Drug Dosing in Kidney Disease — Viva

Q1: Build the prescription (foundation)

Examiner: “Give me your framework for dosing any medicine in kidney disease.”[1][2]

Candidate: “I define the drug and indication, assess the current kidney-function trajectory, use the kidney metric and units required by the current label or local monograph, account for body size and dialysis, separate loading from maintenance, plan effect and toxicity monitoring, and reassess whenever physiology changes.”[1][2]

If the candidate says only ‘reduce the dose according to eGFR’:[1][2]

Examiner: “Why is that unsafe?”[1][2]

Candidate: “The same drug can have different renal instructions by indication and jurisdiction. A falling or recovering creatinine is not steady state. Body size, protein binding, volume of distribution, residual kidney function and dialysis can all change exposure. Some drugs need interval change, some dose change, some no renal change, and some measured exposure.”[1][2]

Q2: Which kidney estimate?

Examiner: “Cockcroft-Gault or eGFR?”[2][4]

Candidate: “I do not choose by slogan. I use the estimator and units used in the drug's current evidence or label. Some older labels and pivotal anticoagulant trials use Cockcroft-Gault creatinine clearance; US metformin labeling uses indexed eGFR; KDIGO supports validated eGFR for many other dosing decisions.”[2][4]

Branch A — body size differs greatly from 1.73 m²[2]

Examiner: “The label expects absolute mL/min but the laboratory reports mL/min/1.73 m². What next?”[2]

Candidate: “If the source expects absolute units, I consider de-indexing: absolute GFR equals indexed eGFR multiplied by BSA and divided by 1.73. I do not de-index if the label itself uses indexed eGFR.”[2]

Branch B — frailty, amputation or cirrhosis[2][3]

Examiner: “Creatinine is likely misleading. What next?”[2][3]

Candidate: “Use combined creatinine-cystatin C eGFR when available; if estimates remain discordant and the decision is high consequence or the therapeutic window is narrow, consider measured GFR or clearance. Cystatin C also has non-GFR determinants, so it is not infallible.”[2][3]

Branch C — pregnancy[12]

Examiner: “Can you use routine eGFR?”[12]

Candidate: “Routine creatinine- and cystatin-based eGFR equations are not validated for drug dosing in pregnancy. I use serial serum creatinine and the clinical trajectory; for a high-consequence dose that needs a clearance estimate, I seek obstetric-nephrology/pharmacy input and use a pregnancy-appropriate measured method rather than silently applying a standard eGFR equation.”[12]

Q3: Evolving AKI

Examiner: “Creatinine rose rapidly today. What happens to your estimate?”[1][5]

Candidate: “Static equations assume approximate steady state and lag behind changing filtration. In worsening AKI they may overstate current clearance; during recovery they may understate improvement. I do not assign an arbitrary fixed GFR band. I trend creatinine and urine output, assess haemodynamics and fluid balance, reconstruct prior doses, use drug levels where useful, and reassess after each dose.”[1][5]

Examiner: “Would you hold every renally cleared drug?”[1][2]

Candidate: “No. For each medicine I name the current indication, balance the immediate toxicity or physiological risk against harm from interruption, decide whether an alternative or urgent specialist plan is needed, and document monitoring, review and restart. I do not infer a class-wide stop or continue rule without a class-specific source.”[2][10]

If the candidate mentions kinetic eGFR:[5]

Examiner: “Is kinetic eGFR the answer?”[5]

Candidate: “It can describe changing filtration and inform expert review, but it is not a universally validated replacement for drug-specific evidence, levels and repeated clinical assessment.”[5]

Q4: Loading versus maintenance

Examiner: “Does kidney failure mean a smaller loading dose?”[1][6]

Candidate: “Not automatically. Loading exposure follows target concentration and volume of distribution. Sepsis, oedema and fluid resuscitation can expand the volume of distribution of hydrophilic drugs. Maintenance exposure follows clearance and the drug's PK/PD target.”[1][6]

Examiner: “Why might two antibiotics be adjusted differently?”[6]

