Drug dosing and nephrotoxin review in renal impairment

01Purpose and principlesWhat the treatment does and how it fits into care.

Kidney impairment changes medicines through more than filtration. Reduced excretion can accumulate a parent drug or active metabolite; uraemia can alter protein binding and pharmacodynamic sensitivity; oedema and critical illness change distribution; dialysis removes some molecules but not others; and kidney disease magnifies consequences such as hyperkalaemia, bleeding and sedation. Safe prescribing therefore combines current function, trajectory, body composition, indication, route, treatment duration and measurable effect.

The value printed beside creatinine is not automatically the dosing value. Laboratory eGFR is normalised to a body surface area of 1.73 m² and is useful for CKD staging. Cockcroft–Gault estimates creatinine clearance using age, sex, creatinine and a selected weight, and is required for DOAC dosing because eGFR can overestimate function and increase bleeding. Both fail when creatinine is changing quickly and both are vulnerable to very low or high muscle mass; measured GFR or specialist pharmacokinetic monitoring may be needed for high-stakes decisions.

Medication review should protect as well as deprescribe. A modest expected creatinine change after renin–angiotensin system blockade does not equal structural nephrotoxicity, and SGLT2 inhibitors have kidney and cardiovascular benefits in appropriate CKD. Conversely, a familiar medicine can become dangerous after dehydration, obstruction or interacting treatment. State whether each item is continued, adjusted, withheld, replaced or stopped; why; what parameter will be checked; and who is responsible for resumption.

Key points

Start with the medicine's indication and urgency. Dose adjustment that makes an antimicrobial ineffective or permanently removes kidney- and heart-protective treatment can be as harmful as accumulation.
Decide whether kidney function is stable. Creatinine-based eGFR and Cockcroft–Gault creatinine clearance assume relative steady state and can substantially mislead during rapidly evolving AKI.
For most medicines in an average-sized stable adult, BNF renal advice commonly uses eGFR, but the exact monograph or Summary of Product Characteristics determines which estimate and threshold apply.
Use Cockcroft–Gault creatinine clearance for direct-acting oral anticoagulants and consider it for nephrotoxic or narrow-therapeutic-index medicines, older people and extremes of body composition in line with MHRA advice.
A renal dose may mean a smaller maintenance dose, a longer interval, both, a different formulation or avoidance. Loading doses are often governed more by distribution and clinical urgency than by renal clearance.
Ask whether the person receives haemodialysis, haemodiafiltration, peritoneal dialysis or continuous kidney replacement therapy, when the last and next sessions occur, and whether residual urine function remains.
Nephrotoxicity is contextual. NSAIDs may reduce renal perfusion; aminoglycosides and vancomycin can injure tubules; ACE inhibitors, ARBs and SGLT2 inhibitors can alter creatinine yet provide substantial long-term cardiorenal benefit.
During vomiting, diarrhoea, sepsis or hypotension, temporarily withholding selected haemodynamically active or accumulation-prone medicines may be appropriate, but every hold requires an indication-specific restart and monitoring plan.
Reconcile community prescriptions, inpatient charts, over-the-counter analgesics, herbal products, recent contrast and short antibiotic courses. Hidden ibuprofen or duplicate metformin frequently defeats an otherwise careful review.
When the licensed information is unclear, or the patient has AKI, dialysis, unusual body size, pregnancy, transplant immunosuppression or several interacting drugs, use a renal pharmacist and specialist resources rather than improvising.

02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.

Haemodynamic AKI combinationRed flag

Intercurrent volume loss or sepsis combined with NSAID exposure, renin–angiotensin blockade and diuretic treatment can sharply reduce glomerular perfusion. The physiology and original indications determine which items are paused and restored.

Renally cleared neurotoxicityRed flag

New drowsiness, myoclonus, confusion, hallucinations, ataxia or respiratory depression after opioids, gabapentinoids, sedatives or certain antimicrobials suggests parent-drug or metabolite accumulation.

Anticoagulant accumulationRed flag

Bleeding, bruising, haemoglobin fall or occult blood after dehydration or renal decline may reflect excessive DOAC exposure, especially when eGFR rather than current Cockcroft–Gault clearance guided selection.

