Physiology and Pharmacology
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| Drug | show 🗑
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| show | Any biological binding/recognition element for drugs
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| Pharmacodynamics | show 🗑
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| Specificity | show 🗑
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| show | The strength of interaction between a drug and a receptor
Chemical forces between drug and receptor include electrostatic forces, hydrogen bonds, VDW forces and hydrophobic bonds
A drug is not statically located - can dissociate
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| What determines probability of drug occupying its binding site | show 🗑
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| Efficacy | show 🗑
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| Law of mass action | show 🗑
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| show | 1 = proportion of receptors occupied + proportion not occupied
1 = Par +pr
The fraction of receptors occupied and free
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| show | Rate of decrease of inactive = constant x conc inactive
= constant x Pr
Rate of decrease of Pr = K+1 x Pr
dPr/dt = K+1 x Pr dt
Rate constant has units s^-1
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| show | Rate of decrease of unoccupied = constant x {A} x Conc unoccupied
= constant x [A] x Pr
Rate of decrease of Pr = K+1 x [A] x Pr
dPr/dt = K+1 x [A] x Pr dt
Rate constant has units M^-1s^-1
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| Hill-Langmuir equation | show 🗑
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| show | The equilibrium dissociation constant - a measure of agonist affinity
The concentration of the drug which results in 50% of the receptors being occupied
Expressed in molar units - a concentration
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| show | At equilibrium the number of drug molecules binding is equal and opposite to those unbinding
K+1[A](Bmax-B) = K-1B
B/[A] = Bmax/Ka - B/Ka
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| show | A plot of B/[A] against B
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| Basic principles of drug binding | show 🗑
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| show | Binding can be assessed directly bit it is the biological response we wish to assess
Plotted as dose response curves
Response = ([A]e)/([A]+Ka)
e - efficacy - intended as an agonist specific term
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| EC50 | show 🗑
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| show | EC50 tends to be lower than Ka
Response to an agonist is proportional to the receptor occupancy by Ka and EC50 do not tend to collide
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| show | Ec50,<Ka can be explained by spare receptors
Number of receptors present is larger than the number needed to provoke full response
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| show | Full agonist
Partial agonist - same binding site but lower efficacy (cannot produce maximal response)
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| show | Salbutamol - B2 adrenoreceptor - asthma
Morphine - Opioid receptor - relieve moderate to severe pain
Sumatriptan - Serotonin receptor - treatment of migraine
Ropinirole - D2 receptor - parkinsons disease
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| show | Buprenorphine - opioid receptor - opioid dependence
Verenicline - a4/b4 nAChR - nicotine dependence
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| Antagonists | show 🗑
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| Competitive antagonists | show 🗑
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| Ra | show 🗑
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| Relationship between conc of antagonist and receptor occupation by agonist | show 🗑
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| show | Ra = 9[B]/Kb)+1
Expressed as log(Ra-1) = log[B] -logKb
Ra depends on {B{ and equilibrium constant of the competing drug
The value of Ra allows estimation of Kb
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| show | Antagonist that presents reactive groups that can give rise to covalent bonds with the receptor binding site
Not associated with an increase in EC50
Increasing concentration of agonist does not overcome the effect - maximal response not achieved
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| Non competitive antagonist | show 🗑
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| Examples of reversible competitive antagonists | show 🗑
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| Examples of irreversible competitive antagonists | show 🗑
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| show | Ketamine - Glutamate receptor - intravenous anaesthetic
Verapamil - L type VGCC - hypertension, cardiac arrythmia and angina
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