Detailed pharmacology and use in Pediatric patient for : Azithromycin Amoxicillin Cefixime Cephalexin Cefopodixime Meropenem Vancomycin
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Finding Sources
Reading File
Finding Sources
Reading File
Finding Sources
Here is the comprehensive pediatric pharmacology reference for all 7 antibiotics:
Pediatric Pharmacology: 7 Key Antibiotics
1. AZITHROMYCIN
Drug Class
Macrolide antibiotic (azalide subclass).
Mechanism of Action
Binds irreversibly to the 50S ribosomal subunit (23S rRNA), blocking translocation and inhibiting bacterial protein synthesis. Bacteriostatic at standard doses; may be bactericidal at high concentrations. Uniquely concentrates in phagocytes (neutrophils, macrophages), achieving tissue concentrations 10-100x higher than serum - contributing to its anti-inflammatory and immunomodulatory properties.
Spectrum
- Gram-positives: Streptococcus pyogenes, S. pneumoniae (resistance increasing)
- Atypicals: Mycoplasma pneumoniae, Chlamydia trachomatis/pneumoniae, Legionella
- Gram-negatives: H. influenzae, Moraxella catarrhalis, Bordetella pertussis, Neisseria gonorrhoeae
- Others: Mycobacterium avium complex (MAC), Borrelia, Bartonella
- NOT active against: S. aureus (especially MRSA), Enterobacteriaceae
Pharmacokinetics
- Oral bioavailability: ~37% (food reduces absorption in capsule form; suspension can be taken with food)
- Half-life: Extremely long - 68 hours (enables once-daily dosing and short 3-5 day courses)
- Distribution: Large Vd (31 L/kg); concentrates in tissue and phagocytes
- Metabolism: Minimal hepatic (primarily excreted unchanged in bile)
- Elimination: Biliary/fecal (no dose adjustment needed in renal impairment; caution in severe hepatic disease)
Pediatric Dosing
| Indication | Dose | Duration |
|---|---|---|
| Community-acquired pneumonia (atypical) | 10 mg/kg on Day 1 (max 500 mg), then 5 mg/kg/day Days 2-5 (max 250 mg) | 5 days |
| Pharyngitis/tonsillitis | 12 mg/kg/day (max 500 mg) | 5 days |
| Otitis media | 30 mg/kg x1 dose OR 10 mg/kg/day x3 days | 1 or 3 days |
| Pertussis treatment/prophylaxis | < 6 months: 10 mg/kg/day x5 days; > 6 months: 10 mg/kg Day 1 then 5 mg/kg Days 2-5 | 5 days |
| Chlamydial pneumonia (infants) | 20 mg/kg/day x3 days | 3 days |
| MAC prophylaxis (HIV) | 20 mg/kg/week (max 1200 mg) | Ongoing |
Special Pediatric Warnings
- IHPS (Infantile Hypertrophic Pyloric Stenosis): Azithromycin (and erythromycin) are associated with IHPS in infants < 6 weeks of age - monitor closely and inform parents. - Red Book 2021
- QTc prolongation: Risk of cardiac arrhythmia; use caution with other QT-prolonging drugs
- Macrolide resistance: Rates > 90% in pediatric Mycoplasma isolates in China/Japan - Murray & Nadel's Respiratory Medicine
- Not recommended for neonates (< 1 month) unless no alternative
Common Pediatric Uses
- Atypical (walking) pneumonia - first-line for Mycoplasma/Chlamydial pneumonia
- Pertussis (whooping cough) - treatment and post-exposure prophylaxis
- Group A strep pharyngitis (penicillin-allergic patients)
- Otitis media (penicillin allergy or treatment failure)
- STIs in adolescents (chlamydia, gonorrhea - in combination)
- MAC prophylaxis in HIV-infected children
2. AMOXICILLIN
Drug Class
Aminopenicillin (extended-spectrum penicillin, beta-lactam).
Mechanism of Action
Binds to Penicillin-Binding Proteins (PBPs), inhibiting the final transpeptidation step of peptidoglycan cell wall synthesis. Bactericidal. Time-dependent killing: efficacy depends on the time free drug concentration remains above MIC (T > MIC). Destroyed by beta-lactamases.
