ISOCAINE HYDROCHLORIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ISOCAINE HYDROCHLORIDE (ISOCAINE HYDROCHLORIDE).
Isocaine hydrochloride is a local anesthetic that stabilizes neuronal membranes by blocking voltage-gated sodium channels, thereby inhibiting the initiation and propagation of action potentials.
| Metabolism | Primarily via hepatic esterases (plasma pseudocholinesterase) to produce para-aminobenzoic acid (PABA) and diethylaminoethanol. |
| Excretion | Renal: Approximately 90% of the dose is excreted as metabolites (primarily conjugated with glucuronic acid) in urine. Fecal: About 10% eliminated unchanged or as metabolites in feces. Biliary excretion is negligible. |
| Half-life | Terminal elimination half-life is approximately 2.5 hours in healthy adults. In patients with hepatic impairment, half-life may be prolonged to 6–8 hours; in severe renal impairment, half-life may extend to 4–6 hours. |
| Protein binding | Approximately 70–80% bound to plasma proteins, primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd is approximately 1.5–2.0 L/kg, indicating extensive tissue distribution. Clinical meaning: High Vd suggests rapid distribution into peripheral tissues, which may influence loading dose requirements. |
| Bioavailability | Subcutaneous: 100% (complete absorption from injection site). Epidural: 100% (directly into systemic circulation). Oral: Not available due to extensive first-pass metabolism. |
| Onset of Action | Intravenous: 30–60 seconds. Epidural: 5–15 minutes. Subcutaneous infiltration: 1–5 minutes. |
| Duration of Action | Intravenous: 15–30 minutes (single dose). Epidural: 60–90 minutes (with epinephrine). Subcutaneous infiltration: 30–60 minutes (with epinephrine). Duration prolonged by addition of epinephrine. |
| Molecular Weight | 270.8 |
1-2% solution infiltrated subcutaneously or locally, maximum dose 4.5 mg/kg (with epinephrine) or 3.0 mg/kg (without epinephrine), not to exceed 300 mg.
| Dosage form | INJECTABLE |
| Renal impairment | No specific adjustment required; use with caution in severe renal impairment (eGFR <30 mL/min) due to risk of accumulation of metabolites. |
| Liver impairment | Child-Pugh Class A: No adjustment; Child-Pugh B: Reduce dose by 50% and monitor for toxicity; Child-Pugh C: Avoid use due to decreased metabolism. |
| Pediatric use | Weight-based: 0.5-1% solution infiltrated subcutaneously or locally, maximum 2.0 mg/kg with epinephrine, 1.5 mg/kg without epinephrine; maximum total dose 100 mg. |
| Geriatric use | Reduce dose by 20-30% due to decreased hepatic clearance and increased sensitivity; maximum dose 3.5 mg/kg with epinephrine, 2.5 mg/kg without epinephrine. |
| 1st trimester | Avoid; potential for fetal bradycardia and decreased uterine blood flow at high doses. |
| 2nd trimester | Use only if clearly needed; monitor fetal heart rate. |
| 3rd trimester | Use only if clearly needed; may cause fetal bradycardia and maternal hypotension. |
Clinical note
Comprehensive clinical and safety monograph for ISOCAINE HYDROCHLORIDE (ISOCAINE HYDROCHLORIDE).
| Placental transfer | Crosses placenta rapidly; fetal plasma concentrations approximate maternal levels. |
| Breastfeeding | Excreted into breast milk in small amounts; unlikely to cause adverse effects in infants. Use caution with high doses or prolonged treatment. |
| Lactation Rating |
■ FDA Black Box Warning
Not available (no FDA boxed warning identified for this drug).
| Serious Effects |
Hypersensitivity to amide-type local anestheticsSevere hypotensionHeart block (second- or third-degree)Severe bradycardiaPorphyria
| Precautions | Risk of systemic toxicity if administered intravascularly or in excessive doses, Caution in patients with hepatic disease, pseudocholinesterase deficiency, or cardiovascular disease, Avoid use in patients with known hypersensitivity to ester-type local anesthetics or PABA, Monitor for signs of CNS and cardiac toxicity during administration |
| Food/Dietary | No significant food interactions known. Avoid alcohol within 24 hours after procedure as it may increase side effects (e.g., dizziness). |
Loading safety data…
| L2 (Safer) |
| Teratogenic Risk | Isocaine hydrochloride (mepivacaine) is classified as FDA Pregnancy Category C. In first trimester, animal studies have shown fetal harm but no adequate human studies; use only if clearly needed. Second and third trimesters: no known teratogenicity, but may cause fetal bradycardia and decreased uterine blood flow due to vasoconstriction; use lowest effective dose. |
| Fetal Monitoring | Monitor maternal vital signs, ECG, and oxygen saturation. Fetal heart rate monitoring recommended during labor and delivery to detect bradycardia or distress. |
| Fertility Effects | No known adverse effects on fertility in humans. Animal studies have not shown impaired fertility. |
| Clinical Pearls | Isocaine hydrochloride (meptylcaine) is an ester-type local anesthetic used for infiltration and nerve block. Onset within 2-5 minutes, duration 1-2 hours due to rapid hydrolysis by plasma pseudocholinesterase. Caution in patients with pseudocholinesterase deficiency (prolonged effect/toxicity). Do not inject into inflamed or infected sites (reduced efficacy). Avoid exceeding recommended doses (e.g., 20 mL of 1% solution in healthy adult) to prevent systemic toxicity. Use with vasoconstrictor (e.g., epinephrine 1:200,000) to slow absorption and prolong action. Contraindicated in patients with known ester anesthetic allergy (avoid cross-reactivity with other esters). |
| Patient Advice | Avoid eating or drinking for 2 hours after procedure if mouth or throat is numb to prevent biting injury. · Report any symptoms of allergic reaction (rash, swelling, difficulty breathing) or systemic toxicity (dizziness, metallic taste, tinnitus, seizures). · Do not drive or operate machinery for at least 24 hours after use due to potential residual effects. · Inform your doctor if you have a history of low pseudocholinesterase levels, liver disease, or allergy to other anesthetics. · The numbness will gradually wear off over the next 1-2 hours. |