Intravenous infusion and multiple dosing

13 important questions on Intravenous infusion and multiple dosing

What is a distribution phase?

When you have a log scale and you can draw two lines in it, it means that the first period is a distribution phase. In this phase also elimination is starting.

What is curve stripping?

You can substract the two different curves (distribution and elimination) from eachother and a new curve will occur.

This will tell you something about the speed of the distribution. Also halflife can be read from this curve.

With more compartments involved, the volume of distribution will become more complicted:

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How does an orally given graph look like?

First phase is the absorption phase. Second phase is the elimination phase. To state that the elimination phase is pure elimination, you have to compare the slope with the same phase of an intravenous given dose. If the drug reacts the same with the same slope, than you can state it is pure elimination.

What is a relative bio-availability?

In this graph you can not calculate the absolute bio-availability because for that you need a IV administration curve or AUC. But you can calculate the relative bio-availability by comparing those two lines.

Bio-availability is never calculated for intravenous administration. But all other ways can be calculated.

How does an infusion graph look like?

First the concentration goes up, and then there will follow a steady state. Clearance is working against the concentration.

After 5 halflifes, the steady state will be reached.

How to calculate the steady state?

Expressed in mg/time(per kilo). Never express it in volume!

What to do in accute situations?

If the infusion takes to long to reach the steady state, than you could increase the pump untill the state is reached and then put the speed down. If this is not posible you can for example also give an injection first and then start the infusion. If the steady state is reached, the infusion can keep it there stable.

Why do formulations differ?

By changing the formulation of a drug, you can play with the kinetics. Therefore there are different formulations.
Threre are therapeutic reasons and pharmaceutical, technical or economical reasons.

Where do formulations differ?

They can differ in physico-chemical properties of the active compound(s). The drug vehicle or production process.

Tablets are the most liked administer of drugs, but how are they made?

They are often prepared by compression of powders. But the compression is really complicated because the tablet can fall apart easily, or it can become to hard and not good dissolvable.

What are the reasons for layerd tablets?

It is more stable
Controlled release
It has different effects in the gastro- intesitnal tract
pharmacokinetic properties
therapeutical reasons

What is an osmotic tablet?

Some kind of 'plastic' tablet, the active compound is in a container. There is salt present to attrack water. If the water goes in, the compound is pressed out.

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