Lecture 30 Flashcards
What are the mechanisms of drug permeation?
- aqueous diffusion (paracellular)
- lipid diffusion (trancellular)
- special carriers
- endo and exocytosis
What is absorption when it comes to drugs?
transfer of a drug from its site of administration to the bloodstream
What form is complete absorption or delivery
IV
Explain the oral route of drugs
most convenient; absorption may be slower and less complete
suffers from first-pass effect (must go through gut wall and liver)
What are the enteral routes of drugs?
sublingual- by pass first-pass effect
rectal - partial avoidance
What are the paraenteral routes?
intravenous
intramuscular
subcutaneous
intradermal
What are other routes of drug administration?
oral inhalation
nasal inhalation
topical
transdermal
What factors influence drug absorption?
- pH
- surface area
- blood flow to desired site
- contact time
- P-glycoprotein
What are most drugs?
either weak acids or weak bases
What is the effect pH has on drug absorption?
The protonated form of a weak acid is the more liposoluble form
The unprotonated form of a weak base is the more liposoluble form
What kinds of drugs are excreted faster?
Weak acids are excreted faster in alkaline urine; weak bases are excreted faster in acidic urine.
Where does most drug absorption occur?
the small intestine bc of the large surface area
What is P-glycoprotein?
it is a transporter protein that is used to transport drugs across the cell membrane
reduces drug absorption
what is bioavailability?
Fraction of administered dose of a drug that
reaches the systemic circulation
how is bioavailability measured?
Bioavailability is determined comparing the AUC
after a particular route of administration with the
AUC after IV injection.
the area under the curve reflects the extent of absorption.
What is drug distribution
It is the process by which a drug leaves the
blood stream and enters the extracellular fluid
and /or the cells of the tissues
what affects drug distention?
blood flow
drug binding
capillary permeability
drug hydrophobicity
What kinds of drugs can enter the CNS?
highly liposoluable or have an active transporter
How does drug elimination occur?
metabolism and excretion
How does metabolism lead to drug elimination?
many drugs are lipophilic and are not easily excreted
drugs are broken down into hydrophilic compounds which ends biological activity and elimination from the body.
What enzymes are responsible for the metabolism of 80 percent of all drugs used?
cytochrome P450 system
What drugs increases the synthesis of one or more P450 isoforms?
rifampin
phenobarbital
carbamazepine
what are xenobiotic receptors?
They help regulate the transcriptional activation of genes
What are the clinical consequences of enzyme induction?
A drug can increase its own metabolism
A drug can increase the metabolism of a coadministered drug.
This may reduce drug plasma concentrations below therapeutic levels
What are drugs that inhibit cytochromes P450?
- Cimetidine
- Erythromycin
- Chloramphenicol
- Grapefruit juice
What is the most common form of drug elimination?
renal excretion
