Expansion
Gram positive, Gram negative, anaerobic and atypical cover
Mnemonic
Match the organism group to the class:
- Gram positive cocci - penicillins, flucloxacillin for Staphylococcus aureus, vancomycin and teicoplanin for MRSA, benzylpenicillin for Streptococcus
- Gram negatives - gentamicin, cephalosporins, ciprofloxacin, piperacillin-tazobactam, carbapenems for ESBL producers
- Anaerobes - metronidazole, co-amoxiclav, clindamycin, carbapenems
- Atypicals (Mycoplasma, Chlamydia, Legionella) - macrolides, tetracyclines, quinolones. Beta lactams do not work, because these organisms have no conventional cell wall
- Pseudomonas - piperacillin-tazobactam, ceftazidime, meropenem, ciprofloxacin, aminoglycosides
“Metronidazole below the diaphragm, macrolides for the atypicals, flucloxacillin for the skin.”
Bactericidal versus bacteriostatic matters in endocarditis, meningitis and neutropenia, where cidal agents are required: beta lactams, glycopeptides, aminoglycosides, quinolones and metronidazole.
The four Cs drive Clostridioides difficile: co-amoxiclav, cephalosporins, ciprofloxacin and clindamycin.
Expansion
| Coverage | Agents |
|---|---|
| Gram positive | Penicillin, flucloxacillin (staphylococci), vancomycin, teicoplanin, linezolid, clindamycin |
| Gram negative | Gentamicin, ciprofloxacin, ceftriaxone, piperacillin-tazobactam, meropenem |
| Anaerobes | Metronidazole, clindamycin, co-amoxiclav, piperacillin-tazobactam, carbapenems |
| Atypicals (Mycoplasma, Legionella, Chlamydia) | Macrolides, tetracyclines, quinolones |
| Pseudomonas | Piperacillin-tazobactam, ceftazidime, meropenem, ciprofloxacin, gentamicin |
| MRSA | Vancomycin, teicoplanin, linezolid, daptomycin |
Useful shortcuts:
- Flucloxacillin is the drug of choice for Staphylococcus aureus skin and soft tissue infection, because it resists staphylococcal penicillinase
- Benzylpenicillin remains first line for Streptococcus and for meningococcus
- Atypical organisms lack a cell wall, which is why beta-lactams are useless against them and cell-wall-independent agents are required
- Gentamicin has excellent Gram negative cover but poor tissue penetration, no anaerobic cover, and requires monitoring
Broad spectrum agents such as co-amoxiclav, piperacillin-tazobactam and carbapenems should be reserved, since they drive resistance and C difficile.