Renal Pharmacology & Medication Safety

Drug dosing in CKD, nephrotoxin avoidance, steroid stewardship, sick day rules, and critical drug interactions in nephrology practice

KDIGO CKD 2024 AKI Best Practices Medication Safety Deprescribing

Andrew Bland, MD, FACP, FAAP | University of Dubuque PA Program

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Drug-Induced AKI: Mechanism Before Label visual summary. Open for the full image and text version.
Drug-Induced AKI: Mechanism Before Label: full graphic and text version
Renal Medication Safety: Dose, Reconcile, Reassess visual summary. Open for the full image and text version.
Renal Medication Safety: Dose, Reconcile, Reassess: full graphic and text version

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1. Drug Dosing in CKD: Principles of Renal Clearance

When to Adjust Drug Doses

Key Pharmacokinetic Principles

PrincipleImpact in CKDClinical Action
Reduced GFR Decreased clearance of renally eliminated drugs → accumulation → toxicity Reduce dose and/or extend interval; use Cockcroft-Gault for drug dosing (FDA convention) unless package insert specifies CKD-EPI
Altered protein binding Uremia displaces drugs from albumin (e.g., phenytoin, warfarin) → higher free fraction Measure free drug levels when available (free phenytoin); expect enhanced effect at "therapeutic" total levels
Volume of distribution Fluid overload in CKD/nephrotic syndrome increases Vd for hydrophilic drugs May need higher loading doses for aminoglycosides, vancomycin in fluid-overloaded patients
Tubular secretion Decreased organic anion/cation transporter function in CKD Affects metformin, TMP, creatinine secretion; trimethoprim raises creatinine without true GFR change
Dialyzability Small, water-soluble, low protein-bound drugs are removed by dialysis Use drug-specific postdialysis or supplemental dosing for dialyzable medicines (e.g., selected beta-lactams and aminoglycosides). Metformin is contraindicated at eGFR below 30 and is not a maintenance dialysis medicine.
Cockcroft-Gault vs. CKD-EPI for Drug Dosing: Most FDA package inserts base renal dosing on creatinine clearance (Cockcroft-Gault), not eGFR (CKD-EPI). Cockcroft-Gault uses actual body weight (or adjusted body weight if obese) and is not normalized to BSA. In clinical practice, for most drugs, using CKD-EPI eGFR is a reasonable approximation, but for narrow therapeutic index drugs (vancomycin, aminoglycosides, DOACs), Cockcroft-Gault is preferred.

