CoreEquationsCardiovascularSystem1

CoreEquationsCardiovascularSystem1 - Cardiovascular System...

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Cardiovascular System 1 Core Equations Fall 2010 1 Nora Laiken, PhD CORE EQUATIONS IN THE CARDIOVASCULAR SYSTEM 1 BLOCK 1, 2 Lecture Equation Comments Drug-Receptor Interactions Fractional saturation = [D] / {[R] + [DR]} Therapeutic index = LD 50 / ED 50 Concepts in Clinical Pharmacology Fick’s law of diffusion: dQ/dt = D · PC · A · dC/dx *Henderson-Hasselbalch equations: Weak acid: pH = pK a + log [A - ]/[HA] Fraction non-ionized = 1/(1 + 10 pH - pK ) Weak base: pH = pK a + log [B]/[HB + ] Fraction non-ionized = 1/(1 + 10 pK - pH ) Volume of distribution: V d = Dose/Cp o Body fluid compartments: TBW = 0.60 · Body weight ECF = 1/3 of TBW = 0.20 · Body weight ICF = 2/3 of TBW = 0.40 · Body weight Plasma = 1/4 of ECF = 0.05 · Body weight ISF = 3/4 of ECF = 0.15 · Body weight *First-order kinetics: -dCp/dt = k e · Cp t 1/2 = 0.69 / k e *Zero-order kinetics: -dCp/dt = k e *Bioavailability = (AUC) oral / (AUC) IV Dose is expressed per unit body weight Units: volume/body weight (e.g., liters/kg) Note that Cp o can be difficult to determine; best method is to administer the drug IV and extrapolate a linear elimination curve to t=0 Non-obese young adult male Units of k e : time -1 (e.g., min -1 , hr -1 ) Constant fraction of drug eliminated per unit time Most common kinetics Graph of log Cp vs. t is linear
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CoreEquationsCardiovascularSystem1 - Cardiovascular System...

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