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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.
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confidenceinterval
Even if they weigh the same, won't their different body compositions give different volumes of distribution? Would that change the loading dose?
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syoung07
@confidenceinterval, the loading dose wouldnt change, the maintenance dose would.
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chaosawaits
@confidenceinterval, exactly my thought! "Patient factors which affect Vd include age, gender, body muscle/fat proportion, level of hydration, water distribution (oedema, effusions, ascites, pregnancy) and extracorporeal sites of distribution (circuit, filters, oxygenator etc)." So even though they weigh the same, one is male and one is female so body fat % is going to be significantly different. This is why women are affected by alcohol more easily. They are also significantly different in age. The Vd should be different for each of these patients and therefore the loading dose should also be different.
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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.
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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
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belleng
loading dose is independent of DOSE (should have said dose, not concentration in plasma) & FREQUENCY
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submitted by โkeycompany(351)
Loading Dose is the only answer that is independent of drug clearance.