Narrow-index toxicityRed flag

Nausea, visual disturbance or arrhythmia with digoxin; tremor, ataxia or confusion with lithium; and seizures or marrow suppression with other high-risk agents require immediate medicine-specific assessment and levels where interpretable.

Drug-induced kidney phenotypeRed flag

AKI after NSAIDs, antimicrobial exposure, proton-pump inhibitors, immune therapies, contrast or calcineurin inhibitors can be haemodynamic, tubular, interstitial, crystal-related or microangiopathic. Urine and systemic findings help localise the mechanism.

Dialysis timing problem

Loss of efficacy after haemodialysis, administration just before a clearing session or failure to give a required post-dialysis supplement suggests that modality and schedule were omitted from the prescription decision.

03Assessment before treatmentTests and checks that guide safe selection.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Serial creatinine, eGFR and urine outputFirst step
Why
Determine whether renal function is stable enough for an estimate and identify the direction and speed of change.
Interpretation and limitations
A stable plateau supports use of the medicine's specified equation. In AKI, respond to trend, urine output and toxicity rather than treating the automatically reported eGFR as precise.
02
Cockcroft–Gault creatinine clearance
Why
Provide the dosing estimate required for DOACs and selected nephrotoxic, narrow-index or substantially renally eliminated medicines.
Interpretation and limitations
Verify a recent weight and the locally appropriate actual, ideal or adjusted weight convention. The result remains an estimate and is invalidated by rapidly changing creatinine.
03
Potassium, sodium, bicarbonate, magnesium, calcium and glucose
Why
Detect pharmacodynamic complications and biochemical conditions that increase toxicity.
Interpretation and limitations
Hyperkalaemia may reflect RAAS blockade, potassium-sparing drugs, trimethoprim, acidosis or tissue injury; hypoglycaemia can persist when renally cleared insulin or sulfonylurea exposure outlasts intake.
04
Full blood count and liver profile
Why
Identify bleeding, marrow toxicity and non-renal clearance impairment that changes a medicine's overall exposure.
Interpretation and limitations
A haemoglobin fall on anticoagulation requires a bleeding search even without visible blood. Combined hepatic and renal dysfunction can make a nominal renal adjustment insufficient.
05
Therapeutic drug concentration
Why
Guide selected agents such as aminoglycosides, vancomycin, lithium or digoxin when timing and clinical question make the result interpretable.
Interpretation and limitations
Record dose and sample time. A concentration outside its correct peak, trough or post-distribution window may mislead; clinical toxicity can require action before the result returns.
06
Urinalysis, urine ACR and sediment microscopy
Why
Distinguish haemodynamic accumulation from a new intrinsic renal injury phenotype.
Interpretation and limitations
Bland urine supports but does not prove a perfusion mechanism. Pyuria, casts, blood, crystals or new protein can direct investigation toward interstitial, glomerular or crystal-related toxicity.
07
Medication administration and dialysis record
Why
Reconstruct actual exposure, missed doses, interacting medicines and clearance by a renal replacement session.
Interpretation and limitations
Prescription lists do not prove administration. Link each dose to dialysis start and finish, residual urine, filter or modality and any post-session replacement specified by pharmacy guidance.
08
ECG and targeted toxicity assessment
Why
Detect immediate electrical or physiological effects from hyperkalaemia, digoxin, QT-active medicines, opioid accumulation or hypoglycaemia.
Interpretation and limitations
A normal ECG does not exclude dangerous hyperkalaemia or evolving drug toxicity. Treat the patient and biochemical severity under the relevant emergency pathway.

04Treatment approachPreparation, options, escalation and aftercare.

01New prescriptionSelect an evidence-based renal regimenFirst stepA medicine is being started or renewed in a person with known or suspected kidney impairment.

1Confirm indication, urgency, allergy, pregnancy, current and baseline renal trajectory, recent weight, body composition, dialysis status and all interacting or duplicate products.
2Consult the current BNF monograph and SmPC to identify whether eGFR, Cockcroft–Gault clearance or specialist monitoring drives the dose, interval, contraindication and loading strategy.
3EscalationPrescribe the selected regimen with explicit review parameters, duration and escalation threshold; seek renal-pharmacy advice for AKI, dialysis, narrow-index treatment or disagreement between estimates.

02Acute illnessReview, hold selectively and plan restartVomiting, diarrhoea, sepsis, hypotension, poor intake or evolving AKI in a person taking renal-active medicines.

