Prescribing in renal impairment: dose adjustment and drugs to avoid
RezzyPrescribing in renal impairment is one of those "bread and butter" topics for the AKT. It’s all about making sure we don't accidentally cause toxicity because the kidneys aren't clearing drugs or their metabolites as they should.
I'll start by finding a helpful visual on how we approach these dose adjustments.
When we talk about renal impairment, the big rule is: Start low and go slow.
The loading dose is usually the same (to reach therapeutic levels quickly), but the maintenance dose or the dosing interval must be adjusted because the drug stays in the system longer.
One high-yield point for the AKT: For most drugs, we use eGFR, but for certain high-risk drugs (like Gentamicin, Vancomycin, and Digoxin) or in the elderly/extremes of body weight, we must use the Cockcroft-Gault formula to calculate Creatinine Clearance (CrCl).
I've put together a table of the most common "offenders" you'll see in exam questions.
| Drug Category | Drugs to Avoid (if severe) | Drugs to Adjust (Dose/Interval) |
|---|---|---|
| Analgesics | NSAIDs (risk of AKI), Codeine/Morphine (metabolites accumulate) | Oxycodone, Fentanyl (safer but monitor) |
| Antidiabetics | Metformin (risk of lactic acidosis if eGFR <30) | Sulfonylureas (risk of hypoglycemia) |
| Antibiotics | Nitrofurantoin (ineffective and toxic if eGFR <45) | Gentamicin/Vancomycin (levels!), Penicillins |
| Anticoagulants | DOACs (e.g., Rivaroxaban - avoid if CrCl <15) | Enoxaparin (LMWH - dose reduce) |
| Cardiovascular | Spironolactone (hyperkalemia risk) | ACE inhibitors/ARBs (monitor K+ and Creatinine) |
| Others | Lithium, Methotrexate | Digoxin (toxicity risk), Allopurinol |
AKT Tip: If a patient's creatinine rises by >20% or eGFR drops by >15% after starting an ACE inhibitor, you might need to stop it or investigate for renal artery stenosis!
That table covers the most common exam scenarios. Remember, for Nitrofurantoin, the cut-off is an eGFR of 45 (though some guidelines say 30 if it's a short course for UTI).
Let me pull up some lessons and flashcards so you can really lock this in for your AKT.
📚 Renal Prescribing Lessons
Those lessons on Dosing in renal impairment and Antimicrobial dosing are exactly what you need for the AKT.
To really test your recall, let's look at some flashcards. I've picked a few that focus on the most common drugs that need adjustment.
🗂️ Renal Prescribing Flashcards
Tap to study 27 flashcards in the Oncourse app
You've got the theory down! To make sure you don't mix these up during the exam, let's try a quick game of Synapses.
I'll give you a mix of drugs, and you can group them by whether they should be avoided, dose-adjusted, or if they're generally safe in renal impairment. Ready to test your rizz?
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