What is the comparative effectiveness of azithromycin 250mg orally (po) versus azithromycin 200mg/5ml liquid formulation for adults and children with common bacterial infections?

Azithromycin 250mg Tablet vs 200mg/5mL Suspension: Comparative Effectiveness

Both azithromycin 250mg tablets and 200mg/5mL suspension are bioequivalent formulations that deliver identical clinical outcomes when dosed appropriately—the choice between them depends entirely on patient age, ability to swallow tablets, and dosing precision requirements, not on differential effectiveness. 1, 2

Bioequivalence and Clinical Efficacy

The formulations are pharmacologically equivalent when proper dosing is maintained:

• Tablet formulation (250mg): Standard adult dosing delivers 500mg on day 1, then 250mg daily for days 2-5, achieving mean peak serum concentrations of 383 ± 142 ng/mL with sustained tissue levels 3

• Suspension formulation (200mg/5mL): Provides identical systemic exposure when volume-adjusted—12.5 mL delivers 500mg equivalent, 6.25 mL delivers 250mg equivalent 1

• Both formulations achieve the same area under the curve (AUC 0-24h of 3,109 ± 1,033 ng·h/mL) and maintain therapeutic tissue concentrations for 7-10 days post-treatment due to azithromycin's 68-hour tissue half-life 3, 2

Formulation Selection Algorithm

For adults and adolescents ≥12 years who can swallow tablets:

• Use 250mg tablets for convenience, lower cost, and elimination of dosing calculation errors 1, 2
• Standard regimen: 500mg (two tablets) day 1, then 250mg (one tablet) daily days 2-5 2

For children <12 years or patients unable to swallow tablets:

• Use 200mg/5mL suspension with weight-based dosing: 10 mg/kg (max 500mg) day 1, then 5 mg/kg (max 250mg) daily days 2-5 1, 2
• Critical: Verify bottle concentration before calculating mL dose—assuming all suspensions are 200mg/5mL can lead to dosing errors 1

For single-dose regimens (chlamydial infections):

• Adults: Four 250mg tablets (1 gram total) as single observed dose 2
• Suspension alternative: 50 mL of 200mg/5mL concentration delivers equivalent 1 gram dose 1

Clinical Context Considerations

Pediatric infections demonstrate equal efficacy across formulations:

• Respiratory tract infections in children respond equally well to suspension (91.7% efficacy) when dosed at 10 mg/kg day 1, then 5 mg/kg days 2-5 4, 3
• Streptococcal pharyngitis requires higher dosing (12 mg/kg daily for 5 days) regardless of formulation to prevent recurrence 5, 6

Adult respiratory infections show no formulation-dependent differences:

• Community-acquired pneumonia: 3-day course (500mg daily) or 5-day course (500mg day 1, then 250mg daily) achieve identical clinical success rates (80-88%) 7
• Atypical pneumonia responds equally to both regimens at equivalent total doses 7

Administration and Tolerability

Suspension-specific considerations:

• Better tolerated than amoxicillin/clavulanate in children, with only 2% reporting adverse effects versus 13% with penicillin V 6
• Can be administered with or without food, but separate from aluminum/magnesium antacids by ≥2 hours to prevent 50% reduction in absorption 1, 5
• Pediatric patients report suspension formulation is "easy to take" in 92% of cases 4

Tablet-specific advantages:

• Eliminates volume measurement errors and concentration verification steps 1
• Preferred for directly observed therapy in single-dose regimens (chlamydia, travelers' diarrhea) 2
• Lower cost per treatment course in most healthcare settings 1

Common Pitfalls to Avoid

Critical dosing errors with suspension:

• Never assume concentration without checking label—some formulations are 100mg/5mL, requiring double the volume 1
• For 200mg/5mL concentration: 500mg dose = 12.5 mL (not 5 mL or 10 mL) 1

Indication-specific dosing requirements:

• Streptococcal pharyngitis requires 12 mg/kg/day for 5 days in children, not the standard 10 mg/kg day 1 then 5 mg/kg regimen, to prevent treatment failure 5, 6
• Single 1-gram doses are only appropriate for chlamydial infections and specific travelers' diarrhea—not for respiratory infections 1, 2

Resistance and safety monitoring:

• Macrolide resistance in Streptococcus pneumoniae is increasing; azithromycin should not be first-line for suspected pneumococcal infections in high-resistance areas 8
• Long-term therapy (>5 days) requires baseline ECG if QTc risk factors present, with contraindication if QTc >450ms (men) or >470ms (women) 2