What antibiotic is recommended for possible folliculitis or a swollen lymph node under the arm?

Antibiotic Treatment for Possible Folliculitis or Swollen Lymph Node Under the Arm

For possible folliculitis or swollen lymph node under the arm, a 5-day course of an antibiotic active against streptococci and staphylococci such as dicloxacillin, cephalexin, or clindamycin is recommended as first-line treatment. 1

Diagnosis Considerations

• Folliculitis is an infection of the hair follicle, usually caused by Staphylococcus aureus, where inflammation is limited to the epidermis 1
• Furuncles ("boils") are deeper infections extending through the dermis into subcutaneous tissue, forming small abscesses 1
• Swollen lymph nodes may be associated with cellulitis or other soft tissue infections 1
• Cultures of skin aspirates or biopsies are not routinely recommended for typical cases but should be considered in patients with malignancy, severe systemic features, or unusual predisposing factors 1

First-Line Treatment Options

• For typical folliculitis without abscess formation:

  • Dicloxacillin, cephalexin, or clindamycin for 5 days 1
  • A 5-day course is as effective as a 10-day course if clinical improvement occurs 1

• For folliculitis with small pustules:

  • Topical mupirocin is effective for limited disease 1
  • Systemic therapy is preferred for numerous lesions to decrease transmission 1

Treatment Based on Clinical Presentation

For simple folliculitis:

• Oral cephalexin 500mg four times daily for 5 days 1
• Alternative: clindamycin 300-450mg three times daily for 5 days 1

If furuncle (boil) is present:

• Incision and drainage is the recommended treatment for large furuncles 1
• Antibiotics may not be necessary after adequate drainage unless there is:
  • Extensive surrounding cellulitis
  • Systemic inflammatory response syndrome (SIRS)
  • Markedly impaired host defenses 1

If MRSA is suspected:

• Consider MRSA coverage if there is:
  • History of prior MRSA infection
  • Purulent drainage
  • Penetrating trauma
  • Injection drug use
  • Nasal colonization with MRSA 1
• Options include:
  • Clindamycin 300-450mg three times daily for 5-7 days 1
  • Doxycycline 100mg twice daily for 5-7 days 1, 2
  • Trimethoprim-sulfamethoxazole (SMX-TMP) plus a beta-lactam if both streptococci and MRSA coverage is desired 1

Special Considerations

• If folliculitis is recurrent or chronic:

  • Consider evaluation for underlying conditions like diabetes 1
  • Search for local causes such as foreign material 1
  • Consider decolonization regimen with intranasal mupirocin and chlorhexidine washes for recurrent S. aureus infections 1
  • For gram-negative folliculitis (often seen after long-term tetracycline treatment), isotretinoin may be effective 3

• For refractory cases:

  • Rifampicin has shown effectiveness in some cases of folliculitis decalvans 4
  • Isotretinoin has demonstrated success in treating resistant folliculitis decalvans 5

Important Caveats

• MRSA is an unusual cause of typical folliculitis without abscess formation 1
• Beta-lactam monotherapy (like cephalexin) is recommended for non-purulent infections without evidence of MRSA 1
• Elevation of the affected area is important to promote drainage of edema and inflammatory substances 1
• Systemic corticosteroids may be considered as an adjunct in selected non-diabetic adult patients with significant inflammation 1
• Treatment should address any underlying conditions that may predispose to infection 1

Follow-up Recommendations

• If no improvement after 5 days of treatment, consider:
  • Extending antibiotic duration 1
  • Obtaining cultures to guide therapy 1
  • Evaluating for deeper infection or underlying conditions 1