M&R 9.1 - Pharmokinetics Flashcards
What is pharmokinetics?
What the body does to a drug
What is drug formulation?
A mixture in a particular state supplied to a patient
What needs to be considered when supplying a drug?
- Solid? - Solubility and acid stability in stomach
- Liquid? - Quickly absorbed in the gut
- Compliance? - Is it simple e.g. 1 per day is easier
- Drug-drug interactions
What can happen if the wrong drug formulation/administration is given?
Adverse effects e.g. poisoning, unnecessary treatment etc
What is drug administration?
The path in which a drug is taken into the body
What are the benefits of using a specific site of drug administration?
- Concentrates drug at site of action
- Limits absorption in other areas
- Limits side affects
Give some sites of drug administration (7)
- Sublingual (under the tongue)
- Oral
- Inhalation
- Transdermal patch
- Rectal
- Topical )on skin)
- Intravenously, intramuscularly, subcutaneously
What needs to be considered when administering a drug?
- Safety of route
- Health of patient e.g. unable to swallow = no oral
- Prevention of complications
What is oral bioavailability?
The proportion of a drug given orally (or any other way except IV) that reaches circulation without changing
How is oral bioavailability measured?
- Amount (1st pass metabolism, gut absorption)
- Rate (Pharmaceutical factors e.g. tablet, liquid)
What is the therapeutic ratio?
- Maximum tolerated dose/ minimum tolerated dose
- Shows how dangerous a drug is
What does a narrow therapeutic index indicate? Why?
- Drug is more dangerous
- Concentration to get unwanted adverse side effects is close to the concentration to get desired therapeutic ratio
How can the therapeutic ratio be changed? Why?
- Change in formulation
- Absorbs/dissolves more slowly so doesn’t peak in toxic concentration range
What is first pass metabolism?
- Drug is administered orally
- Absorbed by the digestive system
- Transported by hepatic portal system and portal vein
- Reaches liver FIRST before being metabolised
What is the significance of first pass metabolism?
Due to being metabolised in the liver first, the concentration of the drug is decreased greatly before reaching systemic circulation
Which methods of administration do not undergo the first pass effect? Why?
- Sublingual
- Intramuscular etc
- Inhalation
- Rectal
- Travel around the rest of the body before reaching the liver
How can liver cirrhosis affect oral bioavailability?
- Decreases hepatic clearance
- Not broken down in liver so more is unchanged
- Increases bioavailability
What does a high hepatic extraction signify?
Low bioavailability
What is volume distribution?
The theoretical volume that the drug is distributed into if done instantly
How can volume distribution be measured?
- Extrapolate plasma concentration to 0 time
- Amount given/ plasma concentration at 0 time
How does albumin act as a reservoir for drugs?
- Binds to albumin
- Dissociation = increased free drugs
- Is eliminated/ goes to target receptor and produces an effect
What does drug displacement cause? When is this important?
- Protein binding drug interactions
When:
- High binding to albumin
- Small volume of distribution (increases concentration)
- Low therapeutic ratio
What is the relationship between dose and albumin binding sites during at class 1 (object)?
Dose is SMALLER THAN albumin binding sites
What is the relationship between dose and albumin binding sites during at class 2 (precipitant)?
Dose is GREATER THAN albumin binding sites
