MD3002 Flashcards
What is bioavailability?
The fraction of unchanged drug which reaches the systemic circulation.
What would the bioavailability of an IV drug be?
100% bioavailability - all drug directly to blood stream.
What will the bioavailability of an oral drug be?
Will never be 100% due to barriers to absorption.
What must be bio equivalence of generic brand be?
Around 80-125%.
What percentage of drugs are now given as generics?
80%.
What are some reasons against using generic drugs?
Clinical difference of up to 20-25%.
Subtle differences in absorption (epilepsy drugs).
Mechanical differences (eg asthma inhalers).
What are 3 advantages of the oral route?
Cheap.
Safe.
Convenient.
What are two disadvantages to using the oral route?
Patient compliance.
Bioavailability.
Where is the main site of drug absorption?
The small intestine.
Large surface area and more neutral pH.
Where are weak bases ionised?
In an acidic pH.
Where are weak acidis unionised?
In an acidic pH.
Why are weak acids still absorbed in the small intestine, where the oH is neutral and not acidic?
Large surface area of the small intestine compensates for the fact that most drug will be unionised in a neutral pH.
What is the Henderson Hasselbach equation for a weak acid?
pKa-pH= log (AH)/(A)
What is the Henderson Hasselbach equation for a weak base?
PKa-pH=log(BH)/(B).
Why would there be a delay in drug absorption?
Gastric emptying.
What will be the results of increased GI motility on drugs absorption?
Drug absorption will be decreased due to an increased transit time.
What will be the effect on drug absorption when given SUBCUTANEOUSLY.
Slow absorption due to blood flow.
This slow release can be used as an advantage.
What would be the effects on drug absorption when given INTRAMUSCULARLY?
Lipophilic?
Polar drugs?
High MW/very lipophobic drugs?
Lipophilic drugs rapidly.
Polar dugs via bulk flow.
Lipophobic drugs via lymphatics.
Highly perfumed and rapid uptake of drug.
Can still be used as a depo if in eg oil.
Which route of admin has the highest risk of accidental overdose and why?
Inhalation.
Due to rate of onset
Which route of administration is commonly used to avoid the risk of a needle stick injury.
Intranasal - rich, easily accessible, vascular plexus which I also avoids first pass metabolism.
Where are the two units of control in the reflex mechanism of vomiting?
The Vomiting centre in the medulla.
The CTZ in the 4th ventricle.
What is the CTZ sensitive too?
Chemical stimuli.
Where is the site if action of drugs which stimulate/inhibit emesis?
The CTZ.
How is motion sickness caused?
Caused by a discrepancy between what your eyes see and semi circular canals feel.
Origin of stimulus is therefore the semi circular canal.
What are the four areas which feed into the vomiting centre in the medulla.
Higher cortical centres (emotions).
CTZ.
Stomach and intestine.
Labyrinths (vestibular apparatus).
Name 8 different factors which can stimulate vomiting.
Sensory nerve endings in the stomach or intestine.
Vagal sensory endings in the pharynx.
Drugs/endogenous emetic substances.
Disturbances of the vestibular apparatus.
Sensory stimuli from the heart and viscera.
Rise in ICP.
Smells, emotions and sights.
Endocrine factors (oestrogen and progesterone).
Migraines.
Which drug is used to induce emesis?
Ipechachuana.
How does ipechachuana work?
It acts locally in the stomach.
Action is important due to the presence of alkaloids.
What alkaloids are present in ipechachuana?
Emetine.
Cephaline.
What are the 5 categories of anti emetics?
H1 Receptor antagonists. Muscarinic antagonists. Phenothiazines. Metoclopramide. Cannabinoids. Steroids. 5-HT3 antagonists.
What do H1 antagonists do?
Effective against motions sickness.
Meclozine.
Cyclozine.
Diphenhydramine - sedative effects.
What do muscarinic antagonists do?
Block Muscarinic receptor impulses from the labyrinth and visceral afferent.
Widely used to prevent motion sickness.
Eg hyoscine.
What are phenothiazines?
They are neuroleptics. Eg chlorpromazine. Used for sedation in schizophrenia. Used in 1/10th dose for Emesis. Effective against CTZ triggered vomiting, not stomach induced.
What is metoclopramide?
A dopamine antagonist which acts in the CTZ.
What are cannabinoids?
Tetrahydrocannobinol (THC) and its synthetic derivative Nabollne.
Effective in decreasing emesis caused by cytotoxic drugs.
What do steroids do in emesis?
Effective against chemotherapy evoked emesis.
Will also help to decreased intracranial P which may be evoking emesis.
What are examples of steroids used to help emesis?
Dexamethosone and methyl prednisalone.
What do 5-HT3- antagonists do in emesis?
Neuroleptics which are only provided for severe emesis.
Ondansetron.
What are the 4 classes of purgatives?
Bulk laxatives.
Osmotic laxatives.
Faecal softeners.
Stimulant laxatives.
What are some examples of bulk laxatives?
Bran, methyl cellulose, agar.
How do bulk laxatives work?
Speed up the transitions through the gut.
Take water with it to mechanically increase peristalsis.
How do osmotic laxatives work?
Chemicals retain water to = a bonus of fluid which mechanically triggers peristalsis.
What are some examples of osmotic laxatives?
Magnesium sulphate, lactulose.
How do faecal softeners work?
Faeces absorb water and help break up.
What are some examples of facial softeners?
Liquid paraffin, sulphicuccinate.
What do stimulant purgatives do?
Trigger sensory nerves to increase peristalsis.
What are some examples of stimulant purgatives?
Castor oil.
Senna.
How do muscarinic agonists/anticholinesterases work to help constipation?
Increase parasympathetic effect on the gut.
Used in life threatening paralysis.
How does domperidome/motililium work?
Dopamine antagonist.
Blocks at stomach.
Tightened entry, relaxes exit and increases contractions.
Decreases vomiting and feelings of sickness.
Prevents regurgitation of food.
Which two factors come together to result in diarrhoea?
An increase in GI motility and a decrease in absorption.
What are the 3 approaches for treatment?
Maintenance of fluid balance.
Anti infective agent.
Anti inflammatory agent to absorb toxin.
What are the two categories of anti motility agents?
Opiates/Muscarinic antagonists.
Adsorpants.
What are some Muscarinic antagonists used in diarrhoea?
Codeine.
Morphine.
Loperamide.
What are some adsorbents used in diarrhoea?
Pectin, chalk, charcoal, methyl cellulose
Bind to toxin.
What is the most common bile pathology?
Gall Stones.
Cholesterol choleliathiasis.
Is these are calcified surgery will be needed.
What two drugs will be used to dissolves gall stones?
Chenodeoxycholic acid (CDCA). Ursodeoxycholic acid (UDCA).
Which drugs will be used to decrease the synthesis of cholesterol?
Statins.
Which drugs will be used to help gall stone pain?
Not morphine - contraction SO oddi.
Buperenone or Pethidine are better.
Atropine and organic vasodilators also play a role.
