Pharmacokinetics Calculator

Inputs

Enter known parameters, and optionally paste observed time-concentration pairs. Leave unknown fields blank when you want them derived.

Route

Regimen

Dose

Bioavailability (F)

For IV bolus, F is fixed to 1.

Volume of distribution (Vd)

Clearance (CL)

L/hr

Half-life

If provided, Ke is derived as ln(2)/t1/2.

Elimination rate constant (Ke)

1/hr

Optional; overrides half-life if entered.

Absorption rate constant (Ka)

1/hr

Dosing interval (tau)

Used for steady state and target maintenance dose.

Target concentration (optional)

Used to suggest loading and maintenance doses.

Observed Time-Concentration Data (optional)

Paste pairs as "time, concentration" per line. Example: 0, 12.4

Terminal points for Ke fit

Uses the last N positive concentrations.

Bioavailability from Reference AUCs (optional)

If you have paired oral and IV studies, estimate F from AUC and dose.

AUC (oral)

Dose (oral)

AUC (IV)

Dose (IV)

Simulation Settings (optional)

Duration

Step

Smaller steps create more rows.

Reset

Example Data Table

Sample values demonstrate a typical oral model with steady-state settings.

Input	Value	Output (selected)	Result
Dose	500 mg	Half-life	6 hr
Route	Oral	Ke	0.1155 1/hr
F	0.8	CL	4.62 L/hr (if Vd=40 L)
Vd	40 L	AUC0-inf	86.6 mg*hr/L (model)
Ka	1.2 1/hr	Tmax / Cmax	~2.1 hr / ~7.2 mg/L
tau	12 hr	Css,avg	~1.56 mg/L (model)

Exact outputs depend on supplied fields and data usage.

Formula Used

Elimination constant: Ke = ln(2) / t1/2
Clearance and distribution: CL = Ke * Vd, and Vd = CL / Ke
IV bolus concentration: C(t) = (Dose / Vd) * e^(−Ke*t)
Oral concentration (first-order absorption): C(t) = (F*Dose*Ka)/(Vd*(Ka−Ke)) * (e^(−Ke*t) − e^(−Ka*t))
Exposure: AUC0-inf = (F*Dose) / CL (model-based)
Steady state (average): Css,avg = (F*Dose) / (CL*tau)
Steady state (accumulation): R = 1 / (1 − e^(−Ke*tau))
Observed trapezoidal exposure: AUC0-last = Σ (Ci+Ci+1)/2 * dt
Terminal extrapolation: AUC0-inf = AUC0-last + Clast/Ke
MRT (optional): MRT = AUMC0-inf / AUC0-inf

How to Use This Calculator

Select route and regimen, then enter dose and known parameters.
Enter either half-life, Ke, or CL and Vd to define elimination.
For oral dosing, provide Ka to model absorption and peaks.
Optionally paste time-concentration pairs to compute AUC and Ke.
Press Calculate to view results above the form.
Download CSV or PDF to archive outputs and simulations.

Educational tool only; validate with professional workflows.

FAQs

1) What does clearance represent?

Clearance is the effective volume of fluid cleared of drug per unit time. It connects dose to exposure: higher clearance generally produces a smaller AUC for the same dose.

2) Why do I need Ka for oral dosing?

Ka governs absorption speed and peak timing. If Ka is close to Ke, the peak becomes hard to define and the simple one-compartment absorption model may be unreliable.

3) When should I paste time-concentration data?

Use it when you have measured samples. The calculator estimates AUC using trapezoids and approximates terminal Ke from the last few positive points.

4) How is half-life related to Ke?

For first-order elimination, half-life is t1/2 = ln(2)/Ke. Larger Ke means faster elimination and a shorter half-life.

5) What is steady state and how long does it take?

Steady state occurs when average concentrations stop rising with repeated dosing. A practical guide is 4–5 half-lives; this tool also shows 90%, 95%, and 99% times.

6) What is the accumulation factor R?

R measures buildup during repeated dosing. It depends on Ke and tau: shorter tau or slower elimination increases accumulation.

7) Why might my results show warnings?

Warnings appear when inputs are missing or unusual, such as Ka ≤ Ke, nonpositive dose, or F outside typical ranges. They help detect unit errors early.

8) Can I use this for clinical dosing decisions?

This calculator is for education. Real dosing decisions require patient-specific data, validated models, assay details, and professional review using accepted clinical workflows.