Bumetanide is increasingly being used for experimental treatment of
brain disorders, including neonatal
seizures,
epilepsy, and
autism, because the neuronal
Na-K-Cl cotransporter NKCC1, which is inhibited by
bumetanide, is implicated in the pathophysiology of such disorders. However, use of
bumetanide for treatment of
brain disorders is associated with problems, including poor brain penetration and systemic adverse effects such as diuresis, hypokalemic
alkalosis, and
hearing loss. The poor brain penetration is thought to be related to its high ionization rate and
plasma protein binding, which restrict brain entry by passive diffusion, but more recently brain efflux transporters have been involved, too. Multidrug resistance
protein 4 (MRP4),
organic anion transporter 3 (OAT3) and organic
anion transporting
polypeptide 2 (OATP2) were suggested to mediate
bumetanide brain efflux, but direct proof is lacking. Because MRP4, OAT3, and OATP2 can be inhibited by
probenecid, we studied whether this
drug alters brain levels of
bumetanide in mice.
Probenecid (50 mg/kg) significantly increased brain levels of
bumetanide up to 3-fold; however, it also increased its plasma levels, so that the brain:plasma ratio (~0.015-0.02) was not altered.
Probenecid markedly increased the plasma half-life of
bumetanide, indicating reduced elimination of
bumetanide most likely by inhibition of OAT-mediated transport of
bumetanide in the kidney. However, the
diuretic activity of
bumetanide was not reduced by
probenecid. In conclusion, our study demonstrates that the clinically available
drug probenecid can be used to increase brain levels of
bumetanide and decrease its elimination, which could have therapeutic potential in the treatment of
brain disorders.