Vancomycin: nephrotoxicity (higher with high troughs and with piperacillin–tazobactam or other nephrotoxins), vancomycin infusion reaction (formerly "red man syndrome" — flushing, itching, rash of the face, neck, and upper body, hypotension with rapid infusion; histamine release, not a true allergy), ototoxicity (rare), neutropenia, phlebitis.

Daptomycin: myopathy and rhabdomyolysis (rising CK), eosinophilic pneumonia.

Aminoglycosides: nephrotoxicity (usually reversible), ototoxicity — cochlear (tinnitus, high-frequency hearing loss) and vestibular (vertigo, ataxia), often irreversible; neuromuscular blockade (respiratory paralysis with neuromuscular blockers or myasthenia gravis).

Tetracyclines: GI upset, esophageal ulceration (pill esophagitis), photosensitivity, tooth discoloration and enamel hypoplasia in children (tetracycline and minocycline; doxycycline much less), intracranial hypertension, vaginal candidiasis; minocycline — dizziness, skin pigmentation.

Macrolides: GI upset (erythromycin most), QT prolongation and torsades, hepatotoxicity, ototoxicity at high doses, infantile hypertrophic pyloric stenosis with erythromycin (and azithromycin) in young infants.

Clindamycin: diarrhea and C. difficile infection (boxed warning), rash, metallic taste.

Linezolid: myelosuppression (thrombocytopenia, especially beyond 2 weeks), serotonin syndrome with serotonergic drugs, peripheral and optic neuropathy (long courses), lactic acidosis, hypoglycemia in diabetes.

Fluoroquinolones (boxed warnings): tendinitis and tendon rupture (Achilles; risk higher over age 60, with corticosteroids, and after kidney, heart, or lung transplant), peripheral neuropathy (may be permanent), CNS effects (agitation, confusion, delirium, seizures, psychiatric effects), exacerbation of myasthenia gravis; also QT prolongation, dysglycemia (hypo- and hyperglycemia, especially in older adults on diabetes drugs), aortic aneurysm and dissection, photosensitivity, C. difficile.

TMP-SMX: rash (up to SJS/TEN), hyperkalemia (trimethoprim acts like amiloride), bone marrow suppression, hemolysis in G6PD deficiency, crystalluria, raised creatinine, photosensitivity, hypoglycemia.

Metronidazole: metallic taste, nausea, dark urine, headache, peripheral neuropathy and encephalopathy with long courses, disulfiram-like reaction with alcohol.

Nitrofurantoin: nausea, brown urine (harmless), acute pulmonary reactions (fever, cough, dyspnea) and chronic pulmonary fibrosis, hepatotoxicity, peripheral neuropathy, hemolysis in G6PD deficiency.

• Aminoglycosides: kidney impairment, hearing loss, myasthenia gravis; pregnancy only when indicated (fetal ototoxicity mainly with streptomycin; gentamicin is used, e.g., for intraamniotic infection, with levels); avoid with loop diuretics (ototoxicity), vancomycin, NSAIDs, contrast, amphotericin B, cisplatin (nephrotoxicity); potentiate neuromuscular blockers
• Tetracyclines: pregnancy and children under 8 for tetracycline and minocycline. Doxycycline for up to 21 days can be used at any age when indicated (e.g., tick-borne rickettsial disease, per AAP/CDC); chelation with antacids, calcium, dairy, iron, zinc, and magnesium — separate doses; avoid combining with isotretinoin (additive intracranial hypertension)
• Macrolides: QT risk factors and other QT drugs; clarithromycin and erythromycin inhibit CYP3A4 → toxicity of colchicine, simvastatin/lovastatin (rhabdomyolysis), warfarin, cyclosporine/tacrolimus, some calcium channel blockers; azithromycin has few CYP interactions
• Clindamycin: history of C. difficile colitis
• Linezolid: serotonergic drugs (SSRIs, SNRIs, MAOIs, tramadol, meperidine) and tyramine-rich foods and sympathomimetics (hypertensive reaction); uncontrolled hypertension, pheochromocytoma
• Fluoroquinolones: avoid for uncomplicated infections (acute sinusitis, bronchitis, uncomplicated cystitis) when alternatives exist (FDA 2016); myasthenia gravis; history of tendon disorders; QT risk; known aortic aneurysm; pregnancy and children (generally avoided unless no alternative); chelation with antacids, calcium, iron, zinc, sucralfate — give the fluoroquinolone 2 hours before or 6 hours after (ciprofloxacin label); raises theophylline and warfarin effects
• TMP-SMX: sulfonamide allergy, G6PD deficiency, first trimester and near term (neural tube defects; kernicterus), infants under 2 months, severe kidney or liver disease, folate deficiency; hyperkalemia with ACE inhibitors, ARBs, spironolactone; raises warfarin (bleeding), methotrexate (marrow suppression), phenytoin, and sulfonylurea (hypoglycemia) effects
• Metronidazole: alcohol (and products containing propylene glycol) during and for 72 hours after (label); disulfiram use within 2 weeks (psychosis); warfarin (raised INR); lithium; QT drugs; caution in liver disease and neurologic disorders; first-trimester use for trichomoniasis per current CDC guidance is acceptable
• Nitrofurantoin: creatinine clearance below 30 mL/min (Beers Criteria; low urine levels and more toxicity), at term (38–42 weeks), during labor, and in infants under 1 month (hemolytic anemia), G6PD deficiency; not for pyelonephritis or systemic infection
• Vancomycin: kidney impairment (adjust by levels); other nephrotoxins; loop diuretics (ototoxicity)
• Daptomycin: statins (myopathy — consider holding)

