DUOCAINE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DUOCAINE (DUOCAINE).
Lidocaine and prilocaine are amide-type local anesthetics that block sodium ion channels in nerve cell membranes, inhibiting the initiation and conduction of nerve impulses.
| Metabolism | Both lidocaine and prilocaine are metabolized in the liver primarily by CYP1A2 and CYP3A4 (lidocaine) and amidases (prilocaine). |
| Excretion | Duocaine (lidocaine and prilocaine) undergoes hepatic metabolism; less than 10% of lidocaine and prilocaine are excreted unchanged in urine. Metabolites are excreted renally (lidocaine: 70-80% as 4-hydroxy-2,6-xylidine; prilocaine: >85% as o-toluidine metabolites). Biliary/fecal elimination is minimal (<5%). |
| Half-life | Terminal elimination half-life for lidocaine: 1.5-2 hours; prilocaine: 1.5-2.5 hours. In hepatic impairment or congestive heart failure, half-life may increase 2-3 fold; in neonates, half-life is prolonged (prilocaine: 3-8 hours). |
| Protein binding | Lidocaine: 60-80% bound to alpha-1-acid glycoprotein (AAG) and albumin; prilocaine: 55-70% bound to AAG and albumin. Binding is concentration-dependent and decreases in inflammatory states. |
| Volume of Distribution | Lidocaine: Vd approximately 1.1-1.7 L/kg; prilocaine: Vd approximately 1.8-2.5 L/kg. Distributes widely with high tissue uptake; reduced Vd in heart failure and cirrhosis. |
| Bioavailability | Oral: 25-35% (extensive first-pass metabolism); topical: 3-10% of applied dose absorbed systemically (dependent on area, duration, and skin integrity); rectal: 50-80%; intramuscular: 100%. |
| Onset of Action | Topical application: 30-60 minutes for full anesthetic effect; intradermal injection: 2-5 minutes; epidural: 5-15 minutes; intravenous: 45-90 seconds. |
| Duration of Action | Topical: 1-2 hours (anesthesia persist up to 4 hours after removal); injection: 1-3 hours (with epinephrine, up to 5 hours). Duration is dose-dependent and affected by vascularity of site. |
Topical: Apply a thin layer to affected area up to 3-4 times daily. Maximum 30 g per application.
| Dosage form | INJECTABLE |
| Renal impairment | No dosing adjustment required for renal impairment. |
| Liver impairment | No dosing adjustment required for hepatic impairment. |
| Pediatric use | Not recommended for children under 2 years. For children 2-12 years, apply sparingly to affected area no more than twice daily. |
| Geriatric use | Use with caution; apply smallest effective amount due to increased risk of systemic toxicity. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DUOCAINE (DUOCAINE).
| Breastfeeding | Lidocaine: excreted in breast milk in small amounts; M/P ratio ~0.4-1.1. Estimated infant dose ~1-2% of maternal weight-adjusted dose; considered compatible with breastfeeding if used short-term. Prilocaine: excreted in breast milk; M/P ratio not well defined; estimated infant dose <2% of maternal dose; risk of methemoglobinemia in neonates if high maternal doses; caution with prolonged use. Overall, topical use (small doses) considered safe; epidural or high-dose use may require breastfeeding interruption for a few hours or discard milk if concern. |
| Teratogenic Risk | Duocaine is a fixed-dose combination of lidocaine and prilocaine. Lidocaine: Pregnancy category B; based on animal studies, no fetal harm observed in animal reproduction studies, but no adequate human studies. Prilocaine: Pregnancy category B; similar to lidocaine—no evidence of teratogenicity in animal studies, but methemoglobinemia risk to fetus if maternal overdose. First trimester: risk likely low based on animal data; second trimester: safe for epidural use with standard doses; third trimester: safe for local anesthesia. Overall, FDA considers low teratogenic risk with standard doses, but methemoglobinemia risk exists with prilocaine. |
■ FDA Black Box Warning
WARNING: METHEMOGLOBINEMIA - Cases of methemoglobinemia have been reported in association with the use of lidocaine/prilocaine, especially in infants and children following application for longer than recommended times. Do not exceed recommended dosing and application intervals.
| Serious Effects |
Hypersensitivity to lidocaine, prilocaine, or other amide anesthetics; history of methemoglobinemia; application to areas with compromised blood supply.
| Precautions | Methemoglobinemia in children <12 months; use with caution in patients with G6PD deficiency, cardiac disease, or hepatic impairment; avoid application to eyes or broken skin; monitor for signs of systemic toxicity. |
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| Fetal Monitoring | Monitor maternal vital signs (heart rate, blood pressure) and ECG for lidocaine toxicity (arrhythmias, CNS depression) during high-dose or epidural use. Monitor fetal heart rate during labor if used for obstetric anesthesia; no specific monitoring for topical use. In case of prilocaine overdose, monitor methemoglobinemia (SpO2 gap, cyanosis) and consider co-oximetry. |
| Fertility Effects | No known adverse effects on fertility in animal studies. Lidocaine and prilocaine do not have documented negative effects on human fertility with standard clinical use. |