Drugs And Their Action

The primary objective of medicinal chemistry is the design and discovery of new compounds that are suitable for use as drugs. The discovery of a new drug requires not only its design and synthesis but also the development of testing methods and procedures, which are needed to establish how a substance operates in the body and its suitability for the use as drug. This essentially requires fundamental research into the biological and chemical nature of the diseased state. Drug design and discovery require input from specialists in other fields, such as biochemistry, mathematics, computing, pharmacology and medicine.

What are drugs?
Drugs are defined as chemical substances that are used to prevent or cure diseases in humans, animals and plants. The activity of drug is its pharmacological effect on the subject, for example, its analgesic or B-blocker action. Since drugs act by interfering with biological processes, no drug is safe.

Classification of drugs.
Drugs are classified in a number of ways depending on chemical structure and pharmacological action, including the site of action and target system.

The pharmacokinetic phase.
The pharmacokinetic phase of drug action includes the Absorption, Distribution, Metabolism and Elimination (ADME) of the drug. Many of the factors that influence drug action apply to all aspects of the pharmacokinetic phase. Solubility, for example, is an important factor in the absorption, distribution and elimination of a drug.

Bioavailability of a drug.
The bioavailability of a drug is defined as the fraction of the dose of a drug that is found in general circulation. It is influenced by such factors as ADME. Bioavailability varies with body's physiological condition.

Prodrugs.
Prodrugs are compounds that are biologically active but are metabolized to an active metabolite, which is responsible for the drug's action. They are classified as either bioprecursor or carrier prodrugs. Prodrugs may be designed to improve absorption, patient acceptance, reduce toxicity and also for slow release of drugs in the body.

Synthesis quality control.
The efficiency of drug production will depend on being able to identify and assess the chemical purity of the drug and also that of the intermediate compounds involved at each step in the synthesis. Physical methods, such as HPLC and GC, are often used for these purposes.
In some synthetic routes, an intermediate product may be used in the next stage of the synthesis with out it being isolated and purified.This procedure is known as telescoping. It has an advantage of avoiding handiling very toxic intermediates.It also makes the dealing with non-crystalline and oil products easier.