A 72-year-old woman (62 kg) with CKD is hospitalized with non-severe community-acquired pneumonia. She had anaphylaxis to cefuroxime, so the team selects levofloxacin. Her calculated CrCl is 28 mL/min. Which levofloxacin regimen is most appropriate?

750 mg IV once, then 750 mg every 48 hours

500 mg IV once, then 250 mg IV every 24 hours

750 mg IV, then 500 mg IV every 48 hours

A 76-year-old woman (weight 68 kg) with stage 4 CKD is hospitalized with an acute, hemodynamically stable pulmonary embolism. SCr is 2.3 mg/dL. The team chooses enoxaparin for initial treatment. Using the Cockcroft-Gault equation, which regimen is most appropriate?

Enoxaparin 70 mg SC every 24 hours

Enoxaparin 70 mg SC every 12 hours

Enoxaparin 30 mg SC every 24 hours

Enoxaparin 100 mg SC every 24 hours

A 72-year-old woman (60 kg) has acute pyelonephritis without sepsis and is improving after 48 hours of IV ceftriaxone. Urine culture grows E. coli susceptible to TMP-SMX, ciprofloxacin, nitrofurantoin and ceftriaxone. She took ciprofloxacin 4 months ago. CrCl is 25 mL/min. Which oral step-down regimen is most appropriate?

TMP-SMX DS 1 tablet once daily to complete 7 days

Fosfomycin 3 g orally as a single dose

TMP-SMX DS 1 tablet twice daily to complete 14 days

Nitrofurantoin 100 mg twice daily to complete 7 days

A 69-year-old man with type 2 diabetes takes metformin ER 2,000 mg once daily with dinner. His eGFR has declined over 2 years and is now stable at 38 mL/min/1.73 m²; A1c is 7.0%. He has no lactic acidosis risk factors other than CKD. Which change is most appropriate?

Reduce metformin ER to 1,000 mg daily

Continue metformin ER 2,000 mg daily

Stop metformin now because eGFR is below 45

Switch to metformin IR 1,000 mg twice daily

A 72-year-old woman (60 kg) with CKD stage 4 (CrCl 22 mL/min) is admitted with Pseudomonas aeruginosa hospital-acquired pneumonia susceptible to cefepime. The usual regimen for normal renal function is cefepime 2 g IV every 8 hours. Which cefepime regimen is most appropriate?

2 g once, then 2 g every 24 hours

2 g every 8 hours, no adjustment

1 g once, then 1 g every 24 hours

2 g once, then 2 g every 48 hours

An 80-year-old woman (weight 55 kg, SCr 1.8 mg/dL) takes gabapentin 600 mg three times daily for postherpetic neuralgia. She presents with somnolence, dizziness, and myoclonic jerks. Using the Cockcroft-Gault equation, which gabapentin regimen is most appropriate once symptoms resolve?

Gabapentin 300 mg three times daily

A 66-year-old man with end-stage kidney disease on hemodialysis three times weekly had a seizure after an ischemic stroke and is starting maintenance levetiracetam. He has no hepatic disease. Which levetiracetam regimen is most appropriate?

500 mg daily plus 250 mg after each dialysis

500 mg once weekly after dialysis

250 mg every 48 hours with no post-dialysis dose

BCPS Renal Dosing: Cockcroft-Gault CrCl vs eGFR

Q: Is creatinine clearance the same as GFR?

No. The tubules also secrete creatinine, so measured creatinine clearance runs somewhat above true GFR. The Cockcroft-Gault equation estimates creatinine clearance rather than GFR.

Q: Which equation should a pharmacist use?

The one the label uses for that drug, and for staging the one the lab reports. KDIGO 2024 accepts eGFR for most dosing, with the body-size indexing removed for people far from average size and for drugs with a narrow margin.

Q: Do some drugs need a dose after dialysis?

Yes. Drugs that hemodialysis removes in meaningful amounts need a supplemental dose or a dose timed after the session, and the label’s dialysis section says which. The nephrology and urology monograph covers the wider dialysis picture.

Q: Why do some labels list eGFR instead?

Newer labels and drugs whose trials enrolled by eGFR, such as SGLT2 inhibitors and metformin, give their limits as eGFR. Read the column heading every time.