Spectrum
- Gram-positives: Streptococcus spp. (A, B, pneumoniae), Enterococcus faecalis, Listeria
- Gram-negatives: H. influenzae (non-beta-lactamase producing), E. coli (many resistant), Salmonella, Shigella, Proteus mirabilis
- NOT active against: MRSA, beta-lactamase-producing organisms, Pseudomonas, Klebsiella, atypicals
Pharmacokinetics
- Oral bioavailability: 80-90% (excellent - not affected by food; superior to ampicillin)
- Half-life: ~1-1.3 hours (children may have shorter T1/2 than adults)
- Distribution: Good tissue penetration; crosses inflamed meninges; crosses placenta
- Protein binding: ~20%
- Elimination: Primarily renal (60-70% excreted unchanged in urine); dose-adjust in renal impairment
Pediatric Dosing
| Indication | Dose | Duration |
|---|---|---|
| Acute otitis media (standard) | 40-45 mg/kg/day divided q8-12h (max 90 mg/kg/day for high-risk/resistant) | 5-10 days |
| Streptococcal pharyngitis | 25-50 mg/kg/day divided q8-12h | 10 days |
| Community-acquired pneumonia (mild-moderate) | 80-100 mg/kg/day divided q8h | 7-10 days |
| Urinary tract infection | 20-40 mg/kg/day divided q8h | 7-14 days |
| Dental/procedure prophylaxis | 50 mg/kg PO 1 hour before (max 2 g) | Single dose |
| Lyme disease (early) | 25-50 mg/kg/day divided q8-12h (max 500 mg/dose) | 14-21 days |
High-dose amoxicillin (80-90 mg/kg/day) is recommended for AOM when drug-resistant S. pneumoniae (DRSP) is suspected (daycare attendance, recent antibiotic use, age < 2 years). - Goodman & Gilman's
Special Pediatric Considerations
- Rash: Maculopapular rash common in patients with concurrent EBV (infectious mononucleosis) - not a true allergy
- Amoxicillin-clavulanate: Preferred when beta-lactamase-producing organisms suspected (H. influenzae, Moraxella); pediatric dose 25-45 mg/kg/day (amoxicillin component). Do NOT double the clavulanate dose - Dermatology 5e
- Drug of choice for acute otitis media and streptococcal pharyngitis in most pediatric guidelines
- Well tolerated; can be given as sweet suspension - good compliance in children
3. CEFIXIME
Drug Class
Third-generation oral cephalosporin (beta-lactam).
Mechanism of Action
Inhibits bacterial cell wall synthesis by binding PBPs (especially PBP3), preventing peptidoglycan cross-linking. Bactericidal, time-dependent killing. Stable against many beta-lactamases.
Spectrum
- Gram-negatives (excellent): E. coli, Klebsiella, Proteus, H. influenzae, Moraxella, N. gonorrhoeae, Salmonella
- Gram-positives (limited): Streptococcus spp. only; NO activity against S. aureus, Enterococcus
- NOT active against: Pseudomonas, Enterococcus, MRSA, anaerobes
Pharmacokinetics
- Oral bioavailability: ~40-50% (tablets); suspension has higher bioavailability (~50%)
- Half-life: 3-4 hours (longer than older oral cephalosporins)
- Protein binding: ~65-70%
- Elimination: ~50% excreted unchanged in urine, ~10% in bile; dose-adjust for GFR < 60 mL/min
Pediatric Dosing
| Indication | Dose | Duration |
|---|---|---|
| UTI (general) | 8 mg/kg/day once daily OR divided q12h | 7-14 days |
| Otitis media | 8 mg/kg/day OD or divided q12h | 10 days |
| Pharyngitis / tonsillitis | 8 mg/kg/day OD | 10 days |
| Gonorrhea (adolescents) | 400 mg PO single dose | Once |
| Typhoid (off-label) | 15-20 mg/kg/day divided q12h | 7-14 days |
Max dose: 400 mg/day - Campbell Walsh Wein Urology
Special Pediatric Considerations
- Useful when oral treatment of gram-negative infections is needed (step-down from IV)
- Good option for UTIs with resistant organisms not susceptible to first-line agents
- Side effects: Abdominal pain, diarrhea, flatulence, rash
- Not available in IV form - purely oral agent
- Excellent for completing course of uncomplicated pyelonephritis after initial IV therapy
4. CEPHALEXIN
Drug Class
First-generation oral cephalosporin (beta-lactam).
Mechanism of Action
Binds PBPs, inhibiting peptidoglycan transpeptidation. Bactericidal. More susceptible to beta-lactamases than later-generation cephalosporins. Excellent gram-positive coverage with some gram-negative activity.
