Samsca Dosage/Direction for Use

Usual Dosage in Adults: Hyponatremia: Patients should be in a hospital for initiation and re-initiation of therapy to evaluate the therapeutic response and because too rapid correction of hyponatremia can cause osmotic demyelination resulting in dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma and death.
The usual starting dose for Samsca is 15 mg administered once daily without regard to meals. Increase the dose to 30 mg once daily, after at least 24 hrs, to a maximum of 60 mg once daily, as needed to achieve the desired level of serum sodium. During initiation and titration, frequently monitor for changes in serum electrolytes and volume. Avoid fluid restriction during the first 24 hrs of therapy. Patients receiving Samsca should be advised that they can continue ingestion of fluid in response to thirst (see Precautions).
Adjunct Treatment of Volume Overload in Heart Failure: Samsca should be used as adjunct therapy to other diuretics (loop or thiazide diuretics, aldosterone antagonists, etc).
The usual dose is 15 mg once daily but it is recommended to start from 7.5 mg/day for patients whose serum sodium is <125 mEq/L or for whom rapid volume decrease is considered inappropriate. In order to avoid nocturnal urination, it is recommended to take Samsca in the morning. Treatment with Samsca should be initiated in hospital and patients should be frequently monitored for serum sodium especially during the first day of treatment.
Drug Withdrawal: Following discontinuation from Samsca, patients should be advised to resume fluid restriction and should be monitored for changes in serum sodium and volume status.
Special Populations: There is no need to adjust dose based on age, gender, race, cardiac or hepatic function (see Pharmacology under Actions and Precautions).
Renal Impairment: There is no need to adjust the dose in patients with mild to severe renal impairment; tolvaptan has not been evaluated in patients with creatinine clearance <10 mL/min or in patients undergoing dialysis. No benefit can be expected in patients who are anuric (see Pharmacology under Actions and Contraindications).
Co-Administration with CYP3A Inhibitors, CYP3A Inducers and P-gp Inhibitors: CYP3A Inhibitors: Tolvaptan is metabolized by CYP3A and use with strong CYP3A inhibitors causes a marked (5-fold) increase in exposure (see Contraindications). The effect of moderate CYP3A inhibitors on tolvaptan exposure has not been assessed. Avoid co-administration of Samsca and moderate CYP3A inhibitors (see Precautions and Interactions).
CYP3A Inducers: Co-administration of Samsca with potent CYP3A inducers (e.g., rifampin) reduces tolvaptan plasma concentrations by 85%. Therefore, the expected clinical effects of Samsca may not be observed at the recommended dose. Patient response should be monitored and the dose adjusted accordingly (see Precautions and Interactions).
P-gp Inhibitors: Tolvaptan is a substrate of P-gp. Co-administration of Samsca with inhibitors of P-gp (e.g., cyclosporine) may necessitate a decrease in Samsca dose (see Precautions and Interactions).
Co-Administration with Vasopressin Analogs: In addition to its renal aquaretic effect, Samsca is capable of blocking vasopressin V_2-receptors involved in the release of coagulation factors (eg, von Willebrand's factor) from endothelial cells. Therefore, the effect of vasopressin analogs eg, desmopressin (DDAVP) may be attenuated in patients using such analogs to prevent or control bleeding when co-administered with Samsca.