Clearance II- Hepatic

Clearance II- Hepatic - Clearance II- Hepatic...

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Unformatted text preview: Clearance II- Hepatic Continuous/Multiple Dosing Am ount Present versus Tim e Tim e 0 5 1 0 1 5 2 0 2 5 Amount Present 5 10 15 20 Ra = 4 %loss = 0.5 SS= 8 If beaker = 4 L then Cl = 4*0.5=2 L/min Ra = 4 %loss = 0.25 SS= 16 Quantitative Relationships Amount reaches a steady state Steady state depends on Rate of Administration - R A Rate of Excretion - R E Clearance proportionality constant C pss,avg = R A / Cl T Inverse if clearance reduced, Css increases Clearance Artificial not really that x ml/min totally cleared but mathematically behaves that way (Gatorade example) Fundamental the body works this way Moving fluids with known rates R A = Cl * C pss, avg Pharmacology determines Cp, Cl determines administration rate Maintenance Dose To maintain steady state at SS R A = R E R A = Cl * C pss, avg R A = S*F*Dose/tau = Cl * C pss, avg Therefore Cl = [S*F*dose/tau]/C pss, avg Dose = [Cl *C pss, avg *tau]/S*F Maintenance Dose Infusion Rate mass/time (mg/hr) dose/tau (R A ) if constant infusion can call is R Maintenance Dose required to produce desired C pss, avg MD =Dose = [Cl *C pss, avg *tau]/S*F iv infusion tau is duration of infusion (mg/hr for example) Oral tau is time between dosing* q6hr (Note for oral dosing this is an approximation) Half-Life Clearance determines wash out rate Half-life time for half to be cleared t = ln2*V d /Cl ln 2 = 0.693 ~ 0.7 Factors affecting Cl Body weight (size) Renal and Hepatic Function extraction ratio Protein Binding Cardiac Output Body Weight Size Function is proportional to size...
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This note was uploaded on 08/26/2010 for the course PHRM 231 taught by Professor N/a during the Fall '07 term at UConn.

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Clearance II- Hepatic - Clearance II- Hepatic...

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