An , 65-year-old male is transferred to the intensive care unit due to septic shock. The critical care team decides to rapidly initiate broad-spectrum antibiotic therapy, which includes a novel antimicrobial, Drug X. The clinical pharmacist provides the following pharmacokinetic parameters for Drug X in critically ill adults:
- Volume of distribution ():
- Systemic clearance ():
- Oral bioavailability ():
The target peak plasma concentration () required for therapeutic efficacy against the suspected pathogen is . To rapidly achieve this target level, an intravenous loading dose is ordered.
What intravenous loading dose (in mg) should be administered to this patient?
Answer: 800 mg
Answer
800
The primary objective of a loading dose is to rapidly achieve a target therapeutic plasma concentration () by filling the patient's entire volume of distribution (). The pharmacological formula for a loading dose is . First, the total for this patient is calculated as . Second, because the medication is to be administered intravenously, its bioavailability () is considered to be complete, or (). Therefore, the required loading dose is . The systemic clearance () provided in the scenario is extraneous information for a loading dose calculation; clearance dictates the maintenance dose rate necessary to match drug elimination over time.
Step-by-Step Solution
Key Concept
The loading dose of a medication is determined exclusively by the total volume of distribution () and the desired target plasma concentration (), and is independent of the drug's clearance rate.