Clinical Clinical Pharmacokinetics of Pharmacokinetics of

ProcainamideProcainamideDr. Muslim SuardiDr. Muslim Suardi

Faculty of Pharmacy Faculty of Pharmacy University of Andalas University of Andalas

20201313

INITIAL DOSAGE INITIAL DOSAGE DETERMINATION METHODSDETERMINATION METHODS

• The pharmacokinetic dosing method • Literature based recommended dosing

TheThe Pharmacokinetic Pharmacokinetic Dosing MethodDosing Method

• t1/2 & ke estimate• Vd estimate • Selection of appropriate Pk model &

equations• Css selection

ProblemProblem

• LK is a 50yo, 75-kg (5 ft 10 in) male with ventricular tachycardia who requires therapy with oral PROC SR-tab. He has normal liver & cardiac function. Suggest an initial oral PROC dosage regimen designed to achieve a PROC Css equal to 4 µg/mL.

1. 1. Estimate t1/2 & ke according to Estimate t1/2 & ke according to disease states & conditions present disease states & conditions present

in the patientin the patient

• The expected PROC t1/2 for an individual with normal hepatic & renal function is 3.3h. The ke is computed using the following formula:

• k = 0.693/t1/2 = 0.693/3.3 h = 0.210 h−1.

2. 2. Estimate Vd & Cl Estimate Vd & Cl

• The patient is not obese, so the estimated PROC Vd will be based on ABW: V = 2.7 L/kg*75 kg = 203 L.

• Estimated PROC Cl is computed by taking the product of the Vd & ke:

• Cl=kV = 0.210 h−1 * 203L = 42.6 L/h

3. 3. Compute Dosage RegimenCompute Dosage Regimen

• Oral SR PROC tab will be prescribed to this patient (F=0.83). Because the patient has a rapid PROC Cl & short t1/2, initial τ will be set to 6h.

• The dosage equation for oral PROC is D = (Css*Cl*τ) / F = (4 mg/L*42.6L/h*6h) / 0.83 =1231mg, rounded to 1250 mg every 6h.

3. Continued3. Continued

• SS PROC & NAPA Csr could be measured after SS is attained in 3–5t1/2. Since the patient is expected to have a t1/2 equal to 3.3h for PROC & 6h for NAPA, the Css could be obtained any time after the first day of dosing (5 t1/2 = 5*3.3 h = 16.5 h for PROC, 5 t1/2 = 5*6h = 30 h for NAPA).

3. Continued3. Continued

• PROC & NAPA Csr should also be measured if the patient experiences a return of their arrhythmia,

• or if the patient develops potential signs or symptoms of PROC toxicity.