A 58-year-old patient on long-term atorvastatin 40 mg daily had gemfibrozil added 10 days ago for hypertriglyceridemia. The patient now reports severe diffuse muscle pain, weakness, and dark cola-colored urine. Which laboratory test is the priority for the nurse to expect?

The clinical picture — severe diffuse muscle pain, weakness, and cola-colored urine in a patient on a statin plus a fibrate — is classic for rhabdomyolysis. The priority laboratory study is creatine kinase (CK), which rises markedly (often >10× ULN, sometimes >10,000 U/L) and confirms the diagnosis, plus a basic metabolic panel to detect the most life-threatening complications: hyperkalemia (cardiac arrest risk) and acute kidney injury from myoglobin precipitation. LFTs (choice 1) may be drawn as a baseline but are not the immediate diagnostic priority. Lipid panel (choice 3) is irrelevant to the acute event. CRP/ESR (choice 4) are nonspecific markers and not the priority workup.

In-depth explanation

Statin-fibrate combination — particularly atorvastatin or simvastatin with gemfibrozil — markedly increases the risk of rhabdomyolysis through CYP-mediated drug interaction (gemfibrozil inhibits hepatic uptake and metabolism of statins via OATP1B1 and CYP2C8). Clinical triad: muscle pain (often diffuse and severe), weakness, and dark urine (myoglobinuria, often described as "tea-colored" or "cola-colored"). The acute danger is twofold: (1) hyperkalemia from rapid release of intracellular potassium from injured muscle — can cause sudden cardiac arrhythmia, and (2) acute kidney injury from myoglobin precipitation in renal tubules. Priority workup: CK (confirms rhabdo), BMP for K+ and creatinine, urinalysis for myoglobin, and ECG. Initial management: stop the offending drugs, aggressive IV crystalloid (often 200–300 mL/hr targeting urine output), monitor and treat hyperkalemia, and prepare for possible dialysis if AKI does not respond.

Clinical scenario

<p>A <strong>58-year-old patient</strong> on long-term <strong>atorvastatin 40 mg daily</strong> had <strong>gemfibrozil added 10 days ago</strong> for hypertriglyceridemia. The patient reports <strong>severe diffuse muscle pain</strong>, <strong>weakness</strong>, and <strong>dark cola-colored urine</strong>.</p>

Key concepts

• Rhabdomyolysis — Acute breakdown of skeletal muscle releasing intracellular contents (CK, myoglobin, potassium) into circulation. Causes include drug interactions (statins + fibrates), trauma, prolonged immobilization, hyperthermia, and seizures. Defining lab is CK >5–10× upper limit of normal.
• Statin-Fibrate Drug Interaction — Combining a statin (atorvastatin, simvastatin) with gemfibrozil markedly increases statin plasma levels via inhibition of OATP1B1 transporter and CYP2C8 metabolism, multiplying the risk of myopathy and rhabdomyolysis. Fenofibrate has a lower interaction risk and is generally preferred when combination therapy is needed.
• Acute Kidney Injury from Myoglobin — Released myoglobin precipitates in renal tubules, causing pigment-induced AKI. Aggressive isotonic IV fluid resuscitation aimed at urine output of 200–300 mL/hr is the cornerstone of prevention. Untreated, dialysis may be required and mortality rises sharply.