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Learning objectives

Learn about available data from pharmacokinetic studies, calculate pharmacokinetic parameters, and understand their implications for therapy and dosage regimens. Explore how pharmacokinetic parameters can be used in drug design and formulation development.

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Learning objectives

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  1. Learning objectives • To know what data is available from pharmacokinetic studies in man and how to handle it • To know how to calculate the basic pharmacokinetic parameters of clearance, t(half); volume of distribution, bioavailability; Kel • To understand the implications of these parameters for satisfactory therapy and the construction of suitable dosage regimens for patients • To know how knowledge of pharmacokinetic parameters can be exploited in drug design and formulation development.

  2. Pharmacokinetics • Study of ADME on a quantitative basis In man study blood, urine, faeces, expired air. Measure urine volume & concentration of drug conc in urine x vol per min = RENAL plasma concentration CLEARANCE If neither secreted nor reabsorbed then clearance = clearance of inulin = 120 ml/min If completely cleared by secretion then clearance = clearance of p-hippuric acid = renal blood flow = 700 ml/min

  3. Plasma concentration -tKel Ct=Co e lnCt = lnCo - Kel t logCt = logCo - Kel . t 2.303 y = c m x

  4. Bioavailability Plasma concentration i.v. route (AUC)o / (AUC)iv oral route Time (hours)

  5. =1.5;antilog 1.5 = 31.6 logCt = logCo - Kel . t 2.303 TIME (hours) log plasma concentration

  6. Pharmacokinetic parameters • Volume of distribution V = DOSE / Co • Plasma clearance Cl = Kel .V • plasma half-life (t1/2) directly from graph or t1/2 = 0.693 / Kel • Bioavailability (AUC)x / (AUC)iv

  7. Multiple dosing • On multiple dosing plasma concentration will rise and fall with each dose andwill increase until administration = elimination ie. steady state is reached. • At steady state hourly dose rate (D=dose; T=interval between doses in hours) D/T = clearance x plasma conc or steady state conc = D/(T x clearance) • At each dose the level will oscillate through D/V

  8. plasma conc toxic effective Cumulation and use of loading doses Time

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