Lighting a backfire to quench the blaze: a combined drug approach targeting the vanilloid receptor TRPV1.

Drug interactions and drug specificity are core themes for the pharmacologist. The paper discussed in this Viewpoint exploits the former to attain the latter. How can one improve local anesthetics so that they block pain but permit normal sensation? QX-314 is a charged derivative of lidocaine without anesthetic activity because it cannot diffuse across the cell membrane to access the neuronal voltage-dependent sodium channel. Capsaicin is a selective activator of the TRPV1 channel, the localization of which is restricted to sensory C-fiber neurons involved in nociception. Because the large pore size of the activated TRPV1 allows passage of large cations such as QX-314, combined treatment with capsaicin and QX-314 puts QX-314 uniquely into that subclass of neurons mediating pain, thereby achieving sensational specificity.