Indications
Tolvaptan is used to treat low sodium levels in the blood (hyponatraemia) caused by a condition called SIADH, in which the body holds on to too much water. In some countries it is also used to slow the decline in kidney function in adults with autosomal dominant polycystic kidney disease (ADPKD), an inherited condition in which cysts grow in the kidneys.
How It Works
The hormone vasopressin (antidiuretic hormone) tells the kidneys to keep water in the body. Tolvaptan blocks the vasopressin V2 receptors in the kidneys, so more water is passed in the urine without losing extra sodium. This raises the sodium level in the blood. In polycystic kidney disease, blocking vasopressin also slows cyst growth.
Dosage and Administration
Treatment for low sodium must be started in hospital, where sodium levels are checked often, because raising sodium too quickly can cause serious brain damage. The dose is as prescribed and adjusted according to blood tests. Tablets are taken once a day (or in split doses for kidney disease), with or without food, but not with grapefruit juice. Drink water whenever you feel thirsty unless told otherwise. Do not stop or change the dose without your doctor’s advice.
Interactions
- Strong enzyme blockers such as Ketoconazole, Clarithromycin and Ritonavir, and grapefruit juice: greatly raise Tolvaptan levels and should be avoided.
- Rifampicin and other enzyme inducers: lower Tolvaptan levels.
- Other medicines that raise sodium or potassium, such as hypertonic saline, potassium supplements or potassium-sparing diuretics: risk of levels rising too much.
- Digoxin: levels may rise.
Contraindications
Do not take Tolvaptan if you are allergic to it, need an urgent rise in sodium, cannot feel or respond to thirst, have low blood volume, have very high sodium, cannot pass urine, have liver disease or raised liver tests (for the kidney use), are taking a strong enzyme blocker, are pregnant, or are breastfeeding.
Side Effects
Very common effects include thirst, dry mouth, passing large amounts of urine, needing to urinate at night, tiredness and constipation. Tolvaptan can cause serious liver injury, and sodium can rise too fast.
Get urgent medical help if you notice yellowing of the skin or eyes, dark urine, pain in the upper right abdomen, loss of appetite, nausea or severe tiredness (possible liver injury); or difficulty speaking or swallowing, drowsiness, confusion, muscle spasms, weakness in arms or legs, or fits (possible too-rapid sodium rise); or signs of severe dehydration such as dizziness and very little urine.
Pregnancy and Lactation
Tolvaptan must not be used in pregnancy, as it may harm the baby. Women who can become pregnant should use effective contraception during treatment. Do not breastfeed while taking Tolvaptan.
Precautions and Warnings
Regular blood tests for sodium, potassium and liver function are essential, especially in the first weeks. Always have water available. Tell your doctor if you have vomiting or diarrhoea or cannot drink, as you may become dehydrated. People with diabetes may have higher blood sugar readings.
Overdose
An overdose may cause heavy urination, severe thirst, dehydration and a rapid rise in sodium. Seek medical help straight away.
Therapeutic Class
Vasopressin V2 receptor antagonist (vaptan).
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.