Mr. Smith is a 154 pound male who developed an upper respiratory infection. The

Question

Mr. Smith is a 154 pound male who developed an upper respiratory infection. The antibiotic erythromycin was prescribed. The clearance and (f) Vd of this antibiotic are 20 mL/min and 0.571 L/kg, respectively.

A. What maintenance dose needs to be administered every 4 hours to eventually obtain an average steady state plasma concentration of 4 mg/L? And what intravenous loading dose would you give to achieve a therapeutic plasma concentration of 4 mg/L rapidly? What is the bioavailability of this drug?

Explanation / Answer

Answer:

A. CL = 20mL/min, TC = 4 mg/L

Dosing rate = TC * CL * dose rate/bioavailability

Bioavailability = 1 because the drug is given IV

4 mg/L * 1 L/1000 mL * 20 mL/min * 60 min/1 hr * 4 hr = 19.2 mg

Loading dose = Vd * TC

Vd = 0.571 L/Kg = 0.571 *69.85 L = 39.88 L (154 pounds = 69.85 kg)

So, Loading dose = 39.88 L * 4 mg/L = 159.53 mg

Bioavailability = 1 because the drug is given IV

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