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Objective: Explain the variation in dosing intervals for medications

Objective: Explain the variation in dosing intervals for medications. Introduce Half-Life (t 1/2 ) Relate Half-Life to Dosing intervals of aspirin and Aleve pain relievers Longevity of a Single Dose Time to Therapeutic Steady State. Half-Life-t 1/2.

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Objective: Explain the variation in dosing intervals for medications

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  1. Objective: Explain the variation in dosing intervals for medications • Introduce Half-Life (t1/2) • Relate Half-Life to • Dosing intervals of aspirin and Aleve pain relievers • Longevity of a Single Dose • Time to Therapeutic Steady State

  2. Half-Life-t1/2 The time it takes a substance to decrease to half of a previous value. 2H2O2 O2 + 2H2O Hydrogen Peroxide t1/2 = 654 minutes, appx 11 hours √

  3. Hydrogen Peroxide Half-Life Half-Life is a good predictor of how long a substance will exist 50%> 25%> 12.5%> <6.25% 2 1 3 4

  4. Drug Half-Life The time required for the total amount of a drug in blood plasma to diminish by half, once the drug reaches its peak concentration. Peak Time to Peak: 1.5hrs t1/2 = 2hrs √ Time to peak

  5. Examples of Different Drug Half-Lives Peak Amounts

  6. Dosing Intervals Half-Life In general, next dose is given once the previous dose reaches its half-life Normal Dose Interval is based on one Half-Life PDR: Physicians Desk Reference √

  7. Draw Half-Life curves for Aspirin and Aleve Estimate the Amount and Percent of Drug remaining after two Half-Lives

  8. 50% 25%

  9. 50% 25%

  10. Why do Drugs Have Different Half-Lives? • Pharmacokinetics • Absorption • Distribution • Metabolism • Excretion O- Na+ Sodium Molecular Structure Bond Polarity √

  11. Half-Life and Longevity of a Single Dose Rule of thumb: For a single dose, a drug is eliminated from the body after five half-lives.

  12. Half-Life and Therapeutic Steady State Level Rule of thumb: It takes five dose intervals for a drug to reach a therapeutic steady state level. 5 About How Many Half-Lives? √

  13. Q: What if a drug has too long of a half life to relieve a condition? A: A loading dose is administered followed by maintenance doses

  14. Examples of Drugs administered with Loading + Maintenance doses Digoxin: Treat arrhythmia t1/2 = 1.6 days. 8 To reach therapeutic steady statewould take __?__ days or five half lives. Medrol: Steroid to reduce inflammation How much time would pass to attain a therapeutic steady state amount? t1/2 = 18-26 hours About 5 days

  15. What to Know… • Half-Life: The time it takes a substance to decrease to half of a previous value. • Half-Life is a good predictor of how long a substance will exist. • Drug Half-Life: The time required for the total amount of a drug in blood to diminish by half, once the drug reaches its peak concentration. See PDR • How to construct a half-life curve for a drug. • A dose interval is approximately one Half-Life. • Pharmacokinetics is the study of reaction rates of drugs in biological systems. • Rule of thumb: For a single dose, a drug is eliminated from the body after five half-lives. • Rule of thumb: It takes five dose intervals or five half-lives for a drug to reach a therapeutic steady state amount.

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