Comment on: Low-Dose Quetiapine-Induced Severe Rhabdomyolysis

Dear Editor

There are only few severe rhabdomyolysis reports following quetiapine overdose and therapeutic dosage.^1–4 Here, we report a case of developing rhabdomyolysis after 6 months of quetiapine therapy. To our knowledge, this is the first case to describe rhabdomyolysis in a quetiapine-treated patient with chronic kidney disease taking therapeutic dosage.

A 54-year-old man was admitted to the hospital with nausea, vomiting, myalgias, weakness of both hands and lower limb that caused a reduction in everyday activity for 10 days. He had a known medical history of chronic renal disease, coronary artery disease, hypertension, cerebrovascular disease, anxiety, and bipolar depression. He was treated with 20 mg/day of escitalopram supplementary to quetiapine 25 mg/day because of anxiety and bipolar depression 6 months ago. Moreover, medications included metoprolol 50 mg/day, olmesartan 10 mg/day, and acetylsalicylic acid 100 mg/day. Both his physical examination and ECG (QTc interval) were normal. The patient's laboratory findings were as follows: blood urea nitrogen 19.6 mmol/L, creatinine 264 µmol/L, creatinine phosphokinase (CPK) 3865 U/L (normal 0–170), aspartate aminotransferase (AST) 162 U/L, alanine aminotransferase (ALT) 75 U/L, and myoglobin 3157 ng/mL (normal 0–38.5); other laboratory values were within normal ranges. Urine dipstick chemical analysis suggested moderate blood presence but there were no erythrocytes identified by microscopic examination, suggesting myoglobulinuria. Serum quetiapine tests could not be performed because of technical difficulties.

The patient was diagnosed with rhabdomyolysis based on his clinical presentation and laboratory values. After exception of other causes of rhabdomyolysis, quetiapine was discontinued. He was given extensive hydration including intravenous normal saline with bicarbonate. On the fourth admission day, CPK, AST, and ALT levels had dropped to 1272, 128, 68 U/L, respectively. Serum myoglobin was decreased to 566 ng/mL and serum creatinine decreased to 202 µmol/L. CPK, AST, ALT, and myoglobin were returned to normal levels after ten days.

Our patient, who had no evidence of seizure or hints for intoxication, had depressive episodes for years and took escitalopram before. CPK level rapidly turned normal after quetiapine discontinued. Therefore, this patient was considered as rhabdomyolysis due to quetiapine treatment.

The new generation antipsychotics (NGAs) are frequently prescribed as first-line drugs in the treatment of psychotic and mood disorders. CPK elevation has been observed during treatment with NGAs such as clozapine, loxapine, or olanzapine.⁵ However, only few cases about rhabdomyolysis associated with quetiapine have been reported so far.^1–4 We described the first case of quetiapine-induced rhabdomyolysis in a patient with chronic renal disease.

Quetiapine is primarily metabolized by sulfoxidation and oxidation with the cytochrome P450 (CYP) 3A4 isoenzyme and the 7-hydroxylated and the N-dealkylated metabolites are pharmacologically active.⁶ Escitalopram is metabolized by the CYP isoenzymes CYP2C19, CYP2D6, and CYP3A4. The combination of quetiapine with escitalopram may inhibit the elimination of quetiapine and consequently may increase drug level.

One possible pathophysiological hypothesis explains CPK elevation during antipsychotic treatment as the result of a dysregulated sympathetic nervous system. According to this hypothesis, the inhibition of the sympathetic nervous system by dopaminergic neurons is suppressed by antipsychotic agents, and overdoses of catecholamines have been shown to lead to muscle cell necrosis.³ Moreover, our patient might have had a tendency to rhabdomyolysis because of having chronic kidney disease.

In conclusion, NGAs are replacing traditional antipsychotics and are widely prescribed by clinicians. If there is a patient complaining about muscle pain during therapy with quetiapine, rhabdomyolysis should be suspected. In this situation, we suggest to have monitored closely muscle enzymes and renal functions, especially in patients with chronic kidney disease, while discontinuing quetiapine.

Mevlut Ceri

Department of Nephrology, Ankara Education and Research Hospital, Ankara, Turkey. E-mail: [email protected]

Selman Unverdi

Department of Nephrology, Ankara Education and Research Hospital, Ankara, Turkey. E-mail: [email protected]

Mustafa Altay

Department of Endocrinology, Gazi University, Faculty of Medicine, Ankara, Turkey. E-mail: [email protected]

Murat Duranay

Department of Nephrology, Ankara Education and Research Hospital, Ankara, Turkey. E-mail: [email protected]