11.2 Drug-Induced Disease and Drug Use Disorders

11.2 Drug-Induced Disease and Drug Use Disorders

Quick Answer: Drug-induced diseases have signature culprit drugs by organ system — DILI patterns (Hy's law), amiodarone pulmonary toxicity, AIN from penicillins/PPIs/NSAIDs, SJS/TEN from allopurinol, sulfonamides, and anticonvulsants, fluoroquinolone tendinopathy. Drug use disorders (DSM-5) include opioid, sedative/hypnotic, stimulant, cannabis, and tobacco use disorders, treated with MAT (buprenorphine, methadone, naltrexone), counseling, harm reduction (naloxone, syringe exchange, fentanyl testing), and structured controls (REMS, PDMPs).

Drug-Induced Diseases by Organ System

Pulmonary Toxicity

Amiodarone pulmonary toxicity (amiodarone-induced pneumonitis or pulmonary fibrosis) is a life-threatening complication of a drug with iodine moieties and a long half-life (up to 100 days). Risk correlates with cumulative dose and duration (>6 months, >400 mg/day). Presentation includes progressive dyspnea, cough, diffuse interstitial infiltrates on imaging. Management: discontinue amiodarone, consider corticosteroids. Nitrofurantoin pneumonitis (acute or chronic) presents with lung infiltrates and eosinophilia; resolves with discontinuation. Methotrexate pneumonitis presents with dry cough, dyspnea, and ground-glass opacities; treat by stopping MTX and giving corticosteroids. Bleomycin causes dose-dependent pulmonary fibrosis; risk increases above 450 units cumulative and is worsened by renal impairment and oxygen exposure.

Drug-Induced Liver Injury (DILI)

DILI is classified by the R ratio (ALT/ALP ratio normalized to ULN): hepatocellular (R ≥5), cholestatic (R ≤2), or mixed (R >2 and <5). Common culprits and patterns:

Hy's law is the most important predictor of severe DILI: ALT or AST ≥3× ULN with bilirubin ≥2× ULN (without ALP elevation indicating obstruction or other cause) and no alternative explanation. A positive Hy's law case predicts ≥10% mortality and the suspected drug must be discontinued immediately.

Renal Toxicity

Acute interstitial nephritis (AIN) is a hypersensitivity reaction presenting with fever, rash, eosinophilia, and acute kidney injury typically 7–10 days after exposure (shorter on re-exposure). Common culprits: penicillins (especially methicillin), proton pump inhibitors (PPIs), NSAIDs, cephalosporins, sulfonamides, rifampin, ciprofloxacin, allopurinol, mesalamine, 5-HMs. Treatment: discontinue the offending agent; corticosteroids for severe or persistent AKI.

Crystal nephropathy occurs when poorly soluble drugs or metabolites precipitate in renal tubules: acyclovir (especially with rapid IV push or inadequate hydration), indinavir (HIV protease inhibitor), sulfonamides (older agents), methotrexate (high dose). Hemolytic-uremic syndrome (HUS) is associated with quinine (the classic "quinine HUS") and some chemotherapeutics.

Other renal injury patterns: aminoglycoside proximal tubular toxicity (nonoliguric AKI), vancomycin (interstitial nephritis and AKI), lithium (chronic interstitial nephritis, nephrogenic DI), cyclosporine/tacrolimus (afferent arteriolar vasoconstriction), NSAIDs (afferent arteriolar vasoconstriction → AKI; can trigger AKI in volume-depleted patients).

Hematologic Toxicity

Drug-induced thrombocytopenia — heparin (HIT, an IgG antibody against PF4-heparin complex; causes paradoxical thrombosis, platelet drop ≥50% 5–14 days after exposure; discontinue all heparin and switch to argatroban or bivalirudin), quinine (quinine-induced thrombocytopenia), GP IIb/IIIa inhibitors (abciximab, eptifibatide, tirofiban).

Agranulocytosis — clozapine (requires REMS ANC monitoring: weekly for 6 months, then biweekly, then monthly), antithyroid drugs (methimazole, propylthiouracil — warn about sore throat and fever; check CBC), colchicine (chronic use in renal impairment), sulfasalazine, chemotherapy.

Hemolysis in G6PD deficiency — triggers include sulfonamides, primaquine, dapsone, nitrofurantoin, rasburicase, methylene blue, fava beans. Screen G6PD before prescribing high-risk drugs in at-risk populations (African, Mediterranean, Southeast Asian ancestry).

Endocrine Toxicity

Drug-induced diabetes: glucocorticoids (counter-regulatory), atypical antipsychotics (especially olanzapine and clozapine, with weight gain and insulin resistance), thiazide diuretics (mild hyperglycemia), beta blockers (mask hypoglycemia symptoms). SIADH with hyponatremia: SSRIs (especially in elderly females), carbamazepine, oxcarbazepine, vincristine, cyclophosphamide, thioridazine, chlorpropamide. Management: fluid restriction, hypertonic saline for severe symptomatic hyponatremia, demeclocycline or vaptans (rarely).

Dermatologic Toxicity

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are severe mucocutaneous reactions with skin detachment (SJS <10% BSA, TEN >30% BSA, SJS-TEN overlap 10–30%). Classic culprits: allopurinol, sulfonamides (especially TMP-SMX), anticonvulsants (carbamazepine, lamotrigine, phenytoin), NSAIDs (especially oxicams), nevirapine. HLA-B*1502 testing is recommended in patients of Asian ancestry before carbamazepine (covered in 11.4). Management: stop the offending drug, supportive care in a burn unit.

