STEPTRACKERMICROBIOLOGY + PHARMACOLOGY | DRUG TOXICITY | RAPID-FIRE REVIEW

Antimicrobial Adverse Effects & Interactions

Every signature toxicity in one table, plus the drugs to avoid in pregnancy and the interactions that come up again and again.

FOCUS ON
Group toxicities by organ: kidney (aminoglycosides, amphotericin, vancomycin, polymyxins, cidofovir, foscarnet, tenofovir DF, acyclovir crystals, β-lactam interstitial nephritis), ear (aminoglycosides, vancomycin), marrow (ganciclovir, zidovudine, chloramphenicol, flucytosine, linezolid, TMP-SMX), liver (INH, rifampin, pyrazinamide, azoles, nevirapine), heart rhythm/QT (macrolides, fluoroquinolones, azoles, bedaquiline), nerves (INH, metronidazole, linezolid, NRTIs), skin/SJS (sulfonamides, nevirapine, abacavir hypersensitivity). Pregnancy — avoid: tetracyclines, fluoroquinolones, aminoglycosides, ribavirin, griseofulvin, albendazole, efavirenz (caution); sulfonamides near term. Strong CYP inducers: rifampin, griseofulvin; inhibitors: macrolides (not azithro), azoles, ritonavir/cobicistat.
SIGNATURE TOXICITY
DRUG
MECHANISM / NOTE
PAGE
Nephrotoxicity + ototoxicity
Aminoglycosides
Worse with loop diuretics, vancomycin
11.03
Flushing during fast infusion
Vancomycin
Histamine release
11.02
Seizures
Imipenem, cefepime (renal failure), FQs, INH overdose
INH overdose → pyridoxine
11.02
Interstitial nephritis
Penicillins (nafcillin, methicillin), cephalosporins, sulfonamides, rifampin
Fever, rash, eosinophiluria
11.01
Teeth staining, photosensitivity
Tetracyclines
Ca²⁺ binding
11.03
QT prolongation
Macrolides, FQs, azoles, bedaquiline, quinine/quinidine
Torsades risk with other QT drugs
11.03
C difficile colitis
Clindamycin, FQs, cephalosporins, broad penicillins
Any antibiotic possible
10.03
Thrombocytopenia, serotonin syndrome
Linezolid
Weak MAO inhibition
11.03
Gray baby, aplastic anemia
Chloramphenicol
Neonatal glucuronidation deficit
11.03
Hyperkalemia, SJS, kernicterus
TMP-SMX
ENaC block · bilirubin displacement
11.04
Tendon rupture, aortic aneurysm
Fluoroquinolones
Elderly, steroids
11.04
Disulfiram-like reaction
Metronidazole, cefotetan, griseofulvin
Avoid alcohol
11.04
Pulmonary fibrosis
Nitrofurantoin
Long-term prophylaxis
11.04
Hemolysis in G6PD deficiency
Primaquine, dapsone, sulfonamides, nitrofurantoin, chloroquine
Oxidant stress
9.03
Peripheral neuropathy, lupus
Isoniazid
B6 depletion · slow acetylators
11.05
Orange body fluids, CYP induction
Rifampin
OCP and ART failure
11.05
Gout · optic neuritis
Pyrazinamide · ethambutol
Uric acid · red-green vision
11.05
Nephrotoxicity, hypokalemia, rigors
Amphotericin B
Ergosterol pores
11.06
Gynecomastia
Ketoconazole
Blocks steroidogenesis
11.06
Crystal nephropathy
Acyclovir (IV), indinavir, sulfadiazine
Hydrate
11.07
Myelosuppression
Ganciclovir, zidovudine, flucytosine
Check CBC
11.07
Hypocalcemia, hypomagnesemia, seizures
Foscarnet
Chelates divalent cations
11.07
Hypersensitivity (HLA-B*57:01)
Abacavir
Test before starting
11.08
Lipodystrophy, hyperglycemia
HIV protease inhibitors
CYP3A4 inhibition
11.08
Methemoglobinemia
Dapsone, primaquine
Treat with methylene blue (not in G6PD)
11.05
Cinchonism (tinnitus, headache, vertigo)
Quinine, quinidine
Also hypoglycemia, QT
9.03

Mechanism — CYP interactions

InducersRifampin, griseofulvin, efavirenz
→
↓ levels of partner drugOCP, warfarin, ART, tacrolimus fail
InhibitorsClarithromycin, erythromycin, azoles, ritonavir
→
↑ levels of partner drugStatin myopathy, tacrolimus toxicity, bleeding

Pregnancy

AVOID
REASON
SAFER CHOICE
Tetracyclines
Teeth, bone
Azithromycin, amoxicillin
Fluoroquinolones
Cartilage
Cephalosporins
Aminoglycosides
Fetal ototoxicity
—
Sulfonamides (near term)
Kernicterus
Nitrofurantoin (not at term), cephalexin
Ribavirin, griseofulvin
Teratogens
—
Chloramphenicol
Gray baby
—

How it's tested

COMMON CONFUSIONDrug-related rise in creatinine without real kidney injury (trimethoprim, cobicistat, dolutegravir block tubular secretion) vs true nephrotoxicity (aminoglycosides, amphotericin).
THE TRAPPenicillins, cephalosporins, azithromycin and nitrofurantoin (before term) are the usual safe answers in pregnancy — tetracyclines and fluoroquinolones are the usual wrong ones.
YOUR APPROACHOrgan affected → shortlist of culprit drugs → which one the patient takes → stop or adjust, check interactions.

If you see… think…

Deafness + rising creatinine → aminoglycoside
Achilles rupture → fluoroquinolone
Flushing of face and neck during a rapid infusion → vancomycin infusion reaction
Orange urine → rifampin
Red-green color loss → ethambutol
Gray baby → chloramphenicol
Hypokalemia + nephrotoxicity with fever on infusion → amphotericin B
Hemolysis in a Mediterranean man after malaria drug → primaquine (G6PD)
Rash in a patient with mono on amoxicillin → EBV-related, not allergy
Statin myopathy after clarithromycin → CYP3A4 inhibition