1Two equations, two jobs

Cockcroft and Gault published their equation in 1976 to estimate creatinine clearance from age, weight and a single serum creatinine: CrCl = (140 − age) × weight in kg ÷ (72 × serum creatinine in mg/dL), multiplied by 0.85 for women. The result is an absolute clearance in mL/min, and drug sponsors used it for decades to sort pharmacokinetic study subjects into renal-function groups. That history is why a label table reads in CrCl.

CKD-EPI was built for a different task. It estimates glomerular filtration rate and normalizes it to a standard body surface area of 1.73 m², so that a small person and a large person with the same kidney health land on the same CKD stage. The 2021 creatinine equation dropped the race coefficient, and a creatinine-plus-cystatin C version exists for when creatinine misleads.

1.1Where the two drift apart

The gap is widest at the edges of age and size. In an older, light patient with little muscle, the indexed eGFR can run well above the Cockcroft-Gault estimate, and plugging that eGFR into a CrCl table can put the patient in a higher-dose row. In a very large patient the error flips direction. Neither estimate is valid while creatinine is still rising or falling, as in acute kidney injury.

2Which number for which decision

Matching the kidney-function estimate to the task, per KDIGO 2024 and FDA labeling practice
Decision	Use	Units
Staging CKD and the KDIGO risk grid	CKD-EPI eGFR (creatinine, or creatinine plus cystatin C)	mL/min/1.73 m²
A label table written in creatinine clearance	Cockcroft-Gault CrCl	mL/min
Metformin and SGLT2 inhibitor starts	eGFR, because those labels and guidelines are written in it	mL/min/1.73 m²
Narrow-margin drugs at extremes of body size	eGFR with the indexing removed, or a measured clearance	mL/min
Maintenance hemodialysis	Neither estimate; follow the label’s dialysis section and the session schedule	—

To de-index an eGFR, multiply it by the patient’s body surface area and divide by 1.73.

3Inputs that move the estimate

Body weight: The equation was derived with actual weight. In obesity many protocols substitute adjusted body weight; when a label names a weight, the label wins.
Low muscle mass: Frailty, amputation or long immobility lower creatinine production, so a normal-looking creatinine can hide poor clearance. Rounding creatinine up to a floor value is a local habit; no label requires it.
Unstable creatinine: Every estimating equation assumes a steady state. During acute kidney injury, the number on the report lags behind the kidney.
Units on the report: mL/min/1.73 m² means indexed eGFR; mL/min means an absolute clearance. Check the units before you read off a table.

4Renal dosing, worked through

Calculate before you choose. Several of these cases give you age, weight and creatinine and leave the clearance to you.

Study cases written by our editors, not BPS items. The real BCPS exam is computer-based multiple choice, answered in order with no going back.

Case 1 of 7 · 0 answered

How case rounds work

Pick an option to see the verdict and a note on every option. Keys while the round has focus: 1–5 or A–E answer, ← → move between cases. Nothing is saved or sent anywhere.

