Reinhardt's Rundown: Pharmacokinetic Properties of Medications

Focus: Elimination Half-Life of a Drug

Definition

• Elimination Half-Life (t₁/₂):
  • The time it takes for the concentration of a drug in the plasma or bloodstream to reduce to half its original value.

Example: Zolpidem (Ambien)

• Zolpidem:
  • A hypnotic used for treating insomnia.
  • Example half-life: ~3 hours.

Elimination Process

• Initial Dose: 10 mg at 9 PM
  • Midnight (3 hours later):
    • 50% of dose eliminated.
    • 5 mg remains in bloodstream.
  • 3 AM (another 3 hours later):
    • Another 50% eliminated.
    • 2.5 mg remains.
  • 6 AM (another 3 hours later):
    • 1.25 mg remains.
  • 9 AM (another 3 hours later):
    • 0.625 mg remains.
  • Noon (12 PM):
    • 97% of the drug eliminated.
    • A very small amount remains.

Key Points

• Approximately 5 half-lives are needed for 97% of the drug to be eliminated.
• 7 half-lives for 99% elimination.

Considerations

• Therapeutic Elimination: Understanding half-lives helps determine when a drug is considered therapeutically eliminated from the blood.
• Detection: The elimination does not guarantee non-detectability in blood tests or drug screens.

Upcoming Topics

• Next video will cover how a medication's half-life informs dosing frequency.
• Real-life examples using ACE inhibitors, common for treating blood pressure and heart failure.

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This summary encapsulates the key points from the lecture on elimination half-life and how it applies to drugs like zolpidem, with a brief look at upcoming content on dosing and ACE inhibitors.