An introduction to general pharmacology
In this branch of science we study the effect of drugs or other chemicals on living system [Rang HP et. al., 2007]. Therefore, before discuss broadly about pharmacology, we need to introduce drug.
This is the application of the knowledge about the drug and disease for the treatment of a particular disease with appropriate drug [Tripathi KD, 2004]. It is worthy to describe the drug here.
From the very beginning the definition of drug is given in many times. The drug is a medicine which could be used for the diagnosis, prevention, mitigation (reducing severity of disease or pain), treatment or cure of a disease [Tripathi KD, 2004].
Examples of drug according to purpose of uses:
i. Diagnosis: Phentolamine (non selective $\alpha$ adrenergic agonist) is used to diagnose Pheochromocytoma (by increased catecholamine secretion) [Tripathi KD, 2004]
ii. Prevention: Vaccines are used to prevent communicable diseases (eg. poliomyelitis by polio virus is prevented using polio vaccine) [Neil Z. Miller, 2004]
iii. Mitigation: Oseltamivir (anti viral agent) reduces the severity of pandemic influenza (by H1N1 virus) [Muthuri S et. al., 1023]
iv. Treatment: Insulin (hormone) is used to treat type I diabetes mellitus (due to impaired activity or destruction of beta cell of islets of Langerhans of pancreas) [Tripathi KD, 2004].
v. Cure: Paracetamol (non steroidal anti inflammatory agents) is used to cure fever [Tripathi KD, 2004].
But, all the category of drugs can not be categorized by this definition. Like when one is deficient of a hormone, minerals, vitamins etc. he/she can not be called a patient but the recipient will suffer for that and need to take the agent from outsource (like iron, folic acid, calcium etc) and the substance, called the supplement, must be included in the category of drug. Therefore, World Health Organization (WHO) has given a new definition of drug in 1996.
Drug (as per WHO) Any chemical substance that is administered or intended to be used to modify or explore the physiological system or pathological states for the benefit of the recipient [Tripathi KD, 2004].
Drug (alternative definition) A chemical compound of known structure, other than nutrients or any essential dietary ingredients, that is administered in a living system to get a desired biological response [Rang HP et. al., 2007]
Medicine A chemical preparation of one or more drug usually not necessarily, along with other inactive ingredients, which is intended to be administered to get a therapeutic response
Classification of drugs according to mechanism of action
i. Pharmacodynamic agents: Acts by a affecting a specific target of the host. Example: Proton pumps inhibitors (eg. Pantoprazole) reduce the hydrochloric acid (HCl) production by inhibiting Na+K+ATPase [Tripathi KD, 2004].
ii. Chemotherapeutic agents: This type of chemical acts on the causative agents of the disease (eg. virus, bacteria, protozoa etc.) either by inhibiting their multiplication (static effect) or by killing the organisms (cidal action) in stead of affecting the host cells. Example: Isoniazid
acts as anti-tubercular agent by inhibiting the of mycolic acid synthesis of mycobacterium tuberculosis (bacteriocidal) [Tripathi KD, 2004].
[Muthuri S et. al., 1023] Muthuri S, Venkatesan S, Myles PR, Nguyen-Van-Tam JS, The Use of anti-viral in an influenza pandemic: Scientific Evidence Base Review, Department of Health, Elizabeth Paterson, vol. 16, 2013.
[Neil Z. Miller, 2004] Neil Z. Miller, The polio vaccine: a critical assessment of its arcane history, efficacy, and long-term health-related consequences, Medical Veritas, vol. 1, 239-251, 2004.
[Rang HP et. al., 2007] Rang HP, Dale MM, Ritter J M, Moore P K, Pharmacology, 5th Edition, Elsevier, 2-752, 2007.
Tripathi KD, 2004] Tripathi KD, Essential of Medical harmacology, 5th Edition, Jaypee Brothers Medical Publishers Limited, 3-123, 2004.