Case 01
A 72-year-old woman (62 kg) with CKD is hospitalized with non-severe community-acquired pneumonia. She had anaphylaxis to cefuroxime, so the team selects levofloxacin. Her calculated CrCl is 28 mL/min. Which levofloxacin regimen is most appropriate?
Pick an option: the verdict and a note on every option open here.
Best answer: C.
CAP requires the 750-mg levofloxacin regimen, and for CrCl 20–49 mL/min the label extends the interval to 750 mg every 48 hours while keeping the concentration-dependent peak. 750 mg once followed by 500 mg every 48 hours is the regimen for CrCl 10–19 mL/min and would underdose her. 500 mg then 250 mg every 24 hours is the renal adjustment of the lower 500-mg regimen, which is too low for pneumonia, and 750 mg every 24 hours ignores her renal function.
A
The 500-mg schedule with 250 mg daily is the renal version of the lower regimen and is too weak for pneumonia.
B
750 mg followed by 500 mg every 48 hours is the label schedule for CrCl 10–19, which underdoses her at 28.
C
Correct. Pneumonia needs the 750-mg regimen, and at CrCl 20–49 the label keeps the 750-mg dose and extends the interval to 48 hours.
D
Daily 750 mg ignores a CrCl of 28 and lets levofloxacin accumulate.
Case 02
A 76-year-old woman (weight 68 kg) with stage 4 CKD is hospitalized with an acute, hemodynamically stable pulmonary embolism. SCr is 2.3 mg/dL. The team chooses enoxaparin for initial treatment. Using the Cockcroft-Gault equation, which regimen is most appropriate?
Pick an option: the verdict and a note on every option open here.
Best answer: B.
CrCl = (140 − 76) × 68 ÷ (72 × 2.3) × 0.85 ≈ 22 mL/min, and because enoxaparin is renally cleared the treatment dose for CrCl <30 mL/min is 1 mg/kg once daily (68 mg, rounded to 70 mg). Every-12-hour dosing is for CrCl ≥30 and would accumulate here. The 100 mg dose applies the 1.5 mg/kg once-daily regimen, which is not the renal adjustment, and 30 mg daily is the renally adjusted prophylaxis dose, not treatment.
A
Twice-daily treatment dosing is for CrCl 30 or above; at about 22 mL/min enoxaparin would accumulate.
B
Correct. Cockcroft-Gault gives about 22 mL/min, so treatment is 1 mg/kg once daily: 68 mg, rounded to 70 mg.
C
30 mg once daily is the renally adjusted prophylaxis dose and would undertreat an acute PE.
D
100 mg is the 1.5 mg/kg once-daily regimen, which is not the renal adjustment and overdoses her.
Case 03
A 72-year-old woman (60 kg) has acute pyelonephritis without sepsis and is improving after 48 hours of IV ceftriaxone. Urine culture grows E. coli susceptible to TMP-SMX, ciprofloxacin, nitrofurantoin and ceftriaxone. She took ciprofloxacin 4 months ago. CrCl is 25 mL/min. Which oral step-down regimen is most appropriate?
Pick an option: the verdict and a note on every option open here.
Best answer: A.
IDSA 2025 cUTI guidance supports oral step-down for an improving patient, with 7 days total for a non-fluoroquinolone and avoidance of a fluoroquinolone used in the past 12 months; at CrCl 15–30 mL/min TMP-SMX is given at half the usual dose, so DS once daily. The usual twice-daily dose ignores her renal function, and 14 days is longer than needed. Nitrofurantoin and single-dose fosfomycin do not reach adequate kidney tissue concentrations for pyelonephritis, and nitrofurantoin should also be avoided at CrCl below 30 mL/min (Beers 2023).
A
Correct. TMP-SMX is halved at CrCl 15–30 (one DS tablet daily), and 7 days total fits a non-fluoroquinolone step-down for cUTI.
B
A single fosfomycin dose does not reach adequate kidney tissue levels for pyelonephritis.
C
Twice-daily DS dosing ignores her CrCl of 25, and 14 days is longer than current guidance requires.
D
Nitrofurantoin barely reaches renal tissue, so it fails in pyelonephritis, and Beers advises avoiding it below CrCl 30.
Case 04
A 69-year-old man with type 2 diabetes takes metformin ER 2,000 mg once daily with dinner. His eGFR has declined over 2 years and is now stable at 38 mL/min/1.73 m²; A1c is 7.0%. He has no lactic acidosis risk factors other than CKD. Which change is most appropriate?
Pick an option: the verdict and a note on every option open here.
Best answer: B.
Metformin should not be started at an eGFR of 30–45, but patients already taking it can continue at a reduced dose (generally a maximum of 1,000 mg/day) with eGFR monitoring every 3–6 months; it is contraindicated only below 30. Stopping it now forfeits effective, low-cost therapy. Continuing 2,000 mg/day, or switching to the same total dose as IR, keeps exposure too high for his renal function.
A
2,000 mg/day is too much exposure at an eGFR of 38; the usual ceiling at 30–45 is about 1,000 mg/day.
B
Correct. At an eGFR of 30–45 metformin already in use can continue at a reduced dose, about 1,000 mg/day, with eGFR checks.
C
Metformin is contraindicated only below 30; stopping at 38 gives up effective, low-cost therapy.
D
Switching to IR keeps the same 2,000 mg total, so the exposure problem is unchanged.
