MM is a 54-year-old, 68-kg male being treated with procainamide 750 mg regular release capsules every 6 hours for arrhythmia.

Question

MM is a 54-year-old, 68-kg male being treated with procainamide 750 mg regular release capsules every 6 hours for arrhythmia. The following steady-state concentration is available: Css = 1.5 mg/L (obtained immediately predose). Calculate a dose that will achieve a Css = 2.5 mg/L

Answer 1

68 y/o male on oral procainamine 750mg q6hr.

If Css = 1.5mg/L we want to calculate the dose necessary to reach Css= 2.5mg/L.

We need to use our PK equations to solve this.

MD = (Cl * Css * t) / f

We can use algebra to make a new equation

MD = (Cl * Css * t) / f

0 = (Cl * Css * t) / (f * MD)

then we can make two equations equal to each other and solve for the missing maintenance dose.

(Cl * Css₁ * t) / (f * MD₁) = (Cl * Css₂ * t) / (f * MD₂)

Dosing interval is the same and bioavailability won't change in the therapeutic range so we can cancel those out. Clearance will be the same.

( Css₁) / (MD₁) = (Css₂) / (MD₂)

(1.5mg/L) / (750mg) = (2.5mg/L) / (X mg)

x = 1250mg

technically it will take 5 half-lives to reach the new steady state this way