Candidate: “Time-dependent beta-lactams need adequate time above MIC, so frequency or prolonged infusion may matter. Concentration-dependent aminoglycoside regimens may preserve a dose and alter the interval. Exact dose, level timing and targets are agent-, indication-, population- and protocol-specific.”[6]

Q5: Vancomycin branch

Examiner: “What vancomycin target do you know?”[7]

Candidate: “For serious invasive MRSA, the 2020 consensus target is AUC24/MIC 400 to 600 mg·h/L within the first 24 to 48 hours, assuming a broth-microdilution MIC of 1 mg/L. It is not a generic target for every infection. Trough-only 15 to 20 mg/L is not an equivalent target; Bayesian AUC estimation can support early assessment before steady state.”[7]

Examiner: “Vancomycin plus piperacillin-tazobactam—automatic cefepime?”[8]

Candidate: “No. The combination is associated with more creatinine-defined AKI in observational studies, but confounding and inhibited creatinine secretion or pseudo-AKI are plausible. A prospective biomarker study found no parallel cystatin C, BUN, dialysis or mortality signal. I choose an alternative only after considering source, cultures, local resistance, allergy and the alternative's toxicity, including cefepime neurotoxicity and renal dosing.”[8]

Q6: Read the label, not a universal table

Examiner: “Give one example where indication changes a renal dosing rule.”[2]

Candidate: “In the sponsor's US ELIQUIS label revised April 2025, adult nonvalvular atrial fibrillation uses 2.5 mg twice daily when at least two are present: age at least 80 years, weight at most 60 kg and serum creatinine at least 1.5 mg/dL. That two-of-three rule is not the VTE treatment schedule. Other indications and jurisdictions can differ.”[2]

Examiner: “Why can you not generalise that threshold to every anticoagulant indication?”[2]

Candidate: “Because the instruction varies by drug, indication, kidney metric and jurisdiction. I name the exact indication and read the current local product label rather than transfer one threshold or dose-reduction rule to another indication.”[2]

Examiner: “What is the allopurinol principle?”[11]

Candidate: “For gout, start low—100 mg/day or lower in CKD—and titrate while monitoring to the serum urate target below 6 mg/dL rather than imposing an eGFR-based low maintenance ceiling. The ACR guideline recommends HLA-B*58:01 testing before treatment in selected higher-risk ancestry groups, not universal testing.”[11]

Q7: Dialysis branch

Examiner: “Which drugs need a post-dialysis top-up?”[1][9][13]

Candidate: “I would not answer from a generic list. Dialysability depends on the drug and actual prescription, dose timing and residual kidney function. I name the modality—intermittent HD, CAPD, APD, prolonged intermittent therapy or CRRT—and use a current indication-specific source and TDM where available.”[1][9][13]

Branch A — CRRT[9]

Examiner: “Can you convert CRRT to a fixed GFR?”[9]

Candidate: “No. I record modality, effluent rate, residual kidney function, downtime, adsorption and filter changes. A fixed ‘CRRT equals GFR 20 to 40’ conversion is unsafe.”[9]

Branch B — peritoneal dialysis[13][14]

Examiner: “Can you transfer a CAPD long-dwell regimen directly to APD?”[14]

Candidate: “No. CAPD and APD are not interchangeable. I record residual kidney function, exchange volume, exchange frequency or cycler schedule, cycle and dwell duration including any long dwell, route and dose timing. Clearance and exposure are drug- and prescription-specific, and PD data are limited; I use a current indication-specific PD source and TDM rather than extrapolating CAPD to APD or giving a generic post-dialysis top-up.”[13][14]

Branch C — intermittent haemodialysis[1][9]

Examiner: “Dose before or after?”[1][9]

Candidate: “That depends on the drug, session and therapeutic goal. Some directly sourced regimens are timed after HD; others use intradialytic administration or drug-specific levels. I do not infer a replacement dose from water solubility or a generic list.”[1][9]

Q8: Monitoring and temporary holds

Examiner: “What do you monitor besides creatinine?”[1]

