Pharmacology Flashcards
3 main drug targets
Receptors, transporters, enzymes
4 types of receptors that can be targeted by drugs
Ligand gated ion channels
- Rapid action (milliseconds)
- Nicotonic, AcH, glycine receptors
G protein coupled receptors
- Slow signal transduction (seconds to mins)
- Multiple parts meaning more time for effect
- When drugs binds to receptor GDP becomes active (GTP) causing activation of downstream targets
- Receptors can work in different way based on the second messenger pathways present → 1 receptors can couple to different G proteins with different alpha subunits
Kinase linked receptors
- Very slow response (mins - hours)
- Communicate to intracellular surface to activate enzyme cascade causing increase in certain output
- Large signal amplification that will lead to changes at DNA level such as altered gene transcription
Nuclear receptors
- Very slow response (hours)
- In cytoplasm waiting for hormones
- Hormones cross membrane and bind to receptors within cell targets. Migrate together to DNA within the nucleus binding to key sequences in DNA to cause transcription of desired proteins.
- The resultant mRNA moves into cytoplasm for translation
Transporters as drug targets
Can block the reuptake transported on the pre synaptic terminal. Leading in increased time a neurotransmitter is present and thus improving signalling.
Enzymes as drug targets
Enzymes can be blocked through either competitive inhibition (bind to active site) or non competitive inhibition (bind elsewhere and change shape of active site)
Agonists
Agonists bind to a receptor and activate it
Increased amount of agonist can lead to greater response with more receptors, however there will be a concentration at which the max number of receptors have been bound.
- Full agonist - bind and have full physiological effect
- low affinity agonist - may not fit as well into the receptor binding sit and comes off faster. Does not activate receptor to the same extent.
4 types of antagonists
Competitive
- Binds to same site as agonist and blocks
- Countered by increasing agonist dose
Non competitive
-Binds somewhere elese and changes the receptor shape
-No change to EC50 (still same effect) but decrease in Rmax
Uncompetitive antagonists
-Receptors become permemently bound to antagonism
Functional/physiological antagonism
-Occurs in tissue due to 2nd messenger pathway
-2 drugs act on different receptors and antagonist the action NA/A
Components of graphical representation
EC50, Potency Efficacy, Therapeutic index
EC50 = concentration where drug has 50% of its effect
Potency = increase will mean less drug is needed for same effect
Efficacy = how effective a drug is at activating a receptor
Therapeutic index - when this is low the desired effects and toxic effects are close in concentration
What is ADME
(administration)
Absorption
Distribution
Metabolism
Excretion
Parenteral and Enteral administration
Parenteral don’t use GIT (IV, intramuscular, inhalation, subcutaneous)
Enteral do (oral, sublingual, rectal (avoids first pass))
Factors that can effect absorption
- Concentration gradient
- Lipophilicity of drig
- Blood flow at the site
- SA
- Gut motility (this may be decreased in illness)
- Formulation/rate of drug release - coating to protect from stomach acid
- GI tract content
What is first pass effect and bioavailability
If a drug is taken orally (or enters blood stream) drug will pass through the liver at some point → main place for metabolism of drug
When this happens it will reduce the concentration of drug available to work
Bioavailability is between 100% and 0% (if 0 then cant take orally) → morphine has bioavailability of 20% this means that 80% will be metabolism in the liver before it can access circulation
Bioavailability = the fraction absorbed into the systemic circulation (how much actually makes it into the blood stream)
First pass metabolism effected by liver and gut wall
Can be avoided by administering drug rectally
What is volume of distribution
Size and comp of patient need to be considered
Volume of distribution = amount in blood concentration
Distribution and protein binding
Once in the blood a drugs ability to work on receptors may depend on amount of proteins within the blood.
The less a drug binds to the proteins in blood the more available it is to work on receptors.
High protein binding will lead to a decrease in free drug. Low protein binding will mean that a drug can more easily traverse cell membranes of diffuse to tissue receptors.
How can multiple drugs effect distribution of each other
Doses of multiple drugs may need to be considered as decrease one may lead to an increase in available binding proteins and indirectly decrease the dose of another drug. This can also work in reverse were adding a drug may increase the concentration of another.
Importance of bound drugs
A bound drug is inactive and may act as a reservoir.
