Pharmacology -Part 2 Flashcards
Give examples of patient risk factors that increase their chance of drug interactions
Poly-pharmacy Old age Genetics e.g. slow/fast metabolism Hepatic disease Renal disease
What is the therapeutic index of a drug?
A comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxicity
Give examples of drug related risk factors that increase their chance of drug interactions
NARROW Therapeutic index
Steep dose/response curve
Saturable metabolism
Give example of saturable metabolism
Paracetamol and alcohol are metabolised at a SET RATE
What 4 factors make up the pharmacokinetics of a drug
Absorption
Distribution
Metabolism
Elimination
What factors can be influenced Absorption in pharmacokinetics of drug metabolism?
Motility Acidity Solubility Non-absorbed complex formation Direct action on enterocytes
How does Erythromycin influence Motility in absorption in pharmacokinetics
Increases Gut Motility
What 2 drugs have the commonest interaction causing motility changes?
Oral contraceptive pill
Antibiotics
What drugs can influence the pH/acidity of the stomach and thus affect absorption in pharmacokinetics
Antacids and Proton Pump Inhibitors
These change pH of the stomach so if take with another medication, the absorption of the drug can be altered
Give example of solubility being affected in drug metabolism due to interaction.
Eating avocado (high in fat) and taking a fat soluble drug e.g. anti-coagulant
Drug will dissolve meaning there will be less or no drug absorption
Give example of a fat soluble drug
Anti-coagulant
What would be effect on drug absorption if took a fat soluble drug with high fat food such as avocado
Drug will dissolve meaning there will be less or no drug absorption
Give example of drug not being absorbed due to formation of a large complex in body
Cholestyramine +
Thyroxin, Warfarin or Digoxin
(large complexes formed in intestinal lumen)
What are enterocytes
Intestinal absorptive cells
What is effect of Grapefruit juice on uptake of certain drugs?
Grapefruit juice inhibits P-glycoprotein resulting in increased uptake of certain drugs
What can cause a decrease in distribution of drug concentration in plasma (not including being use by target cells)
Drug can bind to proteins in plasma, thus reducing distribution and meaning effect is lowered.
What drugs can have a reduced distribution due to protein binding in the plasma
Sulphonamide antibiotics
Warfarin
What wavelength of light is absorbed by CYP450?
450nm
What can be metabolised by CYP450?
Haemoproteins
Many other substrates, including Endogenous (body products) and Exogenous (durugs, toxins and food) products
What classes of CYP450 are found in humans
Classes 1, 2, 3
When would you give drug to inhibit CYP450
To block metabolism of drug (that would usually be metabolised by CYP450), leaving more of the drug free in plasma and Increasing its effects.
When would you not inhibit CYP450, even if drug is metabolised by CYP450
If pro-drug
If block metabolism then effects of it will be decreased
What is effect of drug of CYP450 induction?
Increased metabolism of drug causing decreased therapeutic effects
When would CYP450 induction increase effects of a drug?
Pro-drug
Increase in metabolism leads to more of active form so increased effects
What CYP is affected by grapefruit juice?
Grapefruit juice affects CYP3A4
Results in increased bioavailability and can therefore make a drug more effective.
What makes up the majority and minority of drug excretion
Renal excretion is majority
Biliary excretion is minority
True or False:
Renal excretion is not pH dependent
False
Renal excretion is pH dependent
In what circumstance would a weak base be excreted faster?
If the urine is acidic
In what circumstance would a weak acid be excreted faster?
If urine is alkaline
How can you alter the excretion of a weak acid or weak base
By altering pH of urine
Give examples of weak acids that are drugs
Aspirin
Ibuprofen
Paracetamol
Warfarin
What can be done to increase excretion of aspirin if given an overdose?
Alkalinise urine as aspirin is a weak acid
Give examples of weak bases that are drugs
Amphetamine
Atropine
Propranolol
Salbutamol
Give general examples of pharmacodynamic mechanisms of drug interaction
Receptor based
Signal Transduction
Physiological systems
Give example of agonist receptor based drug interaction
Alcohol and Benzodiazepine at GABA A receptor
drugs bind to receptor
Give example of a partial agonist receptor based drug interaction
(Partial binding/activation at receptor)
Buprenorphine for Opioid Addiction
Give example of a antagonist receptor based drug interaction
(blocks receptor -can be competitive or non-competitive)
Beta-blockers and Asthma (competitive)
Why should you never give Beta-Blockers to Asthmatic
Asthmatics will be on B-agonists to help with bronchodilation
If using beta-blockers then will cause bronchoconstriction and increase risk of asthma attack
Why do you not give Beta-blockers to a diabetic
Beta-blockers in a diabetic:
Results in action at B3 receptor (in adipose tissue) which normally detect and alter blood glucose.
However action at B2 receptor can suppress hypoglycaemic awareness so they will not detect fall in glucose.
Why do you not give ACE inhibitors with NSAIDs?
High degree of nephrotoxicity
Can you give Ca channel antagonist and Beta-blocker?
No
Symptoms of heart failure may worsen because these drugs reduce the ability of the heart to pump blood.
(Also sexual function can be impaired)
*What is effect of giving Digoxin and Furosemide?
- Digoxin works on cardiac fibres and its effect is increased if there are low levels of potassium in blood plasma
- Furosemide is a diuretic that lowers arterial pressure but favours the loss of potassium
- This could lead to hypokalaemia, which could increase the toxicity of digoxin
How can you avoid prescribing drugs causing interactions
Prescribe rationally
BNF
Medicines infroamtion service
Effect of avocado and warfarin
Avocado reduces effectiveness of warfarin - could increase risk of blood clots
Effect of Grapefruit juice on Calcium channel blockers
Increases effectiveness of calcium channel blockers
Effect of Grapefruit juice on Anti-rejection medication
Increases effectiveness of anti-rejection medication
Effect of Garlic on Anti-platelet activity
Garlic increases anti-platelet activity so can increase risk of bleeding
Effect of Soya on NSAIDs or Warfarin
Soya increases effectiveness of NSAIDs and warfarin so can increase risk of bleeding
Effect of Ginger on Anticoagulants
Ginger reduces effectiveness of anticoagulants so increases risk of bleeding