Lidocaine Hcl: Uses, Side effects, Overdose, Interactions

Chemistry 

C14H12N2O.HCl

2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide

Brand name Xylocaine

General

Lidocaine hydrochloride was synthesized by Löfgren and Lundquist in 1943, and was clinically introduced in 1948. It remains one of the most widely used local anaesthetics. It can be administered parenterally for a peripheral nerve block (PNB), intravenously, or applied topically at strengths of 2–4%. The addition of epinephrine 1:200 000 to 1:100 000 slows the vascular absorption of lidocaine and prolongs its effects

Available concentrations

0.5%
1% with/without epinephrine 1/200 000
2% with/without epinephrine 1/200 000
4% (topical)
5% (medicated plaster)
Dose mg/kg
3 (without epinephrine)
7 (with epinephrine)

Additional dose guidelines

600 mg by topical application in 24 h
200 mg for PNB
500 mg for PNB (with epinephrine)
Elderly: doses may need to be reduced depending on age and physical state
Onset time: Fast (2–5 min)
Duration of anaesthesia: Short (45–60 min)
Peak plasma levels: 15–30 min
Relative toxicity:Low: 1 (toxicity values for the other drugs will be compared to lidocaine)
Mean half life:1.5 hr
Protein binding: 65–75%
Volume of distribution: 90 L

Metabolism

Lidocaine is metabolized by the liver with only a small amount (3%) found unchanged in urine. The three main mechanisms of metabolism are shown below: N-de-ethylation > monoethylglycinexylidide (MEGX) > glycinexylidide
Hydrolysis of glycinexylidide
5-hydroxylation of lidocaine’s benzene ring
Lidocaine possesses convulsant activity. Hepatic disease or reduced hepatic blood flow (as in congestive cardiac failure) will lower metabolic capacity
Potency: Medium
Excretion：Renal
Relative lipid solubility： 150
pKa: 7.86

Drug interactions

Cimetidine – inhibits hepatic metabolism
Propranolol – reduces systemic clearance by up to 40% by reducing hepatic metabolism

Additional information

Lidocaine is contraindicated in patients with known hypersensitivity to local anaesthetics of the amide type and in patients with porphyria. Reactions due to overdose with lidocaine (high plasma levels) are systemic and involve the central nervous and cardiovascular systems. Effects include medullary depression, tonic and clonic convulsions, and cardiovascular collapse.
Solutions in multidose vials may contain hydrobenzoate derivatives and have been associated with allergic reactions in some patients. As with all of the amide local anaesthetics protein binding is reduced in the neonate (50% versus 64% in the adult), which necessitates reduced doses if adverse reactions are to be avoided.

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