Pharmacology Flashcards
1 drug that is an antacid
magnesium hydroxide
where is the chemoreceptor trigger zone
in the medulla, but outside of the BBB
forumla to work out the volume of distribution
amount in body/conc in plasma
describe the difference in renal excretion and metabolism of drugs of a newborn compared to normal
renal clearance is 20% of adults deficient in phase 2 conjugation therefore increased conc in blood and increased half life
what is zero order elimination
you saturate the elimination process at a certain concentration, and therefore with more drug administered.. you get increasing concentration with no steady state achieved
drug distribution is driven by what
circulation
why is the peak concentration higher in a slow distributing drug with iv administration
because it stays in the blood for longer
what are the causes of interpatient variability
age genetic factors idiosyncratic reactions disease drug-drug interaction
which drugs are used for motion sickness as well as nausea and vomiting
H1 receptor anatagonists and muscurinic receptor antagonists
most drugs are eliminated at a rate that is…
proportional to the conc in plasma
2 drugs that are proton pump inhibitors
omeprazole esomeprazole
definition of constipation
infrequent defection less than 3x per week, often with straining, with hard, uncomfortable stools
side effects of H1 receptor antagonists used for vomiting/nausea
extremely sedative
what is the name of the opoid that causes constipation
loperamide
what things in the body act as drug reservoirs
plasma proteins cells fat - leads to slow distribution
major problem with using CNS D2 anatagonists
can cause extrapyramidal side effects - worst case scenario = tardive dyskinesia
action of proton pump inhibitors
decreases gastric acid secretion by inhibiting the proton pump in the parietal cells
why are prostaglandin E analogues not regularly used
can induce abortion but increasing the motility of the uterus
what are 2 bulking agents used for constipation
bran psyllium
major lifestyle factors that lead to constipation
- inadequate dietary fibre - inappropriate fluid intake - inappropriate bowel habits - inadequate activity and exercise - DRUGS - spinal injury - dementia - depression
forumla for renal clearance
GFR + TS - TR
how do prostaglandin E analogues treat PUD
increased mucous secretion and mucosal blood flow and decreases gastric acid secretion
2 major actions of metoclopramide
- anti-emetic - increases gastric motility
how do you calculate bioavailability
area under the curve for oral absorption / area under the curve for iv adminstration x 100
for a drug with oral absorption with first order elimination, the rate of change of drug in the body is related to
absorption rate and elimination rate
what factors affect drug distribution
molecular size - small can cross vascular endothelium ability to bind to plasma proteins - unbound can cross vascular endothelium lipid solubility - can pass into cell membranes
when you change first order kinetics of a drug to a log vs time graph - what three things can you calculate
- VD - half life - clearance
what is first pass metabolism
metabolism of a drug when it passes through the liver
when are the only times that drug-drug interactions are important
when drug B has a narrow therapeutic index conc-response curve to B should be steep
what is bioavailability
the proportion of active drug which enters systemic circulation
describe the effects of disease on drugs
can effect: - absorption (gastric stasis, malabsorption) - metabolism (liver cirrhosis) - excretion (renal failure)
what side effects do prostaglandin E analogues have
- abortion - colic and diarrhoea by stimulating the bowel
what are the features of a drug that follows first order kinetics
- rapid rise - drug has half life - peak conc related to dose and volume of distrubtion
How do antacids work
neutralise the gastric acid (dont decrease production)
what are the features of a drug with first order kinetics using low term iv infusion
- at steady state, the rate of infusion = rate of elimination - concentration at the steady state is proportional to infusion rate - pattern of accumulation reflect multiple dosing
what is the difference between metabolism and excretion
metabolism - chemical changes excretion - physical expulsion
1 drug that is a prostaglandin E analogue
misoprostol
actions of the 3 steps in renal excretion
- glomerular filtration (takes drugs out of blood) - tubular secretion (takes drugs out of blood) - tubular reabsorption (puts drugs back into blood)
how do cytoprotective agents treat PUD
coat the ulcer site and therefore heals ulcers by stopping the acid from getting to them
drug that is a 5HT3 receptor antagonist
ondansetron
action of faecal softeners and lubcricants
detergents - enhance mixture of water into faeces –> makes faeces softer
for a first order kinetic drug - what is the formula for the rate of elimination
-KX (K = elimination rate constant, X = amount of drug in body)
what do spasmolytics do
blocks muscurinic receptors on the muscle –> stops the increased gut motility - reduces pain associated with ulcers
action of H2 receptor antagonists in treating peptic ulcer disease
decrease gastric acid secretion by blocking effects of histamine on parietal cells
action of osmotic saline laxatives
slowly absorbed ions which cause osmotic fluid retention –> colonic stimulation by distention due to increased fluid volume
1 drug that is a H2 receptor antagonist used for treating PUD
Ranitidine
drug that is a faecal softener
docusate
describe the difference in renal excretion and metabolism of drugs in the elderly
renal function decreases from age 20 deficient in cytochrome p450 causes increased half life and conc in blood of drug
