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 reduce 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:

• \( t_{1/2} \) — Half-life (hours)
• \( V_d \) — Volume of distribution (liters)
• \( CL \) — Clearance (liters/hour)
• \( \ln(2) \) — Natural logarithm of 2 (~0.693)

Explanation: The equation shows that half-life is directly proportional to volume of distribution and inversely proportional to clearance.

3. Importance of Half-life Calculation

Details: Knowing a drug's half-life helps determine appropriate dosing intervals, predict steady-state concentrations, and estimate how long a drug will remain in the body after discontinuation.

4. Using the Calculator

Tips: Enter volume of distribution in liters and clearance in liters/hour. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical half-life range for drugs?
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: How does half-life affect dosing?
A: Drugs with shorter half-lives typically require more frequent dosing to maintain therapeutic levels.

Q4: Can half-life change in patients?
A: Yes, factors like renal/hepatic impairment, age, and drug interactions can significantly alter half-life.

Q5: What's the difference between t_1/2α and t_1/2β?
A: These represent distribution and elimination half-lives in two-compartment models, with α phase being faster.