Diagnostic assistance provided by a pharmacist for the syndrome of inappropriate antidiuretic hormone secretion caused by carboplatin plus nab-paclitaxel chemotherapy in an elderly patient with lung cancer: a case report.

Abstract

Background: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common cause of hyponatremia. Although SIADH induced by carboplatin (CBDCA) plus nab-paclitaxel (nab-PTX) has been reported, there is limited evidence for SIADH being suspected by pharmacists during chemotherapy in elderly patients and contributing to early intervention through diagnostic support for physicians.

Case presentation: An 84-year-old man was diagnosed with stage 3A squamous cell carcinoma of the right lung. Genetic mutations and expression of programmed cell death protein ligand 1 were < 1%. The patient was started on CBDCA area under the curve of 5 mg/mL·min on day 1 plus nab-PTX 70 mg/m² on days 1, 8 and 15 once every 3 weeks. The serum sodium level immediately before the start of chemotherapy was 141 mmol/L. On day 8, it decreased to 119 mmol/L, and the physician started oral sodium chloride (3 g/day) administration. Because the pharmacist suspected that this hyponatremia may be due to chemotherapy-induced SIADH, the pharmacist suggested an examination of plasma and urine osmolality and urinary sodium levels to the physician. The serum creatinine level, plasma osmolality, urine osmolality, and urinary sodium level were 1.06 mg/dL, 253 mOsm/kg, 355 mOsm/kg, and 59 mEq/L, respectively; furthermore, the patient was not dehydrated. Based on the findings, a diagnosis of chemotherapy-induced SIADH was made. The physician and pharmacist conferred and decided to continue chemotherapy with frequent monitoring of serum sodium levels. Subsequently, the serum sodium level improved to 139 mmol/L on day 20 without additional treatment, and oral administration of sodium chloride was discontinued on day 22. The patient completed five cycles of chemotherapy. Computed tomography revealed a partial response throughout chemotherapy. Furthermore, sodium levels did not decrease again throughout chemotherapy. The Naranjo Adverse Drug Reaction Probability Scale score was 5 points, which is categorized as "probable."

Conclusions: We encountered a case in which the patient developed chemotherapy-induced SIADH but was able to continue chemotherapy because of early pharmacist intervention. In elderly patients without genetic mutations and few treatment options, even if they develop SIADH, chemotherapy should be continued with monitoring of serum sodium levels by physicians and pharmacists.