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submitted by usmleuser007(112),

Someone care to explain why [time to steady-state concentration] is not the correct answer?

omerta  In pharmacokinetics, steady state refers to the situation where the overall intake of a drug is fairly in dynamic equilibrium with its elimination. In practice, it is generally considered that steady state is reached when a time of 4 to 5 times the half-life for a drug after regular dosing is started. The time to reach steady state is defined by the elimination half-life of the drug. So in a patient with renal dysfunction, the plasma half-life is going to be prolonged and the time to reach steady state will increase proportionally. +4  
belleng  loading dose is independent of the concentration of the drug in the plasma and the dose frequency...this is why you give a patient who is seizing a huge dose of anti-seizure meds in order to reach a theraputic range on the first dose despite the high risk of toxicity and side effects...primary objective when seizing is stoping the seizure so you want to increase the dose response curve with a massive load +  
belleng  loading dose is independent of DOSE (should have said dose, not concentration in plasma) & FREQUENCY +  


submitted by usmleuser007(112),

Someone care to explain why [time to steady-state concentration] is not the correct answer?

omerta  In pharmacokinetics, steady state refers to the situation where the overall intake of a drug is fairly in dynamic equilibrium with its elimination. In practice, it is generally considered that steady state is reached when a time of 4 to 5 times the half-life for a drug after regular dosing is started. The time to reach steady state is defined by the elimination half-life of the drug. So in a patient with renal dysfunction, the plasma half-life is going to be prolonged and the time to reach steady state will increase proportionally. +4  
belleng  loading dose is independent of the concentration of the drug in the plasma and the dose frequency...this is why you give a patient who is seizing a huge dose of anti-seizure meds in order to reach a theraputic range on the first dose despite the high risk of toxicity and side effects...primary objective when seizing is stoping the seizure so you want to increase the dose response curve with a massive load +  
belleng  loading dose is independent of DOSE (should have said dose, not concentration in plasma) & FREQUENCY +  


submitted by drdoom(188),

You have to think about this using the concept of CONDITIONAL PROBABILITY. Another way to ask this type of question is like this: “I show you a patient with spontaneous pneumothorax. Which other thing is most likely to be true about that person?” Or you can phrase it these ways:

  • Given a CONDITION (spontaneous pneumo), what other finding is most likely to be the case?
  • Given a pool of people with spontaneous pneumothorax, what other thing is most likely to be true about them?

In other words, of all people who end up with spontaneous pneumo, the most common other thing about them is that they are MALE & THIN.

If I gave you a bucket of spontaneous pneumo patients -- and you reached your hand in there and pulled one out -- what scenario would be more common: In your hand you have a smoker or in your hand you have a thin male? It’s the latter.

someduck3  Is this the best approach to all of the "strongest predisposing risk factor" type questions? +  
drdoom  There is a town of 1,000 men. Nine hundred of them work as lawyers. The other 100 are engineers. Tom is from this town. He rides his bike to work. In his free time, he likes solving math puzzles. He built his own computer. What is Tom's occupation most likely to be? Answer: Tom is most likely to be a lawyer! Don't let assumptions distract you from the overwhelming force of sheer probability! "Given that Tom is from this town, his most likely occupation (from the available data) = lawyer." +2  
drdoom  There is a town of 1,000 spontaneous pneumo patients. Six hundred are tall, thin and male. The other 400 are something else. Two hundred of the 1,000 smoke cigarettes. The other 800 do not. What risk factor is most strongly associated with spontaneous pneumo? (Answer: Not being a smoker! ... because out of 1,000 people, the most common trait is NOT smoking [800 members].) +3  
impostersyndromel1000  this is WILD! thanks guy +3  
belleng  beautiful! also, i think about odds ratio vs. relative risk...odds ratio is retrospective of case-control studies to find risk factor or exposure that correlates with grater ratio of disease. relative risk is an estimation of incidence in the future when looking at different cohort studies. +  
drdoom  @impostersyndrome I love me some probability and statistics. Glad my rant was useful :P +  
hyperfukus  @drdoom i hate it which is why your rant was extremely useful lol i learned a ton thanks dr.doom! +1  
dubywow  I caught he was thin. The only reason I didn't pick Gender and body habitus is because he was not overly tall (5'10"). I talked myself out of it because I thought the body habitus was too "normal" because he was not both thin AND tall. Got to keep telling myself to not think too hard on these. Thanks for the explanation. +  


submitted by usmleuser007(112),

Note: the questions stated "respiratory burst" suggesting an URT infection.

1) this rules out anything but respiratory infection (non rep infection: E. coli, E. faceium)

2) G6PD deficiency more susceptible to catalase positive organisms -- this rules out (all strep organisms)

3) Left with H. influenzae & Straph. aureus (BOTH are catalase positive)

4) Encapsulated organism are most concerning when there is asplenia.

imnotarobotbut  Respiratory burst has nothing to do with a respiratory infection. It describes the process of phagocytosing a bacteria and using NADPH oxidase/ROS to lyse it +3  
belleng  Aspergillus is still in the running, it is catalase positive as well...but not a choice +