I usually assumed that the GFR was zero or close to it in patients with AKI. All GFR calculations you quote are based on a steady state, and AKI is not a steady state, so I agree that they overestimate true GFR. Therefore, I assumed zero and dosed accordingly. Always follow drug levels when possible.

The criteria for the diagnosis of AKI is based on serum creatinine & urine output & not on GFR , as the decline in GFR is very rapid . I agree with Murray Levin on the policy of dosing of drugs in AKI . Drug induced AKI is an important complication in CKD & hence caution is needed in dosing of drugs .

I'm not a clinician, so bear that in mind please.  Our own research shows that a short duration creatinine clearance (we used 4h) may be better.  If the patients are catheterised then this is easy to measure.

Something else to be aware of is that if creatinine is elevated it does not necessarily mean that GFR is (still) depressed. Sometimes GFR has recovered but this is not yet evident in the creatinine concentration (it may or may not be evident in Urine Output).  We recently developed a very simple test to see if creatinine was likely to fall using the ratio of an estimated production of creatinine to its excretion.

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