Pharmacokinetics

Clearance Calculator

Works out drug clearance (CL) from a single dose and its AUC, or from an infusion rate and the steady-state level.

Clearance (CL)

Enter the dose and the AUC to see the clearance.

Inputs

Dose (mg)

The IV dose given.

AUC (mg·h/L)

mg·h/L

Area under the concentration–time curve, 0 to infinity.

Volume of distribution Vd (L) — optional

Enter it to also get the half-life: t½ = 0.693 × Vd / CL.

Try an example drug

Clearance scale

Total clearance bands used for the interpretation.

< 0.5 L/hSevere impairment

0.5 – 2 L/hReduced

2 – 10 L/hNormal

10 – 30 L/hHigh

≥ 30 L/hFlow-limited

CL = Dose / AUC (single dose)

CL = R₀ / Css (steady-state infusion)

t½ = 0.693 × Vd / CL

Dose in mg divided by AUC in mg·h/L gives litres per hour. At steady state the rate in (R₀, mg/h) equals the rate out (CL × Css), so rearranging gives CL = R₀ / Css.

Half-life depends on both clearance and distribution: a large Vd or a small CL makes it longer. 0.693 is ln 2.

Worked example: Clearance and half-life from a single IV dose

A volunteer in a teaching study receives 400 mg of Drug X as an IV bolus. The area under the plasma concentration–time curve, extrapolated to infinity, is 64 mg·h/L, and the volume of distribution is 45 L. Find the total clearance and the half-life.

Dose (IV): 400 mg
AUC₀–∞: 64 mg·h/L
Vd (optional field): 45 L
Method: Single dose

Clearance
CL = Dose ÷ AUC = 400 mg ÷ 64 mg·h/L = 6.250 L/h
Check the units
mg ÷ (mg·h/L) = L/h
Per kilogram (70 kg reference)
6.25 L/h ÷ 70 kg = 0.0893 L/h/kg
Half-life
t½ = 0.693 × Vd ÷ CL = 0.693 × 45 L ÷ 6.25 L/h = 4.99 h

CL = 6.250 L/h (≈ 104 mL/min); t½ ≈ 4.99 h.

Every hour the body clears the drug from about 6.25 L of plasma. Because Vd is 45 L, that is roughly 14 % of the volume per hour (kₑ = CL ÷ Vd ≈ 0.139 h⁻¹), which is why the half-life is about 5 hours. This is an educational calculation on illustrative values; whether a clearance is 'normal' depends on the drug, so it does not by itself describe a patient's organ function.

Common mistakes

Using an oral dose and AUC and calling the answer total clearance. Dose ÷ AUC after an oral dose is CL/F; divide by F (or multiply the dose by F first) to get true clearance.

Using a truncated AUC (0 to the last sample) instead of AUC₀–∞. A smaller AUC overestimates clearance.

Mixing units: AUC in µg·h/mL is numerically the same as mg·h/L, but AUC in µg·h/L with a dose in mg gives a clearance 1000 times too small.

Converting L/h to mL/min wrongly. Multiply by 1000 and divide by 60 (6.25 L/h = 104 mL/min), not the other way round.

Drawing the 'steady-state' level before about 4–5 half-lives of constant infusion. The level is still rising, so R₀ ÷ Css overestimates clearance.

Dividing by 70 kg for every patient. The per-kg figure here is for a 70 kg reference adult; use the patient's actual weight in practice.

Assumptions and limitations

Assumes linear (first-order) pharmacokinetics: clearance is the same at every concentration. Saturable elimination breaks this.

Dose ÷ AUC gives total systemic clearance only for an intravenous dose that is completely available.

R₀ ÷ Css assumes a true steady state and a constant infusion rate; a loading dose or a changing rate invalidates it.

The interpretation bands and the organ chart are general teaching aids, not drug-specific ranges.

Guide: Pharmacokinetic Parameters: AUC, Clearance, Half-Life and BioavailabilityThe concept in full, with practice questions.Ke CalculatorTurn CL and Vd into the elimination rate constant, kₑ = CL ÷ Vd.Volume of Distribution CalculatorFind the Vd you need for the half-life from an IV dose and C₀.Bioavailability CalculatorFind F, so an oral CL/F can be converted to true clearance.

References

Ducharme MP, Shargel L, editors. Shargel and Yu's Applied Biopharmaceutics & Pharmacokinetics. 8th ed. New York: McGraw Hill; 2022.
Rowland and Tozer's Clinical Pharmacokinetics and Pharmacodynamics: Concepts and Applications. 5th ed. Philadelphia: Wolters Kluwer; 2019.

Common questions

Clearance is a volume of plasma completely cleared of drug per unit time. The amount removed per hour (mg/h) is CL × concentration, so it changes as the level changes while CL stays constant for first-order drugs.

You can, but the answer is apparent oral clearance, CL/F, because only the bioavailable fraction F reached the circulation. Divide by F — or multiply the dose by F first — to get true clearance.

It takes about 4–5 half-lives of constant infusion to reach roughly 94–97% of the plateau. A level drawn earlier underestimates Css and so overestimates clearance.

The calculator has no weight input, so it scales to a standard 70 kg adult. For a real patient, divide the clearance by their actual weight instead.

Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy