Dosage Regimen Design

Approaches to Dosage Regimen

• Empirical Dosage Regimen

• Individualized Dosage Regimen

• Dosage Regimen on Population Averages

• Fixed Model

• Adaptive Model

• Fixed Model

From clinical trials (phase 2)

• Adaptive Model

Dose/wt

DOSE FREQUENCY:

the time interval between doses.

High Dosing Frequency (T < t1/2)

Lesser fluctuations but shows both therapeutic and toxic responses.

Optimum Dosing Frequency (T = t1/2)

Therapeutically successful

Less Dosing Frequency (t > t1/2)

Large fluctuations; therapeutically unsuccessful.

• Dosage regimen –

systematized dosage schedule for a drug therapy.

• Drug accumulation –

the build up of drug in the blood/body through sequential dosing.

• Steady-state condition -

achieved at a time when, under a given dosage regimen, the mass of drug administered is equal to the mass of drug eliminated over a dosing interval.

Loading dose –

a single intravenous bolus dose administered in order to reach steady-state condition instantly.

Maintenance dose –

dose administered every dosing interval to maintain the steady-state condition

Loading Dose
• IV Route

• DL = Css VD

• DL = R0 / k

Loading Dose

EV Route

• DL = CssVD / F

Maintenance Dose depends upon:

• The therapeutic index of the drug.

• The half-life of the drug.

• Convenience of dosing.

Maintenance Dose formula

Dose Ratio

• The ratio of loading dose to maintenance dose.

• 𝜏 = t1/2

, dose ratio equals 2.0

• 𝜏 > t1/2

, dose ratio is smaller than 2.0

• 𝜏< t1/2

, dose ratio is greater than 2.0

Steady-State Concentration