What are the main antibiotics used in clinical practice and their typical dosing regimens?

Main Antibiotics Used in Clinical Practice

Beta-Lactam Antibiotics

Penicillins

For methicillin-susceptible Staphylococcus aureus (MSSA) infections, nafcillin or oxacillin 1–2 g IV every 4 hours is the first-line treatment for adults, with cefazolin 1 g IV every 8 hours as an alternative. 1

• Penicillin G is dosed at 2–4 million units IV every 4–6 hours for adults in streptococcal necrotizing infections, combined with clindamycin 600–900 mg IV every 8 hours 1
• Pediatric dosing for penicillin G is 60,000–100,000 units/kg/dose IV every 6 hours 1
• Amoxicillin-clavulanate 875/125 mg orally twice daily is the preferred oral agent for animal bite wounds 1
• Ampicillin-sulbactam 1.5–3.0 g IV every 6–8 hours provides coverage for mixed aerobic-anaerobic infections 1

Cephalosporins

Cephalexin 500 mg orally four times daily (every 6 hours) is the standard regimen for outpatient skin and soft tissue infections caused by MSSA. 2

• Pediatric cephalexin dosing is 25–50 mg/kg/day divided into 4 doses for mild infections, or 75–100 mg/kg/day for MSSA infections 2
• Cefazolin 1 g IV every 8 hours (33 mg/kg/dose every 8 hours in children) is used for serious staphylococcal infections 1
• Ceftriaxone 1–2 g IV every 24 hours provides broad-spectrum coverage for severe infections including Vibrio vulnificus and Aeromonas when combined with doxycycline 1
• Cefuroxime 500 mg orally twice daily or 1 g IV every 12 hours covers Pasteurella multocida in animal bites 1

Carbapenems

• Meropenem 1 g IV every 8 hours (20 mg/kg/dose every 8 hours in children) is used for necrotizing infections 1
• Imipenem-cilastatin 1 g IV every 6–8 hours provides broad-spectrum coverage for mixed infections 1
• Ertapenem 1 g IV daily (15 mg/kg/dose every 12 hours for children 3 months–12 years) is an alternative for complicated infections 1

Glycopeptides and Lipopeptides

Vancomycin

For MRSA infections, vancomycin 15–20 mg/kg/dose IV every 8–12 hours (targeting trough levels of 15–20 mcg/mL) is the cornerstone of therapy. 1

• Pediatric vancomycin dosing is 15 mg/kg/dose IV every 6 hours 1
• For complicated bacteremia and endocarditis, vancomycin 30–60 mg/kg/day IV in 2–4 divided doses is recommended 1
• A loading dose of 25–30 mg/kg is indicated in seriously ill patients 1

Teicoplanin

• Teicoplanin 6–12 mg/kg/dose IV every 12 hours for 3 doses, then daily, is an alternative glycopeptide 1
• Pediatric dosing is 10 mg/kg IV every 12 hours for 3 doses, then 6–10 mg/kg daily 1

Daptomycin

• Daptomycin 4 mg/kg/dose IV daily for skin infections, or 6 mg/kg/dose IV daily for bacteremia in adults 1
• Pediatric dosing is 6–10 mg/kg/dose IV daily 1
• Daptomycin is contraindicated for pneumonia due to inactivation by pulmonary surfactant 1

Oxazolidinones

Linezolid

Linezolid 600 mg orally or IV twice daily provides excellent MRSA coverage with the advantage of oral bioequivalence. 1

• Pediatric dosing is 10 mg/kg/dose every 8 hours, not to exceed 600 mg/dose 1
• Linezolid is effective for both complicated skin infections and MRSA pneumonia 1

Fluoroquinolones

Moxifloxacin

Moxifloxacin 400 mg orally or IV once daily provides respiratory and anaerobic coverage. 3

• Duration is 7–14 days for community-acquired pneumonia, 7–21 days for complicated skin infections, and 10 days for acute bacterial sinusitis 3
• Administer at least 4 hours before or 8 hours after multivalent cations (magnesium, aluminum, iron, zinc) 3

Ciprofloxacin and Levofloxacin

• Ciprofloxacin 500–750 mg orally twice daily or 400 mg IV every 12 hours covers Pseudomonas and gram-negative organisms 1
• Levofloxacin 500 mg IV/orally every 24 hours is used for respiratory infections and anthrax prophylaxis 1

Macrolides and Azalides

Azithromycin

Azithromycin dosing varies by indication but typically involves 500 mg on day 1, then 250 mg daily for 4 days in adults. 4

• Pediatric dosing is 12 mg/kg once daily for 5 days or 20 mg/kg once daily for 3 days 4
• Azithromycin prolongs QTc interval in a dose-dependent manner, particularly when combined with other QT-prolonging drugs 4

Tetracyclines

Doxycycline

Doxycycline 100 mg orally or IV twice daily is first-line for Vibrio vulnificus, Aeromonas, and atypical pathogens. 1

• Pediatric dosing is 2 mg/kg/dose twice daily for children >45 kg; adult dose for those <45 kg 1
• Tetracyclines are contraindicated in children <8 years and pregnancy category D 1

Minocycline

• Minocycline 200 mg loading dose, then 100 mg orally twice daily for MRSA skin infections 1
• Pediatric dosing is 4 mg/kg loading dose, then 2 mg/kg/dose twice daily 1

Folate Antagonists

Trimethoprim-Sulfamethoxazole (TMP-SMX)

TMP-SMX 1–2 double-strength tablets orally twice daily is a cost-effective oral option for outpatient MRSA skin infections. 1

• Pediatric dosing is trimethoprim 4–6 mg/kg/dose twice daily 1
• TMP-SMX is pregnancy category C/D and contraindicated in third trimester and infants <2 months 1

Lincosamides

Clindamycin

Clindamycin 300–450 mg orally three times daily or 600–900 mg IV every 8 hours covers MRSA and anaerobes. 1

• Pediatric dosing is 10–13 mg/kg/dose every 6–8 hours, not exceeding 40 mg/kg/day 1
• Clindamycin carries increased risk of Clostridioides difficile infection compared to other oral agents 1
• Clindamycin combined with penicillin is the regimen of choice for clostridial myonecrosis 1

Combination Therapy for Necrotizing Infections

For mixed necrotizing infections, piperacillin-tazobactam 3.37 g IV every 6–8 hours plus vancomycin is the preferred empiric regimen. 1

• Pediatric dosing is 60–75 mg/kg/dose of the piperacillin component every 6 hours plus vancomycin 10–13 mg/kg/dose every 8 hours 1
• Alternative regimens include cefotaxime 2 g IV every 6 hours plus metronidazole 500 mg IV every 6 hours 1