pharmacokinetics and pharmacodynamics Flashcards
what is pharmacokinetics and pharmacodynamics
how drugs affect the body’s physiology
what are the 4 phases of how a drug effects the body
- absorption
- clinical effect
- metabolism
- excretion
what are the 5 routes of administration of a drug
- oral
- intravenous injections
- intramuscular injections
- subcutaneous injections
- inhalation
what is a misconception of asthma inhalers way of absorption
not Inhalation as inhalers have powder in them which do not make it far enough into the alveoli to be absorbed the way - instead absorbed like a cream
what are the advantages and disadvantages of oral administration
advantages - people don't mind taking pills disadvantages - slow onset - variable absorption (may lose some in stomach, gut mucosa not good at absorption) - gastric acid may destroy drug - needs to get through liver
what are the other factors that affect oral drugs absorption
- lipid solubility and ionisation
- drug formulation
- gastrointestinal motility
- interactions with other substances in the gut
- GIT diseases
how does lipid solubility and ionisation affect absorption of oral drugs
will only be absorbed if lipid soluble
how does drug formulation affect absorption of oral drugs
- may have coating which lets different parts of a drug be absorbed at different times
- coating would need to dissolve first (could take hours or be immediate)
how can GIT diseases affect absorption of oral drugs
Crohn’s disease - bowel would be removed so can’t absorb as well/much
what is first pass metabolism
all blood from GIT drains into the hepatic portal vein and into the liver which then metabolises drug
- al blood from GIT must pass through liver before entering systemic circulation
how does first pass metabolism work
- drug needs to pass through the liver where it will meet hepatocytes and be metabolised before entering the circulation
- can lose a lot of the drug through this
- but knowing this can mean drugs are designed to allow some to be lost in liver but still having enough to work
how can first pass metabolism activate the drug
- can make an active form of an inactive drug (pro-drug)
- means less needed by oral route
- e.g. valaciclovir turns into acyclovir
how can first pass metabolism inactivate the drug
- all is lost in liver through metabolism
- means more is needed by oral route to get the desired effect
- glyceryl trinitrate
how is drug dosage effected by first pass metabolism
- might need to increase/decrease dose to allows right amount into circulation
what are does based off of
a healthy individual
how are drugs from the mouth absorbed
- anything from the mouth doesn’t go through first pass metabolism as doesn’t pass through hepatic portal vein
- goes dow veins in neck once absorbed and then into systemic circulation
- different dosage is then needed than oral tablet
what are the advantages of non-oral drugs (injections)
- predictable metabolism
- no first pass metabolism (goes straight to the circulation- amount given is amount received in blood)
- works quickly
what are the disadvantages of non-oral drugs
- allergic reaction are more severe as affects the whole body
- access difficult (patients don’t like giving themselves injections)
- cost higher (expensive to ensure purity is checked)
what is bioavailability
how much does the drug work
- proportion of an ingested drug that is available for clinical affect
what is intravenous bioavailability
100%
why is oral drugs bioavailability less than intravenous
- due to first pass metabolism
- lots of variables affect it - can change daily in the same person
how is bioavailability modified
- dosage form
- destruction in the gut
- poor absorption
- first pass metabolism
what are clinical trials used for
guarantee does and what happens/effects
why is amoxicillin used more instead of penicillin
because it is more predictable in its bioavailability
