Expansion
Site predicts organism, and organism predicts the antibiotic
Expansion
| Infection | Likely organism | Typical first line |
|---|---|---|
| Community acquired pneumonia | Strep pneumoniae, atypicals | Amoxicillin, adding a macrolide if severe |
| Hospital acquired pneumonia | Gram negatives, Staph aureus | Broad spectrum per local policy |
| Cellulitis | Strep pyogenes, Staph aureus | Flucloxacillin |
| Uncomplicated UTI | E coli | Nitrofurantoin or trimethoprim |
| Pyelonephritis | E coli | Co-amoxiclav or a cephalosporin |
| Meningitis | Meningococcus, pneumococcus | Ceftriaxone, plus amoxicillin if over 50 or immunosuppressed to cover Listeria |
| Infective endocarditis | Streptococci, staphylococci | Per local protocol after cultures |
| C difficile | Oral vancomycin first line | |
| Neutropenic sepsis | Gram negatives including Pseudomonas | Piperacillin-tazobactam within one hour |
Two principles matter more than the table. Take cultures before starting wherever possible, since a positive culture allows narrowing and a negative one may allow stopping. And review at 48 to 72 hours, using the culture and clinical response to de-escalate, switch to oral, or stop.
Nitrofurantoin requires adequate renal function to concentrate in urine and is ineffective in pyelonephritis, since it does not achieve tissue levels.