Pharmacokinetics Flashcards
What are the 6 rights of prescribing?
- Right patient
- Right drug
- Right route
- Right dose
- Right time
- Right outcome
What is the first journey of drugs?
What is pharmacokinetics?
‘What the body does to the drug’
What are the uses of pharamcokinetics?
- Facilitates safe and effective use of medicines
- Determines optimal dosage regimen (dose, route, dose interval, duration of treatment)
- Predicts potential drug interactions
What are the 4 stages of pharamcokinetics?
- Absorption
- Distribution
- Metabolism
- Excretion
What is absorption?
Drug transfer from its site of administration to the systemic circulation (blood).
What are the 4 enteral routes of drug administration?
- Oral
- Rectal
- Sublingual
- Buccal
What factors affect enteral absorption?
- Gastrointestinal (GI) motility
- Absorptive area
- GI blood flow
- Drug particle size and formulation
- Drug physicochemical properties
- Drug binding
What factors affect Drug physicochemical properties of solubility?
- Lipid Soluble = Non-ionized molecules (NaCl)
- Hydrophilic (Polar) = Ionized molecules (Na+; K+)
So:
The more lipid soluble a drug the ________ the absorption
The more water soluble a drug the _______ the absorption
So:
The more lipid soluble a drug the greater the absorption
The more water soluble a drug the less the absorption
What factors affect Drug physicochemical properties of pH?
- Acidic Drugs are better absorbed in acidic media
- Basic Drugs are better absorbed in basic media
- Acidic (Aspirin) better absorbed in the stomach
- Basic (Diazepam) better absorbed in intestines
- Acidic drugs are better excreted in ____ media
- Basic drug better excreted in _____ media
- Acidic drugs are better excreted in basic media
- Basic drug better excreted in acidic media
Can be important in poisoning!!
What are the 4 routes of parenteral drug administration?
Name 4 other routes of drug administration
- Topical
- Transdermal
- Inhalational
- Intrathecal (straight into CSF)
Label the lines
Name the key pharmacokinetics concepts
- Absorption
- First-pass (pre-systemic metabolism)
- Bioavailability
- Bioequivalence
- Volume of distribution
- Cytochrome P450 enzyme system
- Half-life
- Steady state
- Clearance
What is bioavailability?
Fraction of the administered (oral) dose of a drug that reaches the systemic circulation.
What is the equation for bioavailability?
Label each line
If a drug has an oral bioavailability of 20%, the oral dose needed for therapeutic effectiveness will need to be approximately ___ times higher than the corresponding IV dose
5
What is first pass (pre-systemic) metabolism?
This refers to metabolism of the drug prior to reaching systemic circulation.
What is the effect of first pass metabolism on bioavailability?
What is bioequivalence?
Bioequivalence = Two drugs are considered bioequivalent when there is no significant difference in the rate or extent of bioavailability at the same molar dose and under the same conditions
What is the relevance of bioequivalence?
Relevance:
Different formulations from different companies
Different batches of drugs from the same company
Where do most drugs end up after absorption?
Systemic circulation
What is drug distribution?
- Process by which the drug is transferred reversibly from the systemic circulation into the tissues as concentrations in the blood increase, and from the tissues into blood when the blood concentrations decrease during elimination.
- Distribution of the drug into vascular, interstitial and intracellular compartments.
How does drug distribution occur?
- Most drugs transfer by passive diffusion
- Across capillary walls down a concentration gradient
- Into interstitial fluid until concentration of free drug molecules in interstitium is equal to that in plasma
Which drugs undergo which type of transport across membranes?
What is plasma protein binding?
•Drugs bind non-specifically to albumin in plasma