Antibiotics I
Beta-lactams, vancomycin, aminoglycosides and fluoroquinolones
Rules for every antibiotic
- Ask about allergies and what the reaction was. Most people labelled "penicillin-allergic" can actually tolerate it when tested.
- Cultures before the first dose, but never delay antibiotics in sepsis.
- Take exactly as prescribed for the full prescribed course.
- Report ≥3 watery stools in 24 h (C. diff): contact precautions, soap and water hand hygiene (alcohol gel doesn't kill spores).
- Superinfection: thrush, vaginal yeast infection.
Birth control and antibiotics Updated
Most antibiotics (including penicillins, cephalosporins and tetracyclines) do not reduce hormonal contraceptive effectiveness (CDC). The important exception is rifampin/rifabutin: use a backup method. Vomiting or severe diarrhea can still reduce pill absorption.
| Class | Examples | Key points |
|---|---|---|
| Penicillins | amoxicillin, amoxicillin-clavulanate, ampicillin, penicillin G, piperacillin-tazobactam | Rash, anaphylaxis, diarrhea. Observe after first dose. Penicillin G benzathine is IM only: never IV (can cause cardiac arrest). |
| Cephalosporins | cefazolin, cephalexin, ceftriaxone, cefepime | Cross-reaction with penicillin allergy is low (~1–2%); follow policy if the penicillin reaction was severe. Ceftriaxone: don't mix with calcium IV solutions (precipitates; especially newborns). Cefepime: confusion and seizures in kidney impairment. |
| Carbapenems | meropenem, imipenem, ertapenem | Broad spectrum. Seizure risk (imipenem). Lowers valproic acid levels: avoid together. |
| Vancomycin | IV; oral (for C. diff only) | MRSA, serious gram-positive infections. Infuse over ≥60 min (longer for bigger doses). Vancomycin infusion reaction (formerly "red man syndrome"): flushing, itching, rash of face/neck/upper body, low BP → slow or pause the infusion; antihistamine. Not a true allergy. Nephrotoxicity (worse with piperacillin-tazobactam), ototoxicity. Oral vancomycin isn't absorbed: it treats C. diff in the gut. |
| Aminoglycosides | gentamicin, tobramycin, amikacin; neomycin (oral) | Nephrotoxicity (creatinine, urine output) and ototoxicity (tinnitus, hearing loss, vertigo: may be permanent). Peak and trough levels. Can worsen myasthenia gravis. Neomycin isn't absorbed (bowel prep). |
| Fluoroquinolones (-floxacin) | ciprofloxacin, levofloxacin, moxifloxacin | Boxed warnings: tendon rupture (age >60, steroids, transplant), peripheral neuropathy, confusion and other CNS effects, worsening myasthenia gravis. Also aortic aneurysm, blood sugar swings, QT prolongation, photosensitivity. Separate from antacids, calcium, iron, zinc (2 h before or 6 h after). Avoid for simple UTI, sinusitis or bronchitis when other options exist. |
Vancomycin monitoring Updated
For serious MRSA infections, current guidelines (2020) recommend dosing by AUC (area under the curve) 400–600, not trough levels alone. If your facility uses troughs, draw the trough just before the next dose.
Priority
Anaphylaxis (hives, wheeze, throat tightness, low BP): stop the drug, call for help, IM epinephrine (anterolateral thigh) first, then airway, oxygen, fluids, antihistamine, steroid.