The role of tolvaptan in managing hyponatremia in small cell lung cancer patients with SIADH: a retrospective study of 23 cases

BACKGROUND: Existing studies have shed light on the treatment of small cell lung cancer (SCLC), but data on tolvaptan for the treatment of hyponatremia in SCLC patients remain scarce. Furthermore, the most appropriate initial dose has not been identified. This study aimed to assess the effectiveness, safety, and survival rate associated with tolvaptan in regard to controlling hyponatremia in SCLC patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and to explore the appropriate initial dose. METHODS: A total of 23 SCLC patients with SIADH treated with tolvaptan were retrospectively reviewed between 2011 and 2019, and the efficacy and safety of tolvaptan were evaluated and compared between a 3.75 mg dose and doses higher than 3.75 mg. Then, the Kaplan-Meier method was used to calculate overall survival (OS) and draw survival curves. RESULTS: In our center, patients had a mean age of 61.7±8.2 years. The mean plasma sodium level after hypertonic saline treatment was (120.7±7.5) mmol/L. The doses of tolvaptan were distributed as follows: 3.75 mg (10 patients), 5 mg (5 patients), 7.5 mg (4 patients), and 15 mg (4 patients). After 3 days of tolvaptan treatment, the mean plasma sodium level was (136.0±4.1) mmol/L, which was significantly higher than the plasma sodium level on admission and before tolvaptan treatment (P<0.05). The mean time for tolvaptan to correct the plasma sodium level was (3.7±5.8) days, and no significant difference was found between the 3.75 mg group and the above 3.75 mg group (P>0.05). Adverse events were observed in 1 patient who presented with severe lethargy and confusion. The median OS was 14.1 months. CONCLUSIONS: In summary, no significant difference was found between the 3.75 mg group and the above 3.75 mg group. Less than 15 mg of tolvaptan is enough to stabilize sodium levels for most patients. There is a risk of overcorrection of plasma sodium when using 15 mg of tolvaptan. Tolvaptan can quickly improve performance status and may bring survival benefits to patients. The effect of tolvaptan in patients with SCLC and SIADH should be confirmed.