What is the preservative used in 2% Lignocaine (Lidocaine) for local infiltration?

Preservatives in 2% Lignocaine for Local Infiltration

The preservative used in 2% lignocaine (lidocaine) for local infiltration is methylparaben, which may cause allergic reactions in sensitive individuals. 1

Preservative Details and Allergic Considerations

• Methylparaben is used as a preservative in multiple-dose vials of lignocaine (lidocaine) hydrochloride 1
• True allergic reactions to lignocaine are rare, with genuine immunologic reactions representing only about 1% of all adverse reactions 2
• Allergic reactions to lignocaine may actually be attributed to paraben allergy in preservative-containing amide preparations rather than to the anesthetic agent itself 2
• Cross-reaction between amide and ester type local anesthetics is rare and usually attributed to paraben allergy in preservative-containing amide preparations or cosensitization 2

Alternative Options for Patients with Lignocaine Allergy

For patients with true allergy to lignocaine or its preservatives, alternative options include:

• Switching to an ester type of local anesthetic, as cross-reaction between amide and ester types is rare 2
• Using 1% diphenhydramine, though it has a longer onset of action (5 minutes vs. 1 minute for lignocaine) and limited efficacy 2
• Bacteriostatic saline (0.9% benzyl alcohol in normal saline) can be used as another alternative 2
• For small excisions and biopsies in patients with sensitivity or allergy to lignocaine, injection of diphenhydramine or bacteriostatic normal saline may be useful 2

Clinical Considerations When Using Lignocaine

• Preservative-free lignocaine is available and may be preferred in certain situations, particularly for patients with known sensitivity to preservatives 3
• The maximum safe dose of lignocaine with epinephrine is 7 mg/kg in adults and 3.0 to 4.5 mg/kg in children 2
• For local infiltration without epinephrine, the maximum safe dose is 4.5 mg/kg in adults and 1.5 to 2.0 mg/kg in children 2
• The British Thoracic Society recommends limiting the total dose of lignocaine to 8.2 mg/kg in adults (approximately 29 ml of a 2% solution for a 70 kg patient), with extra care in the elderly or those with liver or cardiac impairment 2

Safety Considerations

• Toxic blood levels (>5 mg/l) or signs of toxicity are uncommon when using lignocaine during procedures such as bronchoscopy 2
• The regional blood flow of the injected site is a determinant of lignocaine absorption and resultant pharmacokinetics - areas with lower blood flow may allow for higher doses without toxicity 4
• Signs of lignocaine toxicity follow a progression of central nervous system excitement, including circumoral numbness, facial tingling, slurred speech, metallic taste, auditory changes, and hallucinations 2
• More severe toxicity can progress to seizures, central nervous system depression, and in severe cases, cardiac failure or arrest 2

Formulation Considerations

• 2% lignocaine gel formulations may be better accepted by patients and yield lower blood levels compared to spray formulations 2
• Alkalinization of lignocaine with sodium bicarbonate can reduce pain on injection and result in quicker onset of anesthesia 5
• For dilute solutions such as 0.4% and 0.5% lignocaine, higher maximum doses may be acceptable (500 mg for plain lignocaine and 670 mg with adrenaline) 6

When using 2% lignocaine for local infiltration, clinicians should be aware of the presence of methylparaben as a preservative and consider preservative-free alternatives for patients with known or suspected preservative allergies.