OAT interactions

The organic anion transporters move drug out of the blood and into the renal tubule for excretion — OAT is Out At the Tubule.

Substrates here are actively secreted rather than passively filtered, so blocking the transporter raises their serum level even though glomerular function has not changed.

Probenecid is the prototype inhibitor, and it was used deliberately for this effect long before it was thought of as an interaction: it raises and sustains penicillin levels. Amoxicillin, penicillin V, cloxacillin, dicloxacillin, ticarcillin and the cephalosporins cefdinir, cefuroxime, ceftriaxone and cephalexin are all handled this way. Cobicistat and rifampin are the other inhibitors shown.

Where it becomes dangerous is methotrexate, whose narrow margin turns a blocked tubule into marrow suppression and mucositis. Acyclovir, cidofovir, levofloxacin, nitrofurantoin and tapentadol are the remaining substrates.

OAT substrates carry few other kinetic interactions, which is the expected pattern for renally cleared drugs: nothing about them depends on CYP capacity.