Case 05
A 72-year-old woman (60 kg) with CKD stage 4 (CrCl 22 mL/min) is admitted with Pseudomonas aeruginosa hospital-acquired pneumonia susceptible to cefepime. The usual regimen for normal renal function is cefepime 2 g IV every 8 hours. Which cefepime regimen is most appropriate?
Pick an option: the verdict and a note on every option open here.
Best answer: C.
The first dose of a β-lactam is not reduced in renal impairment because it is needed to reach effective concentrations quickly; the maintenance dose is then adjusted to CrCl, and for CrCl 11–29 mL/min the 2 g every 8 hours regimen becomes 2 g every 24 hours. Leaving the full dose unadjusted causes accumulation and cefepime-induced neurotoxicity (encephalopathy, seizures). Halving the first dose underdoses at the start of a serious infection, and every 48 hours undershoots this CrCl range.
A
An unadjusted regimen at CrCl 22 lets cefepime accumulate and risks encephalopathy and seizures.
B
Halving the first dose underdoses a serious Pseudomonas infection right when concentrations matter most.
C
Correct. The first dose is kept in full, then the 2 g every 8 hours regimen becomes 2 g every 24 hours at CrCl 11–29.
D
Every 48 hours undershoots her CrCl range and leaves troughs too low for Pseudomonas.
Case 06
An 80-year-old woman (weight 55 kg, SCr 1.8 mg/dL) takes gabapentin 600 mg three times daily for postherpetic neuralgia. She presents with somnolence, dizziness, and myoclonic jerks. Using the Cockcroft-Gault equation, which gabapentin regimen is most appropriate once symptoms resolve?
Pick an option: the verdict and a note on every option open here.
Best answer: D.
CrCl = (140 − 80) × 55 ÷ (72 × 1.8) × 0.85 ≈ 22 mL/min; gabapentin is cleared unchanged by the kidney, and the labeled range for CrCl 15–29 mL/min is 200–700 mg/day as a single daily dose, so her 1,800 mg/day caused toxicity. Gabapentin 600 mg twice daily fits CrCl 30–59 mL/min, and 300 mg three times daily is the starting dose for normal renal function. Pregabalin is also renally cleared, and 300 mg/day far exceeds the 25–150 mg/day limit at this CrCl.
A
Pregabalin is also renally cleared, and 300 mg/day is far above the 25–150 mg/day limit at this CrCl.
B
900 mg/day is a normal-function starting regimen and too much for a CrCl of about 22.
C
1,200 mg/day in two doses fits CrCl 30–59, not 22.
D
Correct. CrCl is about 22 mL/min, so gabapentin is limited to 200–700 mg/day as one daily dose; 300 mg fits.
Case 07
A 66-year-old man with end-stage kidney disease on hemodialysis three times weekly had a seizure after an ischemic stroke and is starting maintenance levetiracetam. He has no hepatic disease. Which levetiracetam regimen is most appropriate?
Pick an option: the verdict and a note on every option open here.
Best answer: B.
Levetiracetam is cleared by the kidneys and about half of the body’s drug is removed during a 4-hour hemodialysis session, so ESKD patients receive a reduced daily dose (500–1,000 mg once daily) plus a supplemental 250–500 mg after each dialysis. 1,500 mg twice daily is a full dose for normal kidney function and would accumulate, causing sedation and behavioral effects. Every-48-hour dosing without a post-dialysis supplement, or weekly dosing, leaves levels too low after dialysis removes the drug.
A
Weekly dosing leaves levels far too low, especially after each dialysis session removes the drug.
B
Correct. In ESKD on hemodialysis levetiracetam is 500–1,000 mg daily plus a 250–500 mg supplement after each session.
C
Without a post-dialysis supplement, levels drop after every session and seizure protection is lost.
D
3,000 mg/day is a full normal-kidney dose and would accumulate, causing sedation and behavioral effects.

5Clearance, eGFR and dialysis

Is creatinine clearance the same as GFR?

No. The tubules also secrete creatinine, so measured creatinine clearance runs somewhat above true GFR. The Cockcroft-Gault equation estimates creatinine clearance rather than GFR.

Which equation should a pharmacist use?

The one the label uses for that drug, and for staging the one the lab reports. KDIGO 2024 accepts eGFR for most dosing, with the body-size indexing removed for people far from average size and for drugs with a narrow margin.

Do some drugs need a dose after dialysis?

Yes. Drugs that hemodialysis removes in meaningful amounts need a supplemental dose or a dose timed after the session, and the label’s dialysis section says which. The nephrology and urology monograph covers the wider dialysis picture.

Why do some labels list eGFR instead?

Newer labels and drugs whose trials enrolled by eGFR, such as SGLT2 inhibitors and metformin, give their limits as eGFR. Read the column heading every time.

6References

KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD, chapter on medication management. As of October 27, 2026.
KDIGO guideline page: CKD evaluation and management. As of October 27, 2026.

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