Spectrum
- Gram-positives (excellent): MSSA (methicillin-sensitive S. aureus), Streptococcus spp. (not enterococcus)
- Gram-negatives (limited): E. coli, Klebsiella, Proteus mirabilis (basic)
- NOT active against: MRSA, Pseudomonas, Enterococcus, Bacteroides, most Enterobacteriaceae
Pharmacokinetics
- Oral bioavailability: ~90% (excellent)
- Half-life: ~0.9-1.2 hours (requires q6h dosing)
- Protein binding: ~15%
- Elimination: Excreted unchanged in urine (>90%); dose-adjust in renal impairment
- Crosses placenta; low concentrations in breast milk
Pediatric Dosing
| Indication | Dose | Duration |
|---|---|---|
| Skin/soft tissue infections (MSSA) | 25-50 mg/kg/day divided q6h (up to 100 mg/kg/day for severe) | 7-10 days |
| Uncomplicated UTI | 25-50 mg/kg/day divided q6h | 7-10 days |
| Streptococcal pharyngitis (PCN-allergy) | 25-50 mg/kg/day divided q6-12h | 10 days |
| Cellulitis / impetigo | 25-50 mg/kg/day divided q6h | 7-10 days |
| Endocarditis prophylaxis | 50 mg/kg PO 1h before procedure (max 2 g) | Single dose |
| Osteomyelitis (step-down) | 75-100 mg/kg/day divided q6h | Continued per course |
Max dose: 4 g/day - Campbell Walsh Wein Urology
Special Pediatric Considerations
- First-line oral agent for MSSA skin and soft tissue infections in children
- ~10-15% cross-reactivity with penicillin allergy in adults; only ~2% in children (Dermatology 5e)
- Four times daily dosing is a compliance challenge in pediatrics - can be extended to q8h in mild infections
- Good safety profile; well-tolerated
5. CEFPODOXIME (Note: "Cefopodixime" is the same drug as Cefpodoxime proxetil)
Drug Class
Third-generation oral cephalosporin (beta-lactam); prodrug ester.
Mechanism of Action
Cefpodoxime proxetil is an oral prodrug hydrolyzed in the GI tract to active cefpodoxime. Binds PBPs (high affinity for PBP3 of gram-negatives), inhibiting cell wall synthesis. Bactericidal, time-dependent. Resistant to many beta-lactamases.
Spectrum
- Gram-positives: Streptococcus spp. (including S. pneumoniae), MSSA (weaker than cephalexin)
- Gram-negatives: H. influenzae (including beta-lactamase-producing), Moraxella catarrhalis, E. coli, Klebsiella, Proteus, N. gonorrhoeae
- NOT active against: MRSA, Pseudomonas, Enterococcus, Bacteroides
Pharmacokinetics
- Oral bioavailability: ~50% (enhanced by food - take with meals)
- Half-life: ~2.2 hours
- Protein binding: ~40%
- Elimination: ~29-33% excreted unchanged in urine; dose-adjust in GFR < 30 mL/min
Pediatric Dosing
| Indication | Dose | Duration |
|---|---|---|
| Acute otitis media | 10 mg/kg/day divided q12h (max 400 mg/day) | 5-10 days |
| Pharyngitis/tonsillitis | 10 mg/kg/day divided q12h | 5-10 days |
| Sinusitis | 10 mg/kg/day divided q12h | 10 days |
| UTI (uncomplicated) | 10 mg/kg/day divided q12h | 7-14 days |
| Lower respiratory tract infections | 10 mg/kg/day divided q12h | 5-14 days |
| Gonorrhea (adolescents) | 200 mg PO single dose | Once |
Age: Generally approved for children ≥ 2 months of age. Available as oral suspension for young children.
- Side effects: Abdominal pain, diarrhea, nausea, rash - Campbell Walsh Wein Urology
Special Pediatric Considerations
- Broader-spectrum than cephalexin with q12h dosing - better compliance
- Useful for AOM when H. influenzae or Moraxella resistance to amoxicillin suspected
- Oral suspension has a characteristic taste that some children dislike
- Advantage over cefixime: slightly better gram-positive coverage (useful for mixed infections)
6. MEROPENEM
Drug Class
Carbapenem (beta-lactam antibiotic).
