Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
NALOXONE HYDROCHLORIDE AND PENTAZOCINE HYDROCHLORIDE vs FLOLAN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Pentazocine is a mixed agonist-antagonist opioid that binds to mu-opioid receptors (partial agonist) and kappa-opioid receptors (agonist), producing analgesia. Naloxone is a pure opioid antagonist that competitively blocks mu, kappa, and delta receptors; when administered orally, naloxone undergoes extensive first-pass metabolism, reducing systemic absorption and primarily blocking the effects of pentazocine if the combination is misused parenterally.
Epoprostenol is a prostaglandin I2 (prostacyclin) analogue that directly vasodilates pulmonary and systemic arterial beds, inhibits platelet aggregation, and has antiproliferative effects on vascular smooth muscle.
Moderate to severe pain relief; combinations are used to reduce abuse potential.
Pulmonary arterial hypertension (PAH) (WHO Group I) in NYHA Class III-IV patients to improve exercise capacity and hemodynamics,Pulmonary arterial hypertension in patients who require chronic IV therapy,Off-label: Severe Raynaud's phenomenon, primary pulmonary hypertension in neonates, and as a bridge to lung transplantation
Oral: One tablet (naloxone 0.5 mg / pentazocine 50 mg) every 3-4 hours as needed for pain; maximum 12 tablets daily.
Initial: 4 ng/kg/min via continuous IV infusion, then titrated in increments of 1-2 ng/kg/min at intervals of at least 15 minutes based on clinical response. Typical maintenance dose: 20-40 ng/kg/min; range: 10-80 ng/kg/min.
Pentazocine has an elimination half-life of 2-3 hours in healthy adults, which may be prolonged in patients with hepatic impairment. Naloxone has a terminal half-life of 0.5-1.5 hours in adults, with a rapid decline in plasma levels; the short half-life limits its duration of opioid antagonism.
3–5 minutes (terminal elimination half-life; rapid inactivation necessitates continuous IV infusion).
Pentazocine is metabolized primarily by hepatic conjugation (glucuronidation) and oxidation via CYP2C19 and CYP2D6; naloxone is extensively metabolized by the liver, primarily via glucuronidation (UGT2B7).
Epoprostenol undergoes rapid hydrolysis at neutral p H and is also metabolized by enzymes including 15-hydroxyprostaglandin dehydrogenase to inactive metabolites (6-keto-PGF1alpha, 6,15-diketo-PGF1alpha, and 6,15-diketo-13,14-dihydro-PGF1alpha).
Pentazocine is primarily metabolized in the liver and excreted in urine as conjugates of glucuronide and sulfate, with about 60% of a dose excreted renally within 24 hours as metabolites and unchanged drug (less than 5% unchanged). Naloxone undergoes extensive hepatic metabolism to naloxone-3-glucuronide, which is excreted renally; approximately 50% of a dose is excreted as conjugates in urine within 6 hours.
Renal: 70% (as inactive metabolites); biliary/fecal: negligible.
Pentazocine: Approximately 35-65% bound to plasma proteins (mainly albumin). Naloxone: Approximately 32-45% bound to plasma proteins (mainly albumin).
Approximately 50% bound to albumin.
Pentazocine: Vd ~2-3 L/kg, indicating extensive tissue distribution. Naloxone: Vd ~2-3 L/kg, also indicating wide distribution.
0.03–0.1 L/kg; small Vd consistent with limited extravascular distribution.
Oral pentazocine: 20-30% due to first-pass metabolism. Intramuscular pentazocine: 100%. Subcutaneous pentazocine: 100%. Oral naloxone: <2% due to extensive first-pass metabolism. Intramuscular and subcutaneous naloxone: 100%. Intravenous: 100% for both.
Intravenous: 100% (only route of administration).
GFR 30-50 m L/min: Administer every 6 hours; GFR 10-29 m L/min: Administer every 8-12 hours; GFR <10 m L/min: Administer every 12 hours or consider alternative.
No specific dose adjustment required; monitor fluid and electrolyte balance due to potential hypotension.
Child-Pugh Class A: No adjustment; Child-Pugh Class B: Reduce dose by 50% or extend interval; Child-Pugh Class C: Avoid use.
No specific dose adjustment required; consider reduced clearance in severe hepatic impairment (Child-Pugh class C) with cautious titration.
Not recommended for children under 12 years. For older children (≥12 years): Pentazocine 50 mg (with naloxone 0.5 mg) orally every 3-4 hours as needed; maximum 6 tablets daily.
