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 formula:

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:

• How often to administer the drug
• Time to reach steady state concentration
• Duration of drug effect after discontinuation
• Adjustment of dosing in renal/hepatic impairment

4. Using the Calculator

Tips:

• Enter volume of distribution in liters
• Enter clearance in liters/hour
• Both values must be positive numbers
• Result is given 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 also the time to reach steady state with regular dosing.

Q3: How does renal impairment affect half-life?
A: If clearance decreases (e.g., due to kidney disease), half-life increases, often requiring dose reduction or longer intervals.

Q4: What's the relationship between half-life and dosing interval?
A: Drugs are typically given at intervals equal to their half-life to maintain therapeutic levels without excessive fluctuation.

Q5: Can half-life vary between individuals?
A: Yes, due to factors like age, weight, genetics, liver/kidney function, and drug interactions affecting clearance or volume of distribution.