GI SYSTEM ANATOMY and PROTEIN BINDING

INTERACTION BETWEEN HUMAN BODY AND DRUGS

Introduction

Drugs are the substance that are used to treat a disease. These are chemical substances derived from different sources (living or non- living things) which are sued to alter the functions of living/ bacterial tisseus by reacting with them.

Uses of drugs

Drigs are used for:

1. Diagnosis of diseases

2. Prevention of diesases

3. Treatment of diseases.

This chapter deals with the relationship between drug and the human body; the mechanism of drung' action, uses of drugs and the body's response to drugs.

Drugs are prepared in laboratories and experimented so that they are free of unacceable toxic substances which can harm the clients. Then only they are approved for use of human. The study of action of drug in man is called clinical pharmacology.

Clinical Pharmacology can be divided into two brances.

1. Pharmacokinetics.

Means what the human body dees to drungs it is the study of the movement of drugs in the body.

2. Pharmacodynamics

Means what a drug does to the human body. The knowledge about pharmacokinetics and pharmacodynamics is essential to know how the drugs are used for the best advantade of the patient.

Protein Binding

Most drugs bind to proteins, either albumin or alpha-1 acid glycoprotein (AAG), to a greater or lesser extent. Drugs prefer to be free, it is in this state that they can travel throughout the body, in and out of tissues and have their biological effect. The downside of this is that they are easy prey for metabolising enzymes.

As you would expect, more highly bound drugs have a longer duration of action and a lower volume of distribution. Generally high extraction ratio drugs' clearance is high because of low protein binding and, conversely, low extraction ratio drugs' clearance is strongly dependent on the amount of protein binding.

Why is this important? If a drug is highly protein bound, you need to give loads of it to get a theraputic effect; as so much is stuck to protein. But what happens if another agent comes along and starts to compete with the drug for the binding site on the protein? Yes, you guessed it, the amount of free drug is increased. This is really important for drugs that are highly protein bound: if a drug is 97% bound to albumin and there is a 3% reduction in binding (displaced by another drug), then the free drug concentration doubles; if a drug is 70% bound and there is a 3% reduction in binding, this will make little difference.

The drugs that you really need to keep an eye on are: warfarin, diazepam, propranolol and phenytoin. For example, a patient on warfarin is admitted with seizures, you treat the patient with phenytoin, next thing you know - his INR is 10.

The amount of albumin does not appear to be hugely relavent. In disease states such as sepsis, the serum albumin drops drastically, but the free drug concentration does not appear to increase