Renal and hepatic dose adjustment in children — formative SAQs

SAQ 1 — Bedside Schwartz eGFR, KDIGO staging and a renal dose-adjustment plan (10 marks)

A 9-year-old boy, 132 cm tall, has CKD follow-up. His serum creatinine is 1.7 mg per dL on a modern enzymatic assay. He is well and stable. He now needs a course of a renally cleared antibiotic for a urinary tract infection. ^{[1] [4]}

Questions

1. State the bedside Schwartz equation in full with units, calculate this child's estimated GFR, and state the KDIGO category. (5 marks) ^{[1] [4]}
2. Outline the stepwise dose-adjustment plan for his antibiotic, including dose versus interval, the role of the loading dose, and how you would monitor and document. (5 marks) ^[5]

Model answer

Calculation and staging (5). The bedside Schwartz equation gives eGFR in mL per min per 1.73 m2 equal to 0.413 times height in cm divided by serum creatinine in mg per dL. That is 0.413 times 132 divided by 1.7, which equals 0.413 times 77.6, about 32 mL per min per 1.73 m2. A stable value of 32 falls in KDIGO category G3b, which covers 30 to 59 mL per min per 1.73 m2, and at this level most renally cleared drugs need a dose reduction. ^{[1] [4]}

Plan (5). First, identify that the drug is renally cleared, so the kidney matters most. Estimate organ function with a measured height (already done). Look up the operative G3b dose in the BNFc or the local paediatric formulary rather than recalling it. Give the loading dose in full, because it depends on volume of distribution rather than clearance; then reduce the maintenance dose or extend the interval per the formulary recommendation. If the drug is high-risk (for example an aminoglycoside or vancomycin), order a level drawn at the correct time and tailor the dose to it. Document reason prescription is not standard on the chart, counsel the family, and recheck the dose if organ function changes. ^[5]