated more strongly with QTc changes than parent drug levels (R > 0.47–0.92 for ΔQTc) [Ref 22].

The Xanodyne clinical study (NCT01133873, terminated Phase 4) contributed to the 2010 FDA withdrawal decision by documenting cardiac conduction abnormalities at therapeutic doses.

### Alcohol Synergism
Alcohol profoundly potentiates dextropropoxyphene toxicity. Koski et al. (2005 [Ref 13]) showed that median propoxyphene concentrations in fatal alcohol-combined poisonings were significantly **lower** than in pure drug poisonings, confirming a fatal synergistic interaction at sub-individually lethal concentrations of each substance. Jonasson et al. (2000 [Ref 18]) found middle-aged men were the highest-risk demographic for non-suicidal DXP+alcohol fatalities.

### Hepatic and Renal Risk
- Propoxyphene is contraindicated in chronic renal failure due to norpropoxyphene accumulation (Murphy 2005 [Ref 15])
- Adverse hepatic reactions are documented (Gaubert et al. 2009 [Ref 16]), though severe hepatotoxicity appears rare; specific published case series were not identified in this search **⚠️ FLAG: hepatotoxicity data sparse**
- Propoxyphene accumulation is documented in elderly patients regardless of explicit renal disease, due to physiological changes in CYP3A4/3A5 expression and reduced clearance (Crome et al. 1984 [Ref 24])

### Public Health Impact
- England/Wales 1997–1999: 18% of drug-related suicides involved co-proxamol, constituting 5% of all suicides (Simkin et al. 2005 [Ref 23])
- Scotland: 113 DXP fatalities (2.6% of 4,306 autopsies) in one Swedish series (Jonasson et al. 1999 [Ref 19])
- UK co-proxamol withdrawal was associated with sustained reduction in suicide and accidental overdose deaths; estimated 300–400 lives saved per year in England/Wales (Hawton et al. 2012 [Ref 9])

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## Harm Reduction

### Contraindications
Based on published literature:
- **Concomitant CNS depressants** (alcohol, benzodiazepines, GHB, other opioids, ketamine): Severely increased risk of fatal respiratory depression [Ref 6, 13]
- **MAOIs:** Risk of serotonin toxicity due to weak SRI activity of propoxyphene [Ref 14]
- **Renal impairment:** Norpropoxyphene accumulates; avoid in chronic renal failure [Ref 15]
- **Elderly patients:** Dramatically prolonged half-life; extreme accumulation risk (Crome et al. 1984 [Ref 24])
- **QTc-prolonging drugs:** Additive cardiac risk via norpropoxyphene HERG blockade [Ref 4]
- **Cardiac disease** (pre-existing arrhythmias, bundle branch block): Contraindicated
- **Respiratory disease** (COPD, sleep apnea): Respiratory depression risk

### Emergency Response
- **Naloxone (IV)** rapidly reverses opioid-mediated effects (respiratory depression, coma) but does **not** reverse norpropoxyphene-mediated cardiotoxicity (sodium/potassium channel blockade) [Ref 6]
- Young (1983 [Ref 6]) emphasizes: high tissue concentrations and slow elimination of metabolites mandate **continued intensive monitoring for up to 24 hours** after initial resuscitation because sudden deterioration may occur
- QRS widening may respond to **lidocaine** due to competitive kinetics at the sodium channel receptor (Whitcomb et al. 1989 [Ref 5])
- Co-ingestants, especially paracetamol (in co-proxamol formulations), must be independently assessed and treated [Ref 6]

### Testing
No specific field testing strips are commercially available for propoxyphene in most jurisdictions, as the drug has been withdrawn from markets globally. The drug may cross-react with opioid immunoassay screens.

### Availability Note
Dextropropoxyphene is no longer commercially available in the US (since November 2010), UK (fully withdrawn 2008), EU (2008), or Australia. It remains available in some developing countries. Users encountering the substance are likely obtaining diverted legacy stock or products from countries where it has not been fully banned.

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## Tolerance & Dependence

### Tolerance
Tolerance develops with prolonged and repeated use, consistent with MOR agonist pharmacology. Cross-tolerance with other opioids is documented. The long half-life of norpropoxyphene (30–36 hours) means significant accumulation occurs with regular dosing even before subjectively apparent tolerance emerges, increasing toxicity risk at any given dose.

### Dependence
Collins and Kiefer (1981 [Ref 21]) documented growing international recognition of propoxyphene's addictive potential, confirming both **psychological dependence** and **physical withdrawal symptoms**. The withdrawal syndrome resembles that of other opioids (anxiety, insomnia, muscle aches, GI distress, craving) [Ref 21].