Candidate: “I monitor the intended clinical effect, correctly timed concentrations where a drug-specific source supports them, urine output, electrolytes and drug-specific toxicity. In hypoalbuminaemia or uraemia, I interpret any total concentration in clinical context rather than applying an unsourced generic free-level correction.”[1]

Examiner: “Give safe sick-day advice.”[10]

Candidate: “I specify the trigger; name each medicine to pause and why; identify medicines that must continue or need urgent advice; state when to seek review and what to monitor; and document the restart condition, responsible clinician and follow-up test. Evidence for universal community stop lists is limited, and failure to restart can cause harm.”[2][10]

Final one-liner

Examiner: “Summarize.”[1][2]

Candidate: “Define the indication, follow the changing kidney trajectory, read the current label in the correct units and jurisdiction, design loading and maintenance exposure separately, monitor, and reassess—including after dialysis or a temporary hold.”[1][2]

References14Show ledgerHide ledger

1. [1]Lea-Henry TN, Carland JE, Stocker SL, et al. Clinical Pharmacokinetics in Kidney Disease: Fundamental Principles Clin J Am Soc Nephrol, 2018.PMID 29934432
2. [2]Levin A, Ahmed SB, Carrero JJ, et al. Executive summary of the KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease: known knowns and known unknowns Kidney Int, 2024.PMID 38519239
3. [3]Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race N Engl J Med, 2021.PMID 34554658
4. [4]Wilhelm SM, Kale-Pradhan PB. Estimating creatinine clearance: a meta-analysis Pharmacotherapy, 2011.PMID 21923452
5. [5]Chen S. Retooling the creatinine clearance equation to estimate kinetic GFR when the plasma creatinine is changing acutely J Am Soc Nephrol, 2013.PMID 23704286
6. [6]Eyler RF, Shvets K. Clinical Pharmacology of Antibiotics Clin J Am Soc Nephrol, 2019.PMID 30862698
7. [7]Rybak MJ, Le J, Lodise TP, et al. Therapeutic Monitoring of Vancomycin for Serious Methicillin-resistant Staphylococcus aureus Infections: A Revised Consensus Guideline and Review by the American Society of Health-system Pharmacists, the Infectious Diseases Society of America, the Pediatric Infectious Diseases Society, and the Society of Infectious Diseases Pharmacists Clin Infect Dis, 2020.PMID 32658968
8. [8]Miano TA, Hennessy S, Yang W, et al. Association of vancomycin plus piperacillin-tazobactam with early changes in creatinine versus cystatin C in critically ill adults: a prospective cohort study Intensive Care Med, 2022.PMID 35833959
9. [9]Hoff BM, Maker JH, Dager WE, Heintz BH. Antibiotic Dosing for Critically Ill Adult Patients Receiving Intermittent Hemodialysis, Prolonged Intermittent Renal Replacement Therapy, and Continuous Renal Replacement Therapy: An Update Ann Pharmacother, 2020.PMID 31342772
10. [10]Watson KE, Dhaliwal K, McMurtry E, et al. Sick Day Medication Guidance for People With Diabetes, Kidney Disease, or Cardiovascular Disease: A Systematic Scoping Review Kidney Med, 2022.PMID 36046611
11. [11]FitzGerald JD, Dalbeth N, Mikuls T, et al. 2020 American College of Rheumatology Guideline for the Management of Gout Arthritis Care Res (Hoboken), 2020.PMID 32391934
12. [12]Hart LA, Anderson GD. Methods of Estimating Kidney Function for Drug Dosing in Special Populations Clin Pharmacokinet, 2018.PMID 29357102
13. [13]Vilay AM. Antibiotic Dosing in Chronic Kidney Disease and End-Stage Renal Disease: A Focus on Contemporary Challenges Adv Chronic Kidney Dis, 2019.PMID 30876619
14. [14]Mancini A, Piraino B. Review of Antibiotic Dosing with Peritonitis in APD Perit Dial Int, 2019.PMID 31296775