renal impairment dosing

If the body's main drain is partly blocked, you must pour in less or pour less often, or the sink overflows. When the kidneys fail, drugs that depend on the kidney for removal are cleared more slowly, so the same dose schedule lets them build up to toxic levels. Renal impairment dosing is the practice of scaling the dose to the remaining kidney function.

The first step is to gauge kidney function, usually with an estimated glomerular filtration rate or creatinine clearance. Drugs that are mostly renally eliminated, and especially those with a narrow therapeutic window such as aminoglycosides, digoxin, lithium and many direct anticoagulants, need the most careful adjustment. Doses are reduced roughly in proportion to the loss of clearance.

There are two levers. You can lower each dose while keeping the interval, which steadies the average level but lowers the peaks; or you can keep the dose and lengthen the interval, which preserves the peaks but lets levels fall further between doses. The choice depends on whether the drug needs a high peak or a steady trough to work, and therapeutic drug monitoring often guides the final adjustment.