Drug reaction with eosinophilia and systemic symptoms (DRESS) — delayed (2–8 weeks), rash, fever, lymphadenopathy, eosinophilia, hepatitis, and visceral involvement. Culprits: aromatic anticonvulsants (phenytoin, carbamazepine, phenobarbital), allopurinol, sulfonamides, dapsone, minocycline, vancomycin. Treatment: stop the drug, systemic corticosteroids.

Acute generalized exanthematous pustulosis (AGEP) — rapid onset (<4 days) of sterile nonfollicular pustules on an erythematous base, fever, leukocytosis. Culprits: beta-lactams (especially aminopenicillins), macrolides, diltiazem, terbinafine. Self-limited after drug discontinuation.

Musculoskeletal Toxicity

Fluoroquinolones carry an FDA warning for tendinopathy and tendon rupture (Achilles most common), muscle weakness and exacerbation of myasthenia gravis, CNS effects, and QT prolongation. Risk increases with corticosteroid co-administration and age >60. Glucocorticoids and chronic PPI use (≥1 year) increase osteoporosis and fracture risk; calcium, vitamin D, and bisphosphonate prophylaxis may be warranted. Statins cause myalgia, myositis, and rare rhabdomyolysis (higher with high-dose statins, gemfibrozil co-administration, and certain CYP interactions).

Drug Use Disorders

DSM-5 Framework

DSM-5 unifies substance use disorders on a single spectrum from mild (2–3 criteria), moderate (4–5), to severe (6+) over a 12-month period. The 11 criteria include hazardous use, social/interpersonal problems, neglect of major roles, tolerance, withdrawal, larger/longer use than intended, repeated attempts to cut down, much time spent using, physical/psychological problems caused by use, activities given up, and craving. Tolerance and withdrawal alone do not define a disorder for patients on prescribed medications.

Opioid Use Disorder (OUD)

Medications for Addiction Treatment (MAT) — formerly known as medication-assisted treatment — combine pharmacotherapy with counseling:

• Buprenorphine (partial μ agonist, ceiling on respiratory depression): office-based via DEE X-waiver (post-MAT Act, no separate waiver required but training recommended); formulations include sublingual, subdermal implant, monthly Sublocade injection.
• Methadone (full μ agonist): only via federally regulated Opioid Treatment Programs (OTPs) for OUD; useful for severe dependence and chronic pain with OUD.
• Naltrexone (μ antagonist): only after 7–10 days opioid-free to avoid precipitated withdrawal; monthly Vivitrol injection.
• Naloxone (antagonist for overdose reversal): intranasal or IM; co-prescribed with opioids for overdose prevention; standing orders in many states.

Sedative/Hypnotic and Anxiolytic Use Disorder

Benzodiazepines carry tolerance, dependence, and withdrawal risks. Withdrawal can be life-threatening (seizures, delirium). Management: long taper (10% per week or slower), switch to a long-acting agent (diazepam, clonazepam) for smoother taper, phenobarbital or low-dose buprenorphine protocols in supervised settings. Avoid combining benzodiazepines with opioids (additive respiratory depression — boxed warning).

Stimulant Use Disorder

Stimulant use disorder (cocaine, methamphetamine, prescription amphetamines) has no FDA-approved pharmacotherapy. Treatment is behavioral — contingency management (strongest evidence), CBT, motivational interviewing, and Matrix Model for methamphetamine. Treat comorbid conditions (depression, ADHD) appropriately.

Cannabis Use Disorder

Cannabis use disorder is increasingly recognized with legalization. Withdrawal includes irritability, anxiety, sleep disturbance, and appetite loss. No FDA-approved pharmacotherapy; CBT and motivational enhancement therapy are first-line. Synthetic cannabinoids (K2, Spice) carry greater toxicity.

Tobacco Use Disorder

Three first-line FDA-approved pharmacotherapies:

• Nicotine Replacement Therapy (NRT): patches (long-acting baseline) + short-acting (gum, lozenge, inhaler, nasal spray) for breakthrough cravings; combination NRT is more effective than monotherapy.
• Varenicline: α4β2 nicotinic receptor partial agonist — generally most effective monotherapy; reduce dose with renal impairment; neuropsychiatric warnings softened by EAGLES trial data but still monitored.
• Bupropion SR: norepinephrine-dopamine reuptake inhibitor; avoid in eating disorders, seizure disorders, and with MAOIs; start 1–2 weeks before quit date.

Second-line: clonidine, nortriptyline. Combine pharmacotherapy with behavioral counseling (5 A's: Ask, Advise, Assess, Assist, Arrange).

Harm Reduction and Structural Controls

Harm reduction meets patients where they are: syringe exchange programs reduce HIV/HCV transmission and link to treatment; supervised consumption sites reduce overdose mortality; fentanyl test strips and xylazine awareness inform risk; naloxone distribution (standing orders, pharmacy access, co-prescribing with opioids) reverses overdose. REMS programs — ER/LA opioid REMS (prescriber education), TIRF REMS (immediate-release fentanyl restricted to opioid-tolerant patients), transmucosal buprenorphine REMS (now merged with broader MAT training). Prescription Drug Monitoring Programs (PDMPs) are state-run databases tracking controlled substance prescriptions; pharmacists query them to identify multiple prescribers, early refills, and drug combinations suggestive of misuse.

Misuse, Abuse, Diversion, and Pseudoaddiction

Misuse = use for a medical purpose but in a manner other than prescribed. Abuse = use for non-medical purposes or recreational effects. Diversion = transfer of a controlled substance from the lawful distribution chain to an unlawful one (doctor shopping, forgery, theft, internet pharmacies). Pseudoaddiction describes behavior that mimics addiction (demanding higher doses, clock-watching) but is driven by inadequately treated pain; the behavior resolves when pain is adequately managed — a key concept to distinguish from true opioid use disorder.