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Dosage Calculation: Maintenance Dose and Loading Dose – Elimination Kinetics

by Pravin Shukle, MD
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    Let's talk about the concept of maintenance and loading doses. Let's use an example of warfarin. Warfarin is a drug that requires very close monitoring of therapeutic levels. Here's a patient who takes 1 mg of warfarin. Clearly 1 mg is not going to cut it for this patient, so we need to give him more everyday. If he takes 1 mg every single day for 9 days, eventually we will get to the effective concentration that we want. But that seems like a long time. Why don't we give him a whole bunch of medication at first, or what we call a loading dose? So here's an example of a patient who took 10 mg on day 1, you can see the concentration really climbs, and then after that we give him 1 mg a day. That's the concept of a loading dose. So, in warfarin, we use loading doses all the time. The loading dose can be calculated. It is a formula using bioavailablity, the target concentration, and the volume of distribution. So, it's Vd times the concentration divided by the bioavailability. Now, the dosing rate, or how often we give the medication, is the clearance times the desired plasma concentration, once again divided by bioavailablity. Let's use bioavailability and volume of distribution to calculate dosing. Here is a case study of a 15 year old woman who has pneumonia. She requires an antibiotic called superchillin, which of course doesn't exist. It has a volume of distribution of 31 litres, and has an oral bioavailabity of about 55 %. The required plasma concentration is 55 ??g/ml. What is the loading dose? Well, let's do the calculations together. We know that the loading dose is the volume of distribution multiplied by the concentration, and divided by bioavailablity. Let's plug...

    About the Lecture

    The lecture Dosage Calculation: Maintenance Dose and Loading Dose – Elimination Kinetics by Pravin Shukle, MD is from the course Pharmacokinetics and Pharmacodynamics. It contains the following chapters:

    • Calculating Doses
    • Case Study: Dosing
    • Case Study: Dosing

    Author of lecture Dosage Calculation: Maintenance Dose and Loading Dose – Elimination Kinetics

     Pravin Shukle, MD

    Pravin Shukle, MD


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