MEPERIDINE AND ATROPINE SULFATE
Clinical safety rating: avoid
MAOIs can cause serotonin syndrome and hyperpyrexia Life-threatening respiratory depression may occur.
Meperidine is a synthetic opioid agonist primarily at mu-opioid receptors, producing analgesia; atropine is a competitive antagonist of muscarinic acetylcholine receptors, reducing gastrointestinal motility and secretions.
| Metabolism | Meperidine is primarily metabolized by hepatic CYP3A4 and to a lesser extent CYP2B6 and CYP2C19, producing normeperidine (active metabolite) via N-demethylation; atropine is metabolized by hepatic hydrolysis. |
| Excretion | Meperidine: Renal excretion of unchanged drug (~5-10%) and metabolites, primarily normeperidine (active), with <5% biliary/fecal. Atropine: Renal excretion (~30-50% unchanged), remainder as metabolites, minimal biliary/fecal. |
| Half-life | Meperidine: Terminal half-life 3-4 hours (normal renal function), prolonged in hepatic disease (up to 7-10 hours) and renal impairment (normeperidine accumulates). Atropine: Terminal half-life 2-4 hours. |
| Protein binding | Meperidine: 60-80% bound to albumin and alpha-1-acid glycoprotein. Atropine: 18-50% bound to albumin. |
| Volume of Distribution | Meperidine: Vd 3-5 L/kg (wide tissue distribution, crosses placenta). Atropine: Vd 2-4 L/kg. |
| Bioavailability | Oral meperidine: ~50-60% (first-pass effect). Atropine: Oral bioavailability ~50% (variable). IM/IV: 100%. |
| Onset of Action | IM: 10-15 minutes; IV: 1-2 minutes; SC: 10-15 minutes; Oral: 30-60 minutes. |
| Duration of Action | Analgesic effect: 2-4 hours (IM/IV). Anticholinergic effects (atropine): 4-6 hours. Note: Normeperidine accumulation may prolong CNS effects. |
| Molecular Weight | Meperidine: 247.33 Da; Atropine sulfate: 676.82 Da (as salt); monohydrate: 694.84 Da |
1-2 mL (meperidine 50 mg/mL + atropine 0.4 mg/mL) IM or IV push (over 2-3 minutes) every 3-4 hours as needed.
| Dosage form | INJECTABLE |
| Renal impairment | GFR 10-50 mL/min: reduce meperidine dose by 25% and extend interval to every 6 hours. GFR <10 mL/min: avoid meperidine (risk of normeperidine accumulation). Atropine: no adjustment. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce meperidine dose by 50%. Child-Pugh C: avoid meperidine (decreased clearance). Atropine: use with caution in severe hepatic impairment. |
| Pediatric use | Meperidine: 1-1.5 mg/kg IM/IV every 3-4 hours (max 100 mg per dose). Atropine: 0.01-0.02 mg/kg IM/IV (max 0.4 mg per dose). For combination, adjust each component accordingly. |
| Geriatric use | Reduce meperidine dose by 25-50% (max 50 mg per dose), extend interval to every 4-6 hours due to increased sensitivity and risk of CNS effects. Atropine: use with caution; lower initial doses recommended. |
| 1st trimester | MEPERIDINE crosses the placenta. Limited human data; avoid use in first trimester unless benefit outweighs risk. Atropine sulfate crosses the placenta; use caution. Both drugs are not recommended due to potential teratogenic effects. |
| 2nd trimester | Use only if clearly needed. Meperidine may cause neonatal respiratory depression and withdrawal; atropine may cause fetal tachycardia. No well-controlled studies. |
| 3rd trimester | Avoid prolonged use or high doses near term due to risk of neonatal respiratory depression, withdrawal, and meconium aspiration. Atropine may cause neonatal tachycardia and hyperthermia. Combination use not recommended. |
Clinical note
MAOIs can cause serotonin syndrome and hyperpyrexia Life-threatening respiratory depression may occur.
| FDA category | Positive |
| Placental transfer | Meperidine: crosses placenta rapidly (within 2 minutes) with fetal/maternal ratio of 0.5-0.7. Atropine: crosses placenta with fetal concentrations lower than maternal. |
■ FDA Black Box Warning
Meperidine carries a risk of respiratory depression, addiction, abuse, and misuse; concurrent use with benzodiazepines or CNS depressants may lead to profound sedation, respiratory depression, coma, and death.
| Common Effects | Sedation |
| Serious Effects |
Hypersensitivity to meperidine, atropine, or belladonna alkaloidsSevere respiratory depressionAcute or severe bronchial asthmaParalytic ileusMyasthenia gravis (atropine contraindicated)Narrow-angle glaucoma (atropine contraindicated)Tachycardia secondary to thyrotoxicosis or cardiac insufficiency (atropine)Concurrent use or within 14 days of MAO inhibitors (meperidine contraindicated)
| Precautions | Respiratory depression; hypotension; CNS depression; risk of serotonin syndrome (meperidine); anticholinergic effects (atropine); tolerance and dependence; normeperidine accumulation in renal impairment increasing seizure risk. |
| Food/Dietary |
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| Breastfeeding | Meperidine is excreted into breast milk in small amounts, but may cause neonatal sedation and respiratory depression; safer alternatives (e.g., morphine) preferred. Atropine is excreted in trace amounts; may cause anticholinergic effects in infant. Caution advised; monitor infant for sedation, poor feeding, or constipation. |
| Lactation Rating | L3 (Moderately Safe) - Meperidine; L2 (Probably Compatible) - Atropine; combination rating L3 |
| Teratogenic Risk | Meperidine: Limited human data; animal studies show no teratogenicity at clinically relevant doses. Atropine: Crosses placenta; no major teratogenic risk reported. First trimester: Avoid unless necessary due to limited safety data. Second and third trimesters: Use only if clearly indicated; may cause neonatal respiratory depression and altered heart rate variability. Risk of maternal respiratory depression and fetal hypoxia with high doses. |
| Fetal Monitoring | Monitor maternal respiratory rate, oxygen saturation, sedation level, and bowel function. Fetal heart rate monitoring for signs of distress or tachycardia (atropine). Neonatal monitoring for respiratory depression, bradycardia, and anticholinergic effects post-delivery. |
| Fertility Effects | No known adverse effects on fertility from either meperidine or atropine. Meperidine may suppress ovulation at high doses due to prolactin inhibition; atropine has no reported fertility impact. |
| Avoid alcohol consumption as it may enhance central nervous system depression and increase risk of respiratory depression. No specific food restrictions; administer preoperatively on an empty stomach per standard fasting guidelines (NPO). |
| Clinical Pearls | Meperidine (pethidine) is an opioid agonist with anticholinergic properties; atropine is added to reduce vagal bradycardia and gastrointestinal hypermotility. The combination is used preoperatively for sedation and to reduce salivation and respiratory secretions. Meperidine has a short half-life (2–4 hours) and is metabolized to normeperidine, a neurotoxic metabolite with proconvulsant activity; avoid prolonged use or high doses (>600 mg/day) especially in renal impairment. Atropine may counteract meperidine-induced biliary spasm? but caution in glaucoma or prostatic hypertrophy. |
| Patient Advice | This medication is given before surgery to help you relax and reduce secretions. · Do not drink alcohol or take other sedatives while under the effects of this drug. · May cause drowsiness, dizziness, or blurred vision; avoid driving or operating machinery. · Inform your doctor if you have a history of seizures, kidney disease, glaucoma, or difficulty urinating. · Report any severe nausea, slow heartbeat, or breathing difficulties to your healthcare provider immediately. |