1. Allergy history and cultures before the first dose (see Principles of Antimicrobial Therapy)
2. Vancomycin
   • Infuse over at least 60 minutes (no faster than about 10 mg/min; longer for larger doses)
   • Infusion reaction: stop or slow the infusion, give an antihistamine as ordered, restart at a slower rate — not a reason to label a true allergy
   • AUC-guided dosing (target about 400–600 mg·h/L for serious MRSA infection) or troughs per protocol (historically 10–20 mcg/mL (6.9–13.8 µmol/L)); draw trough just before the fourth dose when at steady state or as the pharmacy directs
   • Creatinine and urine output at least every 1–3 days; watch for rising creatinine with piperacillin–tazobactam
3. Aminoglycosides
   • Extended-interval (once-daily) dosing is common — a single level at a set time after the dose is interpreted with a nomogram; traditional dosing uses peak (gentamicin about 5–10 mcg/mL (10.5–21 µmol/L) depending on infection; drawn 30 minutes after the end of a 30-minute infusion) and trough (gentamicin below about 1–2 mcg/mL (2.1–4.2 µmol/L); drawn just before the next dose)
   • Creatinine, BUN, urine output daily or per protocol; hydrate
   • Baseline and ongoing hearing and balance assessment: tinnitus, fullness, vertigo, unsteady gait — report at once
4. Fluoroquinolones: ask about tendon pain, numbness, tingling; blood glucose in diabetes; ECG with QT risk; confusion in older adults
5. Linezolid: weekly CBC, especially beyond 2 weeks; blood pressure; review serotonergic drugs; vision changes on long courses
6. Daptomycin: CK weekly (more often with statins or kidney impairment); report muscle pain or weakness
7. TMP-SMX: potassium (normal 3.5–5.0 mEq/L (mmol/L)) and creatinine; CBC with prolonged use; rash; fluids to prevent crystalluria
8. Macrolides: ECG with QT risk factors; drug-interaction review
9. Nitrofurantoin: kidney function; respiratory symptoms; liver tests with long-term use
10. All: INR in clients on warfarin; new diarrhea → C. difficile testing and contact precautions

• Doxycycline: take with a full glass of water and stay upright for 30 minutes (not at bedtime); separate from dairy, antacids, iron, and calcium; use sunscreen and protective clothing; not in pregnancy
• Fluoroquinolones: stop and report tendon pain or swelling, numbness, tingling, or burning, confusion, or mood changes; separate from antacids, iron, calcium, zinc; report low or high blood sugar symptoms; avoid excessive sun
• Metronidazole: no alcohol during treatment and for 72 hours after (flushing, vomiting, palpitations); metallic taste and dark urine are expected
• TMP-SMX: drink plenty of fluids; report rash, sore throat, fever, unusual bruising; avoid salt substitutes and potassium supplements unless prescribed; sun protection
• Nitrofurantoin: take with food; urine may turn brown; report cough, shortness of breath, or fever
• Linezolid: avoid large amounts of tyramine-rich foods (aged cheese, cured meats, tap beer, soy sauce); report agitation, fever, muscle twitching, or vision changes
• Clindamycin: report diarrhea immediately, even after the course ends
• Aminoglycosides/vancomycin: report ringing in the ears, hearing change, dizziness, or decreased urine
• Azithromycin/clarithromycin: report palpitations or fainting; tell every prescriber you are taking it (interactions)

• Vancomycin: MRSA; infuse over at least 60 minutes; infusion reaction ≠ allergy; AUC or trough monitoring; nephrotoxicity; oral vancomycin only for C. difficile
• Aminoglycosides: nephrotoxicity + ototoxicity (often permanent); peak and trough; avoid with loop diuretics; neuromuscular blockade
• Tetracyclines: not in pregnancy or young children (except short doxycycline courses); upright with water; photosensitivity; no dairy/antacids
• Macrolides: QT; clarithromycin/erythromycin CYP3A4 inhibitors (colchicine, statins, warfarin)
• Clindamycin → C. difficile (boxed warning)
• Linezolid → serotonin syndrome, thrombocytopenia; avoid tyramine
• Fluoroquinolones: tendon rupture, neuropathy, CNS effects, myasthenia exacerbation, QT, dysglycemia; separate from minerals
• TMP-SMX: hyperkalemia, sulfa allergy, G6PD, raises INR; avoid first trimester and near term
• Metronidazole: no alcohol during and 72 hours after; metallic taste; raises INR
• Nitrofurantoin: cystitis only; avoid CrCl below 30 and at term
• Daptomycin: CK monitoring; not for pneumonia