Pharmacology and Medication Management in Nephrology
Principles of renal dosing
Understand how reduced clearance affects drug accumulation and toxicity. Estimate kidney function for dosing, and recognize that some drugs require loading doses that are unchanged while maintenance doses are reduced. Know drugs cleared renally (many antibiotics, gabapentin, metformin with cautions, direct oral anticoagulants) versus hepatically cleared agents. Consider dialysis removal: molecular size, protein binding, and volume of distribution determine whether a drug is dialyzable and whether a supplemental dose is needed after treatment.
Key drug classes
Review diuretics (loop, thiazide, potassium-sparing), antihypertensives (angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers), phosphate binders, vitamin D analogs, calcimimetics, erythropoiesis-stimulating agents with iron, potassium binders, and sodium bicarbonate. Understand mechanisms and monitoring parameters for each. Know nephrotoxins: aminoglycosides, amphotericin, vancomycin, contrast media, nonsteroidal anti-inflammatory drugs, and calcineurin inhibitors.
Traps
Do not stop an angiotensin-converting enzyme inhibitor solely because creatinine rises slightly; a modest rise may be acceptable, but a large rise requires evaluation. Do not confuse hyperkalemia risk from renin-angiotensin blockade with a reason to ignore it. Do not assume all antibiotics need renal adjustment. Watch for timing of levels and for interactions that alter drug concentrations.
Worked example and rule of thumb
A patient with GFR 25 mL/min needs gabapentin. The maintenance dose should be reduced and given less frequently, while the initial dose is often lower. Rule of thumb: for any new drug, ask three questions-is it renally cleared, is it nephrotoxic, and is it removed by dialysis?