Cockcroft-Gault equation — used for medication dose adjustment based on kidney function.
eGFR (CKD-EPI) is automatically reported on most Australian blood tests. It estimates glomerular filtration rate and is used for diagnosing and staging chronic kidney disease (CKD).
Cockcroft-Gault creatinine clearance estimates actual creatinine clearance using the patient's weight. Many drug product information sheets and dosing guidelines still reference Cockcroft-Gault for dose adjustments, especially for drugs with narrow therapeutic windows (e.g. DOACs, aminoglycosides, metformin, lithium, enoxaparin).
The two equations can give different results, particularly in patients who are very heavy, very light, elderly, or have muscle wasting. When dosing medications, use whichever equation the drug's prescribing information specifies.
The original Cockcroft-Gault equation uses actual body weight. However, in obese patients (BMI >30), this overestimates creatinine clearance because excess fat doesn't produce creatinine.
For obese patients, some references recommend using adjusted body weight: IBW + 0.4 × (actual weight − IBW), where IBW (ideal body weight) = 50 + 0.9 × (height in cm − 152) for males, or 45.5 + 0.9 × (height in cm − 152) for females.
For underweight patients, use actual weight. When in doubt, consult the AMH (Australian Medicines Handbook) or a pharmacist.
Many medications require dose adjustment based on kidney function. Common examples include:
DOACs: Rivaroxaban, apixaban, dabigatran — dose reduction or contraindication at low CrCl.
Antibiotics: Gentamicin, trimethoprim, nitrofurantoin, cefalexin — dose or interval adjustment.
Diabetes: Metformin (reduce or stop at CrCl <30), empagliflozin, sitagliptin.
Gout: Allopurinol — start low and titrate slowly in CKD.
Pain: NSAIDs (avoid in CKD), gabapentin, pregabalin, opioids.
Cardiac: Digoxin, ACE inhibitors, spironolactone — require monitoring.
Always check the AMH or product information for specific dosing recommendations.