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Questions 3-4 : Summary

Questions 3-4 : Summary
If an intermittent dialysate was collected between zero to one hour of the dialysis, And then an arterial blood phenobarbital concentration at 0.5 hour was determined to be 40 microgram per milliliter. Then what would be the phenobarbital concentration in that intermittent dialysate. Again, we use the same formula. Since the dialysis clearance is 60 milliliters per minute, and the dialysate flow is 500 and the midpoint arterial concentration is 40. Therefore, the dialysate concentration is 4.8 microgram per milliliters.
And the point that I’m trying to make based on using this example is that if you collect intermittent dialysate in this example between zero and one hour, then the blood collection should be made at the midpoint of zero and one hour which is 0.5 hour, so that when you design an experiment to derive or to determine dialysis clearance, this is how it should be done. Calculation step number four. The pooled total dialysate is 90 liter and the phenobarbital concentration and the total dialysate is 5 microgram per milliliter. So if the loading dose of 1 point 5 gram was injected just before dialysis, and what fraction of the dose was removed during the dialysis period.
And here we have the drug removal printed in orange, is equal to Cd times Vd, the dialysate concentration times the dialysate volume. And the concentration is five milligram per liter times the total volume of 90 liters. That gives you point four five gram of phenobarbital. So the fraction of drug removal is point four five divided by 1.5 which turned out to be point three. So 30 percent of the dose was removed during one dialysis session. So we consider that dialyzable, so the ultimate indicator for dialyzability is the drug removal. The fraction of a drug removal. In this case for phenobarbital is 30 percent. So this is one method that you can use to determine dialyzability.
And use that information to make a decision on whether to adjust the dosing regimen. Of course, in this example you wouldn’t inject or administer the dose just before dialysis, knowing that it is dialyzable, but instead, the dose can be given at the end of dialysis.

In this step, Prof. Lee demonstrates how to solve these questions.

To begin with, there is a tip. If we collect intermittent dialysate in this example between zero and one hour, then the blood collection should be made at the midpoint of zero and one hour, which is 0.5 hour.

The formula we use is the same as the one in the question 2, did you find it?

Finally, the key to the fourth question is the fraction of a drug removal, which is the ultimate indicator for dialyzability.

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Pharmacokinetics: Drug Dosing in Renal Disease

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