lecture 4: different method of drug administation

what are the 3 different method of administration

1. repeated dosing

2. infusion

3. loading dosage

what is dosing interval

time between 2 consecutive dose

what is repeated dosing

1. the drug is being administrated repeatedly at a regular time inteval

2. the administrated drug will replace the amount of drug being excreted

3. the administrated drug will also build up on the remaining dose from the pevious dosing residual

describe the process of repeated dosing

1.        after each dose plasma concentration increase

2.        elimination occur between 2 doeses, cause decrease in blood plasma concentration

3.        the next dose applied added up to the previous remaining dose, this will build up the blood plasma concentration

4.        the plasma concentration need to be within the therapeutic window between the MEC and MTC.

5.        Eventually the drug will reach the steady state.(between Cmax and Cmin)

-shorter dosing interval will cause more fluctuation in the blood plasma

how does the dosing interval and half-life affect the repeated dose

what is infusion

1. small amount of drug will be administrated at constant rate (mg/h) constantly, and it corresponded to the zero-order administration

2. the steady state concentration will be reached after 5 half-live

3. the declined in the plasma concentration is usually caused by the one compartment model and 2-compartment model

what is the rate of infusion and the related infusion rate

• the amount of drug administraed into the bloodstream per unit time during IV

what are the 3 factors affect the blood concentration for infusion

1. rate of iinfusion

2. volume distribution of the drug

3. elimination half-life of the drug

what is the advantage of applying infusion

1. stable blood plasma concentration
   -              unlike the repeated dosing, infusion can provide a stable plasma drug concentration

2. suitable for drug with short half-life

what is the disadvantage of the infusion

1. long-time is needed to reach the steady state: 5 half-life

what is loading dose and maintainance dose

loading dose: increase the blood plasma concentration within a short time

Maintainance dose: the drug needed to maintain the steady state of the drug after loading dosage

How to combine the loading dose with the maintainance dose

1. the loading dose can be first used to increase the blood plasma concentration to an desired level within a short time

2. after reach the desired blood plasma concentration, we can use the maintainance dose to keep the blood plasma concentration at a steady state

equation for the loading dose

Vd: volume of distribution

Css: steady state concentration

compare the repeated dose, infusion, loading dose, in terms of
1. main purpose

2. administration route

3. time to reach the steady state

4. disadvantage

	Repeated dose	Infusion	Loading dose
Main purpose	Maintain the therapeutic exposure over time	Maintain stable plasma concentration	Achieve the target concentration with one dose
Administration method	Intermittent	Continuous	Single bolus injection
Time to reach steady state	4-5half-life	-5half-life	Immediately
Disadvantage	Fluctuation	Requires IV access; slow approach to steady state	Risk of excessive initial concentration if incorrectly calculated

what is therapeutic drug monitoring

• periodically analyse the drug concentration in the blood

what are the 3 functions of the therapeutic drug monitoring

1. standard care for specific drug

2. to adjust the dose
   -              Prevent the drug is below MEC (absence of effect)

   -              Intoxication(>MET)

3. to check patient compliance
   -eg. for certain anti-depressant, to check if the patient follow the treatment