Pharmacokinetics - Nursing

1. Week 11
Pharmacokinetics

2. 1. Absorption
• movement of drug from administration site, across
membranes to circulating fluids
• affected by dissolution of drug thus affecting
bioavailability of drug e.g. Pepcid => dissolves in seconds
where it goes to the stomach and blocks acid secretion
• Liquid absorbed faster
• Digestive motility
• Blood flow
• Drug formulation: size, ionization, pH
• Other foods and meds e.g. iron delays absorption of
antibiotics
• Acids absorbed in acids and bases absorbed in bases

3. 2. Distribution
• transport of drugs through the body => blood
flow
• Some areas have affinity for storage e.g. teeth,
bone marrow, adipose tissue e.g. valium
• Some drugs bind to plasma protein and cannot
cross capillary membranes until released e.g.
Warfarin
• Fetal-placental barrier and blood brain barrier

4. 3. Metabolism
• or biotransformation: process of chemically
converting a drug to a form that is more easily
excreted from the body
• Liver is primary site where metabolism is
achieved by the P-450 system eg. Codeine to
Morphine
• Hepatic enzyme activity decreased in infants and
elderly
• First pass effect: drugs rendered inactive by liver
metabolism thus give IV, rectally, sublingual e.g.
morphine

5. 4. Excretion
• rate of drug removal from body
• Primary site is kidney
• Affected by: liver or kidney impairment
• Blood flow
• Metabolism
• pH
• Ionization
• Drug-protein complexes
• Renal failure?
• Also, respiration, saliva, sweat, breast milk, bile

6. Pharmacokinetics
• Onset
• Peak
• Therapeutic action
• Termination of action
• Plasma half life (t ½)
• Length of time required for the plasma
concentration of a drug to decrease by ½ after
administration
• Loading doses and maintenance doses