Initial: 2 ng/kg/min via continuous IV infusion, titrate by 1-2 ng/kg/min every 15 minutes as tolerated. Maximum dose not established; typical range 5-40 ng/kg/min.
Initiate with half the usual adult dose (one-half tablet) and titrate carefully due to increased sensitivity and risk of respiratory depression.
No specific dose adjustment; start at lower end of dosing range (4 ng/kg/min) and titrate cautiously due to increased sensitivity to hemodynamic effects.
Risk of respiratory depression, particularly in elderly, cachectic, or debilitated patients; risk of addiction, abuse, and misuse; risk of neonatal opioid withdrawal syndrome with prolonged use during pregnancy; risk of life-threatening respiratory depression when used with benzodiazepines or other CNS depressants.
FLOLAN is a potent vasodilator and must be administered by continuous IV infusion through a permanent central venous catheter. Abrupt discontinuation or sudden large dose reductions may result in worsening pulmonary hypertension and death. Only clinicians experienced in PAH treatment should prescribe FLOLAN.
Respiratory depression; hypotension; increased intracranial pressure; seizure risk (pentazocine); opioid-induced hyperalgesia; adrenal insufficiency; severe hypotension; interaction with MAOIs; risk of dependence and withdrawal; gastrointestinal obstruction; impaired renal or hepatic function; head injury.
Do not abruptly discontinue infusion (risk of rebound pulmonary hypertension), monitor for pulmonary edema (if suspect veno-occlusive disease), may cause bleeding complications (due to antiplatelet effects), monitor for sepsis/thrombosis from chronic IV catheter, use caution in patients with hepatic or renal impairment.
Hypersensitivity to pentazocine or naloxone; significant respiratory depression; acute or severe bronchial asthma; GI obstruction; known or suspected paralytic ileus; patients receiving MAOIs or within 14 days.
Long-term use in patients with pulmonary veno-occlusive disease (PVOD), hypersensitivity to epoprostenol or structurally related drugs, or severe left ventricular systolic dysfunction (NYHA Class III-IV heart failure) due to risk of pulmonary edema.
No specific food interactions are reported for this combination. However, grapefruit juice may theoretically affect metabolism via CYP3A4 (pentazocine is metabolized by CYP3A4), but clinical significance is unknown. Advise patients to maintain a consistent diet.
No specific food interactions are reported for epoprostenol. Avoid excessive alcohol as it may worsen hypotension.
Pentazocine crosses the placenta; naloxone has limited placental transfer. No well-controlled human studies. First trimester: Risk cannot be excluded; avoid if possible. Second/Third trimester: Chronic use may cause fetal dependence; neonatal withdrawal syndrome reported. High doses near term may cause neonatal respiratory depression.
FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; however, no adequate and well-controlled studies in pregnant women. Epoprostenol is a potent vasodilator and inhibitor of platelet aggregation; theoretical risk of hemorrhage in the fetus. Use only if clearly needed.
Pentazocine is excreted in breast milk in small amounts (estimated relative infant dose <3%). Naloxone is poorly bioavailable orally. Generally considered compatible with breastfeeding; monitor infant for sedation or poor feeding. M/P ratio for pentazocine is approximately 1.0.
Epoprostenol is not recommended during breastfeeding. No data on presence in human milk, effects on the breastfed infant, or milk production. Due to potential for serious adverse reactions (e.g., hypotension, bleeding), breastfeeding should be discontinued during treatment.
No established dose adjustments for pregnancy; however, pharmacokinetic changes (increased volume of distribution, enhanced clearance) may require higher or more frequent doses of pentazocine for adequate analgesia. Use lowest effective dose and shortest duration.
Pregnancy may alter pharmacokinetics; increase in plasma volume may require dose adjustments. No formal studies; titrate dose based on clinical response (e.g., symptoms of pulmonary arterial hypertension). Monitor for signs of overdose (hypotension, tachycardia) or underdose (worsening dyspnea).
Naloxone in this fixed-dose combination is included to deter opioid abuse by reversing euphoria. The pentazocine component is a mixed agonist-antagonist opioid; naloxone has poor oral bioavailability but becomes active parenterally, precipitating withdrawal in opioid-dependent individuals. Use with caution in patients with impaired renal or hepatic function. Monitor for respiratory depression, especially in opioid-naive patients, as pentazocine alone can cause respiratory depression.
FLOLAN (epoprostenol) is a prostacyclin used for pulmonary arterial hypertension (PAH). It has a very short half-life (3-5 minutes) and must be administered via continuous IV infusion. Abrupt interruption can cause life-threatening rebound pulmonary hypertension. The drug is unstable at room temperature; requires ice packs during administration. Dose titration is done based on symptoms and side effects (e.g., jaw pain, flushing, headache, diarrhea).