If a medication is extensively bound (99%) then even a small change can have massive effects. (1% → 2% free = doubling)
Two types of reactions for metabolism
- Phase 1 reactions - drug may still work (minor change to prepare for next phase)
- Oxidations
- Reduction
- Hydrolysis
- Each increase the water solubility of resulting metabolite
- Phase 2 reactions - unable to bind to receptors
- Glucuronide
- Glutathione
- Sulfate
- Acetate
- All are large water soluble molecules
- Metabolites are more highly ionised, water soluble, more likely to be excreted by the liver and kidneys, less pharmacologically active and less toxic
Factor that can effect drug metabolism
- Genetics
- Age
- Gender
- Other drugs being taken (induction of inhibition of P450s or other CYP enzymes)
- Food
What are pro drugs
Pro drugs = therapeutics that require metabolism to an active metabolite for activity. Codeine is an example
How can drugs effect metabolism of other drugs
Many drugs can affect the metabolism of other drugs by inhibiting or reducing CYP enzyme activity and this is a potential problem when drugs are given at the same time which are both metabolised by the same CYP enzymes. Other drugs may induce or stimulate CYP function which may stimulate breakdown of medication.
- Most CYP enzymes are inducible by drugs and other compounds
- Results in more rapid metabolism, increased elimination and decreased effect
- Most common when 2 drugs are metabolised by same enzyme
- Can result in increased plasma levels and drug toxicity
- Only relevant for drugs primarily removed from the body by metabolism
- Significant for drugs with small therapeutic windows
How can renal disease effect drugs
Drugs that are mainly excreted by the kidneys renal disease can lead to increased plasma concentrations.
Drug metabolites are more likely excreted in urine as they are more water soluble and not as likely to be reabsorbed back into the blood stream.
Renal function decreases in elderly
Describe local inflammation response
Activated macrophages and mast cells at the site of injury release chemical signals causing vasodilation and increase permeability at injury site.
Chemokines release by various kinds of cells attract more phagocytic cells from blood to injury site
Neutrophils and macrophages phagocytose pathogens
Results in redness, heat, pain and swelling → possible loss of function
What controls inflammation (two types of mediators), why is inflammation not instantaneous
Controlled by inflammatory mediators which are intracellular chemical messengers released by inflammatory cells. Major mediators include:
- Eicosanoids - derived of arachidonic acid, include prostaglandins and leukotrienes
- Histamine - stored in mast cells, mediates allergic reaction. Start initial pulse at time of injury
With the exception of histamine inflammatory mediators are not stored, instead they are synthesised and released in response to inflammatory stimuli. This is why inflammation takes time to occur. It also means that histamine is able to be released quickly and start initial actions.
What is Arachidonic acid and how is it released
Arachidonic acid is just stored but in presence of inflammatory stimuli the enzyme Phospholipase A is activated which goes to the phospholipid bilayer to release Arachidonic acid.
What two paths can Arachidonic acid take once release
Free cytosolic (available for enzymes) Arachidonic acid is then able to follow 2 paths, being acted on by:
- Lipoxygenase → leukotrienes
- COX 1 and COX 2 → Prostaglandins and thromboxane
These products are then exported from the cell and activate receptors (normally GPCRs) on nearby cells and/or itself to mediate their effects.
Large diversity of these GPCRs and the effects they may have.
Glucocorticoid MOA
- Carried by transporter glucocorticoid binding protein
- Binds to glucocorticoid receptor complex which is coupled to two proteins which are dissociated
- The activated complexed can move into the nucleus and alter gene transcription
- Increased Lipocortin and decreases COX 2
Anti inflammatory action of SAIDs
Lipocortin-1 inhibits phospholipase A2 AND reduces expression of COX enzymes (important for prostaglandins). Results in reduced production of prostaglandins and therefore decreased inflammation
Indications and side effects of corticosteroids (SAIDs)
Indications of corticosteroids
- Transplant rejection
- Rheumatoid arthritis → injected into joints
- Inflammatory bowel disease such as chronic or ulcerative colitis
- Asthma or allergies
Side effects of corticosteroids
- Immunosuppressive activity increases risk of infections. Plays with the bodies own response. Therefore, only used for short term responses.
- Worsen diabetes
Overview, 3 main functions of NSAIDs and how
- Inhibit prostaglandin synthesis by inhibiting COX 1 and 2
- All have the follow 3 effects → anti inflammatory, anti pyretic (lower body temp) and analgesic (reduce pain)