Mechanism of Action
Binds multiple PBPs (PBP1, PBP2, PBP3, PBP4), inhibiting peptidoglycan synthesis. Bactericidal and time-dependent. Has a bicyclic structure that is highly resistant to most beta-lactamases, including ESBLs and AmpC enzymes. Unlike imipenem, meropenem does not require cilastatin and has low epileptogenic potential, making it preferred in CNS infections.
Spectrum (Broadest of all the listed agents)
- Gram-positives: Streptococcus, MSSA (not MRSA), S. pneumoniae (including penicillin-resistant)
- Gram-negatives: Virtually all Enterobacteriaceae (including ESBL-producers), Pseudomonas aeruginosa, Acinetobacter, H. influenzae, Neisseria
- Anaerobes: Bacteroides fragilis, Clostridium spp.
- NOT active against: MRSA, VRE, Stenotrophomonas, carbapenem-resistant organisms (KPC, NDM, OXA-producers)
Pharmacokinetics
- Administration: IV only (no oral form)
- Half-life: ~1 hour (normal renal function); extended in neonates and in renal impairment
- Protein binding: ~2% (very low)
- CNS penetration: Excellent (drug of choice for gram-negative meningitis/ventriculitis)
- Elimination: ~70% excreted unchanged in urine; requires dose adjustment in renal impairment
Pediatric Dosing
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| General infections (> 3 months) | 20 mg/kg/dose IV | q8h | 1 g/dose |
| Meningitis / CNS infections | 40 mg/kg/dose IV | q8h | 2 g/dose |
| Febrile neutropenia | 20-40 mg/kg/dose IV | q8h | 1-2 g/dose |
| Intra-abdominal / severe polymicrobial | 20 mg/kg/dose IV | q8h | 1 g/dose |
| Cystic fibrosis (Pseudomonas) | 40 mg/kg/dose IV | q8h | 2 g/dose |
Neonates: Dosing differs by gestational age and postnatal age - generally 20 mg/kg q8-12h (see Red Book neonatal dosing tables). After first month of life, pediatric doses apply. - Katzung's 16e
Special Pediatric Considerations
- Reserved for serious, resistant gram-negative infections - use should be guided by culture/sensitivity
- Drug of choice for ESBL-producing organism infections (UTI, sepsis, meningitis)
- Preferred over imipenem in pediatric CNS infections (lower seizure risk)
- For acute pediatric bacterial meningitis where ceftriaxone is insufficient, add meropenem - Harrison's 22e
- Extended infusion (3-4 hours) may improve T > MIC for resistant organisms (PK/PD optimization)
- Monitor renal function closely - dose-adjust per creatinine clearance
- Thrombocytopenia and elevated liver enzymes can occur
7. VANCOMYCIN
Drug Class
Glycopeptide antibiotic.
Mechanism of Action
Binds to D-Ala-D-Ala terminus of peptidoglycan precursors (lipid II), physically blocking transglycosylation and transpeptidation steps in cell wall synthesis. This is a different mechanism from beta-lactams - hence activity against MRSA and MRSA-like organisms. Bactericidal against most organisms; bacteriostatic against enterococci. AUC/MIC-dependent killing (not purely time-dependent or concentration-dependent). Active only against gram-positives.
Spectrum
- Gram-positives ONLY: MRSA, MSSA, CoNS, S. pneumoniae (including penicillin-resistant), S. pyogenes, S. agalactiae, Enterococcus (VRE is resistant), Clostridioides difficile (oral only for CDI)
- NOT active against: ANY gram-negative organism (too large to penetrate outer membrane), VRE (vancomycin-resistant Enterococcus)
Pharmacokinetics
- Administration: IV (for systemic infections); oral (for C. difficile colitis only - not absorbed systemically)
- Half-life: 4-6 hours (adults); significantly variable in neonates/children due to developmental changes in renal function
- Protein binding: ~55%
- Distribution: Poor CNS penetration with normal meninges; increases with inflamed meninges (reaches therapeutic levels in meningitis)
- Elimination: Primarily renal (glomerular filtration); major dose adjustments required in renal impairment
Pediatric Dosing - Standard
| Age Group | Dose | Frequency |
|---|---|---|
| Neonates (< 29 wks GA) | 15 mg/kg/dose IV | q18-24h |
| Neonates (30-36 wks GA) | 15 mg/kg/dose IV | q12h |
| Neonates (> 37 wks GA) | 15 mg/kg/dose IV | q8-12h |
| Infants/Children (> 1 month) | 15 mg/kg/dose IV | q6h |
| Severe MRSA infections | Loading dose 25-30 mg/kg, then 15-20 mg/kg/dose q6h | - |
Max single dose: 750-1000 mg. Max daily dose: 3-4 g/day (depending on indication).
