Pharmacokinetics (AUC, Clearance, Half-Life)

What this is for: Non-compartmental PK from a concentration–time series (trapezoid AUC, clearance, half-life, infusion planning) plus Cockcroft–Gault and CKD-EPI 2021 kidney-function estimates.

The formula: AUC = Σ (t2 − t1) × (C1 + C2) ÷ 2; clearance = dose ÷ AUC(0–inf)

How to use:

In the AUC section, enter the dose and bioavailability F, then the concentration–time points as one row per point: time (h), concentration (mg/L).
Read AUC(0–t), λz, terminal half-life, AUC(0–inf), percentage extrapolated, clearance and Vz.
In Half-Life, Decay & Constant Infusion, enter C0, half-life, elapsed time and target concentration, then the infusion CL, Vd, R0, F and target Css, and the dosing interval τ.
In the kidney section, enter age, body weight, serum creatinine and sex (M or F), using the µmol/L converter first if creatinine is in µmol/L.
Read the Cockcroft–Gault creatinine clearance and the CKD-EPI 2021 eGFR alongside the decay, Css, loading-dose and accumulation results.

AUC (Trapezoid), Clearance & Half-Life

Enter a concentration–time curve; trapezoid areas are summed between consecutive points, lambda-z comes from the last three points (log-linear), and the tail is extrapolated.

Dose (mg)mg

Bioavailability F (1 = IV / complete)

Concentration–time points — one row per point: time (h), concentration (mg/L)

AUC(0–t) — measured area (mg·h/L)

Lambda-z (1/h)

Terminal half-life (h)

Extrapolated tail C_last / lambda-z (mg·h/L)

AUC(0–inf) (mg·h/L)

% of AUC extrapolated

CLEARANCE CL = F × Dose / AUC(0–inf) (L/h)

Volume of distribution Vz = CL / lambda-z (L)

Half-Life, Decay & Constant Infusion

First-order elimination: C(t) = C0 × e^(−ke × t), ke = ln2 / t½. Section B is a constant-rate infusion; section C is repeated dosing.

Starting concentration C0 (mg/L)mg/L

Half-life (h)h

Elapsed time (h)h

Target concentration (mg/L)mg/L

Infusion: clearance CL (L/h)L/h

Infusion: volume of distribution Vd (L)L

Infusion rate R0 (mg/h)mg/h

Infusion: bioavailability F

Target Css (mg/L)mg/L

Dosing interval tau (h)h

Elimination constant ke (1/h)

Concentration at elapsed time (mg/L)

Half-lives elapsed

Time to fall to target (h)

ke = CL / Vd (1/h)

Half-life from CL & Vd (h)

Steady-state concentration Css = R0 / CL (mg/L)

Time to 90% of Css (h)

Loading dose = Css × Vd / F (mg)

Infusion rate for target Css (mg/h)

Accumulation factor 1/(1 − e^(−ke × tau))

Peak/trough ratio e^(ke × tau)

Creatinine Clearance (Cockcroft–Gault) & eGFR (CKD-EPI 2021)

Both are estimates — neither replaces a measured clearance. Sex is M or F.

Age (years)years

Body weight (kg)kg

Serum creatinine (mg/dL)mg/dL

Sex (M / F)

Unit converter: serum creatinine (µmol/L)µmol/L

Creatinine clearance — Cockcroft–Gault (mL/min)

= mg/dL (divide by 88.4)

CKD-EPI 2021 eGFR (mL/min/1.73 m²)

kappa (0.7 F / 0.9 M)

alpha (−0.241 F / −0.302 M)

SCr / kappa

Prefer to work offline or keep a copy? The download link is right below.
Download the Pharmacokinetics (AUC, Clearance, Half-Life) workbook (.xlsx)

Notes & limits (from the workbook): Linear trapezoid overestimates the declining phase slightly vs the log-trapezoid method. If '% extrapolated' is large (>20%), the sampling was too short — AUC(0–inf) and clearance get unreliable. The workbook asks you to copy your last three measured points into the terminal block yourself; this page takes the last three points of the curve automatically, which is the same calculation for the worked example. Half-life/infusion sections assume one-compartment, first-order kinetics. Cockcroft–Gault uses actual body weight here; estimating equations assume stable serum creatinine (not acute injury). For drug dosing, follow the specific drug's label — some specify CrCl, others eGFR.