SAMSCA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SAMSCA (SAMSCA).
Selective vasopressin V2 receptor antagonist; increases free water excretion, resulting in aquaresis and increased serum sodium concentration.
| Metabolism | Primarily metabolized by CYP3A4; minor metabolism via CYP2C19 and CYP2C9. |
| Excretion | Primarily metabolized by CYP3A4; <1% excreted unchanged in urine. 80% of dose excreted in feces, 20% in urine as metabolites. |
| Half-life | Terminal elimination half-life: 8-12 hours in healthy subjects; prolonged in hepatic impairment (up to 20 hours) and heart failure (up to 20 hours). |
| Protein binding | 97% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Approximately 2 L/kg; indicates extensive extravascular distribution. |
| Bioavailability | Oral bioavailability: 42% (range 30-60%) due to first-pass metabolism. |
| Onset of Action | Oral: 2-4 hours for increase in urine output; maximal effect by 4-8 hours. |
| Duration of Action | Duration of aquaresis: 6-8 hours after single dose; clinical effect persists up to 24 hours. Not for long-term use due to risk of liver injury. |
15 mg orally once daily, increased to 30 mg once daily after 24 hours as needed, maximum 60 mg once daily.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for GFR ≥10 mL/min; not recommended if GFR <10 mL/min or anuria. |
| Liver impairment | Child-Pugh Class A: 15 mg once daily; Class B: 15 mg once daily; Class C: not recommended (no data). |
| Pediatric use | Not approved for use in pediatric patients due to lack of safety and efficacy data. |
| Geriatric use | No specific dose adjustment; use with caution due to age-related renal impairment and increased risk of hypernatremia. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SAMSCA (SAMSCA).
| Breastfeeding | Not recommended during breastfeeding. No data on tolvaptan excretion in human milk. However, tolvaptan is highly protein bound (99%) and has a large volume of distribution, suggesting minimal excretion into breast milk. M/P ratio is unknown. Risk of adverse effects in nursing infant (e.g., electrolyte disturbances, hypernatremia) cannot be excluded. |
| Teratogenic Risk | Pregnancy Category C. In animal studies, tolvaptan caused teratogenic effects (reduced fetal body weight, delayed ossification) at clinically relevant doses. There are no adequate and well-controlled studies in pregnant women. Potential fetal risks include hyponatremia, hypovolemia, and neurological effects due to osmotic changes. Use only if potential benefit justifies risk. |
■ FDA Black Box Warning
Initiation and re-initiation of therapy should be in a hospital setting where serum sodium can be monitored closely. Too rapid correction of hyponatremia (exceeding 12 mEq/L per 24 hours) can cause osmotic demyelination syndrome, which may result in dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma, and death.
| Serious Effects |
["Hypersensitivity to tolvaptan or any component of the formulation","Anuria or inability to sense thirst","Hypovolemic hyponatremia","Concomitant use with strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, clarithromycin, ritonavir)","Concomitant use with strong CYP3A4 inducers (e.g., rifampin, carbamazepine, phenytoin)","Uncorrected adrenal insufficiency","Pregnancy"]
| Precautions | ["Too rapid correction of serum sodium can cause osmotic demyelination syndrome; monitor serum sodium and neurological status","Risk of volume depletion and hypotension; discontinue if urine output decreases or hypotension develops","Not recommended for patients on fluid restriction or with anuric renal failure","Hepatic toxicity: elevated liver enzymes have been reported; discontinue if liver injury is suspected","Hyperkalemia: monitor serum potassium levels","Renal impairment: use with caution in patients with CrCl <60 mL/min; not recommended in anuria","Pregnancy: can cause fetal harm; advise effective contraception"] |
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| Fetal Monitoring | Monitor serum sodium, potassium, creatinine, and blood pressure frequently during therapy. Baseline and periodic assessment of liver function tests (LFTs) required due to risk of hepatotoxicity. Fetal monitoring via ultrasound for growth and amniotic fluid volume if prolonged use in pregnancy. |
| Fertility Effects | No human data on fertility effects. In animal studies, tolvaptan did not impair fertility in rats. Potential for transient effects on spermatogenesis based on vasopressin receptor antagonism in testis, but clinical significance unknown. |