Renal function controlled by many factos ,its not just a number,when you decide to adjust doses of  kidney ,so many factors  appears to till you that your child kidney is affect and give you an alarm, as urine output  plus cr cl ,general status as presence of sepsis , any end organ failure,,signs of infection ,improvement of case ,ABX culture,urine analysis ,renal u.s

So ,you have many types of  Acute kidney injury ,according to  GFR, urine analysis ,renal US ,electrolytes abnormalities ,you will know the righ type&right ttt for this case ,not just renal dose adjustment ,but ttt the underlying cause , so finally , you decide based on  renal function including gfr ,u.o.p ,renal us ,urine analysis ,so go to renal dose adjustment ,then you will follow  your drug monograph to assess gfr and studies  made for each degree and presence of any information for each degree of gfr,  you may not find any information for specific stage of gfr because just lack of studies  not about safety or toxicity  ,so   ,your renal function 1st  including the previous ,then gfr ,then your monograph from different resources.