Drug Half-Life Calculator

What is the Half-Life of a Drug?

The half-life of a drug refers to the time required for its concentration in the bloodstream to decrease by half. This metric is essential for evaluating:

• Drug Potency: How long a drug remains effective.
• Drug Toxicity: Risk of adverse effects due to accumulation.

Why is Half-Life Important?

Understanding a drug’s half-life helps in:

• Designing dosage schedules.
• Determining how long a drug stays in the system.
• Evaluating the safety of drugs with narrow therapeutic windows.

How to Use the Calculator

To use the Drug Half-Life Calculator, you need to input the following:

• Half-Life (T): The elimination half-life of the drug in minutes, hours, or days.
• Dosage (mg): The initial amount of the drug administered.

The calculator then generates a table showing the time elapsed, remaining drug dosage, and concentration for at least five half-life cycles.

Formula Used

The calculator employs the formula:
Dosage(t) = Dosage(0) × 0.5(t/T)
Where:

• TTT: Half-life of the drug.
• t: Time elapsed since the first administration.
• Dosage(t) – Amount of drug present in a patient's body after time t
• Dosage(0) – Amount of drug administered at the very beginning.

What's a Healthy Range or Unhealthy Range?

• Healthy Range: Drugs with predictable and controlled half-lives that allow for optimal dosing intervals, maintaining therapeutic effects without toxicity.
• Unhealthy Range: Drugs with very short or prolonged half-lives may lead to subtherapeutic levels or accumulation, causing toxicity.
• Short Half-Life: Requires frequent dosing to maintain efficacy.
• Long Half-Life: Risk of accumulation, especially in patients with liver or kidney impairment.

Example: Drugs with narrow therapeutic ranges (e.g., anticoagulants) require careful monitoring of half-life to avoid complications.