Drug Variability and Harmful effects Flashcards
what is variation
most often quantitative as a drug produces a larger or smaller effect and/or lasts for a longer or short period of time.. while qualitatively exerting the same effect
variation can result from:
a different drug concentration at sites of drug action OR by different responses to the same drug concentration
variation is a different response to same:
concentration
what are the 3 reasons there is individual variation
- pharmacokinetic - ADME: pharmacogenomics and personalized medicine
- pharmacodynamic
- idiosyncratic - because of genetic difference or immunologic response
what are the implications of variaiton
- clinical impact- repsonse vs toxicity
- lack of efficacy
- side effects and drug toxicity
- including unexpected side effects
medication variations are due to
- half life
- lipophilicity
- metabolic pathway
- metabolite activity
- elimination
what is half life
time it takes for serum concentrations to reduce by half in the elimination phase
how many half lives does it take to reach steady state
4.5-5 half lives
what is lipophilicty and what can it affect
ability to cross into fatty tissue, may increase volume of distribution
what are the metabolic pathways that contribute to medication variations
- cytochrome P450
- polymorphisms
- SNPs
- genetic polymorphisms
- HLAB 1502 allele
- membrane transporters
what are polymorphisms
alternative sequences at a locus within a DNA strand (allele) that persists in a population
what are SNPs
DNA sequence variations occur when a single nucleotide in the genome sequence is altered
if the HLAB1502 allele is present:
increases risk of SJS/TEN with carbapenzamine (tegratol)
HLAB1502 allele is common in:
chinese ancestry
what is the membrane transporter we are concerned with in metabolic pathway
p-glycoprotein
what are the type of metabolic activity
active and inactive metabolites
what are the types of elimination
renal and hepatic
what contributes to drug related response variations
- age related changes
- genetics- influence PK by altering the expression of proteins involved in drug ADME- genetic polymorphism
- immunological
- concurrent disease- commonly renal and hepatic
- drug interactions - think CYP 450
quantitative and qualitative variation results when:
the drug produces a larger or smaller effect, acts longer or shorter in duration, while from a qualitative standpoint still demonstrating the same effect (receptor level)
qualitative responses can be different because of:
genetic and immune responses
what is an example of qualitative repsonse
hemolytic anemia secondary to methyldopa and response to antidrug antibodies that get formed
what are the factors contributing to quantitavie and qualitative variation
- ethnicity
- age
- pregnancy
- disease
what are the examples of ethnic variation in african americans
- hydralazine and nitrates offer better mortality benefit in heart failure vs caucasian
- ACEi (enalapril/Vasotec) do not work as well because of lower renin concentrations
what is an example of ethnic variation in chinese
- dont metabolize alcohol as well, results in increased plasma concentrations of acetylaldehyde
- increased sensitivity to the beta blocker propranolol even though metabolized faster
what are the age considerations in ADME
- absorption: hypothermia reduces drug clearance, age lowers core body temp
- distribution- reduced total body water, increased lipid distribution with age- increased body fat
- metabolism- impaired phase 1 metabolism (oxidation, reduction, hydrolysis) = accumulation
- excretion: less efficient in newborns and over the age of 65
what are the pregnancy considerations
- reduced maternal plasma albumin
- increased CO
- increased renal blood flow and GFR
- increased transfer of lipophilic drugs
what are the disease considerations
- may result in pharmacodynamic and pharmacokinetic variation
- renal function
- hepatic function
- gastric stasis
- pancreatic disease
what is the concern with increased concentration of free drug in pregnant patients
toxicity
what are the idiosyncratic reactions
- typically harmful
- do not require large drug doses
- genetic connectino
- immunological factors
what are the considerations with drug interactions
- dietary considerations
- cytochrome P450- phase 1 metabolism
- P-glycoproteins
what are the dietary considerations we should be concerned with
- grapefruit juice inhibits CYP3A4
- vitamin K increases clotting and impacts warfarin
what is codeine broken down into
demethylated to norcodeine and morphine
what are the pharmacodynamic interactions with beta blockers
agents like propranolol reduce effectiveness of beta agonists used for asthma treatment (albuterol)