absorption/half-life Flashcards
How to differentiate between (brand vs generic) and (biologic vs biosimilar)?
- brand vs generic is used for drugs that are of small molecules, most traditional drugs
- Biologic vs biosimilar is used for drugs that are made of large complex monoclonal antibody and is really expensive to make. Biosimilar is the generic version of biologic.
What absorption and distribution factors should the ideal drug have?
- solution formulation (adv: very specific dosing, absorbed quickly, easier for certain population). (dis: expire sooner, bitter taste, storage issues.
- the drug should not be ionized so it doesn’t mess with the stomach pH
- the molecular weight of the drug should be small
- should be more lipophilic so it can be absorbed quickly
What are the factors that affect absorption and distribution of the drugs?
- drug associated: formulation (tablet vs solution vs IV), Ionization state, molecular weight, solubility/lipophilicity
- patient associated: blood flow (different for different demographics), body fluid pH (stomach vs plasma vs urine), food (some foods can interact with certain drugs)
- plasma protein binding (more protein binding, less active the drug will be as it won’t reach to its target the longer it binds to the protein.
- Depot storage
- membrane permeability (can/can’t cross blood brain barrier)
How does food intake affect certain drugs like insomnia drugs?
- food can decrease the affect of certain drugs, for example insomnia drugs
- With food, the drug takes longer to get into the system so it takes longer to fall asleep.
- Without food, the drug goes in the system really fast causing you to fall asleep faster and the affect of the drug wears off sooner so you aren’t drowsy for the rest of the day.
How does depot storage affect drug absorption and distribution?
- depot storage refers to where the drug is stored once in the body and this can affect its ability to reach its target.
- Lipophilic drugs are going to store in adipose tissue (fat). This allows the drug to cross blood brain barrier. Many psych meds need to be lipophilic so they access the BBB.
- The ratio of fat to muscle can impact the effectiveness of the drug. Higher fat amount = drug acts longer and is more effective. Have to be careful with dosing of psychotic lipophilic drugs in elders because the effect can laster longer and can be stronger compared to young individual.
What is a prodrug? example?
Prodrug= drug that doesn’t cause a direct effect, but is precursor for the product that is needed to make effect.
- Ex: Levodopa (parkinson’s): precursor for dopamine. Dopamine can’t cross the blood brain barrier but levodopa can. So levodopa is prescribed so that it can cross the bbb and it is converted to dopamine through decarboxylase.
What are the two phases for drug metabolism?
- Phase 1: oxidation or reduction to more polar forms so it can be excreted through renal (CYP 450 involved in oxidation)
- Phase 2: conjugation to a stable adduct (polar or nonpolar) through glucuronidation so it can be excreted through renal or biliary/stool
What are the routes of drug excretion?
- renal
- biliary
- others (respiratory/lungs)
What are the 3 most common ways the kidneys excrete drugs?
- glomerular filtration via diffusion
- tubular secretion via transporter
- tubular reabsorption vis diffusion
What is half-life (t1/2) of a drug?
- amount of time that is required for the plasma concentration of a drug to decrease by 50% after absorption and distribution are complete
- to get half-life of a drug, from the plotted graph take any 2 data points from the removal phase and divide by 2.
Approximately how many half-lives are required to get rid of most of the drug and reach steady state in most common drugs?
- about 4 half-lives are required to reach steady state in most drugs(that one must take multiple times a day)
How is t1/2 affected by volume and clearance of the drug based on the t1/2 formula?
The relationship between volume of drug for distribution and clearance of drug is inversely proportional. Larger the volume of drug and smaller drug clearance, longer the half-life. Larger the clearance of drug and smaller drug volume, shorter the half-life.
How does the route of drug administration affect the half life?
- Half-life is independent of administration route so it does not affect the half-life of the drug.
What is the steady state?
The steady state is when the amount of drug being absorbed = amount of drug being cleared from the body when the drug is given continuously or repeatedly
- need about 4-5 half lives to reach steady state
- steady state is independent of drug dose
Why is it important to monitor plasma levels of some drugs but not others?
- some drugs could have adverse effect/be toxic to some organs
- non-predictability in dose response
- some drugs need to be in certain therapeutic range
- monitor levels to determine the how it affect as it distributes (pharmocokinetics)
