Pharmacokinetics Flashcards
What is Pharmacokinetics?
What the body does to drugs
What are the main processes in drug therapy?
Drug in- Absorption and Distribution
Drug out- Metabolism and Elimination
How can drugs be administered?
Oral Sublingual Rectal Intavenous Subcutaneous Intramuscular
Where is most of a drug absorbed?
Small intestine
How is the drug absorbed?
Passive diffusion-lipophilic drugs and weak acids and bases
Facilitated diffusion- solute carrier
Secondary Active transport- solute carrier
Pinocytosis
What factors can affect drug absorption?
Gi length Drug lipophilicity Density of SLC (solute carrier) expression in GI Blood flow GI motility Food IpH (low ph destroys some drugs) Gut lumen enzymes Gut wall Liver
What is a phase I enzyme?
Cytochrome P450s
What is a phase II enzyme?
Conjugating
What is bioavailability?
Fraction of a defined dose which reaches its way into a specific body compartment Usually CVS is used
What are the two routes of bioavailability?
Oral and IV
How do you work out bioavailability?
Amount reaching systematic circulation divided by total drug given IV
What do drugs usually bind to?
Proteins
What is the problem with drugs binding with plasma or tissue?
Can not bind to target site
How much is all the body water in the body?
42 litres
How do drugs travel?
From plasma
To interstitial fluid
To intracellular fluid
What is Vd?
Apparent volume of distribution
Model grouping of main fluid compartments as thought all one compartment.
If small means less penetration of interstitial and intracellular compartment
If big means more penetration of interstitial and intracellular compartments
How do you work out volume of distribution?
Drug dose/plasma drug
What does elimination remove?
Exogenous and endogenous molecular species
Where does drug metabolism take place?
Liver
What is drug metabolism phase I?
Cytochrome P450 enzymes
Catalyse reactions such as redox, dealkylation, hydroxylation
Directly eliminate or may move onto phase II
May activate prodrugs e.g. Codeine to morphine
What is drug metabolism phase II?
Cytosolic enzymes
Increase ionic charge
Catalyse sulphation, glucorinadation, gluthione conjugation, methylation and nacetylation
Enhances renal elimination
What are the three super families of cytochrome p450?
CYP 1,2 and 3
Most of drugs transformations
What factors affect drug metabolism?
Age Sex General health Other drugs Genetic variability
What is cyp450 induction?
Concurrent administration of drugs can induce specific cyp450 isozymes
Via transcription and translation and slower degradation
Plasma levels of the drug will then fall
Takes 1-2 weeks
E.g. CBZ is an anti-epileptic
