How do salicylates block guaifenesin?
The kidney (proximal renal tubule) contains receptors to which guaifenesin attaches. Unfortunately experience indicates that those receptors prefer salicylates to Guaifenesin and that, since there are only so many receptors available (we don’t know how many) once occupied by salicylates, there are no parking spaces left for the guaifenesin. Apparently a small amount of salicylate can thus block a large amount of guaifenesin. That’s why it has been proposed that taking more guai will not overcome a known blocker. However, we are apparently very individual in our susceptibility to blocking. Some are very sensitive and others not so much.