1Assess volume, congestion, urine output, creatinine trend, potassium, glucose and toxicity, and stop definite offenders such as non-essential NSAIDs while treating the underlying illness.
2Temporarily withhold or adjust medicines whose haemodynamic effect or accumulation now outweighs benefit, using NICE, BNF and local sick-day or AKI policy rather than a blanket list.
3Document the original indication, criteria and date for review or restart, arrange repeat biochemistry and communicate changes to the patient, GP, pharmacy and specialty team.

03ToxicityStabilise and define exposureClinical or biochemical features suggest accumulation, nephrotoxicity or a dangerous drug interaction.

1Perform ABCDE, stop the suspected medicine, check glucose and ECG where relevant, obtain targeted bloods and contact senior, pharmacy, toxicology or specialist services early.
2Establish exact agent, formulation, dose times, last renal baseline, co-ingestants and dialysis suitability; take correctly timed drug concentrations without delaying supportive treatment.
3Use the agent-specific antidote, reversal or extracorporeal pathway when indicated, monitor for rebound after redistribution, and submit safety reporting where appropriate.

04DialysisFit dosing to the modalityA person receives intermittent or continuous kidney replacement therapy.

1Identify modality, schedule, access, residual function, current filter or prescription and whether the medicine is cleared by that technique based on molecular and protein-binding characteristics.
2Use renal-pharmacy or unit guidance to set maintenance, timing relative to the session and any post-dialysis supplemental dose, preserving an appropriate loading dose for urgent infection when advised.
3Check therapeutic response, concentrations where available and changes after missed, shortened or intensified sessions, then reconcile again at every transfer of care.

05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.

Prevents or treats thromboembolism while matching exposure to renal clearance and the exact clinical indication.

Direct-acting oral anticoagulant

Select the agent and licensed indication-specific regimen from current BNF and SmPC using Cockcroft–Gault creatinine clearance, age, weight and interacting treatment.

eGFR can overestimate function and increase bleeding. Recalculate after dehydration, AKI or weight change; assess haemoglobin, bleeding and interacting P-glycoprotein or CYP medicines, and use specialist advice at low clearance.

Reduces albuminuria and cardiovascular or kidney progression in appropriately selected CKD and heart-failure populations.

Renin–angiotensin system inhibitor

Continue or titrate for the licensed kidney, cardiovascular or blood-pressure indication with creatinine and potassium checks; temporarily withhold during selected dehydrating or hypotensive illness under the care plan.

Can worsen hyperkalaemia or haemodynamic AKI, especially with NSAIDs, depletion or renal-artery disease. A small stable creatinine change is not synonymous with toxicity; avoid accidental permanent discontinuation.

Provides kidney and cardiovascular protection in selected people with CKD, diabetes or heart failure even when glucose-lowering efficacy has diminished.

SGLT2 inhibitor

Use the current licensed indication and kidney-function threshold from BNF, NICE and specialist guidance; pause during acute serious illness, fasting or major surgery according to local policy.

Assess ketoacidosis symptoms even with near-normal glucose, genital infection, volume status and perioperative fasting. An early eGFR dip can be expected, but severe decline requires reassessment.

Treats type 2 diabetes without hypoglycaemia when used alone and may remain appropriate in stable mild-to-moderate CKD within licensed limits.

Metformin

Use the current BNF and SmPC renal threshold and maximum dose for stable function; withhold during severe acute illness, hypoxia, dehydration or significant AKI and reassess before restart.

Accumulation with severe renal failure and tissue hypoxia increases lactic-acidosis risk. Do not rely on an automated eGFR during AKI, and review contrast and acute-illness instructions under local policy.

Provides effective treatment for selected severe or resistant infections where delayed under-dosing can be life-threatening.

Aminoglycoside or vancomycin

Use the local infection and therapeutic-drug-monitoring protocol with an indication-appropriate initial regimen, subsequent concentrations and renal trajectory; involve microbiology or pharmacy.

Both exposure and nephrotoxicity rise with impaired clearance and other nephrotoxins. Record exact sampling time, reassess daily in AKI and use culture-directed narrowing rather than a static estimated dose.

Treats pain or a licensed neuropathic indication while reducing accumulation of active parent drug or metabolites.