Take exactly as prescribed; do not crush or inject tablets, as injected naloxone can cause severe withdrawal in opioid-dependent individuals.,This medication contains naloxone to discourage misuse; injection will cause withdrawal symptoms.,Report any signs of withdrawal (e.g., nausea, vomiting, sweating, agitation) or breathing difficulty.,Avoid alcohol and other central nervous system depressants as they increase risk of respiratory depression.,Do not use with other opioids unless directed, as effects are unpredictable.,Keep out of reach of children; accidental ingestion may cause severe respiratory depression.
This medication is given continuously through an intravenous (IV) line using a portable infusion pump.,Never stop the infusion suddenly; sudden stoppage can cause severe worsening of your condition.,Keep the medication cold (with ice packs) during infusion; it degrades at room temperature.,Report any signs of infection at the IV site, such as redness, swelling, or pain.,Common side effects include headache, jaw pain, flushing, nausea, and diarrhea; these may improve over time.
"Cobicistat is a potent CYP3A4 inhibitor used to boost the pharmacokinetics of antiretroviral agents like atazanavir and darunavir. Naloxone primarily undergoes glucuronidation via UGT1A6 and UGT2B7, with minor CYP3A4 metabolism. Concomitant use with Cobicistat may modestly increase naloxone exposure due to CYP3A4 inhibition, but this is unlikely to be clinically significant given naloxone's wide therapeutic index and short half-life."
"Fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), is primarily metabolized by cytochrome P450 (CYP) 1A2 and 2D6. Naloxone, an opioid antagonist, is reported to inhibit CYP1A2, potentially decreasing the clearance of fluvoxamine. This interaction may lead to increased fluvoxamine plasma concentrations, elevating the risk of serotonin syndrome, QT prolongation, and other dose-dependent adverse effects, especially in patients receiving high doses or those with hepatic impairment."
"Naloxone, an opioid receptor antagonist, may inhibit the cytochrome P450 isoenzyme CYP3A4, which is responsible for the metabolism of ivacaftor. Concomitant administration can lead to reduced clearance of ivacaftor, resulting in elevated serum concentrations. This increase may potentiate the therapeutic effects and adverse reactions of ivacaftor, such as hepatotoxicity and QT prolongation."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about NALOXONE HYDROCHLORIDE AND PENTAZOCINE HYDROCHLORIDE vs FLOLAN, answered by our medical review team.
NALOXONE HYDROCHLORIDE AND PENTAZOCINE HYDROCHLORIDE is a Opioid Agonist-Antagonist that works by Pentazocine is a mixed agonist-antagonist opioid that binds to mu-opioid receptors (partial agonist) and kappa-opioid receptors (agonist), producing analgesia. Naloxone is a pure opioid antagonist that competitively blocks mu, kappa, and delta receptors; when administered orally, naloxone undergoes extensive first-pass metabolism, reducing systemic absorption and primarily blocking the effects of pentazocine if the combination is misused parenterally.. FLOLAN is a Prostacyclin Vasodilator that works by Epoprostenol is a prostaglandin I2 (prostacyclin) analogue that directly vasodilates pulmonary and systemic arterial beds, inhibits platelet aggregation, and has antiproliferative effects on vascular smooth muscle.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between NALOXONE HYDROCHLORIDE AND PENTAZOCINE HYDROCHLORIDE and FLOLAN depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of NALOXONE HYDROCHLORIDE AND PENTAZOCINE HYDROCHLORIDE is: Oral: One tablet (naloxone 0.5 mg / pentazocine 50 mg) every 3-4 hours as needed for pain; maximum 12 tablets daily.. The standard adult dose of FLOLAN is: Initial: 4 ng/kg/min via continuous IV infusion, then titrated in increments of 1-2 ng/kg/min at intervals of at least 15 minutes based on clinical response. Typical maintenance dose: 20-40 ng/kg/min; range: 10-80 ng/kg/min.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between NALOXONE HYDROCHLORIDE AND PENTAZOCINE HYDROCHLORIDE and FLOLAN in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. NALOXONE HYDROCHLORIDE AND PENTAZOCINE HYDROCHLORIDE is classified as Category A/B. Pentazocine crosses the placenta; naloxone has limited placental transfer. No well-controlled human studies. First trimester: Risk cannot be excluded; avoid if possible. Second/Thi. FLOLAN is classified as Category C. FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; however, no adequate and well-controlled studies in pregnant women. Epoprostenol is a potent vasodilator . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.