2. Nephrotoxic Medication Avoidance

CategoryAgentsMechanism of NephrotoxicityRisk LevelManagement
NSAIDs Ibuprofen, naproxen, ketorolac, celecoxib Afferent arteriolar vasoconstriction (inhibit prostaglandin-mediated vasodilation); reduce GFR; papillary necrosis with chronic use; interstitial nephritis HIGH Avoid in CKD 3–5; hold during AKI; see Section 6 for alternatives
Aminoglycosides Gentamicin, tobramycin, amikacin Direct proximal tubular toxicity; accumulates in renal cortex; non-oliguric AKI with granular casts HIGH Extended-interval dosing (once daily); monitor troughs (<1 μg/mL for gentamicin); limit duration to ≤5–7 days; avoid in CKD if alternatives exist
IV Contrast (iodinated) Iohexol, iopamidol, ioversol Direct tubular toxicity + medullary vasoconstriction; risk highest with eGFR <30, diabetes, heart failure, high contrast volume MODERATE Pre-hydration with isotonic saline (1–3 mL/kg/hr for 6–12 hours); minimize contrast volume; hold metformin 48 hours if eGFR <30; iso-osmolar contrast preferred
Vancomycin IV vancomycin Oxidative stress in proximal tubules; AKI risk increases with trough >20 mg/L, concomitant piperacillin-tazobactam, and duration >7 days MODERATE AUC/MIC-guided dosing (target AUC 400–600); avoid trough-based dosing; concomitant pip-tazo increases AKI risk 2–3x vs. vancomycin + cefepime (PMID: 29088001)
Calcineurin inhibitors Tacrolimus, cyclosporine Afferent arteriolar vasoconstriction (acute); chronic tubulointerstitial fibrosis ("striped fibrosis") with long-term use MODERATE Therapeutic drug monitoring; trough-based dosing; avoid supratherapeutic levels; monitor eGFR trend
Lithium Lithium carbonate Nephrogenic diabetes insipidus; chronic tubulointerstitial nephritis; CKD with prolonged use (>10–15 years) MODERATE Monitor SCr and eGFR every 6 months; urine osmolality annually; target trough 0.6–0.8 mEq/L (lower range); amiloride for NDI
PPIs Omeprazole, pantoprazole, etc. Acute interstitial nephritis (AIN); chronic use associated with CKD progression (observational data; causal link debated) LOW-MOD Deprescribe when possible (see Section 5); use lowest effective dose; monitor SCr
Tenofovir disoproxil (TDF) Tenofovir DF (not TAF) Proximal tubular toxicity; Fanconi syndrome (phosphaturia, glycosuria, aminoaciduria, RTA) MODERATE Monitor phosphorus, glucose, urine protein; switch to TAF (tenofovir alafenamide) if renal toxicity develops
Methotrexate High-dose methotrexate Crystal nephropathy (precipitation in tubules at low urine pH) HIGH (high-dose) Vigorous alkaline hydration (target urine pH >7.0); leucovorin rescue; avoid in eGFR <60
Phosphate-based bowel preps Oral sodium phosphate (OsmoPrep, Fleet Phospho-soda) Acute phosphate nephropathy (calcium phosphate crystal deposition in tubules); often irreversible CKD HIGH Avoid entirely in CKD, elderly, volume-depleted, and those on ACEi/ARB/diuretics; use PEG-based preps instead
"Triple Whammy": The combination of ACEi/ARB + diuretic + NSAID is a well-described cause of AKI. Each drug alone is manageable, but together they eliminate the kidney's compensatory mechanisms for maintaining GFR during volume depletion. Counsel patients to hold NSAIDs during acute illness. (Lapi F et al. BMJ 2013;346:e8525, PMID 23299844)

3. Antibiotic Dosing in AKI and CKD

Aminoglycosides

ParameterNormal Renal FunctionCKD 3 (eGFR 30–59)CKD 4–5 (eGFR <30)Hemodialysis
Gentamicin 5–7 mg/kg IV q24h (extended interval) 5–7 mg/kg IV q36–48h; check levels Avoid if possible; if required: loading dose 5–7 mg/kg, then re-dose based on level Loading dose; re-dose after HD based on pre-HD level; not well removed by PD
Monitoring Random level at 6–14 hours (Hartford nomogram); target trough <1 μg/mL; reassess q48–72h; BUN/SCr daily; audiometry if >5 days

Vancomycin

ParameterDetail
Loading dose25–30 mg/kg IV (actual body weight; max 3 g for single dose)
Maintenance15–20 mg/kg IV q8–12h (normal renal function); extend to q24–48h in CKD 4–5
Monitoring (2020 ASHP/IDSA consensus)AUC/MIC-guided dosing preferred over trough-only; target AUC24 400–600 mg·h/L; Bayesian software recommended
HemodialysisLoading dose 25–30 mg/kg; re-dose 500–1000 mg after each HD session based on pre-HD level
AKI risk factorsConcomitant piperacillin-tazobactam (use cefepime instead when possible), AUC >600, ICU patients, obesity, prolonged courses (>7 days)

