Clinical Pharmacokinetics of Phenobarbital
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Transcript of Clinical Pharmacokinetics of Phenobarbital
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Clinical Clinical Pharmacokinetics of Pharmacokinetics of
PhenobarbitalPhenobarbitalDr. Muslim SuardiDr. Muslim Suardi
Faculty of Pharmacy Faculty of Pharmacy University of Andalas University of Andalas
20201313
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INITIAL DOSAGE INITIAL DOSAGE DETERMINATION METHODSDETERMINATION METHODS
• Pharmacokinetic Dosing Method
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Pharmacokinetic Dosing Pharmacokinetic Dosing MethodMethod
Estimation of • Cl • Vd • t1/2 & ke
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ProblemProblem
• GO is a 50-year-old, 75-kg (5 ft 10 in) male with tonic-clonic seizures who requires therapy with oral PHENO. He has normal liver and renal function. Suggest an initial PHENO dosage regimen designed to achieve a steady-state concentration equal to 20 µg/mL.
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11. . Estimate Cl & Vd according Estimate Cl & Vd according to disease states present in to disease states present in
the patient.the patient.• The Cl for an older patient is 4 mL/h/kg. Using
this value, the estimated Cl would equal 0.3 L/h: Cl = 75 kg*4 mL/h/kg = 300 mL/h or 0.3 L/h.
• The estimated Vd would be 53 L: 75 kg*0.7 L/kg = 53 L.
•
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2. 2. Estimate t1/2 & keEstimate t1/2 & ke
• Once the correct Cl & Vd estimates are identified for the patient, they can be converted into the PHENO t1/2 & ke estimates using the following eq:
• t1/2 = (0.693*V)/Cl = (0.693*53L)/ 0.3 L/h = 122 h,
k = Cl/V = 0.3 L/h / 53 L = 0.0057 h−1.
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3. 3. Compute Dosage RegimenCompute Dosage Regimen
• Oral PHENO tab will be prescribed to this patient (F=1).
• The dosage equation for oral PHENO is D = (Css*Cl *) / F = (20 mg/L*0.3 L/h*24h) / 1 = 144 mg Rounded to 120 every 24h
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3. Continued3. Continued
• A SS trough PHENO Csr should be measured after SS is attained in 3–5 t1/2.
• Since the patient is expected to have a t1/2 equal to 122h, the PHENO Css could be obtained any time after 4 weeks of dosing (5t1/2= 5*122h = 610 h or 25 d).
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3. Continued3. Continued
• PHENO Csr should also be measured if the patient experiences an exacerbation of their epilepsy, or if the patient develops potential signs of PHENO toxicity.
• 3. Compute dosage regimen.
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3. Continued3. Continued
• Oral PHENO tablets will be prescribed to this patient (F=1).
• The dosage eq for oral PHENO is D = (Css Cl ) / F = (20 mg/L*0.3 L/h*24 h) / 1 ⋅ ⋅= 144 mg, rounded to 120 every 24 hours.
• A SS trough PHENO Csr should be measured after SS is attained in 3–5t1/2.
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3. Continued3. Continued
• Since the patient is expected to have a half-life equal to 122h, the PHENO Css could be obtained any time after 4 weeks of dosing (5t1/2 = 5*122h = 610 h or 25 d).
• PHENO Csr should also be measured if the patient experiences an exacerbation of their epilepsy, or if the patient develops potential signs of PHENO toxicity.