Expansion
Two non-specific pumps secrete a wide range of drugs and endogenous compounds
Expansion
Two broad, non-specific transport systems in the proximal tubule:
Organic anion transporters (OAT) secrete
- PAH, urate, and many drugs: penicillins, cephalosporins, furosemide, thiazides, methotrexate, salicylate, probenecid, NSAIDs
Organic cation transporters (OCT) secrete
- Creatinine, dopamine, and drugs: cimetidine, trimethoprim, metformin, morphine, procainamide, quinine
Because each system carries many substrates, competition produces predictable interactions:
- Probenecid blocks the anion transporter, prolonging penicillin levels (once used deliberately) and reducing methotrexate clearance (a dangerous interaction)
- Trimethoprim and cimetidine block creatinine secretion, raising serum creatinine without any change in GFR
- NSAIDs and diuretics compete, reducing diuretic delivery to its site of action, which is part of why NSAIDs blunt diuretic efficacy
The systems are also important for clearing protein-bound drugs, since secretion can strip drug from albumin in a way filtration cannot.