Grapefruit interaction with tolvaptan

Tolvaptan (Samsca) is used to treat hyponatremia — too little sodium in the blood.

Patients with heart failure, liver problems (eg, cirrhosis), and the syndrome of inappropriate antidiuretic hormone (SIADH) may have hyponatremia.

First, the details.

  • 20 healthy volunteers swallowed 60 mg tolvaptan with 240 mL of water or reconstituted grapefruit juice.
  • They waited 72 hours between doses.
  • Blood samples for tolvaptan were obtained for 48 hours postdose.

And, the results.

  • When taken with grapefruit juice, tolvaptan concentrations were elevated compared with tolvaptan alone for 16 hours.
  • The elimination half-life (time to eliminate half the drug from the body) of tolvaptan was about the same, 5.7 vs 5.1 hours, respectively.
  • The average maximal blood concentration (Cmax) and the area under the curve (a measure of bioavailability to the body) of tolvaptan increased 1.86- and 1.56-fold respectively when co-administered with grapefruit juice.
  • The adverse event profile was consistent with the usual use of tolvaptan: urinary frequency, thirst, and dry mouth were the most frequently reported events.

The bottom line?

The researchers from Otsuka Pharmaceuticals concluded, “Grapefruit juice increases the bioavailability of tolvaptan, but does not affect its systemic elimination.”

Based on these data, the interaction does not appear to have a significant effect on how the body responds to tolvaptan.

9/9/11 21:16 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at www.Vicus.com, a complementary and alternative medicine website.