Calculator Inputs
Use one elimination input. Clearance is prioritized, then k, then half-life.
Example Data Table
These rows are illustrative sample profiles for quick benchmarking.
| Scenario | Model | Dose (mg) | F (%) | Vd (L) | CL (L/h) | ka (1/h) | τ (h) | Target Css Avg (mg/L) |
|---|---|---|---|---|---|---|---|---|
| Example A | Oral | 500 | 85 | 40 | 4.5 | 1.2 | 12 | 6 |
| Example B | IV Bolus | 250 | 100 | 18 | 2.4 | — | 8 | 4 |
| Example C | Oral | 750 | 70 | 55 | 5.8 | 1.6 | 24 | 5 |
Formula Used
1) Elimination rate constant: k = CL / Vd
2) Half-life: t½ = ln(2) / k
3) IV bolus concentration: C(t) = (Dose / Vd) × e-kt
4) Oral concentration: C(t) = [F × Dose × ka / (Vd × (ka - k))] × (e-kt - e-ka t)
5) Exposure: AUC₀-∞ = (F × Dose) / CL
6) Average steady-state concentration: Css,avg = (F × Dose) / (CL × τ)
7) Loading dose: LD = (Target concentration × Vd) / F
8) Maintenance dose: MD = (Target concentration × CL × τ) / F
The page uses a simplified one-compartment approach. It is useful for estimation, classroom work, and early dosing comparisons.
How to Use This Calculator
- Select the model type: oral absorption or IV bolus.
- Enter dose and volume of distribution.
- For oral calculations, provide bioavailability and ka.
- Enter one elimination input: clearance, k, or half-life.
- Set the evaluation time and dosing interval.
- Add a target average steady-state concentration for dose planning.
- Press calculate to show results above the form.
- Review the chart, prediction table, and exports.
Frequently Asked Questions
1) What does this pharmacokinetics calculator estimate?
It estimates concentration at a chosen time, elimination rate constant, half-life, clearance, volume of distribution, AUC, average steady-state concentration, and practical dose planning values.
2) Which elimination input should I enter?
Enter clearance, elimination rate constant, or half-life. The calculator only needs one. If you enter more than one, it prioritizes clearance first, then k, then half-life.
3) Why is bioavailability ignored for IV bolus mode?
IV bolus dosing is assumed to reach systemic circulation completely and immediately. That means bioavailability is treated as 100 percent by definition in this simplified model.
4) Why does the oral model need ka?
The oral model uses first-order absorption. ka controls how quickly the drug enters circulation. Without ka, the calculator cannot shape the oral concentration-time curve correctly.
5) What does AUC represent?
AUC is the area under the concentration-time curve. It reflects overall systemic exposure to the drug after a dose under the assumptions used here.
6) Is this suitable for real patient dosing?
It is best for education, screening, and quick planning. Real dosing decisions should also consider clinical status, sampling data, nonlinear behavior, organ function, and specialist guidance.
7) Why might Tmax be unavailable?
In the oral one-compartment expression, Tmax is typically defined when ka is greater than k. If absorption is not faster than elimination, the simple analytical Tmax expression becomes unsuitable.
8) What do the CSV and PDF options export?
They export the calculated result summary and the predicted concentration table. That makes it easier to share scenarios, archive runs, or compare profiles outside the page.