Pethidine

# Pethidine ## Overview - **Classification**: Opioid analgesic - **Mechanism**: Synthetic phenylpiperidine opioid, primarily acts as a mu-opioid receptor agonist. Also possesses anticholinergic and local anesthetic properties. ## Primary Indications 1. **Moderate to severe pain**: Short-term management of acute pain. 2. **Pre-operative medication**: For sedation, anxiety reduction, and to supplement anesthesia. 3. **Obstetric analgesia**: For pain relief during labor. ## Adult Dosing ### Standard Dosing **Moderate to Severe Pain** - **Dose**: **50-150 mg** (IM/SC) or **25-100 mg** (IV) - **Frequency**: Every **3-4 hours** as needed - **Route**: Intramuscular (IM), Subcutaneous (SC), Intravenous (IV) - **Duration**: Short-term use, typically <48 hours. Max total daily **600 mg**. **Pre-operative Medication** - **Dose**: **50-100 mg** - **Frequency**: 30-90 minutes before anesthesia - **Route**: IM or SC **Obstetric Analgesia (Labor)** - **Dose**: **50-100 mg** - **Frequency**: Repeat if needed after 1-3 hours - **Route**: IM or SC ### Dose Adjustments - **Renal Impairment**: **AVOID** due to accumulation of neurotoxic metabolite (normeperidine). If essential, significantly reduce dose and extend intervals. - **Hepatic Impairment**: **AVOID**. Metabolism is reduced, increasing parent drug and metabolite levels. - **Elderly Patients**: Start with **lower doses (e.g., 25-50 mg)** and extend dosing intervals due to reduced metabolism/excretion and increased sensitivity. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: **NOT RECOMMENDED**. - **Special Notes**: High risk of respiratory depression and neurotoxicity due to immature metabolism/excretion. Contraindicated. ### Infants (1-12 months) - **Dose**: **NOT RECOMMENDED**. - **Special Notes**: Risk of respiratory depression and normeperidine accumulation. Contraindicated. ### Children (1-12 years) - **Dose**: **0.5-2 mg/kg** - **Frequency**: Every **3-4 hours** as needed - **Route**: IM, SC - **Maximum**: Single dose **100 mg**. Total daily max **600 mg**. - **Special Notes**: Use with extreme caution. Avoid repeated dosing due to normeperidine accumulation. Not a first-line choice. ### Adolescents (13-18 years) - **Dose**: **25-100 mg** - **Frequency**: Every **3-4 hours** as needed - **Route**: IM, SC, IV - **Maximum**: Single dose **150 mg**. Total daily max **600 mg**. - **Special Notes**: Closely monitor for respiratory depression and sedation. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to pethidine. - **Absolute**: Concomitant use or within **14 days** of MAO inhibitors (MAOIs). - **Absolute**: Severe respiratory depression, acute alcoholism. - **Absolute**: Renal impairment (ESRD), severe hepatic impairment. - **Absolute**: Convulsive disorders, increased intracranial pressure. ### Common Adverse Effects - **Very Common (>10%)**: Dizziness, sedation, nausea, vomiting, sweating. - **Common (1-10%)**: Bradycardia, hypotension, dry mouth, constipation, euphoria, dysphoria. - **Serious but Rare**: Respiratory depression, seizures (due to normeperidine), serotonin syndrome, anaphylaxis, drug dependence. ### Key Drug Interactions - **MAO Inhibitors (MAOIs)**: **ABSOLUTELY CONTRAINDICATED**. Risk of severe, fatal reactions (hyperpyrexia, seizures, respiratory depression, coma). - **Other CNS Depressants (e.g., benzodiazepines, alcohol, sedatives)**: Potentiated CNS/respiratory depression, hypotension. Reduce pethidine dose. - **Serotonergic Drugs (e.g., SSRIs, TCAs)**: Increased risk of serotonin syndrome. Monitor closely. - **Phenytoin**: May reduce pethidine levels and increase normeperidine levels. ## Monitoring & Follow-up - **Before Treatment**: Assess pain level, respiratory status, renal/hepatic function. - **During Treatment**: Monitor vital signs (respiratory rate, blood pressure, pulse), sedation level, pain relief every **1-2 hours** initially. - **Clinical Signs**: Watch for excessive sedation, respiratory depression (RR <12 bpm), confusion, seizures, muscle rigidity. ## Clinical Pearls - 💡 **Not first-line**: Pethidine is generally **not a first-line opioid** due to its neurotoxic metabolite (normeperidine) and interaction profile. - 💡 **Short-term use**: Best reserved for **short-term, acute pain** where other opioids are unsuitable (e.g., post-rigors, short procedures). - 💡 **MAOI interaction**: The **MAOI interaction is severe and potentially fatal**. Ensure a **14-day washout** period. - 💡 **Seizure risk**: Normeperidine accumulates, especially in renal impairment, increasing the risk of **seizures** and CNS excitation. - 💡 **IV administration**: Administer **IV slowly** over several minutes to minimize hypotension and other adverse effects. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.