Antibiotic — Community-Acquired Pneumonia Pregnancy: Safe in pregnancy — aminopenicillins are first-line antibiotics in pregnancy

Amoxicillin

Brand names: Amoxil

Adult dose

Dose: 500 mg–1 g

Route: Oral

Frequency: Three times daily for 5 days (CAP) — NICE NG138

Max: 3 g/day (oral); higher doses IV

First-line for mild-moderate community-acquired pneumonia (CRB-65 score 0–1). Combined with doxycycline or clarithromycin for atypical cover in moderate CAP (CRB-65 2). IV amoxicillin 500 mg–1 g TDS for hospitalised patients who cannot take oral. Do not use if Legionella or Mycoplasma strongly suspected.

Paediatric dose

Dose: 40–90 mg/kg/day divided every 8 hours mg/kg

Route: Oral

Frequency: Three times daily for 5 days

Max: 90 mg/kg/day (high-dose protocol for resistant S. pneumoniae)

BNFc: community-acquired pneumonia in children — 40 mg/kg/day divided TDS (standard); 90 mg/kg/day for suspected penicillin-resistant S. pneumoniae

Dose adjustments

Renal

Reduce dose if eGFR <30 mL/min/1.73m² — increase dose interval

Hepatic

No dose adjustment required

Paediatric weight-based calculator

Patient weight (kg)

BNFc: community-acquired pneumonia in children — 40 mg/kg/day divided TDS (standard); 90 mg/kg/day for suspected penicillin-resistant S. pneumoniae

Clinical pearls

NICE NG138 (CAP 2019): amoxicillin 500 mg TDS × 5 days for mild CAP (CRB-65 = 0) in primary care — do not prescribe without clinical diagnosis
CRB-65 scoring: Confusion, RR ≥30, BP systolic <90 or diastolic ≤60, age ≥65 — score 0 = low risk (treat at home with amoxicillin); 1–2 = moderate (consider hospital); 3–4 = high (hospital admission)
Moderate CAP: add doxycycline 200 mg day 1 then 100 mg OD or clarithromycin 500 mg BD for atypical cover (Mycoplasma, Chlamydophila, Legionella)
Avoid in EBV (glandular fever): aminopenicillins cause maculopapular rash in ~90% of EBV patients — confirm diagnosis before prescribing if sore throat + lymphadenopathy
High-dose amoxicillin (90 mg/kg/day, max 3 g/day): used in children for suspected penicillin-non-susceptible S. pneumoniae (post-antibiotic use, vaccine failure)

Contraindications

Penicillin hypersensitivity
Infectious mononucleosis (EBV — maculopapular rash in ~90%)

Side effects

GI disturbance (diarrhoea, nausea)
Rash (common in EBV)
C. difficile infection (low risk — short course)
Anaphylaxis

Interactions

Methotrexate — increased toxicity
Warfarin — may elevate INR
OCP — theoretical interaction (no dose adjustment required per current guidance)

Monitoring

Symptom response at 48–72 hours
CXR at 6 weeks (to confirm resolution — detect underlying malignancy)

Reference: BNFc; BNF 90; BNFc; NICE NG138 (CAP 2019); BTS CAP Guidelines 2009 (updated); PHE antimicrobial guidelines. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways