What is the first‑line antibiotic for acute necrotizing ulcerative gingivitis?

First-Line Antibiotic for Acute Necrotizing Ulcerative Gingivitis

Metronidazole is the first-line systemic antibiotic for acute necrotizing ulcerative gingivitis (ANUG), typically dosed at 500 mg orally every 8 hours for 7–10 days, combined with mechanical debridement and chlorhexidine rinses. 1, 2

Primary Treatment Approach

The cornerstone of ANUG management is mechanical debridement combined with antimicrobial therapy, not antibiotics alone. 3, 2

Immediate Management Steps

• Superficial debridement of necrotic tissue and careful mechanical oral hygiene must be initiated immediately. 2
• 0.12% chlorhexidine rinses should be prescribed as an adjunctive antimicrobial measure. 3, 2
• Daily re-evaluation is essential to monitor response and adjust therapy. 2

Antibiotic Selection

First-Line Systemic Antibiotic

• Metronidazole 500 mg orally every 8 hours is the preferred first-line systemic antimicrobial agent for ANUG. 1, 2
• This choice targets the predominant anaerobic gram-negative bacteria responsible for ANUG, specifically Bacteroides intermedius, Fusobacterium species, fusiform bacilli, and spirochetes. 1, 4, 2

Alternative First-Line Option

• Amoxicillin-clavulanate (Augmentin) is an appropriate alternative first-line agent, particularly when broader coverage is desired. 1

Second-Line Options (Penicillin Allergy)

• Clindamycin is preferred over macrolides in patients with penicillin allergy. 1
• Macrolides may be considered in periodontal disease patients with penicillin allergy, though they are not the preferred alternative. 1

Clinical Context and Microbiology

Bacterial Etiology

• ANUG has a clear infectious etiology involving predominantly anaerobic and aerobic gram-negative bacteria. 4
• The infection is polymicrobial, with Bacteroides intermedius and Fusobacterium species being the main pathogens. 4

Diagnostic Criteria

• Three essential symptoms confirm the diagnosis: sore gums, bleeding gums, and the pathognomonic finding of ulceration and necrosis of interdental papillae. 4

Treatment Duration and Expected Response

• Adequate treatment typically prevents disease progression, with ulcer healing expected within a few days. 4, 2
• Systemic antibiotics should be continued for 7–10 days to ensure complete resolution. 1
• Lack of treatment can lead to progression to necrotizing ulcerative periodontitis (NUP) or even noma in severe cases. 4

Critical Pitfalls to Avoid

• Never rely on antibiotics alone—mechanical debridement is mandatory and must not be delayed. 3, 2
• Do not use antibiotics as monotherapy without addressing the local factors (plaque, calculus, necrotic tissue). 2
• Failure to provide definitive treatment after the acute phase (including treatment of pre-existing gingivitis or periodontitis) can lead to recurrence. 2

Special Populations and Risk Factors

High-Risk Patients Requiring Aggressive Management

• Immunocompromised patients (especially HIV-positive individuals) require more aggressive systemic antimicrobial therapy. 2
• Malnourished patients, those under significant stress, and tobacco smokers are at increased risk and may require earlier systemic antibiotic intervention. 2
• Patients on systemic steroids or with conditions like systemic lupus erythematosus may experience unusually severe ANUG with extensive tissue destruction. 5

Pediatric Considerations

• ANUG is more common in young adults, but reports in malnourished children are not uncommon. 4
• The same antimicrobial principles apply, with dose adjustments for weight.

When Systemic Antibiotics Are Indicated

• Severe cases with extensive tissue involvement warrant immediate systemic antimicrobial therapy. 2
• Non-responding conditions after initial mechanical debridement and local measures require systemic antibiotics. 2
• Systemic signs such as fever, lymphadenopathy, or malaise indicate the need for systemic therapy. 2