Associated with adverse drug interactions - rhabdomyolysis

Red flags

CK markedly elevated (>1000, especially >5x ULN) with myalgia/weakness
Dark/tea-coloured urine, AKI
Hyperkalaemia, hyperphosphataemia, hypocalcaemia on biochemistry
Compartment syndrome signs in an affected limb
Concurrent hyperthermia (sympathomimetic toxicity, NMS, serotonin syndrome, malignant hyperthermia)

Statin-related

Statins, especially combined with fibrates, macrolides, azole antifungals (CYP3A4 interaction raising statin levels), or in renal/hepatic impairment

Toxidrome-associated

Sympathomimetic toxicity (stimulants, cocaine) - agitation, hyperthermia, muscle overactivity
Serotonin syndrome, NMS - rigidity/clonus driving muscle breakdown
Prolonged immobilisation (sedative overdose, coma) -> pressure-related muscle injury

Other drug causes

Antipsychotics (via NMS), colchicine toxicity, diuretics (severe hypokalaemia-associated myopathy), corticosteroid myopathy (chronic, less acute)

Non-drug contributors that compound drug causes

Statin dose and any newly added interacting drug (macrolide, azole, fibrate, grapefruit juice)
Stimulant/sympathomimetic drug use, prolonged immobilisation history (found down)
Myalgia, weakness, dark urine

Muscle tenderness/swelling, weakness
Signs of compartment syndrome (pain out of proportion, pallor, reduced pulses - late)
Temperature, tone/reflexes (toxidrome clues)

CK (peaks 24-72h), UEC (AKI), potassium, phosphate, calcium
Urinalysis - myoglobinuria (blood on dipstick without red cells on microscopy)
ECG for hyperkalaemia

Stop the causative drug (statin, interacting agent, or causative toxidrome-driving drug)
Aggressive IV crystalloid to maintain urine output and prevent AKI - mainstay of treatment
Correct hyperkalaemia per standard protocol
Urinary alkalinisation is not routinely recommended (limited evidence of added benefit over adequate fluid resuscitation)
Treat the underlying toxidrome (cooling, benzodiazepines for sympathomimetic/serotonergic causes; dantrolene for NMS)
Fasciotomy if compartment syndrome develops
Renal replacement therapy if severe AKI/hyperkalaemia refractory to medical management

Statin-fibrate or statin-macrolide/azole combinations are a preventable, commonly missed cause - always check for interacting drugs before attributing myalgia to the statin alone
Myoglobinuria gives a false-positive "blood" on urine dipstick without red cells on microscopy - easily misread as haematuria
CK peaks 24-72h after the insult - an early normal CK does not exclude evolving rhabdomyolysis

"Fluid resuscitation is the actual treatment here, not urinary alkalinisation - and I check for the interacting drug that turned a routine statin dose into this."

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