ReviseMRCEM · Clinical Tools · v2.0

Renal Drug Dose Calculator

BNF 2024 NICE CKD NG203 MHRA DOACs UK Kidney Association KDIGO 2024
⚠ EDUCATIONAL USE ONLY — Not a substitute for clinical pharmacist review, BNF, or local formulary. Always verify before prescribing.
Patient Parameters
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⚡ AKI Mode — Baseline creatinine
Actual body weight — switch to Ideal for oedema, Adjusted for BMI ≥30
eGFR Trend Tracker
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Enter patient parameters and press Calculate to see dose recommendations for all drugs.

Drug–Drug Interaction Checker (Renal Focus)

Select drugs this patient is prescribed to check for clinically significant interactions — with particular focus on nephrotoxicity, renal clearance effects, and combinations dangerous in CKD.

Sick-Day Rules for Renal Patients

When a patient with CKD becomes acutely unwell with vomiting, diarrhoea, or is unable to maintain adequate fluid intake (e.g. pre-operative fasting), certain medications significantly increase the risk of AKI and should be temporarily withheld. These are sometimes called "SADMAN" drugs — or the "sick-day rules."

The SADMAN acronym: SGLP-1 agonists/SGLT2i · ACE inhibitors · Diuretics · Metformin · ARBs · NSAIDs
NSAIDs (ibuprofen, naproxen, diclofenac, etc.)
STOP when unwell
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Stop NSAIDs when: vomiting, diarrhoea, reduced oral intake, fever, or perioperative fasting. Restart only when eating, drinking, and well.
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Why: NSAIDs block prostaglandin-mediated afferent arteriolar dilation. In volume depletion, renal perfusion depends on prostaglandins. Blocking them → AKI. Risk compounded by ACEi, diuretics ("triple whammy").
  • Restart only when eating and drinking normally
  • Long-term NSAID users should have annual U&Es
  • Advise patients to carry a sick-day rules card
ACE Inhibitors / ARBs (ramipril, lisinopril, losartan, candesartan)
STOP when unwell
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Withhold during intercurrent illness with vomiting/diarrhoea, dehydration, or pre-operative fasting (from the morning of surgery).
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Why: ACEi/ARBs block angiotensin II → reduce efferent arteriolar tone → reduce GFR when under-perfused. In volume depletion → AKI. Also risk of hyperkalaemia during illness.
  • Restart 24–48h after fully recovered and maintaining fluid intake
  • Recheck U&Es 1–2 weeks after restarting
  • Do NOT stop abruptly in heart failure without specialist advice
  • Avoid "triple whammy": ACEi + NSAID + diuretic — extremely high AKI risk
Diuretics (furosemide, bumetanide, spironolactone, thiazides)
STOP when unwell
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Withhold loop and thiazide diuretics if patient is vomiting, has diarrhoea, or has reduced fluid intake. Also withhold before surgery (discuss with anaesthetist for heart failure patients).
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Why: Diuretics reduce circulating volume. If already volume-depleted from illness, diuretics exacerbate pre-renal AKI and cause electrolyte disturbances (hypokalaemia, hyponatraemia).
  • Exception: do not stop furosemide in decompensated heart failure without specialist review
  • Spironolactone — additional risk of hyperkalaemia in AKI; stop and recheck K+
  • Restart when eating and drinking normally; recheck U&Es
Metformin
STOP when unwell
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Withhold metformin if: vomiting/diarrhoea, reduced intake, any acute illness, pre-operative fasting, or before IV contrast if eGFR <60.
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Why: Metformin is renally excreted. In AKI or dehydration → metformin accumulates → inhibits mitochondrial complex I → lactic acidosis. Rare but potentially fatal.
  • Restart 48h after IV contrast (check creatinine first if eGFR was 45–60)
  • Restart when eating/drinking and eGFR confirmed stable
  • MHRA: Always withhold before major surgery
SGLT2 Inhibitors (dapagliflozin, empagliflozin, canagliflozin)
STOP when unwell
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Withhold SGLT2i if: acutely unwell (any cause), reduced oral intake, perioperative (stop 3–4 days before elective surgery), or if DKA is suspected.
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Why: SGLT2i cause euglycaemic DKA (ketosis despite near-normal glucose). Risk increased during illness, fasting, or surgery. Also may worsen volume depletion via glycosuria/osmotic diuresis.
  • MHRA 2020: Stop at least 3 days before surgery
  • Restart only when eating and drinking normally, and DKA excluded
  • Euglycaemic DKA: glucose may be only mildly elevated — check ketones!
Lithium
STOP / Urgent Level
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If vomiting, diarrhoea, dehydration, or starting a new interacting drug (NSAIDs, ACEi, thiazides) — withhold lithium and check serum level urgently.
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Why: Lithium is 100% renally excreted. Volume depletion → sodium depletion → lithium reabsorption increased → toxicity. Narrow therapeutic index. NSAIDs/ACEi/thiazides all raise lithium levels dramatically.
  • Lithium toxicity: coarse tremor, ataxia, confusion, vomiting, severe bradycardia, seizures
  • Threshold: level >1.5 mmol/L needs urgent review; >2.0 mmol/L → emergency admission
  • Treatment: IV fluids, whole bowel irrigation, haemodialysis for severe toxicity
Gentamicin / Vancomycin / Nephrotoxic Antibiotics
CAUTION — Review Levels
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In AKI or intercurrent illness with reduced renal clearance: check pre-dose levels before every dose. Extend intervals or hold dose if levels not clearing.
  • Gentamicin pre-dose: target <1 mg/L before each dose
  • Vancomycin: AUC/MIC 400–600 or trough 15–20 mg/L; adjust interval in AKI
  • Aciclovir: ensure 1L IV fluid per dose; reduce frequency in AKI
Key message: Patients should receive written sick-day rules cards. In England, NICE CKD NG203 (2023) recommends all CKD patients are counselled on sick-day rules and self-management. GPs should document which medications to withhold during acute illness.
Contrast-Induced AKI (CI-AKI) Risk Assessment

Based on the Mehran Score (validated for IV contrast in cardiac catheterisation) and NICE/RCR guidance for pre-contrast risk stratification. CI-AKI defined as creatinine rise ≥25% or ≥44 μmol/L within 48–72h of contrast.