Pharmacolgoy

• What is absorption of a drug?

  • From outside of the body to inside of rhe body
  • Routes of administration, the bioavailability and the drug properties
• Oral bioavailability is the fraction of a drug that gets into the systemic circulation. For example a drug with 100% bioavailability would all end up in the blood plasma
• What is the distribution of a drug?

  • How the drug gets from one place to another
  • Includes the volume of distribution, the blood flow, and the drug properties
• Volume of distribution of a drug is a pharmacokinetic parameter that represents a drugs ability to either remain in the plasma or redistribute to other tissue compartments.
• Volume of distribution is represented as Vd
• Volume of distribution = the amount of drug in the body / concentration in plasma
• Drugs are metabolised in 3 phases:

  1. Phase 1 - drugs become more polar and soluble
  2. Phase 2 - follows on from phase 1 (even more polar and soluble)
  3. phase 3 - Increased size, polarity and solubility increases renal excretion
• rate of elimination is the amount of drug cleared from the blood plasma per unit time (mg)
• Drug clearance is the volume of blood cleared of the drug per unit time (ml)
• What is the metabolism of a drug?

  • Changing the drug from one thing to another
  • Involves biotransformation, transforming enzymes and biological properties
• Clearance = The rate of elimination (mg.min-1)/ the concentration of the drug (mg.ml-1)
• The half life is the time (min) taken for plasma concentration to fall by half
• The rate constant of elimination (ke) is the proportion of a drug (unitless) eliminated in 1 unit of time
• 1st order elimination is constant clearance. Zero order elimination is a constant rate of elimination (and a lot more complex)
• The dose rate = clearance X concentration
• In a patient with AKI, what classes of drugs do you need to stop which may further impair kidney function?

  • ACE inhibitors
  • NSAIDS
  • Diuretics
  • ARBs