Clinical & Hospital Pharmacy
Geriatric Dosing & Safety Calculator
Applies 'start low, go slow' dose reductions against Cockcroft-Gault clearance and a frailty index, with AGS Beers Criteria alerts for high-risk drugs.
Standard Geriatric Start-Low (50%)
50mg
50% reduction vs adult standard (100 mg)
Clinical directive
Dosing rule
Patient biometrics & clearance
Cockcroft-Gault needs age, weight, sex and a stable serum creatinine.
This tool is intended for patients aged 65 and over.
Actual body weight.
Must be at steady state.
Frailty staging
Scales the dose in the multi-factorial rule.
Drug & adult dose
Pick a monograph or type any standard adult dose.
The usual adult dose before any geriatric reduction.
Dose comparison across the four rules
What each strategy gives for this patient and drug.
| Rule | Dose | Reduction | Basis |
|---|---|---|---|
| Start low 50% rule | 50 mg | −50% | Flat half of the adult dose |
| Conservative 33% rule | 33.3 mg | −67% | CNS-active / narrow therapeutic index |
| Renal clearance scaled | 37.8 mg | −62% | CrCl 37.8 mL/min → 38% (floor 20%) |
| Frailty & renal adjusted | 32.13 mg | −68% | CrCl × 85% frailty (floor 15%) |
Creatinine clearance comes from Cockcroft-Gault:
CrCl = ((140 − age) × weight kg) / (72 × SCr mg/dL) × 0.85 if female
With the sarcopenia option on, a creatinine below 0.8 mg/dL is raised to 0.8 first, because a low value in a frail elder reflects lost muscle rather than good kidney function and would otherwise inflate the clearance.
The four dosing rules are then:
50% rule: dose = adult × 0.5
33% rule: dose = adult × 0.333
Renal: dose = adult × clamp(CrCl/100, 0.2, 1.0)
Frailty: dose = adult × clamp(CrCl/100 × frailty, 0.15, 1.0)
Frailty coefficients are 100% robust, 85% pre-frail, 70% frail and 55% severely frail. The clamps stop the renal rule falling below a fifth of the adult dose, and the combined rule below 15%. All doses are rounded to two decimals.
Keep learning
References
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31–41.
Common questions
Creatinine comes from muscle. A frail 88-year-old with little muscle can have a creatinine of 0.5 mg/dL and still have poor kidneys; feeding that number into Cockcroft-Gault produces a flatteringly high clearance and an unsafe dose. Rounding to 0.8 is a common, deliberately conservative convention — it is not universal, so check local practice.
Renal scaling suits drugs cleared mainly by the kidney, such as gabapentin or metformin. The 33% rule suits CNS-active, anticholinergic or narrow therapeutic index agents. The flat 50% rule is the general default, and the frailty rule combines renal function with overall physiological reserve for multi-morbid patients.
For drug dosing, Cockcroft-Gault — most dosing studies and package inserts are built on it, and it uses actual body weight. Reported eGFR (CKD-EPI) is normalised to 1.73 m² body surface area and is intended for staging chronic kidney disease, not for calculating a dose.
An American Geriatrics Society list of medications that are potentially inappropriate in older adults, because the risk of harm outweighs the benefit or a safer alternative exists. Benzodiazepines and digoxin above 0.125 mg/day are flagged here. A Beers listing is a prompt to review, not an absolute prohibition.
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