Opioid or gabapentinoid

Select an agent and conservative regimen from current renal prescribing guidance, titrated to pain and adverse effects rather than automatically continuing the community dose.

Sedation, myoclonus, delirium and respiratory depression can emerge after renal decline. Avoid unplanned combinations with other sedatives and seek specialist palliative or pain advice when needs are complex.

Provides anti-inflammatory analgesia for selected conditions when safer options are inadequate.

Non-steroidal anti-inflammatory drug

Avoid routine or prolonged use in CKD and AKI; if a specialist judges a short course essential, use the lowest effective exposure with defined renal, gastrointestinal and cardiovascular monitoring.

Can reduce afferent renal perfusion, retain salt and water, raise blood pressure, worsen hyperkalaemia and cause gastrointestinal bleeding. Over-the-counter use and combination products are often missed.

06Complications, monitoring and follow-upAdverse effects, response and longer-term review.

Recheck creatinine and electrolytes at the medicine-specific interval after initiation, dose change or intercurrent illness, sooner when function is unstable or potassium risk is high.
For DOACs, recalculate Cockcroft–Gault clearance with a current weight and review haemoglobin, liver function, adherence, bleeding and interactions at a frequency increased by frailty or reduced clearance.
For renin–angiotensin blockade or potassium-active treatment, trend potassium and creatinine against baseline and investigate depletion, NSAIDs, obstruction or interacting drugs before attributing every change to the beneficial agent.
For therapeutic drug monitoring, record dose, infusion and sample times and act on the validated local target; do not compare an incorrectly timed value with a trough range.
During AKI, review the chart daily for dose, interval, necessity, accumulation and renal recovery, including antimicrobials, anticoagulants, insulin, analgesics and prophylaxis.
At discharge, reconcile each withheld medicine with a named owner, restart criteria, planned blood test and patient explanation, then confirm the updated list reaches primary care and community pharmacy.
In dialysis, reassess after modality, schedule, filter, residual urine or access changes and after missed sessions because the assumed clearance may no longer apply.

07Special situationsVariants, exceptions and circumstances that change the usual approach.

Renal estimate follows the monograph

CKD staging uses eGFR, but drug studies and licences may use creatinine clearance. The right number is the one specified for that agent and indication, not the easiest value to copy.

Loading and maintenance differ

Renal clearance chiefly alters drug removal and therefore maintenance. In severe infection an adequate loading exposure may still be necessary, followed by measured or adjusted maintenance.

Kidney-protective drugs change physiology

ACE inhibitors, ARBs and SGLT2 inhibitors can produce predictable functional changes while reducing long-term cardiorenal events. Context and trajectory distinguish expected effect from unsafe deterioration.

Dialysability is molecular

Small water-soluble, weakly protein-bound molecules with a low volume of distribution are more readily removed, but modern membranes, modality and treatment duration still require current unit guidance.

Recovery creates a second dosing hazard

A regimen reduced during AKI can become subtherapeutic as filtration improves. Daily review is needed in both directions, particularly for antimicrobials and anticoagulation.

A hold without restart is harm

Temporary cessation during dehydration may be reasonable, yet omission after recovery can worsen heart failure, blood pressure, albuminuria or thrombosis risk. Documentation completes the intervention.

Creatinine reflects muscle as well as filtration

Frailty, amputation, cachexia or muscular build can make both eGFR and clearance estimates discordant with true function. High-stakes dosing may need measured GFR, drug levels or specialist judgement.

08Common pitfallsFrequent interpretation and management errors.

01
Using the laboratory eGFR to dose a DOAC without calculating Cockcroft–Gault creatinine clearance.
02
Applying a steady-state equation during rapidly changing acute kidney injury and reporting a false precision.
03
Reducing an emergency antimicrobial loading exposure automatically and failing to treat sepsis effectively.
04
Labelling ACE inhibitors, ARBs or SGLT2 inhibitors as universally nephrotoxic and never revisiting them after illness.
05
Checking a drug concentration without recording the preceding dose, infusion and sample time.
06
Ignoring residual kidney function, dialysis modality and session timing when copying a maintenance dose.
07
Missing ibuprofen, herbal products or duplicate prescriptions because only the electronic inpatient list was reviewed.
08
Writing 'hold nephrotoxins' at discharge without naming medicines, indications, test timing or restart ownership.