Ampiclox (Ampicillin + Cloxacillin) Dosing for Bacterial Infections
For adults and children over 20 kg with skin and soft tissue infections, the standard dose is 500 mg four times daily (every 6 hours), while children under 20 kg should receive 50-100 mg/kg/day divided into four equal doses. 1, 2
Adult Dosing Recommendations
Standard Infections
- Skin and soft tissue infections (primary pyodermas): 500 mg orally four times daily in equally spaced doses 1, 2
- Respiratory tract infections: 250 mg orally four times daily 1
- Genitourinary or gastrointestinal infections: 500 mg orally four times daily; severe or chronic infections may require larger doses 1
Severe Infections Requiring Parenteral Therapy
- High-dose ampicillin-sulbactam for severe infections: 12 g/day IV divided into four equal doses (3 g every 6 hours) for adults with endocarditis or severe multidrug-resistant infections 3
- Extended infusion regimens: For severe infections, 4-hour infusions optimize pharmacokinetic/pharmacodynamic properties 3
Pediatric Dosing Recommendations
Children Weighing 20 kg or Less
- Genitourinary or gastrointestinal infections: 100 mg/kg/day total, divided into four equally spaced doses 1
- Respiratory tract infections: 50 mg/kg/day total, divided into three to four equally spaced doses 1
- Severe infections (parenteral): 300 mg/kg/day IV divided into 4-6 doses 3
Children Over 20 kg
- Use adult dosing: 500 mg four times daily for most infections 1
- Doses should not exceed adult recommendations 1
Treatment Duration
Standard Course
- Minimum duration: Continue for 48-72 hours after the patient becomes asymptomatic or bacterial eradication is documented 1
- Streptococcal infections: Minimum 10 days to prevent rheumatic fever or glomerulonephritis 1
- Chronic urinary or gastrointestinal infections: May require several weeks of treatment with frequent bacteriologic monitoring 1
Specific Infections
- Acute uncomplicated UTIs: 10 days of treatment 4
- Endocarditis: 4-6 weeks depending on valve involvement 3
- Severe or stubborn infections: May require treatment for several weeks 1
Administration Guidelines
Critical timing consideration: Administer at least 30 minutes before or 2 hours after meals for maximal absorption, as ampicillin absorption is reduced by food despite being acid-resistant 1
Clinical Context and Antibiotic Selection
When Cloxacillin Component is Essential
- Staphylococcus aureus infections: Cloxacillin should be first-line for primary pyodermas, as S. aureus shows 93% sensitivity to cloxacillin but 89.5% resistance to ampicillin alone 2
- Methicillin-sensitive S. aureus (MSSA): The combination provides excellent coverage 2
When Combination Has Limited Value
- The ampicillin-cloxacillin combination has little place in routine treatment except for cellulitis and infected eczemas 2
- For simple skin infections without mixed flora, cloxacillin alone is preferred 2
- Secondary pyodermas with gram-negative organisms may require different antibiotic combinations 2
Common Pitfalls to Avoid
- Underdosing: Do not use smaller doses than indicated above, as this promotes resistance 1
- Inadequate duration: Stopping treatment when symptoms resolve but before 48-72 hours of documented bacterial clearance increases relapse risk 1
- Poor timing with meals: Taking with food significantly reduces absorption and therapeutic efficacy 1
- Using combination unnecessarily: For uncomplicated S. aureus infections, cloxacillin monotherapy is more appropriate than the combination 2
- Ignoring resistance patterns: S. aureus has 89.5% resistance to ampicillin/penicillin, making the cloxacillin component critical for efficacy 2
Special Populations
Gonorrhea Treatment (Single-Dose Regimen)
- Adults: 3.5 grams ampicillin orally as single dose with 1 gram probenecid simultaneously 1
- Follow-up cultures: Obtain from original infection site 7-14 days after therapy 1
- Alternative for PPNG: Sulbactam 500 mg/ampicillin 1000 mg IM single dose with 1 g oral probenecid shows 100% cure rate 5