Question
A 38-year-old man comes to the emergency department with acute shortness of breath that developed after a 10-hour international flight. His pulse is 124/min and pulse oximetry on room air shows an oxygen saturation of 90%. He weighs 50-kg (110-lb). A diagnosis of pulmonary embolism is suspected and intravenous heparin is initiated. If the volume of distribution of heparin is equivalent to 60 mL/kg and the target peak plasma concentration is 0.5 units/mL, which of the following is the most appropriate loading dose for this patient?
| A. |
3000 units
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| B. |
1500 units
|
| C. |
6000 units
|
| D. |
Cannot be calculated as bioavailability is not known
|
Show Answer
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Correct Answer � B
Explanation
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Ans-B-1500 units
3,000 units
Loading dose is equal to (Cp * Vd) / F, where Cp = target peak plasma concentration, Vd = volume of distribution, and F = bioavailability. Note that the target peak plasma concentration in this patient is 0.5 units/mL.
1,500 units
Loading dose is equal to (Cp x Vd) / F, where Cp = peak plasma concentration in units/mL, Vd = volume of distribution (only the total volume), and F = bioavailability. In this patient, the bioavailability of heparin is 1 as it is an intravenous medication. This yields (0.5 units/mL x 3,000 mL)/1 = 1,500 units.
6,000 units
Loading dose is equal to (Cp * Vd) / F, where Cp = target peak plasma concentration, Vd = volume of distribution, and F = bioavailability. Note that the volume of distribution should be provided as a total volume, and not as a volume per body weight. In other words, to find the absolute total volume of distribution for this patient, multiply 60 mL/kg by his body weight. Also remember that bioavailability is 1 because the medication is IV.
Cannot be calculated, as bioavailability is not known
The bioavailability of an IV medication is equal to 1.
