Tolvaptan reduces the level of a hormone that regulates the balance of water and salt (sodium) in the body. High levels of this hormone can cause an imbalance that results in low sodium levels and fluid retention.

Tolvaptan is used to treat hyponatremia (low levels of sodium in your blood) in people with heart failure, liver disease, and certain hormonal imbalances. Tolvaptan improves urine flow without causing the body to lose too much sodium as you urinate.

Tolvaptan may also be used for other purposes not listed in this medication guide.

You should not use this medication if you are allergic to tolvaptan, if you are unable to urinate, if you are unable to tell that you are thirsty, or if you are severely dehydrated and feel like you might pass out.

You should not take tolvaptan if you are using certain other medications. Before you take tolvaptan, tell your doctor about all other medications you use. Your doctor will tell you if any of your medications need to be changed while taking tolvaptan.

Also tell your doctor if you have severe liver disease or cirrhosis, if you have been drinking large amounts of alcohol, or if you are malnourished.

You will receive your first few doses of tolvaptan in a hospital setting where your heart rhythm can be monitored, in case the medication causes serious side effects.

If you stop taking tolvaptan for any length of time, do not start taking it again at home. You will need to be in a hospital under observation any time you start or restart treatment with tolvaptan.

Tell your caregivers at once if you have any of these signs that your hyponatremia is being reversed too quickly: problems with speech or muscle control, trouble swallowing, trouble moving your arms and legs, mood changes, and seizure (convulsions).

Drink plenty of fluids during the first 24 hours of treatment with tolvaptan. Avoid alcoholic drinks. Follow your doctor's instructions about the type and amount of liquids you should drink while treating hyponatremia. In some cases, drinking too much liquid can be as unsafe as not drinking enough.

To be sure this medication is helping your condition, your blood will need to be tested on a regular basis. You may not notice any change in your symptoms, but your blood work will help your doctor determine how long to treat you with tolvaptan.

You should not use this medication if you are allergic to tolvaptan, if you are unable to urinate, if you are unable to tell that you are thirsty, or if you are severely dehydrated and feel like you might pass out.

You should not take tolvaptan if you are taking any of the following medications:

• conivaptan (Vaprisol);

• an antibiotic such as clarithromycin (Biaxin), dalfopristin/quinupristin (Synercid), erythromycin (E.E.S., EryPed, Ery-Tab, Erythrocin), or telithromycin (Ketek);

• antifungal medication such as fluconazole (Diflucan), itraconazole (Sporanox), ketoconazole (Nizoral), or voriconazole (Vfend);

• an antidepressant such as nefazodone;

• heart or blood pressure medication such as diltiazem (Cardizem, Dilacor, Tiazac), nicardipine (Cardene), quinidine (Quinaglute, Quinidex, Quin-Release), or verapamil (Calan, Covera, Isoptin, Verelan); or

• HIV/AIDS medicine such as amprenavir (Agenerase), atazanavir (Reyataz), delavirdine (Rescriptor), fosamprenavir (Lexiva), indinavir (Crixivan), nelfinavir (Viracept), saquinavir (Invirase), or ritonavir (Norvir).

Your doctor will tell you if any of your medications need to be changed while taking tolvaptan.

If you have any of these other conditions, you may need a dose adjustment or special tests to safely take tolvaptan:

• severe liver disease (especially cirrhosis);

• if you are malnourished; or

• if you have been drinking large amounts of alcohol.

FDA pregnancy category C. It is not known whether tolvaptan is harmful to an unborn baby. Before taking this medication, tell your doctor if you are pregnant or plan to become pregnant during treatment.

It is not known whether tolvaptan passes into breast milk or if it could harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.