1. What is Drug Half-Life?

Drug half-life (t₁/₂) is the time required for the concentration of a drug in the body to decrease by half. It's a crucial pharmacokinetic parameter that determines dosing intervals and helps predict drug accumulation and elimination.

2. How Does the Calculator Work?

The calculator uses the half-life equation:

Where:

• \( t_{1/2} \) — Half-life (hours)
• \( k_e \) — Elimination rate constant (h⁻¹)
• 0.693 — Natural logarithm of 2 (ln(2))

Explanation: The elimination rate constant represents the fraction of drug eliminated per unit time, and half-life is inversely proportional to this rate.

3. Importance of Half-Life Calculation

Details: Half-life calculation is essential for determining appropriate dosing regimens, predicting steady-state concentrations, understanding drug accumulation, and planning therapeutic drug monitoring.

4. Using the Calculator

Tips: Enter the elimination rate constant in h⁻¹. The value must be greater than zero. The calculator will compute the corresponding half-life in hours.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical drug half-life range?
A: Drug half-lives vary widely from minutes (e.g., adenosine) to weeks (e.g., amiodarone). Most drugs have half-lives between 1-24 hours.

Q2: How does half-life affect dosing frequency?
A: Drugs with shorter half-lives require more frequent dosing, while drugs with longer half-lives can be dosed less frequently.

Q3: What is the relationship between half-life and steady-state?
A: Steady-state concentration is reached after approximately 4-5 half-lives of consistent dosing.

Q4: Can half-life be affected by patient factors?
A: Yes, factors like age, renal/hepatic function, drug interactions, and genetics can significantly alter drug half-life.

Q5: How is elimination rate constant determined?
A: kₑ is typically determined from the slope of the terminal phase of the drug concentration-time curve on a semi-log plot.