B5 Pharmacological Basis of Therapy Flashcards
What are the goals of treatment?
Symptomatic cure/relief
May involve lifestyle changes e.g. avoidance of causative drugs and food
GORD - propping up in bed and removing belts
Supression of acid release/activity and mucosal protection
Eradication of H.pylori infection if necessary
Sodium carbonate antacid equation
HCO3- + H+ —> CO2 + H2O
Magnesium hydroxide and aluminium hydroxide antacid equation. Why are the provided in combination?
Al(OH)3 + 3HCl —-> AlCl3 + 3H2O
Mg(OH)2 + 2HCl —> MgCl2 + 2H2O
Mixture of the two to avoid side effects e.g. diarrhoea and constipation
How do alginates combat GORD?
Alginic acid combines with saliva to form a viscous foam that floats on the gastric contents forming a raft which protects the oesophagus during reflux
What is Ec50?
Concentration of agonist that gives rise to 50% of maximal response (potency)
What causes the rightward shift of sigmoidal curve on H+ release vs log [histamine] agonist graph?
Antagonist binds at the same site as the agonist and so reduces the action of the agonist by competition. (Competition may be overcome by increasing concentration of agonist) = surmountable
Do antagonists have efficacy?
No, because don’t activate a receptor but block existing receptors
What does affinity measure and what is the affinity constant?
How well a drug binds to a receptor
KA (molar -1) is the affinity constant
What is 1/Ka?
1/Ka = Kd
The dissociation constant is the concentration at which the drug occupies half of the receptor population
What does a low Kd mean?
A low concentration when drug occupies half the receptor population
This means high affinity
What is selectivity determined by?
Relative affinities of drugs to their receptors
What is pA2?
pA2 = -logKd
Used to give log values of more manageable numbers
What do histamine2 receptor antagonists do?
Reduce gastric acid secretion
Provide symptomatic relief
Promote ulcer healing
What activates PPIs? How do they work in the body?
Activated by acidic pH
- enters body
- passes to parietal cells
- pKa means activated at low pH
- localised action
What are the adverse effects of PPIs?
- inhibits H+ secretion by >90% so could lead to absence of HCl (achlorhydria) and increased risk of food poisoning
