Lidocaine Level

Lidocaine is an amide-type local anesthetic available as a crystalline powder soluble in alcohol and normal saline. It suppresses ventricular ectopy in the setting of myocardial infarction and increases the ventricular fibrillation threshold. These actions prevent PVCs from inducing ventricular fibrillation.

Lidocaine is a class IB antiarrhythmic used as a second-line agent and after myocardial infarction in certain groups of patients to treat premature ventricular contractions, ventricular tachycardia, and fibrillation. ^[1]

Normal findings ^[2] :

• Lidocaine has a therapeutic drug range of 1.5-5.0 mcg/mL

• For lidocaine, the toxic drug range is > 5 mcg/mL

Lidocaine levels are not routinely monitored as compared to other cardiac drugs because its effect can be directly observed on the ECG monitor (termination of the arrhythmia).

If the lidocaine blood level is greater than 6 mg/L, serious side effects may be observed, including seizures, cardiovascular depression, AV block, and hypotension.

Lidocaine is administered as an infusion; therefore, levels can be drawn at any time after the steady state is reached. Steady state is usually attained within 18-24 hours. The half-life of lidocaine ranges from 1.5 hours to as long as 5 hours. ^[1]

Collection: Blood is collected in Becton-Dickinson serum separator tubes, SST II, and should be transported as is. Lidocaine is stable in serum or plasma if stored at 2-8 º C for 24 hours. ^[3]

Immunoassays are commercially available for determination of lidocaine levels, but chromatographic methods are preferred, if monitoring of the active metabolite is deemed necessary.

No reports pertaining to hemolysis have been seen to result in low levels of lidocaine. Lidocaine levels are used for dosage adjustment, and an increase or decrease in the lidocaine infusion rate is used to achieve optimal concentration.

Description

Lidocaine is an amide-type local anesthetic available as a crystalline powder soluble in alcohol and normal saline. It suppresses ventricular ectopy in the setting of myocardial infarction and increases the ventricular fibrillation threshold. These actions prevent PVCs from inducing ventricular fibrillation.

The active metabolite of lidocaine is monoethylglycinexylidide (MEGX) and can accumulate in patients with renal failure. Lidocaine is 70% protein bound and 30% unbound, depending on the levels of alpha-1-acid glycoprotein concentrations. This active metabolite also contributes to the toxicity of lidocaine. ^[4]

Indications/Applications

Lidocaine level testing is useful in when the expected response to lidocaine administration is not seen or lidocaine toxicity is observed at low doses.

Considerations

Lidocaine is hepatically and renally cleared; therefore, checking lidocaine levels may be useful in patients with liver disease, congestive heart failure, renal failure, and advanced age, along with concurrent administration of propranolol, carbamazepine, phenytoin, and primidone. ^[1]