Xylocaine
Xylocaine
Generic Name
Xylocaine
Mechanism
* Na⁺ Channel Blockade
* Binds preferentially to the inactivated state of the sodium channel.
* Prevents rapid sodium influx → ↓ depolarization rate.
* Reversible Inactivation
* Rapidly equilibrates between tissue and plasma.
* Onset: 30–60 s (topical), 30–90 s (infiltration).
* Duration: 30–60 min (infiltration); 10–15 min (epidural).
* Adjunct Effects
* Mild vasoconstriction (α‑blockade).
* Anti‑epileptic and anti‑arrhythmic actions due to suppressed excitability of neurons and myocardial cells.
Pharmacokinetics
| Parameter | Value | Notes |
| Absorption | IV: 100 % | SC/IM: ~95 % |
| Distribution | Protein‑binding ≈ 67 % (albumin/α‑1‑acid glycoprotein) | Penetrates CNS and heart tissue |
| Onset | 30–60 s (topical) | 5–15 min (IV) |
| Metabolism | Hepatic CYP1A2, CYP3A4 → inactive metabolites (mono‑ethyl glycinyl) | First‑pass limited due to rapid systemic absorption |
| Elimination | Renal excretion: 30 % unchanged, 20 % as metabolites | Half‑life 1.5–2 h |
| Special Populations | ↑AUC in hepatic impairment; ↑CBF in neonates; ↓CYP1A2 in renal failure |
Indications
* Local Anesthesia – infiltration, block, and topical use for dental, minor surgery.
* Cardiac Arrhythmias – IV for ventricular tachyarrhythmias, ventricular fibrillation, and supraventricular tachycardia.
* Topical Analgesia – lidocaine‑gel for neuropathic pain, post‑herpetic neuralgia.
* Spinal/Epidural – combined with adjuvants for surgical anesthesia.
* Pediatric – used cautiously for pain control and anti‑arrhythmia after dosing validation.
Contraindications
* Contraindications
* Known hypersensitivity to lidocaine or other amide local anesthetics.
* Severe hepatic disease (risk of toxicity).
* Untreated severe hyperthermia > 38 °C (increases neurotoxicity).
* Warnings
* Cardiac – caution in patients with ischemic heart disease; monitor ECG for QRS widening.
* Drug Interactions – CYP1A2/CYP3A4 inhibitors (fluvoxamine, ciprofloxacin) → ↑ serum levels.
* Neurological – CNS excitation, seizures at high plasma concentrations.
* Perioperative – avoid simultaneous use of multiple Na⁺ channel blockers.
Dosing
| Form | Indication | Dose | Administration | Comments |
| IV (1.5 mg/kg bolus) | Ventricular arrhythmia | 0.3–0.5 mg/kg/min infusion | Continuous IV | Max 360 mg/day |
| Infiltration (1–5 mg/mL) | Surgical field | 0.5–2 mL per site | Subcutaneous, perineural | Use epi‑additive as needed |
| Topical Gel 5 % | Post‑herpetic neuralgia | 1–2 puffs < 2 cm² | Apply every 12 h | Avoid mucosal surfaces |
| Epidural (1.5–2 mg/mL) | Labor analgesia | 5–15 mL | Epi or low‑dose with fentanyl | Titrate to analgesia & motor block |
*Maximum daily adult dose: 3 mg/kg (≈ 200 mg) unless renal/hepatic dysfunction.*
Adverse Effects
* Common – burning sensation, pruritus, dizziness, nausea.
* Serious – systemic toxicity (midline or intracerebral hemorrhage), arrhythmias (QTc prolongation), CNS excitation (seizures).
* Toxicity Criteria – plasma concentration > 5 µg/mL (IV) or > 2 µg/mL (infiltration).
Monitoring
| Parameter | Target / Threshold | Frequency |
| ECG | QRS duration 110 bpm | Continuous IV monitoring |
| Serum Lidocaine | < 5 µg/mL (IV) | Hourly if high‑dose infusion |
| Neurologic | Alertness; limb movements | Every 15 min (high‑dose) |
| Respiratory | Adequate ventilation | Continuous in ICU setting |
Clinical Pearls
1. “Lidocaine is the gold‑standard antiarrhythmic for ventricular tachycardia because it can be titrated rapidly and has a short half‑life, allowing quick reversal if needed.”
2. “In obstetric anesthesia, lidocaine epidural (1.5–2 mg/mL) combined with fentanyl yields superior pain relief with lower motor block than high‑dose bupivacaine.”
3. “Always add a 1:1000 epinephrine when infiltrating lidocaine > 2 mL to reduce systemic absorption and prolong local anesthetic effect."
4. “Serious CNS toxicity in adults usually manifests as a tonic–clonic seizure; treat immediately with sodium bicarbonate 1 mEq/kg IV to correct pH and mitigate Na⁺ channel blockade.”
5. “Renal failure increases lidocaine half‑life by ~30 %; consider dose reduction or switch to an alternative (e.g., bupivacaine) in dialysis patients.”
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• *Sources: FDA prescribing information, Goodman & Gilman's Pharmacological Basis of Therapeutics, 15th ed.; 2024 clinical pharmacology guidelines.*