Dosage Calculations

Vd = Q /Cp

t 1/2 = 0.693 Vd /Cl

with continuous slow administration, eventually a steady state will be reached where rate of administration = rate of elimination

Qr = Cp(ss) x Cl

multiple loading doses can be used to reach steady state, at which point maintenance doses are used

Qm = Cp(ss) x Cl x Tm

• in general, Cp(ss) is reaced within 3-4 half-lives

Ql = Cp(ss) x Vd

 

The target concentration strategy:

• determine TC
• predict Vd and Cl based on known or estimated values
• administer loading and/or maintenance doses
• measure response and Cp; wait 3-4 t 1/2 to achieve Cp(ss)
• revise Vd and/or Cl based on Cp
• adjust dose to obtain TC