What is the appropriate antibiotic regimen, including the maximum kid dose (MKD), for a 14-year-old patient with cellulitis, assuming no known allergies to penicillin?

Treatment of Cellulitis in a 14-Year-Old

For a 14-year-old with uncomplicated cellulitis, prescribe oral cephalexin 500 mg four times daily (or 25-50 mg/kg/day divided into 3-4 doses, maximum 4 grams/day) for 5 days, extending only if clinical improvement has not occurred within this timeframe. 1

First-Line Antibiotic Selection

Beta-lactam monotherapy is the standard of care for typical uncomplicated cellulitis, with a 96% success rate, confirming that MRSA coverage is unnecessary in most cases. 1, 2

Recommended Oral Regimens for Adolescents:

• Cephalexin 500 mg orally four times daily (or 25-50 mg/kg/day divided into 3-4 doses) is the preferred first-line agent, providing effective coverage against streptococci and methicillin-sensitive S. aureus 1, 3

• Alternative beta-lactam options include dicloxacillin 250-500 mg every 6 hours, amoxicillin, or penicillin V 250-500 mg four times daily 1, 3

• Amoxicillin-clavulanate 875/125 mg twice daily is appropriate for cellulitis associated with traumatic wounds or animal/human bites 1

Treatment Duration

• Treat for exactly 5 days if clinical improvement occurs (reduced warmth, tenderness, and erythema with resolution of fever) 1, 3

• Extend treatment beyond 5 days ONLY if the infection has not improved within this initial timeframe—do not reflexively extend to 7-10 days based on residual erythema alone 1

• Five-day courses are as effective as 10-day courses for uncomplicated cellulitis, based on high-quality randomized controlled trial evidence 1, 3

When to Add MRSA Coverage

MRSA is an uncommon cause of typical cellulitis and routine coverage is unnecessary. 1, 2, 4 However, add MRSA-active antibiotics when specific risk factors are present:

• Penetrating trauma or injection drug use 1, 2
• Purulent drainage or exudate 1, 2
• Evidence of MRSA infection elsewhere or known nasal MRSA colonization 1, 2
• Systemic inflammatory response syndrome (fever >38°C, tachycardia, altered mental status) 1
• Athletes, prisoners, military recruits, or residents of long-term care facilities 2

MRSA Coverage Options for Adolescents:

• Clindamycin 300-450 mg orally every 6 hours (or 10-13 mg/kg/dose every 6-8 hours, maximum 1.8 grams/day) provides single-agent coverage for both streptococci and MRSA 1, 5

• Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 DS tablets twice daily PLUS a beta-lactam (cephalexin or amoxicillin)—never use TMP-SMX as monotherapy due to inadequate streptococcal coverage 1

• Doxycycline 100 mg orally twice daily PLUS a beta-lactam for children >8 years old and ≥45 kg—never use in children <8 years due to tooth discoloration 1

Pediatric Dosing Specifics

Cephalexin (First-Line):

• 25-50 mg/kg/day divided into 3-4 doses (typically 500 mg four times daily for adolescents weighing >40 kg) 3
• Maximum daily dose: 4 grams 3

Clindamycin (If MRSA Coverage Needed):

• Oral: 10-13 mg/kg/dose every 6-8 hours (typically 300-450 mg every 6 hours for adolescents) 6, 5
• More severe infections: 16-20 mg/kg/day divided into 3-4 equal doses 5
• Maximum daily dose: 1.8 grams 5
• Must be taken with a full glass of water to avoid esophageal irritation 5

Amoxicillin (Alternative Beta-Lactam):

• 50-75 mg/kg/day in 2 doses for typical cellulitis 6
• 90 mg/kg/day in 2 doses for resistant organisms 6

Indications for Hospitalization and IV Therapy

Hospitalize and initiate IV antibiotics if any of the following are present:

• Systemic inflammatory response syndrome (SIRS): fever, tachycardia, hypotension, or altered mental status 1, 3
• Severe immunocompromise or neutropenia 1
• Concern for deeper or necrotizing infection (severe pain out of proportion to exam, rapid progression, skin anesthesia, gas in tissue, bullous changes) 1
• Failure of outpatient treatment after 24-48 hours 1, 3

IV Antibiotic Options for Hospitalized Adolescents:

• Vancomycin 15 mg/kg IV every 6 hours (not to exceed 2 grams per dose) is first-line for complicated cellulitis requiring MRSA coverage 6, 1

• Cefazolin 33 mg/kg/dose IV every 8 hours (maximum 6 grams/day) is preferred for uncomplicated cellulitis without MRSA risk factors 6, 1

• For severe cellulitis with systemic toxicity or suspected necrotizing fasciitis: vancomycin 15 mg/kg IV every 6 hours PLUS piperacillin-tazobactam 60-75 mg/kg/dose (of piperacillin component) every 6 hours IV 6, 1

Essential Adjunctive Measures

• Elevate the affected extremity above heart level for at least 30 minutes three times daily to promote gravity drainage of edema 1, 3

• Examine interdigital toe spaces for tinea pedis, fissuring, scaling, or maceration—treating these eradicates colonization and reduces recurrence risk 1, 7

• Treat predisposing conditions including venous insufficiency, lymphedema, eczema, or chronic edema 1, 7

Common Pitfalls to Avoid

• Do not routinely add MRSA coverage for typical nonpurulent cellulitis without specific risk factors—this represents overtreatment and increases antibiotic resistance 1, 4

• Do not extend treatment to 10-14 days automatically—extend only if clinical improvement has not occurred by day 5 1

• Do not use doxycycline or TMP-SMX as monotherapy for typical cellulitis, as their activity against beta-hemolytic streptococci is unreliable 1

• Do not delay surgical consultation if any signs of necrotizing infection are present (severe pain out of proportion, rapid progression, skin anesthesia, gas in tissue, systemic toxicity) 1

Reassessment and Treatment Failure

• Reassess within 24-48 hours to verify clinical response—look for reduction in warmth, tenderness, and erythema 1

• If no improvement with appropriate first-line antibiotics, consider adding empiric MRSA coverage (clindamycin or TMP-SMX plus beta-lactam), evaluate for abscess requiring drainage, or consider cellulitis mimickers (DVT, contact dermatitis, venous stasis) 1, 2

• Blood cultures are positive in only 5% of cases and are unnecessary for typical cellulitis—reserve for patients with severe systemic features, malignancy, or neutropenia 1