Beta-Lactams in CKD

AgentNormal FunctioneGFR 10–29eGFR <10 / HDKey Notes
Piperacillin-tazobactam 4.5 g IV q6h 2.25 g IV q6h 2.25 g IV q8h; dose after HD Associated with higher AKI risk when combined with vancomycin vs. cefepime + vancomycin
Cefepime 2 g IV q8h 1–2 g IV q24h 1 g IV q24h; dose after HD Neurotoxicity (encephalopathy, seizures, myoclonus) in CKD if not dose-adjusted; check levels if available
Meropenem 1–2 g IV q8h 1 g IV q12h 500 mg–1 g IV q24h; dose after HD Lowers valproic acid levels (avoid combination); seizure threshold lower than imipenem
Amoxicillin-clavulanate 875/125 mg PO q12h 500/125 mg PO q12h 500/125 mg PO q24h Do not use 875 mg formulation if eGFR <30 (excess clavulanate)
Cefepime Neurotoxicity: Under-recognized cause of altered mental status in CKD/ESRD patients. Presents as encephalopathy, myoclonus, or non-convulsive status epilepticus. Risk factors: eGFR <30, age >65, ICU admission. Always dose-adjust and consider cefepime levels if available. Resolves within 24–72 hours of dose adjustment or discontinuation.

4. Steroid Stewardship

Appropriate Indications in Nephrology

IndicationTypical RegimenDuration
RPGN / crescentic GNPulse methylprednisolone 500–1000 mg IV x 3 days → oral taperRapid taper over 3–6 months
Minimal change diseasePrednisone 1 mg/kg/day (max 80 mg)8–16 weeks full dose, then 6-month taper
IgA nephropathy (TESTING trial)Reduced-dose steroid protocol: methylprednisolone 0.4 mg/kg/day (max 32 mg) x 2 months → wean by 4 mg/month6–9 months; only if proteinuria >1 g/day despite RAAS blockade (PMID: 35579642)
Lupus nephritis Class III/IVPulse IV → oral 0.5–1 mg/kg/day → taper to ≤5 mg/day by 12 monthsLong-term low-dose; minimize with steroid-sparing agents (MMF, voclosporin)
ANCA vasculitisPulse IV → oral taper; consider avacopan for steroid-free regimen3–6 month taper (ADVOCATE protocol)
Acute interstitial nephritisPrednisone 1 mg/kg/day for 1–3 weeks → taper over 2–3 months8–12 weeks total; benefit debated; remove offending agent first

Steroid Tapering Principles

Monitoring for Adverse Effects

5. PPI Deprescribing

Why It Matters in Nephrology

Step-Down Approach

StepActionDuration
1Assess indication: Is there an ongoing indication (Barrett's esophagus, severe erosive esophagitis, Zollinger-Ellison, chronic NSAID use with high GI risk)? If yes, continue at lowest effective dose.Assessment
2If no ongoing indication (empiric GERD, uncomplicated dyspepsia, or "started in hospital and never stopped"), initiate step-down.—
3Reduce to lowest PPI dose (e.g., omeprazole 20 mg daily → 10 mg daily, or switch to every other day)2–4 weeks
4Switch to H2RA (famotidine 20 mg BID or 40 mg nightly) or on-demand PPI only2–4 weeks
5Discontinue acid suppression; use antacids PRN; lifestyle modifications (elevate head of bed, avoid late meals, weight loss)Ongoing
Rebound Acid Hypersecretion: Occurs in approximately 30–40% of patients after abrupt PPI discontinuation (even after only 8 weeks of use). Symptoms peak at 2 weeks and resolve by 4–6 weeks. Gradual step-down over 2–4 weeks minimizes rebound. Counsel patients that transient worsening is expected and does not mean the PPI is "needed." PMID: 19362552

