DRUG KINETICS-PART-1-INTRODUCTION

THE DRUG KINETICS-INTRODUTORY

Any thing including a medicine or a drug which was administered into the body through any route will be treated by the body as a foreign material and the body will move it from the site of administration through various intermediate sites and changes to the site of elimination.This movement of the drug by the body is well known as Pharmacokinetics or Drugkinetics

The body is composed of various models and compartments.

A model is a mathematical description of a biosystem and is used to express quantiative relations concisely.

A compartment is a group of tissues with similar blood flow and drug affinity.A compartment may be scattered in many places and cannot be expressed as a true physiologic or anatomical parts of the body.

Drugs moves rapidly into the comparments with high bloodflow and slowly into the compartments of low bloodflow.

Capillaries because of their deep spread and network plays an important role to distribute the drug passively into various tissues of high vasculature due to hydrostatic pressure and high permeability.

1.High drug permeability areas are capillaries at the glomerulus of the kidneys and the sinusoids of the liver.

2.On the contrary low drug permeability areas are the capillaries of the brain which is sorrounded by the glial cells which forms the thick blood brain barrier.This barrier is made of thick fatty glial cells and hence only lipophilic,nonpolar,hydrophobic drugs can cross the barrier very easily and more rapidly.

Drugs which are lipophilic and nonpolar may easily be stored by the body by depositing them in fatty tissues.Hence it is very difficult to the body to eliminate them as like the polar hydrophilic drugs which can be eliminated very easily.

Some drugs which have some affinity for certain ions will be accumulated in that compartment that ion.For example all teracyclines which has high affinity for polyvalent ions like calcium to form chelates will be deposited at bones and teeth.

Similarly some drugs have more affinity for plasma proteins to form large molecules and escapes elimination.Albumin and glycoproteins are best examples of plasma proteins.