Concept of pharmacokinetic models

 

When we take a drug it gets absorbed into the blood streams and gets distributed into different organs,tissues,sometimes it crosses the blood brain barrier and reaches our grey matter, part of drug also gets eliminated, here blood acts as the central compartment ,sometimes when we take a oral drug some part of it gets lost in its way before it reaches our blood stream due to first pass mechanism in case of IV 100% of the drug gets absorbed in our blood streams

Drug distribution or absorption within our body is a very complex process after it comes into our blood it distributes through different tissues, lungs ,intestine,kidney brain in different rates so for further calculating to generate the exact data and the rate kinetics of any drug a hypothetical model is developed by our scientist which is a pharmacokinetic model.

There are two types:-

• compartment modelling

1.  One compartment model
2.  Two compartment model

• non-compartment modelling(model independent approach)

WHY STUDY PHARMACOKINETIC MODEL?

• Characterizing the behavior of drug in patients

Dosage of  a similar drug differ from person to person i.e. a same dosage of drug can be toxic for few people while it proves to be effective in some so what is this conc. different, the rate at which a similar drug acts effectively in some people but not in others all these study can be done with the help of a pharmacokinetic model.

• Predicting the concentration of a drug in various body fluid

This means from the central compartment i.e. our blood how much the drug conc. has travelled to other organs in our body can be calculated or predicted with help of a pharmacokinetic model.

• Predicting the multiple dose concentration curve from single dose
• Calculating optimum doses
• Evaluating the risk of toxicity
• These models also helps in correlating and studying the pharmacological response with drug dose

Concentration of drug in plasma  vs time 

Cmax is the maximum concentration of the drug achieved after a single dose, the peak denotes the Cmax value it's always within the therapeutic window.

Tmax denotes the time which the drug took to attain Cmax level in plasma.

A concentration vs time graph helps to study the dosage of a drug, its action time and at how much concentration it should be given and at what time intervel.

The specific drug concentration should be within the therapeutic range for the proper working of the drug.

                                                                                                                                                             

At the absorption site when a drug is given  IV or orally at that site it's concentration is highest then it decreases few  parts of it gets metabolized and the rest gets excreted, so as this drug gets absorbed after a period of time the concentration of drug at the absorption site goes down.

This study from the graph helps to derive information about dosing of a drug.