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Skip to 0 minutes and 11 seconds Moving on to vancomycin. Here again I have a very brief case for vancomycin therapy. This patient has a case of pneumonia caused by MRSA. The MIC is greater than one minimum per liter for this strain of Staphylococcus aureus. The physician wants to dose vancomycin aggressively to achieve a peak concentration of 28 milligrams per liter and a trough concentration of 17 milligrams per liter. The patient has an estimated creatinine clearance of 60 ml/min and weighs 60 kilograms. Since the estimated creatinine chemist is 60 so we know his renal function is compromised nearly 50 percent. So here we have a series of question to ask What is the estimated K, elimination rate constant? What is the estimated volume of distribution?

Skip to 1 minute and 24 seconds What is the clearance for vancomycin? What loading those would you recommend? And what would you recommend for dosing interval based on the half-life of the drug? And what maintenance dose would you recommend to initiate the therapy? So vancomycin elimination here we have two formulas based on the literature information which says K elimination rate constant is equal to 0.00083 times creatinine clearance plus 0.0044 reciprocal hour The other formula from the patient population is equal to creatinine clearance times 0.06 and here we realize that creatinine clearance can be calculated or estimated by Cockcroft-Gaultl equation or by MDRD equation based on serum creatinine. So calculation step number one.

Skip to 2 minutes and 37 seconds Applying the equation that we presented previously Here K is equal to 0.00083 times creatinine clearance which is sixty plus 0.0044 and it turned out to be 0.0542 reciprocal hour. And since we are dealing with first-order kinetics therefore half-life is 0.693 divided by K and that give us twelve point eight hours for half-life Calculation step number two clearance of the drug or vancomycin is equal to creatinine clearance times 0.06 and that turned out to be three point six liter per hour. Step number three clearance is equal to KV and therefore volume of distribution V is equal to clearance divided by K. And that turned out to be sixty six point four liter for vancomycin.

Skip to 3 minutes and 49 seconds Continue on to step four we want to calculate loading dose and remember the definition of loading dose is the product of peak concentration times volume distribution that is the dose that we want to apply in order to obtain a peak concentration as soon as possible So peak concentration desirable peak concentration is 28 the volume of distribution is sixty six point four and that gives us a dose of 1859.2mg and of course we round it up to two thousand milligrams to be infused over one hour

A case for Gentamycin : 1

Prof. Lee uses a brief case for Gentamycin to demonstrate the previous discussed idea.

Do you still remember how to calculate the half-life and peak concentration?

Please try the following exercise: Adapted from the example in this video, given K=0.231 hr-1, t 1/2=3.0 hr. If her serum Gentamycin concentration is 5 mg/L at 12:30, what is the concentration at 15:30?

The answer is not in the video, so please make your own calculations.

If you have difficulty on it, please go back to the previous video to review the complete idea, or share your problem below.

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This video is from the free online course:

Pharmacokinetics: Drug Dosing in Renal Disease

Taipei Medical University