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NBME 22 Answers

nbme22/Block 1/Question#7

Two patients, a 54-year-old man (Patient X) and a ...

Loading dose

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its in first aid 2019. Loading dose is unchanged in liver or renal dx. (FA 2019 pg233)

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submitted by keycompany(160),

Loading Dose is the only answer that is independent of drug clearance.

nwinkelmann  I totally get this and understand it... but at the same time, couldn't loading dose differ due to renal function if patient has nephrotic syndrome so had less plasma proteins, because it would change the Vd of the drug, right? Per wiki: Volume of distribution may be increased by renal failure (due to fluid retention) and liver failure (due to altered body fluid and plasma protein binding). Conversely it may be decreased in dehydration. +  

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. +5  
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 +