Should lidocaine be injected into a furuncle prior to incision and drainage?

No, Do Not Inject Lidocaine Directly Into a Furuncle

Lidocaine should be infiltrated around the furuncle (perilesional field block), not injected directly into the abscess cavity itself. Injecting anesthetic directly into infected tissue is both ineffective and potentially harmful.

Why Not to Inject Into the Furuncle

Physiologic Barriers

• Acidic pH of infected tissue: The purulent environment within a furuncle is acidic, which prevents lidocaine (a weak base) from converting to its active form. This renders the anesthetic essentially ineffective when injected directly into the abscess 1.
• Increased tissue pressure: Injecting fluid into an already tense, inflamed abscess cavity increases pressure, causing significant pain and potentially spreading infection.
• Risk of bacteremia: Direct injection into infected tissue can theoretically force bacteria into the bloodstream.

Correct Anesthetic Technique for Furuncle Drainage

Recommended Approach

Perform a field block by infiltrating lidocaine in a ring pattern around the furuncle, creating a barrier of anesthesia in the healthy tissue surrounding the lesion 1.

Specific Technique

• Use 1% lidocaine with epinephrine (preferred) or without epinephrine
• Inject circumferentially around the base of the furuncle in healthy, non-infected tissue
• Create a wheel of anesthesia at the dermis-subcutaneous junction
• Aspirate before injecting to avoid intravascular injection 1
• Use incremental injections rather than rapid boluses 1
• Allow adequate time (5-10 minutes) for onset of anesthesia

Dosing Limits

For adults 2:

• Without epinephrine: Maximum 4.5 mg/kg (generally not exceeding 300 mg total)
• With epinephrine: Maximum 7 mg/kg (generally not exceeding 500 mg total)

The Primary Treatment is Incision and Drainage

Incision and drainage is the definitive treatment for furuncles and carbuncles 3. The IDSA guidelines strongly recommend I&D as the primary intervention, with anesthesia serving only as an adjunct to make the procedure tolerable.

Key Points from IDSA Guidelines

• I&D is strongly recommended for large furuncles and all carbuncles (strong recommendation, high-quality evidence) 3
• Systemic antibiotics are not routinely needed unless the patient has SIRS (fever, tachycardia, tachypnea, abnormal WBC) or significant immunocompromise 3
• Culture of purulent drainage is recommended for carbuncles but reasonable to omit in typical cases 3

Common Pitfalls to Avoid

1. Never inject directly into the abscess cavity - it won't work and will cause unnecessary pain
2. Don't skip aspiration before injection - reduces risk of intravascular injection and systemic toxicity 1
3. Don't use excessive volumes - more anesthetic doesn't mean better anesthesia; proper technique matters more
4. Don't rush the procedure - allow adequate time for the anesthetic to take effect (5-10 minutes minimum)
5. Don't forget epinephrine (unless contraindicated) - it prolongs anesthesia duration and reduces bleeding, improving visualization during drainage

Alternative Considerations

If the patient has true lidocaine allergy (rare, <1% of reactions) 1:

• Switch to an ester-type anesthetic (cross-reaction is rare)
• Consider 1% diphenhydramine (slower onset, 5 minutes vs 1 minute)
• Use bacteriostatic saline (0.9% benzyl alcohol in normal saline) 1

The evidence consistently supports perilesional infiltration rather than direct injection into infected tissue for optimal pain control and procedural success.