Pharmacology Flashcards
Which four processes are part of pharmacokinetics?
ADME
1. Absorption
2. Distribution
3. Metabolism
4. Excretion
What is absorption?
The process of uptake of medication into the body
What is the absorption of IV medication?
100%
Why should oral administration of drugs not be used after surgery/in ICU?
Stomach and intestine often delayed or functionally immobile
What is bioavailability?
Fraction of the administered dose of unchanged drug that reaches the systemic circulation (as a % of IV administration)
What is the symbol for bioavailability?
F or BB
The way of administration of a drug determines peak levels in blood. Which administration method reaches peak levels quickest?
IV administration
What is the order of administration methods, based on which peaks fastest?
- IV
- IM
- SC
- Oral
- Rectal
What is the main factor determining the distribution of a drug throughout the body?
Whether it is hydrophilic or lipophilic
What are the main hydrophilic tissues of the body? (2)
- Blood
- Muscles
What are the main hydrophobic tissues of the body? (3)
- Dermis
- Nerves
- Fat tissue
Which measure is used to quantitatively describe drug distribution?
Volume of distribution = Vd -> hypothetical volume in which drug is dispersed
What is the formula to calculate volume of distribution after IV administration?
Vd = Ab/C
Ab = quantity of drug in the body system
C = concentration in blood
What is the formula to calculate volume of distribution after oral adminstration?
Vd = F*dose/plasma concentration
F = bioavailability
Lipophilic drugs have a [small/large] Vd
Large -> they distribute to fat, so the apparent volume of water they are dispersed in is large
Hydrophilic drugs have a [small/large] Vd
Small -> they distribute exclusively into the fluid component
What are the 3 fluid compartments of the body?
- Intracellualr fluid (ICF)
Extracellular fluid (ECF), consisting of: - Interstitial fluid -> fluid outside of cells
- Plasma -> fluid component of blood
What are the volumes of plasma, interstitial fluid and intracellular fluid for a 70 kg person?
Plasma volume = 4L
Interstitial volume = 10L
Intracellular volume = 28L
Which drugs are overrepresented in the plasma?
High molecular weight drugs and drugs that bind to plasma proteins
Where do low molecular weight hydrophilic drugs mainly distribute to?
Intracellular volume
What is metabolism in terms of pharmacokinetics?
Chemical conversion of drugs in the body
Which system is predominantly responsible for the metabolism of drugs?
Cytochrome P450 system
What are generally considered the most important enzymes of the cytochrome P450 system for the metabolism of pharmalogicals? (3)
- CYP3A4
- CYP3A5
- CYP2D6
What is the main change that the liver introduces to drugs? Why?
It turns them from lipophilic into hydrophilic, allowing them to be excreted by the kidney
What are ‘prodrugs’?
Drugs that require metabolism by the liver to become active
Why are there differences in the cytochrome P450 system between individuals?
This system has a lot of genetic polymorphisms and copy number variations
Which three general classes of drug metabolizers are there, based on cytochrome P450 activity?
- Ultra-rapid metabolizers
- Extensive metabolizers = normal
- Poor metabolizers
What effect to poor metabolizers experience from:
1. Prodrugs
2. Normal drugs
- Prodrugs are activated in a less efficient way -> less effect of drug
- Drugs are metabolized in a less efficient way, leading to accumulation and side effects
Which three ways are there for the elimination of drugs? Which is most important?
- Urine = most important
- Bile
- Faeces
Why is it important to have knowledge of pharmacokinetic properties of drugs and patients?
It allows to predict reactions to medicines
What is Tmax?
Timepoint at which the maximum blood concentration is reached
What is Cmax?
Maximum concentration of drug in the blood (=at Tmax)
What is clearance rate?
Elimination out of the body -> volume of plasma cleared of the drug per unit of time
What is T1/2?
Time necessary to decrease blood concentration of medication by 50%
Why is knowledge of the T1/2 of a drug important?
To prevent overdosing in case of repeated doses (prevent accumulation after repeated doses)
What are the main causes of a prolonged T1/2? (2)
- Renal impairment
- Intoxication (=decreased liver function)
How many T1/2 need to pass before medication is cleared from the blood (as a general rule)?
4-5x T1/2
How many T1/2 need to pass before a steady state concentration is reached (as a general rule)?
3-5x T1/2
What is accumulation (in pharmacokinetics)?
Stacking of medication after repeated doses
What does the area under the curve (AUC) represent within pharmacokinetics?
Total exposure to the drug (time*concentration)
Decreased clearance of medication leads to a [decreased/increased] AUC. What is the effect of this?
Increased -> higher chances of side effects and toxicity
What is a therapeutic range?
The range that the drug concentrations needs to reach to be above subtherapeutic levels (=no effects), but not high enough to cause (severe) side effects (toxic levels)
What is pharmacogenetics?
Analysis of DNA to explain/predict responses of patients to drug therapy