Basic principles of pharmacotherapy

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Basic principles of pharmacotherapy

  1. 1. Basic Principles of Pharmacotherapy By Mohammad H. Farjoo
  2. 2. Pharmacotherapy • Why is it necessary ? • Preadministration factors: • Bioequivalency • Absolute (oral to IV) • Relative (test to standard) • Patient compliance • Chronopharmacology • Used in cancer therapy • Applies to CsA , Aspirin & propranolol
  3. 3. What does it depend on ? 1. Pharmacokinetic : Dose– Concentration relationship 1. Absorption (How rapidly?) 2. Distribution (What concentration?) 3. Elimination (How long?) 2. Pharmacodynamy : Concentration–Effect relationship 1. Drug concentration at receptor site 2. Drug – Receptor affinity 3. Post receptor efficiency Pharmacotherapy Sensitivity Disposition
  4. 4. Absorption • Definition • Poor for too hydrophobe/hydrophil drugs • May vary with protein/lipid content of food Eg:CsA , Sirolimus • AUC measures extent of absorption & tmax measures its rate • Sometimes is Ph dependent • First pass effect • Enterohepatic cycle
  5. 5. Disposition • What is it ? • Categorized to : • Distribution • Volume of distribution • Loading dose • Elimination (clearance) • Excretion • metabolism
  6. 6. Volume of distribution • Definition • Vd = Amount of drug / concentration • High Vd means drug escape from vessels & vice versa • Vd is a balance between protein binding in tissue and that of blood • Varies in pathological conditions • Vd of more than 42 Lit. reflects tissue binding
  7. 7. Loading dose • What is it ? • When is it necessary ? • Loading dose = Vd X concentration • Not only amount but rate of administration is important
  8. 8. Elimination (clearance) • What is it ? And why should it occur? • First order : – Elimination rate = CL x Concentration – Depends on drug Concentration (Not CL) – Not saturable – Applies to most of the drugs • Zero order (many other names) – Elimination rate is non linear (so it is dangerous) – Applies to Aspirin , Ethanol , Phenytoin
  9. 9. • Good correlation between renal (But not liver) dysfunction & clearance • Affected by “Inducers & Inhibitors” – Drugs – Smoking & Alcoholism – Food !! • Not all the excretions cause elimination! Elimination (clearance)
  10. 10. Other important factors : • Half life • Protein binding • Drug interactions • Therapeutic drug monitoring (TDM)

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