Endocarditis dosing (Fuster's The Heart):
- 30 mg/kg/24h IV in 2 divided doses (adults), not to exceed 2 g/24h
- Pediatric: 40 mg/kg/24h IV in divided doses
Therapeutic Drug Monitoring (TDM) - CRITICAL
The most recent consensus guideline (ASHP/IDSA/PIDS/SIDP 2020) recommends:
- AUC-guided monitoring (AUC/MIC target 400-600 mcg·h/L, assuming MIC of 1 mg/L) using Bayesian estimation - preferred over trough-only monitoring
- Obtain two levels: one 1-2h after end of infusion AND one 4-6h after end of infusion (earliest after 2nd dose)
- Target trough < 15 mcg/mL to minimize nephrotoxicity
- Avoid AUC > 800 and troughs > 15 mcg/mL
- Most children < 12 years require higher doses to achieve optimal AUC/MIC compared to older children (due to higher renal clearance in young children) - Red Book 2021
Oral Vancomycin (C. difficile colitis)
- 10 mg/kg/dose PO (max 125 mg/dose) 4 times daily x 14 days - Red Book 2021
- Not absorbed from GI tract; acts locally
Infusion-Related Toxicity
- Red Man Syndrome: Flushing, erythema, pruritus, hypotension due to non-immune mast cell degranulation with rapid infusion - NOT an allergy. Prevention: infuse over minimum 60 minutes (longer if > 500 mg), pretreat with antihistamine if needed
- Nephrotoxicity: Risk increases with trough > 15 mcg/mL, concomitant aminoglycosides, prolonged courses
- Ototoxicity: Uncommon at therapeutic levels; higher risk with supratherapeutic levels or concurrent ototoxic drugs
- Thrombophlebitis: Local IV site reaction (use central venous access for high-dose/prolonged therapy)
Special Pediatric Considerations
- First-line for serious MRSA infections (bacteremia, osteomyelitis, pneumonia, CNS infections)
- Combined with cefotaxime or meropenem for empiric bacterial meningitis in neonates and high-risk children - Harrison's 22e
- For suspected MRSA pneumonia complicating influenza: add clindamycin, ceftaroline, or linezolid to vancomycin - Red Book 2021
- Duration and step-down to oral agents (e.g., clindamycin or TMP-SMX for MRSA) guided by clinical response and infection type
Quick Reference Summary Table
| Drug | Class | Route | Key Pediatric Dose | Main Pediatric Use |
|---|---|---|---|---|
| Azithromycin | Macrolide | PO (IV available) | 10 mg/kg Day 1, 5 mg/kg Days 2-5 | Atypical pneumonia, pertussis, otitis media |
| Amoxicillin | Aminopenicillin | PO | 40-90 mg/kg/day ÷ q8-12h | AOM, pharyngitis, CAP, UTI |
| Cefixime | 3rd gen oral cephalosporin | PO | 8 mg/kg/day OD | UTI, typhoid step-down, otitis media |
| Cephalexin | 1st gen oral cephalosporin | PO | 25-100 mg/kg/day ÷ q6h | SSTI (MSSA), UTI, pharyngitis |
| Cefpodoxime | 3rd gen oral cephalosporin | PO | 10 mg/kg/day ÷ q12h | AOM, sinusitis, UTI, LRTI |
| Meropenem | Carbapenem | IV | 20-40 mg/kg/dose q8h | Resistant gram-neg, meningitis, febrile neutropenia |
| Vancomycin | Glycopeptide | IV / PO* | 15 mg/kg/dose q6h (IV) | MRSA infections; *oral only for C. diff |
Sources: Red Book 2021 (AAP Committee on Infectious Diseases), Campbell Walsh Wein Urology, Katzung's Basic & Clinical Pharmacology 16e, Goodman & Gilman's Pharmacological Basis of Therapeutics, Fuster's The Heart 15e, Harrison's Principles of Internal Medicine 22e, Murray & Nadel's Respiratory Medicine, Dermatology 5e.
Clinical Note: All dosing should be verified against current institutional guidelines and adjusted for weight, age, renal function, and severity of infection. Dosing in neonates (especially preterm) requires individualized approach using neonatal-specific tables.
This is a shared conversation. Sign in to Orris to start your own chat.