Nature and Sources of Drugs
Plant sources
The use of plants as medicines has a long history. Opium has been the first known drug
from plant sources. Plants continue to be a significant part of traditional medicine and
herbal medicine. Several important drugs like Taxol, Camptothecin, Morphine and Quinine
have been isolated from plant sources.
Animal sources
Animals have been sources for some drugs. Insulin and heparin are two common names of drugs of animal origin.
Microbial sources
Microorganisms as a source of potential drug candidates were not explored till the discovery of penicillin in 1929. Subsequently several antibiotics have been obtained either from microbial sources or from their semi-synthetic derivatives.
Marine sources.
Marine organisms have also been sources for new drugs. The first active compounds to
be isolated from marine species were Spongouridine and Spongothymidine from the
Carribean sponge Cryptotheca crypta in 1950s. These compounds are nucleotides and show a great potential as anticancer and antiviral agents. Discodermolide, isolated from the marine sponge,Discodermia gissoluta has a strong antitumour activity and has mode of action similar to that of Paclitaxol. Few antibiotics originate from ocean.
In addition to the above mentioned natural sources, two other sources need specific mention. A drug may be derived either as a semi-synthetic product from any of the naturally
occurring resources or it may be of totally synthetic origin.
Several derivatives of antibiotics, β-blockers, anti-protozoal drugs, anti-malarial drugs are of totally synthetic origin. The ex. of the categories of drugs are illustrative only. In recent years most of the new drugs are of synthetic origin based on the knowledge about the receptor.
Essential Drugs Concept
WHO proposed a concept of ‘essential medicines’ in 1977. essential medicines are those that satisfy the priority health care needs of the population.
They are selected with due regard to public health relevance, evidence on safety and efficacy, and comparative cost-effectiveness.
(In the first, 1977 version of list of essential medicines, 208 medicines were identified to address the global burden of disease at that time.In 2007, 30th anniversary of WHO was celebrated. By then 156 of 193 WHO member states have official essential medicine lists, of which 127 countries have been updating it in past 5-10 years. The list of essential medicines published in 2007 contains 340 medicines including drugs for
malaria, HIV/AIDS, tuberculosis, reproductive health, chronic diseases like cancer and diabetes. The list of essential medicines published in October 2007 contained for the first
time “Essential Medicines for children”. The list of essential medicines for children is also
updated every two years. In the year 2015, 19th model list of essential medicines and 5th revised list of essential medicines for children has been published by WHO. The 20th revision of essential medicines and the 6th revision of essential medicines for children is in the
process.)
Routes of Drug Administration
• Enteral
It means through gastro-intestinal tract. It includes oral, sublingual and rectal routes.
• Parenteral
It means through routes other than enteral. It includes all types of injections, inhalations.
• Local
It includes administration of a drug at the site where the desired action is intended. It includes topical administration in oral cavity, gastro-intestinal tract, rectum/anal canal,
eye, ear, nose, bronchi, skin, intra-arterial, injection in deep tissues e.g. joints.
• Systemic
It includes drugs administered to enter the blood to produce systemic effects.
• Oral
It means drugs taken by mouth e.g. tablets, capsules, syrups, mixtures etc.
• Intravenous
It includes drugs injected directly in to blood stream through a vein. It may be administered as: bolus, slow intravenous injection or an intravenous infusion.
• Intrathecal
It includes drugs injected in to the sun-arachnoid space e.g. spinal anaesthetics like lignocaine.
• Intra-articular
It includes drugs injected directly in to the joint space e.g. hydrocortisone injection for rheumatoid arthritis.
• Subcutaneous
It includes drugs injected in to the sub-cutaneous tissues of the thigh, abdomen and arm e.g. adrenalin, insulin etc.
• Intradermal
It includes drugs injected in to the dermis layer of the skin e.g. tuberculin and allergy tests.
• Intramuscular
It includes drugs injected in to large muscles such as deltoid, gluteus maximus and vastus lateralis. A volume of 5-10 ml can be given at a time e.g. paracetamol, diclofenac.
• Intraosseous
It includes injecting a drug directly in to the marrow of a bone.
• Transdermal (patch)
It includes administration of a drug in the form of a patch or ointment that delivers the drug into the circulation for systemic effect.
• Rectal
It includes administration of drugs in the form of suppository or enema in to the rectum.
• Sublingual
In this case, the preparation is kept under the tongue. The drug is absorbed through the buccal membrane and enters the systemic circulation bypassing the liver e.g.
nitroglycerine for acute angina attack.
• Inhalation
It includes volatile gases and liquids which are given by inhalation for systemic effects e.g. general anaesthetics.
• Endotracheal
It includes a catheter inserted in to the trachea for primary purpose of establishing and maintaining an airway to ensure adequate exchange of oxygen and carbon dioxide.