# Drug Clearance Calculator (CL) Calculate drug clearance CL in two modes. (A) Definition: CL = elimination rate / concentration, valid for any pharmacokinetic model. (B) Linear first-order: CL = k · Vd (or derive k from t½ via k = ln2 / t½). Also reports the relationship t½ = 0.693 · Vd / CL. CL is a definitional parameter independent of Vd. Linear mode applies only to first-order elimination — NOT to Michaelis-Menten drugs (phenytoin, high-dose ethanol). Reference: theophylline CL ≈ 2.8 L/h in a 70 kg non-smoking adult. Not medical advice. > Canonical page: https://elysiatools.com/en/tools/drug-clearance-calculator - **Category:** Health - **Keywords:** clearance, drug clearance, CL, elimination rate, elimination rate constant, k, vd, half-life, pharmacokinetics, renal clearance, hepatic clearance, pk, drug, medicine ## Overview Calculate drug clearance (CL) from elimination rate and concentration, or from the first-order relationship CL = k · Vd. In linear mode, derive k from half-life when needed and review the related half-life relationship. This calculator is for pharmacokinetic calculations and is not medical advice. ## Inputs - **Calculation Mode** (select) - **Elimination rate (mg/h)** (number): Mass eliminated per unit time. Required in Definition mode. - **Concentration C (mg/L)** (number): Blood/plasma concentration. Required in Definition mode. - **Elimination rate constant k (h⁻¹)** (number): First-order elimination rate constant. Linear mode: provide k OR t½. - **Half-life t½ (h, alternative to k)** (number): Optional half-life; if provided, k = ln2 / t½. - **Volume of distribution Vd (L)** (number): Apparent volume of distribution. Required in Linear mode. - **Decimal Places** (number) ## When to use - Calculate clearance directly from an elimination rate in mg/h and concentration in mg/L. - Estimate clearance in a first-order elimination model using k and volume of distribution. - Derive the elimination rate constant from a drug half-life and check the CL–Vd–t½ relationship. ## How it works - Choose Definition mode to calculate CL = elimination rate ÷ concentration. - Choose Linear mode and enter Vd with either k or half-life. - When half-life is provided, the calculator derives k using k = ln2 ÷ t½, then calculates CL = k · Vd. - The JSON result reports clearance in L/h and, in linear mode, the calculated k and half-life relationship. ## Use cases - Pharmacokinetics coursework involving clearance, half-life, k, and Vd. - Checking a direct clearance calculation from measured elimination rate and concentration. - Comparing clearance estimates from first-order half-life and volume-of-distribution data. ## Frequently asked questions ### What is drug clearance? Clearance is the apparent volume of plasma or blood cleared of drug per unit time, reported here in L/h. ### Which inputs are required in Definition mode? Enter elimination rate in mg/h and concentration in mg/L. ### Which inputs are required in Linear mode? Enter volume of distribution in liters and either k in h⁻¹ or half-life in hours. ### Can I use both k and half-life? The calculator can use half-life to derive k; linear mode is based on first-order elimination. ### Does linear mode apply to every drug? No. Linear mode applies only to first-order elimination, not to Michaelis–Menten drugs such as phenytoin or high-dose ethanol. ## Related tools - [A-a Gradient (Alveolar-Arterial O₂)](https://elysiatools.com/en/tools/a-a-gradient-calculator): Calculate the alveolar-arterial O₂ gradient to distinguish hypoxemia causes. PAO₂ = FiO₂×(P_atm−47) − PaCO₂/0.8; A-a = PAO₂ − PaO₂. Normal ≈ (Age+10)/4. Elevated → V/Q mismatch, shunt, diffusion impairment. 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