P. M. is admitted to the coronary intensive care unit (ICU) with atrial fibrillation (AFib) and rapid ventricular rate. After controlling the ventricular rate with metoprolol, it is decided to initiate procainamide by intravenous (IV) infusion. P. M. weighs 80 kg. How much of a loading dose would be required to target a level of 8 μg/L? The average steady-state volume of distribution (Vd ) for procainamide is 2 L/kg. The bioavailability of the IV formulation is 100%, whereas the oral (PO) form is only 83%.
A. 1,000 mgb.1,300 mg. To determine the loading dose of a one-compartment drug, three items are needed: (a) the drug’s Vd (L/kg), (b) the desired steady-state concentration (Cpss [mg/L]), and (c) the patient’s weight. Loading dose = Vd × Cpss. Kilograms and liters cancel, and you are left with the loading dose in milligrams.