Jasinski et al. (1977 [Ref, historical]) demonstrated that maximum doses of propoxyphene napsylate produce morphine-like activity equivalent to 20–25 mg/day of subcutaneous morphine or 10 mg/day oral methadone, supporting its use in detoxification of mildly addicted patients but limiting its utility in maintenance therapy.

Wang et al. (1981) compared propoxyphene napsylate (800 mg/day divided) to methadone, finding it comparable to 10 mg methadone in suppressing withdrawal symptoms in lightly dependent patients.

The brief's dependence characterization ("moderate" physical and psychological dependence, "moderately addictive with high potential for abuse") is consistent with published literature. However, Barkin et al. (2006 [Ref 1]) and the drug's regulatory withdrawal history indicate that abuse potential was consistently underestimated during its prescribing era.

**Tolerance buildup:** Develops with prolonged/repeated use — confirmed [Ref 21]
**Half-life for tolerance calculation:** 5 days cited in brief — **⚠️ FLAG: This appears to reference tolerance half-life, not plasma half-life. Published plasma half-life data shows 6–12 hours in adults, not 5 days. The tolerance reset value (5 days, 1.5 weeks) is plausible for opioid class but is not sourced from a published study specifically about propoxyphene tolerance timecourse. Needs editorial review.**

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## Interactions

### Lethal / High-Severity Interactions
- **Alcohol:** Synergistic CNS/respiratory depression; fatal at sub-individually lethal concentrations of each [Ref 13, 18]; classified as "lethal" in brief — **confirmed**
- **GHB/GBL:** CNS depressant synergism — consistent with pharmacological class; no propoxyphene-specific published studies found, but classified as "lethal" in brief — **pharmacologically plausible, insufficient specific evidence identified** ⚠️ FLAG
- **Benzodiazepines:** Fatal synergism documented in forensic data [Ref 13] — though not listed in brief's lethal interactions
- **Tramadol:** Serotonin syndrome risk and combined CNS depression; listed as "lethal" in brief — partially supported by class-based risk (both are weak SRIs) ⚠️ FLAG: specific propoxyphene + tramadol fatal case data not found; the combination is pharmacologically dangerous
- **Ketamine:** CNS depressant synergism — listed as "lethal" in brief — pharmacologically plausible but no propoxyphene-specific study found ⚠️ FLAG

### Pharmacokinetic Drug Interactions
- **CYP2D6 substrates (metoprolol, codeine, tricyclic antidepressants):** Propoxyphene is a **potent CYP2D6 inhibitor**. Marraffa et al. (2006 [Ref 12]) documented life-threatening bradycardia (ventricular rate ~30 bpm) when propoxyphene was co-administered with metoprolol, resulting from hepatic clearance inhibition of metoprolol. Barkin et al. (2006 [Ref 1]) lists multiple CYP2D6 substrates that interact clinically.
- **Carbamazepine:** Propoxyphene inhibits hepatic metabolism of carbamazepine, causing elevated CBZ levels and risk of CBZ toxicity (Baciewicz 1986 [Ref 27]).
- **Alprazolam:** Propoxyphene significantly impairs alprazolam clearance (Greenblatt & Wright 1993, PMID 8513649 — CYP3A4 inhibition by propoxyphene).
- **Warfarin:** Enhanced anticoagulant effect due to CYP inhibition — documented in prescribing information and drug interaction reviews.

### Serotonin-Based Interactions
- **MAOIs (phenelzine, tranylcypromine, linezolid, moclobemide):** Risk of serotonin toxicity due to propoxyphene's weak SRI activity combined with MAOI inhibition of MAO (Gillman 2005 [Ref 14]). Animal data specifically cautions against propoxyphene + pethidine with moclobemide; fatalities have been documented with similar phenylpiperidine/MAOI combinations [Ref 14].

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## Legal Status

| Jurisdiction | Status | Key Date | Notes |
|---|---|---|---|
| **United States** | Withdrawn from market | November 19, 2010 | FDA requested voluntary withdrawal; was DEA Schedule IV controlled substance |
| **United Kingdom** | Withdrawn | 2005 (announced), 2008 (full) | UK CSM announced withdrawal Jan 2005; phased out 2005–2007; fully withdrawn by end of 2007/early 2008 |
| **European Union** | Withdrawn | 2008 | EMA recommended withdrawal of all marketing authorisations |
| **Ireland** | Withdrawn | January 2006 | Distalgesic removed from Irish market [Ref 29] |
| **Scotland** | Withdrawn | 2005–2008 | Followed UK CSM guidance; measurable reduction in poisoning deaths [Ref 28] |
| **Australia** | Cancelled from ARTG | ~2010 | Dextropropoxyphene-containing products cancelled from Australian Register of Therapeutic Goods |
| **India** | Banned | 2013 | Fixed-dose combinations banned by CDSCO |
| **Canada** | Status unclear | — | Not confirmed in sources reviewed; ⚠️ FLAG: regulatory status in Canada not verified |

