Lecture 2 Flashcards
Bioavailability
amount of drug in the bloodstream that is free to bind at target receptors.
Pharmacokinetic (PK) components of drug action
- Route of administration.
- Absorption and Distribution.
- Binding.
- Inactivation.
- Excretion.
Route of Administration
How and where a drug is administered determines how quickly and how completely the drug is absorbed into the blood.
Absorption and Distribution
movement of drug from site of administration to blood circulation.
Binding
drug molecules move to tissues to bind to active target sites (receptors).
Inactivation/biotransformation
occurs primarily as a result of metabolic processes.
Excretion
- The liver metabolites are eliminated from the body with the urine, feces or kidney.
Depot binding
Binding to sites that are not the target site.
Why is depot binding important
- slows down the rate of accumulation of the drug at its site of action.
- diminishes the concentration of the drug at its site of action.
- delays the onset of the drug.
- prolongs the action of the drug.
Enteral adminstration
- use the gastrointestinal (GI) tract.
- agents administered are slow in onset and produce highly variable blood levels of drug.
Phospholipid bilayer
Cell membranes are primarily composed of molecules called phospholipids, which have a negatively charged region and two uncharged tails, arranged in a bilayer.
Passive diffusion
a movement of ions across cell membranes without need of energy input.
Lipid solubility
refers to the capability of a substance to dissolve in lipids, fats, or oils.
Ionization
depends on the pH of the solution and the pKa of a drug,
What do proteins do in the phospholipid bilayer?
they serve as receptors or channels or transporters.
Types of Routes Of Administration
- oral
- topical
- transdermal
- injection
Oral (PO)
- drug must dissolve in stomach fluids and pass through the stomach wall to reach blood capillaries.
- first-pass metabolism
First-pass metabolism
All drugs (and food) given PO enter the liver where they may be chemically altered.
Topical
application to body surfaces such as the skin or mucous membranes
Transdermal
through the skin, administration with skin patches.
Injection
shot, or a dose of medicine given by way of a syringe and a needle.
Subcutaneous (SC)
Drug is injected just below the skin.
Intravenous (IV)
Agent is placed directly into the blood.
Intramuscular (IM)
injected into muscle tissue.
Intraperitoneal (IP)
Drug is injected through abdominal wall.
Intra-arterial
injected straight into the artery.
Intrathecal (epidural)
Through spinal fluid
Intracranial
Drug injection into brain tissue.
Intracerebroventricular
Drug injected into csf filled chambers.
Infusion pump
Implanted under the skin of the scalp.
Inhalation
Drug is absorbed from the lungs.
Gene Therapy
Can be used to increase or block expression of gene product to correct a clinical condition.
Pros & Cons of Oral administration
Advantage
- safe
- self- administered
- economical
- no needles- related complications.
Disadvantage
- slow and highly variable absorption
- subject to first- pass metabolism
- less- predictable blood levels.
Pros & Cons of Intravenous Administration
Advantage:
- most rapid
- most accurate blood concentration.
Disadvantages:
- overdose danger
- cannot be readily reversed
- requires sterile needles and medical technique.
Pros & Cons of Intramuscular Administration
Advantages:
- Slow and even absorption.
Disadvantages:
- localized irritation at the site of injection
- needs sterile equipment.
Pros & Cons of Subcutaneous Administration
Advantages
- slow and prolonged absorption.
Disadvantages:
- variable absorption depending on blood flow.
Pros & Cons of Inhalation Administration
Advantages:
- large absorption surface
- very rapid onset
- no injection equipment needed.
Disadvantages:
- irritation of nasal passages
- inhaled small particles may damage lungs.
Pros & Cons of Topical Administration
Advantages:
- localized action and effects
- easy to self- administer.
Disadvantages:
- may be absorbed into general circulation.
Pros & Cons of Transdermal Administration
Advantage:
- controlled and prolonged absorption.
Disadvantage:
- local Irritation
- useful only for lipid- soluble drugs.