1. What is Drug Half-Life?

The half-life of a drug is the time it takes for the concentration of the drug in the body to be reduced by half. It's a crucial pharmacokinetic parameter that helps determine dosing intervals and duration of drug action.

2. How Does the Calculator Work?

The calculator uses the half-life equation:

Where:

• \( t_{1/2} \) — Drug half-life (hours)
• \( k \) — Elimination rate constant (1/h)
• \( \ln(2) \) — Natural logarithm of 2 (~0.693)

Explanation: The equation shows that half-life is inversely proportional to the elimination rate constant. A higher elimination rate means a shorter half-life.

3. Importance of Half-Life Calculation

Details: Knowing a drug's half-life helps determine dosing frequency, time to reach steady state, and time for complete elimination from the body. It's essential for therapeutic drug monitoring and avoiding toxicity.

4. Using the Calculator

Tips: Enter the elimination rate constant (k) in reciprocal hours (1/h). The value must be greater than 0. The result will be the half-life in hours.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical drug half-life range?
A: 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 many half-lives to eliminate a drug?
A: About 5 half-lives for ~97% elimination. This is why loading doses are sometimes needed for drugs with long half-lives.

Q3: What affects drug half-life?
A: Metabolism, excretion, protein binding, volume of distribution, and patient factors like age, liver/kidney function.

Q4: How is steady state related to half-life?
A: Steady state is reached in about 4-5 half-lives with regular dosing. This is when drug accumulation equals elimination.

Q5: Can half-life change in a patient?
A: Yes, due to changes in organ function, drug interactions, or disease states affecting pharmacokinetics.