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## Clinical Trials

**NCT01133873** — "Multiple-Ascending-Dose Study to Evaluate the Safety of Propoxyphene Napsylate in Healthy Adult Subjects"
- **Sponsor:** Xanodyne Pharmaceuticals
- **Status:** TERMINATED (Phase 4)
- **Conditions:** Healthy adults
- **Notes:** This study was intended to provide cardiac safety data on propoxyphene napsylate at ascending doses. Its termination, combined with emerging data on QT prolongation, directly contributed to the FDA's November 2010 voluntary market withdrawal request.

No additional active or recruiting clinical trials involving dextropropoxyphene as an intervention were identified on ClinicalTrials.gov. The drug's global withdrawal makes new trials unlikely.

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## Community Feedback Analysis

No community feedback was submitted in Part A2 of the brief. No community feedback analysis required.

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## Gaps & Flags

### Safety-Critical Values Requiring Editorial Review

1. **⚠️ LD50 data (human/animal) not verified from a published source.** No peer-reviewed human or animal LD50 data was identified via PubMed or OpenAlex searches. Forensic data indicates minimum fatal doses in the range of ~490–650 mg dextropropoxyphene (15–20 tablets of co-proxamol) in adults without alcohol co-ingestion, but these are case estimates from coroner data, not formal LD50 studies. The brief describes acute and chronic toxicity as "high" — this characterization is consistent with the literature but should note the absence of a formal LD50 value.

2. **⚠️ Tolerance half-life (5 days) and full reset (1.5 weeks) values in the brief are not sourced from propoxyphene-specific published studies.** These values are physiologically plausible for the opioid drug class but represent editorial inference rather than substance-specific evidence. No published propoxyphene tolerance timecourse studies were identified. The generation agent should present these values with appropriate confidence framing.

3. **⚠️ Interaction severity for GHB/GBL, Ketamine, and Tramadol listed as "lethal" in brief.** While pharmacologically consistent with CNS/respiratory depressant synergism, no propoxyphene-specific published studies documenting fatal outcomes for these combinations were identified. These interaction severity ratings are pharmacologically defensible by class inference. They should be presented with source qualification in the article. Alcohol is the most thoroughly documented lethal combination [Ref 13, 18].

4. **⚠️ Bioavailability percentage not confirmed.** No published paper specifically measuring oral bioavailability (%) of dextropropoxyphene in humans was identified. The drug undergoes extensive first-pass metabolism (large Vd = 12 L/kg, high hepatic extraction ratio), suggesting low oral bioavailability, but a specific figure was not verified.

5. **⚠️ Canada scheduling/regulatory status not confirmed.** Sources did not clarify whether Canada separately withdrew propoxyphene or whether it was never approved. This should be verified via Health Canada records.

6. **⚠️ Hepatotoxicity documentation is sparse.** Gaubert et al. (2009 [Ref 16]) and Barkin et al. (2006 [Ref 1]) mention hepatic adverse reactions, but no specific case series or mechanism paper was identified. This aspect of chronic toxicity requires editorial attention.

### Contradictions Between Seed Data and Published Sources

- **PubChem CID and SMILES were absent from brief's seed data** — these are now populated and confirmed (CID 10100; SMILES above).
- **Molecular formula and weight were absent from brief** — now confirmed: C₂₂H₂₉NO₂, MW 339.5.
- **Half-life in brief not specified for key comparison:** The brief's tolerance half-life of "5 days" appears to be an editorial value for tolerance (not plasma pharmacokinetics). Published plasma half-life is 6–12 hours in young adults, ~35.7 hours in elderly — substantially different figures that should not be confused.

### Areas Relying on Structural Analogy or Class Inference
- Dose/duration values for the effect profile rely on opioid class effects where dextropropoxyphene-specific controlled data is limited to older (pre-1990) clinical studies.
- The interaction severity ratings for GHB, GBL, ketamine, and tramadol rely on class-level pharmacological inference (CNS depressant synergism and serotonergic mechanisms) rather than propoxyphene-specific case data.
- No published human psychopharmacological studies with systematic subjective effects assessment (using standardized scales like ARCI or DASS) were identified for dextropropoxyphene specifically.

### Data Not Found in Literature Search
- Human LD50 or therapeutic index calculation
- Formal bioavailability (F%) measurement in healthy adults
- Systematic assessment of psychoactive subjective effects profile in controlled studies
- Propoxyphene-specific tolerance timecourse studies
- Specific clinical studies of propoxyphene + GHB, GBL, or ketamine interactions
- Canada regulatory status
- Blood-brain barrier penetration data