Thursday, June 25, 2026
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Critical Care Pharmacokinetics Calculator

CRRT Clearance Calculator

Estimate continuous renal replacement therapy clearance from effluent flow and a sieving or saturation coefficient, with optional mL/kg/hour intensity for bedside dose review.

Quick Answer

CRRT solute clearance is often estimated as effluent flow (dialysate + replacement + net ultrafiltration) multiplied by a sieving or saturation coefficient, divided by 60 to express mL/min. Effluent intensity in mL/kg/hour compares prescribed dose to KDIGO-style targets (~20–25 mL/kg/h). Use drug-specific coefficients and TDM — not effluent alone — for antibiotic and narrow-index dosing in ICU trials and critical care pharmacy.

Effluent-Based Clearance Estimate
CRRT clearance (mL/min) = (Dialysate + Replacement + Ultrafiltration) x coefficient / 60
All flow rates in mL/hour. Coefficient = sieving coefficient for convection or saturation coefficient for diffusion.

Calculate CRRT Clearance

Estimate solute clearance from dialysate, replacement, ultrafiltration, and a sieving or saturation coefficient.

CRRT flow rates
Drug-specific settings

Use 1 for an ideal freely cleared small solute; use drug-specific data when available.

Optional. Expresses effluent intensity as mL/kg/hour.

Estimated CRRT Clearance
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mL/min
Total Effluent Flow
-
mL/hour
Effluent Intensity
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mL/kg/hour

How to Use This CRRT Calculator

1
Enter the prescribed or delivered dialysate, replacement, and net ultrafiltration rates in mL/hour.
2
Enter a sieving or saturation coefficient. For drug dosing, this should be drug- and membrane-specific whenever possible.
3
Optionally enter weight to compare the CRRT prescription with common effluent-dose conventions in mL/kg/hour.
4
Use the clearance estimate as one part of a dosing assessment that also considers nonrenal clearance, residual kidney function, and therapeutic monitoring.

Pharma & critical care trial context

CRRT clearance estimates support intensive care pharmacokinetic substudies, antibiotic stewardship reviews, and protocol dose tables when renal elimination dominates. Sponsors document effluent prescription, actual treatment hours, modality (CVVH, CVVHD, CVVHDF), pre- versus post-dilution, and concurrent residual diuresis when interpreting exposure in sepsis or AKI trials.

Pair this calculator with the Creatinine Clearance Calculator, GFR Calculator, Clearance Calculator, and Loading Dose Calculator when building renal-adjustment narratives for investigational or licensed medicines in ICU populations.

CRRT drug dosing caveats

Effluent-based clearance is most useful for small, water-soluble, minimally protein-bound drugs where the membrane coefficient is close to 1. It can overestimate or underestimate true drug removal when protein binding, adsorption, pre-dilution, filter clotting, interruptions, or patient-specific volume of distribution are important.

Critical illness can change volume of distribution, albumin concentration, organ perfusion, and nonrenal clearance. For beta-lactams, vancomycin, aminoglycosides, antiepileptics, antifungals, and other high-risk therapies, confirm dosing with CRRT-specific references and therapeutic drug monitoring when available.

Worked Example

Example calculation

Dialysate 1,000 mL/hour + replacement 1,000 mL/hour + ultrafiltration 100 mL/hour = 2,100 mL/hour effluent.

With coefficient 0.8, estimated clearance = 2,100 x 0.8 / 60 = 28 mL/min. For a 70 kg patient, effluent intensity is 30 mL/kg/hour.

Evidence & sources

Frequently Asked Questions

How is CRRT clearance estimated from effluent flow?
For small solutes, CRRT clearance is commonly approximated as effluent flow multiplied by the sieving or saturation coefficient, then converted from mL/hour to mL/min. This is an estimate because membrane performance, pre-dilution, downtime, adsorption, protein binding, and residual kidney function can change delivered clearance.
What is effluent flow in CRRT?
Effluent flow is the sum of dialysate, replacement, and net ultrafiltration rates leaving the circuit. It is often used as a practical proxy for CRRT dose and drug clearance in continuous hemofiltration, hemodiafiltration, and hemodialysis modes.
What is CRRT dose in mL/kg/hour?
Prescribed CRRT dose is frequently expressed as total effluent flow divided by patient weight in mL/kg/hour. KDIGO acute kidney injury guidance and ICU nephrology practice often target roughly 20–25 mL/kg/h as a minimum effluent intensity, recognizing downtime and delivery gaps may require higher prescription.
What coefficient should I use for a drug?
Use a drug-specific sieving coefficient for convective clearance or saturation coefficient for diffusive clearance when available. Hydrophilic, low protein-bound drugs may have coefficients near 1, while protein-bound, highly lipophilic, or membrane-adsorbed drugs may have much lower effective values.
Does this calculator account for pre-dilution replacement fluid?
No. This calculator provides a simple effluent-based estimate and does not correct for pre-dilution, filter fraction, downtime, residual renal clearance, or nonrenal clearance. Pre-filter replacement dilutes plasma and can reduce effective drug clearance compared with post-dilution configurations.
How does CVVH differ from CVVHD and CVVHDF for clearance?
CVVH clearance is driven mainly by convection (replacement + ultrafiltration). CVVHD adds diffusive dialysate flow. CVVHDF combines both. Effluent-based dose summation captures total fluid removed or exchanged, but diffusive versus convective contributions to a specific drug may differ from a single coefficient.
Can CRRT clearance be used directly for drug dosing?
It can support dosing review, but it is not a stand-alone dosing recommendation. Use drug labels, CRRT-specific dosing references, therapeutic drug monitoring, local protocols, and patient response, especially for narrow therapeutic index medicines.
How does protein binding affect CRRT drug removal?
Only unbound drug crosses the membrane efficiently. High protein binding lowers effective sieving or saturation coefficients and can make effluent-based estimates overpredict removal. Albumin loss during CRRT and critical illness can further change free fraction over time.
Should residual kidney function be added to CRRT clearance?
Yes when the patient still produces urine and excretes drug renally. Total drug clearance approximates CRRT clearance plus residual renal clearance plus nonrenal clearance. Ignoring residual function can lead to underdosing, particularly early in CRRT initiation.
How do CRRT interruptions affect delivered dose?
Filter clotting, circuit changes, procedures, and hypotension reduce time on therapy. Average delivered dose is lower than prescribed effluent rate times 24 hours unless downtime compensation is used. Document actual treatment hours in trial PK and TDM records.
Which drugs need CRRT-specific dosing review?
Beta-lactams, vancomycin, aminoglycosides, antiepileptics, antifungals, antivirals, and many sedatives or analgesics with renal elimination often need interval and dose adjustment on CRRT. Consult CRRT dosing references and measure concentrations when TDM is available.
Can this calculator replace nephrology or pharmacy protocol?
No. CRRT prescriptions, anticoagulation, fluid balance, and drug dosing require institutional protocols, specialist input, and patient-specific monitoring. This tool supports educational clearance arithmetic only.

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