Pharmacokinetics 1 Flashcards
What is bioavailability?
Fraction of unchanged drug that reaches the systemic circulation
What gives 100% bioavailability?
IV injection
What are the four ways small molecules cross cell membranes?
1) Diffusing directly through the lipid
2) Diffusing through aqueous pores
3) Transmembrane carrier protein
4) Pinocytosis (mostly macromolecules, not drugs)
Describe lipid diffusion of drugs
- Hydrophilic drugs are soluble in aqueous, polar media
* Lipophilic drugs are soluble in fats and non-polar solutions
What are the polar media?
- blood plasma
- Cytosol
- Intersitial fluid
What are the non-polar media?
- Interior of the lipid bilayer
* Fat
Which type of dugs have low lipid solubility?
Ionised drugs
What does a drugs ionised:unionised ratio depend on?
The pH
What are the main drug properties that affect absorption?
- Lipophilicty
* Ionisation
What are the factors that affect distribution?
- Degree of drug ionisation
- Lipid solubility
- ph of compartments
- Cardiac output and blood flow
- Capillary permeability
- Plasma protein binding
What do phosphate groups have a high affinity for? And what does this mean for their distribution?
- Calcium
* Quickly distributed to the skeleton
What are the pharmacological properties of pilocarpine?
Non selective muscarinic agonist
What are the pharmacological properties of Bethanechol?
Non-selective muscarinic agonist
What are the clinical uses of pilocarpine?
- Constriction of pupils (miosis)
- Glaucoma (to decrease IOP)
- Xerostomia (following head/neck radiotherapy)
What are the clinical uses of bethanechol?
Bladder and GI hypotonia
What is the structure of bethanechol?
Quaternary amine
What is the structure of Pilocarpine
Tertiary amine
What are the 5 stages of drugs in the body
1) Liberation
2) Absorption
3) Distribution
4) Metabolism
5) Excretion
What are the advantages and disadvantages of oral administration?
Advantages:
• Convenient
Disadvantages:
• First pass effect, many barriers and variables
What are the advantages and disadvantages of sublingual administration?
Advantages: • No first pass effect Disadvantages: • Inconvenient • Small dose limit • Taste
What are the advantages and disadvantages of inhalation administration?
Advantages: • Fast • Rapid delivery to blood Disadvantages: • Requires special properties of the drug (atomised, vaporised)
What are the advantages and disadvantages of Topical administration?
Advantages: • Convenient • Localised Disadvantages: • Only local
What are the advantages and disadvantages of transdermal administration?
Advantages:
• Prolonged release
Disadvantages:
• Skin is a very effective barrier
What are the advantages and disadvantages of Intramuscular administration?
Advantages: • Rapid for aqueous • Slow for oil Disadvantages: • Painful • Requires trained personnel