H2RA Alternatives

6. NSAID Alternatives for Pain Management in CKD

Pain TypePreferred AgentsNotes
Mild–moderate pain Acetaminophen (up to 2 g/day in CKD; max 3 g/day with normal liver function) First-line analgesic in CKD; no renal toxicity; avoid in severe liver disease
Neuropathic pain Gabapentin (dose-adjust: 100–300 mg daily if eGFR <30); pregabalin (dose-adjust); duloxetine (avoid if eGFR <30) Gabapentin accumulates in CKD → somnolence, myoclonus; start low, go slow; dialyzable (dose after HD)
Musculoskeletal pain Topical diclofenac gel (minimal systemic absorption); capsaicin cream; lidocaine patches Topical NSAIDs have negligible renal effects for localized joint/muscle pain
Moderate–severe pain Tramadol (reduce dose and frequency in CKD; avoid if seizure risk); low-dose oxycodone (no active renal metabolites) Avoid morphine in eGFR <30 (active metabolite morphine-6-glucuronide accumulates → respiratory depression); avoid codeine (unpredictable CYP2D6 metabolism)
Gout flare (CKD patient) Colchicine 0.6 mg x 1, then 0.3 mg 1 hour later (dose-reduced if eGFR <30; avoid if on P-gp or CYP3A4 inhibitors); low-dose prednisone burst (30 mg x 5 days); intra-articular steroid injection Avoid NSAIDs for gout in CKD; colchicine dose must be reduced; no colchicine with clarithromycin or azole antifungals
Chronic pain / multimodal Physical therapy, cognitive behavioral therapy, acupuncture, TENS unit Non-pharmacologic approaches are underutilized and effective; should be part of every chronic pain plan
Short-course NSAID Exception: A single dose or 2–3 day course of an NSAID may be acceptable in CKD stage 3 for acute pain (e.g., renal colic, post-surgical) when alternatives are inadequate. Ensure adequate hydration, hold ACEi/ARB and diuretics, and monitor SCr. Avoid entirely in CKD 4–5, AKI, transplant recipients, and heart failure.

7. Sick Day Rules: Medications to Hold During Acute Illness

During acute illness with volume depletion risk (vomiting, diarrhea, febrile illness, poor oral intake, perioperative period), temporarily hold medications that can precipitate or worsen AKI. Use the mnemonic SADMANS.

S — SGLT2 Inhibitors

  • Empagliflozin, dapagliflozin, canagliflozin
  • Risk: volume depletion, euglycemic DKA (especially in type 1 DM or prolonged fasting)
  • Resume when oral intake normalizes and euDKA excluded

A — ACE Inhibitors / ARBs

  • Lisinopril, losartan, valsartan, etc.
  • Risk: efferent arteriolar vasodilation reduces GFR in hypovolemia; hyperkalemia
  • Resume when creatinine returns to baseline and volume status restored

D — Diuretics

  • Furosemide, HCTZ, chlorthalidone, spironolactone
  • Risk: exacerbate volume depletion; worsen pre-renal AKI; electrolyte derangements
  • Resume when euvolemic and eating/drinking normally

M — Metformin

  • Risk: lactic acidosis in AKI (metformin accumulates when GFR drops)
  • Hold if unable to eat/drink, vomiting, eGFR drops acutely below 30
  • Resume when SCr stable and oral intake adequate

A — Aldosterone Antagonists (MRAs)

  • Spironolactone, eplerenone, finerenone
  • Risk: life-threatening hyperkalemia in AKI
  • Resume when potassium normal and eGFR stable

N — NSAIDs

  • Ibuprofen, naproxen, celecoxib
  • Risk: afferent arteriolar constriction; "triple whammy" with ACEi + diuretic
  • Use acetaminophen instead during illness
Patient Education is Key: Every CKD patient should receive written sick day rules at diagnosis and at medication changes. Routine sick-day counseling for CKD patients is widely under-implemented; temporary medication holds during acute illness are a foundational AKI-prevention strategy.

What NOT to Hold

8. Medication Reconciliation at Transitions of Care

High-Risk Transitions for Nephrology Patients

Reconciliation Checklist

StepActionCommon Findings
1Obtain complete medication list (patient, pharmacy, EHR, pill bottles)Average discrepancy: 3–5 medications per patient at hospital discharge
2Check each medication for renal dose adjustment at current eGFR30–40% of CKD 4–5 patients have at least one inappropriately dosed medication
3Identify nephrotoxins for removal or substitutionNSAIDs, combination analgesics with NSAIDs, herbal supplements (aristolochic acid)
4Check for dangerous drug interactionsCNI + azole, allopurinol + azathioprine, TMP + methotrexate, K-sparing diuretic + ACEi + NSAID
5Review OTC medications and supplementsMagnesium-containing antacids in CKD 4–5; potassium-containing salt substitutes; high-dose vitamin C (oxalate risk)
6Counsel patient on sick day rulesProvide written instructions; document in chart
7Communicate changes to PCP and pharmacyDischarge summary should explicitly list renally adjusted doses and rationale

