STEPTRACKERPHARMACOLOGY | ADVERSE DRUG REACTIONS | HIGH-YIELD REVIEW

Drug Reactions by Organ

Exam questions often start from the injury and ask for the culprit — this page sorts the classic drug reactions by the organ they damage.

FOCUS ON
Heart: dilated cardiomyopathy (anthracyclines, trastuzumab), torsades (IA, III, macrolides, fluoroquinolones, antipsychotics, ondansetron, methadone), coronary vasospasm (cocaine, triptans, 5-FU). Lung: fibrosis (amiodarone, bleomycin, busulfan, methotrexate, nitrofurantoin), cough (ACEi), bronchospasm (β-blockers, aspirin). Liver: hepatitis (isoniazid, rifampin, pyrazinamide, valproate, ketoconazole, statins), necrosis (acetaminophen, halothane), cholestasis (OCPs, anabolic steroids, amox-clav, erythromycin), steatosis (valproate, amiodarone, methotrexate). Kidney: ATN (aminoglycosides, amphotericin, cisplatin, contrast), AIN (penicillins, NSAIDs, PPIs, diuretics, rifampin), crystals (acyclovir, methotrexate, indinavir, sulfonamides). Blood: agranulocytosis (clozapine, carbamazepine, PTU/methimazole, dapsone, TMP-SMX), aplastic anemia (chloramphenicol, felbamate), hemolysis in G6PD, immune hemolysis (penicillin, methyldopa, cephalosporins), megaloblastic (MTX, phenytoin, TMP). Skin: SJS/TEN (sulfa, anticonvulsants, allopurinol, NSAIDs, nevirapine), photosensitivity (tetracyclines, amiodarone, sulfonamides, thiazides), DRESS.
ORGAN · REACTION
CULPRITS
MECHANISM / CLUE
NOTES
Torsades / long QT
Class IA/III antiarrhythmics, macrolides, fluoroquinolones, haloperidol, ziprasidone, ondansetron, methadone, TCAs, azoles
hERG K⁺ channel block
Worse with ↓ K⁺, ↓ Mg²⁺ · IV magnesium
Cardiomyopathy
Doxorubicin (cumulative), trastuzumab (reversible), alcohol, cocaine
Free radicals · HER2 signaling
Echo monitoring
Pulmonary fibrosis
Amiodarone, bleomycin, busulfan, methotrexate, nitrofurantoin, carmustine
Restrictive pattern, ↓ DLCO
Stop drug, steroids
Hepatocellular injury
Acetaminophen, isoniazid, valproate, halothane, statins, ketoconazole, nevirapine
↑ ALT/AST
Check LFTs, stop drug
Cholestatic injury
Amoxicillin-clavulanate, OCPs, anabolic steroids, erythromycin, chlorpromazine
↑ ALP, bilirubin, pruritus
—
Acute tubular necrosis
Aminoglycosides, amphotericin B, cisplatin, IV contrast, polymyxins, cidofovir
Muddy brown casts
Hydrate
Acute interstitial nephritis
β-lactams (nafcillin), NSAIDs, PPIs, diuretics, rifampin, sulfonamides, allopurinol
Fever, rash, eosinophiluria, WBC casts
Stop drug ± steroids
Agranulocytosis
Clozapine, carbamazepine, PTU, methimazole, dapsone, deferiprone, TMP-SMX, ticlopidine
Fever, sore throat, mouth ulcers
Stop drug, check ANC
Hemolysis (G6PD)
Primaquine, dapsone, sulfonamides, nitrofurantoin, rasburicase, methylene blue, fava beans
Heinz bodies, bite cells
Test G6PD before primaquine/rasburicase
Drug-induced lupus
Hydralazine, procainamide, isoniazid, minocycline, TNF inhibitors
Anti-histone antibodies; spares kidneys and CNS
Resolves after stopping
SJS/TEN · DRESS
Sulfonamides, carbamazepine, phenytoin, lamotrigine, allopurinol, nevirapine, abacavir (HSR)
Mucosal sloughing · fever, eosinophilia, organ involvement
HLA testing for some (B*15:02, B*58:01)
Photosensitivity
Tetracyclines, amiodarone, sulfonamides, thiazides, fluoroquinolones, voriconazole
Exaggerated sunburn
Sun protection
Gingival hyperplasia · hirsutism
Phenytoin, cyclosporine, nifedipine/verapamil · minoxidil, cyclosporine
—
Oral hygiene
Ototoxicity · nephrotoxicity overlap
Aminoglycosides, vancomycin, cisplatin, loop diuretics
—
Avoid combining

Mechanism — types of adverse reaction

Type A — augmentedDose-related, predictable (bleeding on warfarin)
Type B — bizarreIdiosyncratic or immune (SJS, agranulocytosis)
Hypersensitivity I–IVAnaphylaxis to DRESS

Endocrine drug effects

EFFECT
CULPRITS
MECHANISM
Gynecomastia
Spironolactone, ketoconazole, cimetidine, digoxin, finasteride
Antiandrogen / ↑ estrogen
SIADH
Carbamazepine, SSRIs, cyclophosphamide, vincristine
↑ ADH effect
Nephrogenic DI
Lithium, demeclocycline
↓ ADH response
Hyperglycemia
Steroids, thiazides, tacrolimus, atypicals
Various

How it's tested

COMMON CONFUSIONDrug-induced lupus has anti-histone antibodies and rarely involves kidneys or CNS; anti-dsDNA suggests true SLE.
THE TRAPA new rash with fever and eosinophilia weeks after starting allopurinol or an anticonvulsant is DRESS — check liver and kidneys, stop the drug.
YOUR APPROACHOrgan injured → list of usual culprits → which one the patient takes → timing → stop and treat.

If you see… think…

Rash, fever, eosinophiluria, rising creatinine after antibiotic → acute interstitial nephritis
Restrictive lung disease in a patient on antiarrhythmic → amiodarone
Anti-histone antibodies, arthralgia on antihypertensive → hydralazine-induced lupus
Cholestatic jaundice after amoxicillin-clavulanate → drug-induced cholestasis
Fever, sore throat on antipsychotic → clozapine agranulocytosis
Hyponatremia on anticonvulsant → carbamazepine SIADH
Polyuria on mood stabilizer → lithium nephrogenic DI
Gynecomastia on heart failure regimen → spironolactone (or digoxin)
Sunburn on minimal exposure, tick-bite therapy → doxycycline photosensitivity
Torsades after adding azithromycin to methadone → additive QT prolongation