Drug Half-life Calculator

How to calculate Drug Half-life calculator?

The half-life is the time required for the drug concentration to decrease to half of its initial value assuming first-order elimination.

Use the formula: t_1/2 = (t × ln(2)) / ln(C0 / Ct), where C0 is the initial concentration, Ct is the concentration after time t, and ln is the natural logarithm.

Using the Drug Half-life calculator calculator: an example

Example values: initial concentration = 100 mg/L, concentration after 8 hours = 25 mg/L.

Step-by-step calculation:

• Start with C0 = 100 mg/L, Ct = 25 mg/L after t = 8 h.
• Compute ln(C0 / Ct): ln(100 / 25) = ln(4) ≈ 1.386.
• Compute t × ln(2): 8 × 0.693 ≈ 5.545.
• Calculate half-life: t₁/2 = 5.545 / 1.386 ≈ 4.0 hours.

Frequently Asked Questions

What does half-life indicate?

Half-life indicates the time required for the plasma concentration of a drug to fall to half its previous value under the assumed kinetic model.

Which kinetics does this formula assume?

This formula assumes first-order elimination (a single exponential decline). Multi-compartment behavior requires more complex models.

Can I use concentrations in different units?

Yes, you may use any units (e.g., mg/L or µg/mL) as long as C0 and Ct use the same unit so the ratio is dimensionless.

How can I improve the accuracy of the half-life estimate?

Use precise assay measurements, sample during the elimination phase (not distribution), and use multiple timepoints to confirm first-order behavior.