9. Key Drug Interactions in Nephrology

Drug CombinationInteractionClinical ConsequenceManagement
CNI + azole antifungals
(tacrolimus/cyclosporine + fluconazole, voriconazole, itraconazole)
Azoles inhibit CYP3A4 and P-glycoprotein; increase CNI levels 2–5x Nephrotoxicity, neurotoxicity (tremor, seizures), hyperkalemia Reduce CNI dose by 50–75% when starting azole; check trough within 3–5 days; fluconazole has less effect than voriconazole; use micafungin/anidulafungin if possible (minimal CYP interaction)
Allopurinol + azathioprine Allopurinol inhibits xanthine oxidase, blocking azathioprine/6-MP metabolism; 3–5x increase in active metabolite levels Severe pancytopenia, potentially fatal bone marrow suppression Febuxostat is contraindicated with azathioprine or mercaptopurine; it is not a safer substitute for this interaction. Avoid unplanned co-prescribing. If allopurinol and a thiopurine are deliberately combined, an experienced prescriber must make a major thiopurine dose adjustment and arrange close CBC monitoring using the relevant drug labels and specialist protocol.
TMP-SMX + methotrexate TMP inhibits renal tubular secretion of methotrexate; SMX is a weak DHFR inhibitor (additive antifolate effect) Methotrexate toxicity: pancytopenia, mucositis, renal failure Avoid combination; if both required, monitor methotrexate levels and CBC closely
ACEi/ARB + K-sparing diuretic + NSAID
("Triple Whammy")
ACEi/ARB: reduce aldosterone → hyperkalemia; K-sparing diuretic: hyperkalemia; NSAID: reduce GFR + reduce K excretion Severe hyperkalemia, AKI Avoid triple combination; hold NSAID; monitor K+ and SCr when any two are combined
Colchicine + CYP3A4/P-gp inhibitors
(clarithromycin, ketoconazole, cyclosporine)
Markedly increased colchicine levels; colchicine has narrow therapeutic index Fatal colchicine toxicity: multi-organ failure, pancytopenia, rhabdomyolysis Contraindicated in combination if eGFR <30; reduce colchicine dose to 0.3 mg x 1 if combination unavoidable with normal renal function
SGLT2i + insulin / sulfonylureas Additive glucose-lowering effect; SGLT2i may cause euglycemic DKA Hypoglycemia; euglycemic DKA (especially perioperative or fasting) Assess hypoglycemia risk and individualize insulin/sulfonylurea adjustment; avoid excessive insulin reduction. Before scheduled surgery, hold empagliflozin/dapagliflozin/canagliflozin at least 3 days and ertugliflozin at least 4 days, following the product label and treating team.
Meropenem + valproic acid Carbapenems reduce valproic acid levels by 60–90% via multiple mechanisms (enhanced glucuronidation, impaired reabsorption) Seizures from subtherapeutic valproic acid levels Avoid combination; use alternative antibiotic or alternative antiepileptic; interaction persists 2 weeks after carbapenem discontinued
Lithium + ACEi/ARB or diuretics Reduced lithium clearance due to volume depletion and proximal tubule sodium reabsorption Lithium toxicity: tremor, ataxia, seizures, renal failure Monitor lithium levels closely when starting/adjusting ACEi/ARB/diuretics; reduce lithium dose preemptively; check level within 5–7 days
The Allopurinol-Azathioprine Interaction is one of the most dangerous drug interactions in nephrology and transplant medicine. It is frequently tested on board examinations. Always check uric acid-lowering therapy before prescribing azathioprine, and vice versa. Coordinate any change in urate-lowering or immunosuppressive therapy with the treating specialist; immunosuppressants are not interchangeable without reviewing the indication, efficacy, and adverse effects. Official febuxostat labeling: thiopurine contraindication.

References

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Andrew Bland, MD, FACP, FAAP | University of Dubuque PA Program | urinenephrology.org

© 2025. For educational use only. Not a substitute for clinical judgment.