Statins (HMG-CoA Reductase Inhibitors): Side Effects & Contraindications

Mechanism Recap

Side Effects

1. Musculoskeletal (Most Clinically Significant)

• Asymptomatic CK elevation affects ~5% of statin users
• Myalgias are the most common cause of statin discontinuation, occurring more often with advanced age, polypharmacy, reduced renal function, and lower body mass
• Genetic variation in the SLCO1B1 gene (encoding OATP1B1 transporter) is associated with severe statin-induced myopathy and rhabdomyolysis - this can be tested pharmacogenomically
• Risk is significantly increased with concomitant use of: gemfibrozil (greatest risk among fibrates), cyclosporine, macrolide antibiotics (erythromycin, clarithromycin), azole antifungals (itraconazole, ketoconazole), HIV protease inhibitors, amiodarone, verapamil, and nefazodone
• Large amounts of grapefruit juice increase plasma levels of lovastatin, simvastatin, and atorvastatin, raising myopathy risk

• Mild-moderate: stop statin, wait for resolution, rechallenge at lower dose or switch statin
• Severe: stop statin, check CK/creatinine/urine myoglobin; admit + hydrate if CK >10x ULN with worsening creatinine or myoglobinuria
• Important: ~75-80% of patients reporting intolerance to 2+ statins can actually tolerate atorvastatin 20 mg in blinded trials ("nocebo effect" is significant)

2. Hepatotoxicity

• 1-2% of patients develop asymptomatic, reversible aminotransferase elevations (>3x normal)
• Acute hepatitis-like histologic changes and centrilobular necrosis are described in a very small number of cases
• Clinically meaningful transaminase elevations are so rare they do not differ from placebo in meta-analyses - routine LFT monitoring is no longer universally recommended
• Statin hepatotoxicity is NOT increased in patients with chronic hepatitis C, hepatic steatosis, or other underlying liver diseases; statins can generally be used safely in these patients
• Excess alcohol intake increases hepatotoxic risk
• Stop if AST/ALT persistently >3-5x ULN or if jaundice develops

3. New-Onset Diabetes

• Small but statistically significant increased incidence of type 2 diabetes, particularly in patients with pre-existing prediabetes or metabolic syndrome
• Fasting plasma glucose increases minimally in some patients
• The cardiovascular benefit of statins generally outweighs this risk - continue statin, encourage weight loss/exercise, and treat diabetes if it develops

4. Other Common Side Effects (5-10% of patients)

• Gastrointestinal: abdominal pain, diarrhea, bloating, constipation
• Malaise, fatigue, headache, rash

5. Cognitive Effects

• There is no aggregated evidence that statins negatively impact cognitive function (Washington Manual)

Drug Interactions (CYP450)

• CYP3A4 inhibitors (macrolides, azoles, cyclosporine, HIV PIs, amiodarone, verapamil, tacrolimus, nefazodone) increase plasma levels of lovastatin/simvastatin/atorvastatin
• CYP3A4 inducers (rifampin, phenytoin, barbiturates, griseofulvin, thiazolidinediones) reduce their plasma concentrations
• CYP2C9 inhibitors (ketoconazole, metronidazole, amiodarone, cimetidine) increase fluvastatin/rosuvastatin levels
• Pravastatin and rosuvastatin are preferred when using azoles, cyclosporine, or macrolides (but keep doses low)
• Simvastatin has dose-limiting interactions with amlodipine, amiodarone, dronedarone, verapamil, diltiazem, and ranolazine; can increase warfarin and digoxin levels
• Rosuvastatin may also increase warfarin levels

Contraindications

• Use with caution (not necessarily full contraindication) in: elderly patients (higher myopathy risk), patients with renal impairment, hypothyroidism (increases myopathy risk), vitamin D deficiency, primary muscle disorders, and significant alcohol use

Monitoring

• Baseline CK and liver enzymes (AST/ALT)
• Liver enzymes: baseline, 1-2 months, then every 12 months if stable (more frequently if interacting drugs are co-prescribed)
• Routine CK monitoring is not recommended unless symptoms develop
• Fasting glucose/HbA1c in at-risk patients