Tolvaptan
Tolvaptan tablets treat low blood sodium (hyponatraemia) in heart failure and SIADH, sold here as Samsca in 15mg and 30mg strengths.
What tolvaptan is for
Hyponatraemia means the sodium level in the blood has fallen too low. The usual cause is too much water rather than too little sodium: the kidneys keep pulling water back into the body, and the sodium already there gets diluted. Tolvaptan blocks the vasopressin V2 receptors in the kidney — the docking points that carry that signal — so more water leaves in the urine and the sodium reading climbs. It is used in heart failure, in SIADH (where the body makes too much of the hormone that holds water) and in other conditions that leave the body holding fluid. It comes into play when cutting back on drinks has not been enough. A different tolvaptan brand is used long term for polycystic kidney disease; the Samsca tablets sold here are the low-sodium treatment.
How Samsca tablets are taken
Samsca is the tolvaptan sold here, as 15mg and 30mg tablets. One tablet a day, with or without food. Treatment starts in hospital so the sodium level can be followed closely, and the dose goes up no faster than once every 24 hours. If the course carries on at home, the tablet goes at about the same time each day. Drink whenever you feel thirsty and keep water within reach — what you take in replaces what the tablets are passing out.
Side effects to expect — and the one to watch
Passing more urine and feeling thirsty are the medicine doing its job. A dry mouth, constipation, nausea and a tired, weak feeling are common too. The risk that matters most is a sodium level that climbs too quickly, which can injure the nerves (osmotic demyelination syndrome). Difficulty speaking or swallowing, food feeling stuck in the throat, drowsiness, confusion, mood changes, jerky movements you cannot control, weak arms or legs, or a seizure all need emergency treatment. Tolvaptan can also raise liver enzymes; yellowing of the eyes or skin, dark urine and pain in the upper right abdomen are signs of liver injury.
Medicines that change how tolvaptan works
Some drugs alter how much tolvaptan stays in the blood. Clarithromycin, ketoconazole, ritonavir and other strong blockers of the CYP3A4 enzyme push the level up; rifampicin, carbamazepine and St John's wort pull it down. Other diuretics shift fluid and make the sodium level harder to predict while the course runs.
Sources
- Tolvaptan (low blood sodium): MedlinePlus Drug Information — National Library of Medicine
- Polycystic Kidney Disease - The National Kidney Foundation — National Kidney Foundation
Where can I buy Tolvaptan in Hong Kong?
Tolvaptan tablets can be ordered online with delivery to Hong Kong. The range is generic Samsca in 15mg and 30mg tablets, also sold as the plain Tolvaptan tablets. Your order travels by tracked courier, arriving in 5 to 9 business days, with online tracking.
How much does Tolvaptan cost?
It depends on the product, strength and pack size. The tolvaptan product listed here shows its current prices in HKD or the currency you select.
Can I buy generic Samsca in Hong Kong?
Yes, generic Samsca is listed as 15mg and 30mg tablets and contains tolvaptan. It is also sold as the plain Tolvaptan tablets in the same 15mg and 30mg strengths.
What are the other names for tolvaptan?
Jinarc, Jynarque and Samsca are brand names of tolvaptan. Here, tolvaptan can be bought online as generic Samsca. These are generics, not the original brand.
How long can I take tolvaptan for?
Samsca is a short course: the tablets are taken for no longer than 30 days, often starting in hospital. A course that is stopped and restarted later needs the same close watching of sodium levels as the first time.
Can I drink alcohol with tolvaptan?
Heavy drinking raises the risk of the nerve injury that a too-fast sodium rise can cause, so alcohol is best left out while the tablets are being taken.
Why do I have to drink water while taking tolvaptan?
Tolvaptan moves water out of the body, so drinking to thirst tops up what is being lost and helps stop the sodium level jumping. Keep a glass or bottle within reach through the day. People who cannot feel thirst are not given these tablets.
What is the difference between Samsca 15mg and 30mg?
Treatment usually starts at 15mg once a day, and 30mg is used when the sodium level needs a bigger rise. Both strengths are the same tablet in different amounts.
Can I drink grapefruit juice with tolvaptan?
Grapefruit juice raises the amount of tolvaptan in the blood, so it is best left out for the whole course. Plain water is the drink to keep close at hand while the tablets are working.