At what age is an individual considered an adult for lignocaine (lidocaine) dosing purposes?

Age Definition for Lidocaine (Lignocaine) Dosing

For lidocaine dosing purposes, an individual is considered an adult at 15 years of age or when they weigh more than 40 kg.

Evidence-Based Age Classification

The American Family Physician guidelines clearly define adult dosing as beginning at 15 years of age 1. This is specifically stated in the tuberculosis treatment guidelines where the authors explicitly note that "adult dosing as beginning at 15 years of age."

Additionally, weight is an important factor in determining whether adult dosing should be applied:

• Children weighing more than 40 kg should be dosed as adults 1
• This weight-based criterion applies across multiple medication classes

Lidocaine Dosing Considerations by Age Group

Adults (≥15 years or >40 kg)

• Maximum recommended dose with epinephrine: 7.0 mg/kg 1
• Maximum recommended dose without epinephrine: 4.4 mg/kg 1
• For bronchoscopy procedures: Total dose should be limited to 8.2 mg/kg (approximately 29 ml of a 2% solution for a 70 kg patient) 1

Children (<15 years and ≤40 kg)

• Require different dosing calculations
• Should not receive adult doses unless they weigh more than 40 kg
• Doses of amide local anesthetics (including lidocaine) should be decreased by 30% in infants younger than 6 months 1

Special Considerations

Elderly Patients

• Extra caution is needed in elderly patients 1
• Elderly subjects have significantly longer half-lives for lidocaine compared to younger individuals 2
• The British Thoracic Society guidelines specifically recommend extra care in the elderly or those with liver or cardiac impairment 1

Weight-Based Dosing

• Dosing should be based on ideal body weight rather than actual body weight 1
• This is particularly important for overweight or obese patients

Safety Margins

• Despite published maximum doses, evidence suggests that the safety limit should be based on circulating levels of lidocaine rather than fixed volumes 3
• For healthy adults, the suggested upper limit is typically 4.5 cartridges (2 ml each) of lidocaine with adrenaline (180-198 mg lidocaine) 3

Clinical Application

When determining whether to use adult or pediatric dosing:

1. Check patient's age - if ≥15 years, use adult dosing
2. Check patient's weight - if >40 kg, use adult dosing regardless of age
3. Consider comorbidities that might affect lidocaine metabolism (liver disease, cardiac impairment)
4. Adjust dosing downward for elderly patients due to altered pharmacokinetics

This age and weight-based approach to lidocaine dosing helps minimize toxicity risks while ensuring adequate anesthesia or antiarrhythmic effects depending on the clinical indication.