Prilocaine
Citanest
Amide local anesthetic (intermediate-acting)
Na⁺-channel blocker. Metabolized to o-toluidine → oxidizes hemoglobin → methemoglobinemia at high doses.
Indications
- •Infiltration
- •IV regional (Bier block — low toxicity)
- •Dental
- •EMLA component
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Infiltration/Bier | Max 8 mg/kg (highest of the amides) | — |
Maximum dose
8 mg/kg plain (absolute max 600 mg)
Max-dose calculator
single-injection infiltration / blockPlain
560 mg
| Concentration | Max volume (plain) |
|---|---|
| 0.5% (5 mg/mL) | 112 mL |
| 1% (10 mg/mL) | 56 mL |
| 2% (20 mg/mL) | 28 mL |
| 3% (30 mg/mL) | 18.7 mL |
| 4% (40 mg/mL) | 14 mL |
Methemoglobinemia is the dose-limiting toxicity (o-toluidine metabolite). Education only — confirm against the package insert. Max doses are not additive across agents; account for total LA when mixing.
Pharmacokinetics
Onset fast. Duration 60–120 min. Amide hepatic + extrahepatic metabolism.
Side effects
- !METHEMOGLOBINEMIA (dose-dependent — the signature toxicity)
- !LAST (lower than bupivacaine)
Contraindications
- ×Congenital methemoglobinemia / G6PD deficiency
- ×Doses >600 mg
- ×Infants <3 mo (methemoglobinemia)
Reversal / antidote
Methylene blue 1–2 mg/kg IV for symptomatic methemoglobinemia
Clinical pearls
- ★Highest amide max dose (8 mg/kg) — but methemoglobinemia caps real-world use.
- ★Treat methemoglobinemia (chocolate-brown blood, SpO2 stuck ~85%, saturation gap) with methylene blue.
- ★Low systemic toxicity made it a classic Bier-block choice.
Other drugs in Local Anesthetics
- Lidocaine
Blocks voltage-gated Na⁺ channels in nerves (LA) and cardiac myocytes (antiarrhythmic).
- Bupivacaine
Voltage-gated Na⁺ channel blocker. Higher protein binding and lipid solubility than lidocaine → longer duration but greater cardiotoxicity.
- Ropivacaine
S-enantiomer of propivacaine. Less lipid-soluble than bupivacaine → less cardiotoxicity but slightly less potency.
- Tetracaine
Blocks voltage-gated Na⁺ channels. Long-acting ester, metabolized by plasma cholinesterase. High potency + toxicity.
- Chloroprocaine
Na⁺-channel blocker. Extremely rapid plasma-cholinesterase metabolism (half-life seconds) → lowest systemic toxicity of the LAs, ideal for OB epidural top-up.
- Procaine
Na⁺-channel blocker; prototype ester LA. Plasma-cholinesterase metabolized to PABA.
- Levobupivacaine
The S(−)-enantiomer of bupivacaine → similar block with LESS cardiotoxicity + CNS toxicity than racemic bupivacaine.
Suggested reading
- •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
- •FDA package insert
- •ASRA LAST checklist, 2020