what is the volume of distribution
the volume of body water in which a drug appears to be dissolved in after it has distributed throughout the body
2 drugs used as dopamine D2 receptor antagonists
metoclopramide prochlorperazine
what is the lipid solubility of acidic and basic drugs in different pHs
low pH - acidic drugs lipid soluble and basic not high pH - acidic drugs not lipid soluble and basic are
where is the vomiting centre
in the dorsolateral reticular formation of the floor of the 4th ventricle
1 drug that is a H1 receptor antagonists
promethazine
receptors that involve the circulating substances stimulating the chemoreceptor trigger zone that stimulates vomiting
D2 receptors and 5HT3 receptors
how long is the course of treatment of peptic ulcer disease using proton pump inhibitors
~8 weeks
what are pharmacokinetic drug-drug interactions
drug A modifies conc of drug B at its receptor
1 drug that is a muscarinic receptor antagonists used for nausea/vomiting/motion sickness
hyoscine hydrobromide
difference between phase 1 and phase 2 drug metabolism
1 - creates a chemical functional group on the drug (cytocrome p450) 2 - conjugation of water soluble molecule to the functional group on the drug
what are the main classes of drugs used for peptic ulcer disease
- proton pump inhibitors - H2 receptor antagonists - antacids - cytoprotective agents - spasmolytics - Prostaglandin E Analogues
side effects of antacids
- constipation/diarrhoea - cause rebound gastric acid secretion - can tend to effect some prescription drugs - systemic drugs can cause alkalosis, kidney damage and worsen existing HT - Mg can cause coma in kids
action of stimulant laxatives
precise mode of action not known - may stimulate colonic myenteric nerve plexuses, irritate intestinal mucosa or by direct sensory nerve ending irritation –> increase motility
what is the renal clearance
the amount of blood from which drug is removed by the kidneys per time
side effects of 5HT3 R anatagonists
very minor - maybe headache and constipation
how do bulking agents help for constipation
indigestible vegetable fibres - causes greater faecal water retention –> greater volume of intestinal contents –> increased stimulation of reflex bowel activity
what are pharmacodynamic drug-drug interactions
drug A modifies effect of drug B without affecting its conc
features of oral administration with first order elimination
- peak no as high as with IV (due to some elimination during absorption
drug that is a osmotic saline laxative
magnesium sulphate
what is the disadvantage of lipid soluble drugs
high lipid solubility will lead to sequestration in lipid (sit in the fat)
all drug elimination depends on
concentration of drug in the blood
receptors for motion sickness
muscurinic receptors and H1 receptors
how does metoclopramide increase gastric motility
- through acting on 5HT4 –> releases ACh in the nerve plexuses in the gut –> speeds up the movement of the gut - D2 anatagonism –> dis-inhibition
what are the 4 types of laxatives
- bulking agents - faecal softeners and lubricants - osmotic laxatives - stimulant laxatives
drug metabolism involves
a chemical change to a drug by enzymes making is more water soluble for excretion
why do you give a loading dose
if you have a drug with a long half life, it is going to take a long time to reach a steady state concentration. Therefore to get the patient to experience the effect of the drug sooner you give a loading dose
where does drug metabolism occur
mostly in the liver
what can drug reservoirs do
- prolong action (release from store as conc falls) - can quickly terminate action (if stored drug has high capacity) - can lead to slow distribution (if capacity of store is great)
drug that is a neurokinin-1 receptor antagonists
aprepitant
3 actions on receptors that metoclopramide does
- D2 antagonist - weak 5HT3 anatagonist - 5HT4 agonist
drugs that are stimulant laxatives
bisacodyl Senna
what are the maximal values for GFR and renal clearance
GFR = 125 ml/min renal clearance = 800ml/min
what is ADME
- administration and absorption - distribution - elimination - metabolism - excretion
what are the features of a drug with first order kinetics using short term iv infusion
- rate of accumulation decreases as conc increases - peak not as high as for iv bolus - after infusion over, get elimination only
side effect of bulking agents
flatulence
what is the major precaution when taking stimulant and osmotic laxatives
pt can become dehyrated and loose electrolytes
action of deactivated charcoal
gastrointestinal decontaminant - also used to remove poisons from the GI tract
what factors of a drug make it good for local administration
- poorly absorbed - conc so low that if it were to be absorbed - conc will be too low for systemic effect
what factors determine the volume of distribution
- if the drug binds to plasma proteins (greater conc in plasma - VD is small) - if the drug binds to tissues/taken up by cells (VD is large)
how many half lives does a drug go through when giving multiple doses to get to 99% of the drug conc at a steady state
7 half lives
1 drug that is a spasmolytic
hyoscine butylbromide
what affects bioavailability
how much drug is absorbed how much drug undergoes first pass hepatic metabolism and local metabolism
how does the rebound effect of antacids work
antacids stimulate gastrin release –> need to take more and more antacid to neutralise the excessive stimulation of HCL production by gastrin
what is simethicone
agent used for the treatment of flatulence - changes the surface tension of the small air bubbles –> coalescence into big, air bubbles –> easily passed
