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Standard first-order pharmacokinetic elimination formula, a foundational concept taught in pharmacology: N(t) = N0 x (1/2)^(t / t_half), where a drug's amount in the body is cut in half every one half-life. The half-life is a direct user input (not a per-drug lookup table), keeping this a generic pharmacokinetics education tool rather than drug-specific medical advice. This is for general pharmacokinetics education only — explicitly not a tool for making actual dosing decisions. Consult a doctor or pharmacist for real medication dosing and timing.
How it works
Enter an initial dose/amount, the drug's known half-life (in hours), and the elapsed time. The tool applies the standard exponential decay formula to compute the remaining amount and percentage remaining.
- Enter initial dose / amount (any unit).
- Enter drug's half-life (hours).
- Enter elapsed time (hours).
- Click Calculate to see your results.
Examples
Initial dose 100, half-life 6 hours, elapsed 12 hours
12/6 = 2 half-lives elapsed. Remaining = 100 x 0.5^2 = 25 (25% of the initial dose).
Who should use it
- Pharmacology and nursing student education.
- Understanding how "half-life" works conceptually.
Industry applications
- Pharmacology education
- Nursing and pre-med curriculum support
Advantages
- Teaches a foundational, universal pharmacokinetics concept.
- Generic (half-life is user-supplied, not drug-specific).
Limitations
- Real drug elimination can be more complex than simple first-order kinetics (e.g. zero-order kinetics for some drugs, multi-compartment models).
- Not a substitute for actual medical dosing guidance.
Common mistakes to avoid
- Using this tool for actual medication timing/dosing decisions rather than for learning the underlying pharmacokinetic concept.
- Mixing time units (e.g. entering half-life in hours but elapsed time in minutes).
Best practices
- Use this tool only to understand the general shape of first-order drug elimination, and always follow your prescriber's or pharmacist's actual instructions for real medications.
Tips
- After about 5 half-lives, less than 4% of the original amount typically remains — a commonly cited pharmacology rule of thumb for when a drug is considered largely eliminated.