Pharmacokinetics Lecture 1 PDF

Subject Pharmacology Lecture 1 Pharmacokinetics Name: Anas Suleiman Number: 0790028580 1. Half-life (t½) Calculation Formula: t½ = 0.693 × (Vd / Cl) Explanation: Half-life is the time required for the concentration of the drug in the bloodstream to reduce by 50%. It is important for dete...

Subject Pharmacology Lecture 1 Pharmacokinetics Name: Anas Suleiman Number: 0790028580 1. Half-life (t½) Calculation Formula: t½ = 0.693 × (Vd / Cl) Explanation: Half-life is the time required for the concentration of the drug in the bloodstream to reduce by 50%. It is important for determining dosing schedules. Example: For a drug with a volume of distribution (Vd) of 100L and a clearance (Cl) of 10L/h, the half- life would be calculated as: t½ = 0.693 × (100L / 10L/h) = 6.93 hours 2. Volume of Distribution (Vd) Calculation Formula: Vd = Dose / C0 Explanation: The volume of distribution is the apparent volume in which the drug is distributed in the body, assuming uniform distribution. Example: If a 500 mg dose results in an initial concentration (C0) of 10 mg/L, then the Vd is: Vd = 500mg / 10mg/L = 50L 3. Clearance (Cl) Calculation Formula: Cl = Dose / AUC Explanation: Clearance refers to the body's ability to remove a drug, and AUC (Area Under the Curve) measures total drug exposure over time. Example: If a drug has a dose of 100 mg and an AUC of 20 mg·h/L, the clearance would be: Cl = 100mg / 20 mg·h/L = 5 L/h 4. Bioavailability (F) Calculation Formula: F = (AUC oral / AUC IV) × 100 Explanation: Bioavailability measures the fraction of the administered dose that reaches systemic circulation. IV administration provides 100% bioavailability, while oral forms have less. Example: If the AUC of an oral dose is 50 mg·h/L and that of IV is 100 mg·h/L, the bioavailability is: F = (50 / 100) × 100 = 50% 5. Maintenance Dose Calculation Formula: Maintenance Dose = (Css × Cl) / F Explanation: The maintenance dose is used to maintain a drug's steady-state concentration (Css). Css is the target concentration required to achieve the therapeutic effect. Example: With a target Css of 10 mg/L, a clearance (Cl) of 5 L/h, and F of 0.8, the maintenance dose is: Maintenance Dose = (10 mg/L × 5 L/h) / 0.8 = 62.5 mg 6. Loading Dose Calculation Formula: Loading Dose = (Css × Vd) / F Explanation: A loading dose is an initial higher dose used to quickly achieve therapeutic levels, especially for drugs with long half-lives. Example: For a desired Css of 15 mg/L, Vd of 50 L, and F of 0.9, the loading dose would be: Loading Dose = (15 mg/L × 50 L) / 0.9 = 833.33 mg