The FDA has approved Samsca tablets (tolvaptan) to treat hyponatremia, an abnormally low concentration of sodium in the blood. “With the approval of Samsca, physicians will have an additional tool to treat hyponatremia,” said Norman Stockbridge, M.D., director of the Division of Cardiovascular and Renal Products in the FDA’s Center for Drug Evaluation and Research. Samsca is approved to treat hyponatremia associated with congestive heart failure, liver cirrhosis, and the syndrome of inappropriate antidiuretic hormone secretion. When sodium levels drop in the fluid outside of cells throughout the body, water moves into cells to balance the sodium levels and causes the cells to swell. Swelling of the brain cells is thought to cause many of the symptoms of hyponatremia. Those symptoms may include fatigue, weakness, headache, nausea, confusion or decreased consciousness, and convulsions. Severe hyponatremia, which has not been studied with Samsca, can lead to coma and death. Samsca helps raise sodium levels in the blood by removing extra body water in the urine. Patients using the drug in clinical trials had a greater degree of increase in sodium levels in the blood compared with patients taking a pill containing no active drug (placebo). Samsca is being approved with a boxed warning to alert health care professionals and patients that the drug should be started only in a hospital where blood sodium can be monitored closely. Too rapid a rise in sodium can cause a serious condition called osmotic demyelination syndrome (ODS). ODS can lead to coma or death and can also cause symptoms such as trouble speaking, trouble swallowing, drowsiness, confusion, mood changes, seizures and trouble controlling body movement with muscle weakness in the arms and legs. Although no cases of ODS were seen in clinical trials of Samsca, ODS is a known risk and it is essential that physicians be aware of it and avoid rapid rises in sodium. Additionally, the FDA is requiring a Risk Evaluation and Mitigation Strategy that requires a patient Medication Guide be given out when the drug is dispensed. The Medication Guide will provide information about the drug’s benefits and risks. The most common adverse reactions with use of Samsca reported by patients in clinical trials include thirst, dry mouth, weakness, constipation, making large amounts of urine, urinating often, and increased blood sugar levels. Samsca is marketed by Otsuka Pharmaceuticals Co. Ltd., Tokyo, Japan.
