It is not that the various drugs and diets act only by virtue of their qualities. In fact they act by virtue of their own nature or qualities or both on a proper occasion, in a given location, in appropriate condition and situations; the effect so produced is considered to be their action (Karma);
the factor responsible for the manifestation of the effect is known as Virya;
where they act is the Adhisthana (location); when they act is the time, how they act is the Upaya or mode of action; what they accomplish is the achievement or therapeutic effect. (Charaka Smhita)
Chkrapani Dutta further explains that some drugs act by virtue of their own nature; e.g. Danti (Baliospermum montanum Muell-Arg.) is purgative and precious stones are antitoxic. Some other drugs act by virtue of their qualities; e.g. fever is cured by drugs having bitter taste and coldness by the heat of the fire. Some other drugs act by virtue of their own nature as well as their qualities; e.g. cow milk boiled with a gold ring is considered to be aphrodisiac – Rcf. Chikitsa2:3:11, by virtue of the very nature of gold as well as its circularity.
When errhines are administered they eliminate Doshas from the head – that is their action. The factor like heat which is responsible for this action is Virya (potency) relating either to the drug or its quality. The site where the elimination takes place i.e.is the Adhikarana (location); errhines do not act when administered elsewhere. The spring season or the time when the
Basic concepts of Ayurvedic pharmacology 38 head is heavy is the appropriate time or Kala for the administration of this therapy. This therapy is not effective in other seasons or occasions. This therapy is to be administered in accordance with the prescribed procedure.
Pradhamana and Avapidana are to be administered while the patient lies on a bed covered with a bed sheet; his head is projected out of the bed and his eyes are closed. This is Upaya or mode of administration. By the administration of this therapy, heaviness and pain etc., of the head are cured.
This is Phala or the object of treatment.
The modern investigations on the action of drugs are carried out by observing the effects when these are -
1. Administrated to living animals – healthy or diseased.
2. Applied on the isolated organs or other tissues of certain animals &
also on various infecting organisms.
3. Investigated through radio-activate isotopes and by electron microscope.
4. Also administered to a human being in healthy and in diseased states for therapeutic purpose.
While explaining the drug action two points deserve attention (1) where a drug acts and (2) How a drug acts?
Where a drug acts
A drug may act locally, exactly on the tissues it comes in intimate contact with, either on the superficial epithelia of the skin, mouth, upper respiratory tract or other parts of the body where the drug can have direct access (also called direct or topical actions). A drug may act on certain particular tissues or organs having selective affinity by the absorption into the circulation. This is known as specific selective or systematic action of
Basic concepts of Ayurvedic pharmacology 39 the drug.
Recent conceptions of drug action
Whatever may be the mode of administration of a drug and its distribution in the body, it acts only when it reaches certain specific tissue cell either its surface or its interior. This is known as receptor theory.
Highly potent drugs probably act on the tissue through certain receptors which are speculated to be localized on the surface of the cells or are parts of an enzyme system. These fitting like keys in the locks. Cell theory was described by Charak as “Sharira Avayavasthu Paramanu Bhedana Aprisanakyaya Bhavanti’. The action is achieved depending upon localization of receptors and the concentration of drug to which the receptor is exposed. If a drug acts by interaction with relatively non-specialized receptor, that is a receptor that serves functions common to most cells, its effects will be wide spread (Doshapratyanika action). If a drug interacts with specialized receptors its effects are more specific (Vyadhipratyanika action).
Sometimes same drug may exercise different actions in the body by interaction with different Adhikaranas.
Enzymes
The enzymes play an important part in the body activity and many drugs probably act through the enzymes. These are known as pitta modalities which take part in the drug metabolism.
How a drug acts
Some of the drugs act purely by physical means. Oils applied externally to skin (Abhyanga) and internally (Ghritapan )act in this manner.
Basic concepts of Ayurvedic pharmacology 40 Drug may act chemically by its chemical affinity it fixes up to certain tissues, or produces a new active substances at the nerve ends where it acts or it combines with some other substance in the blood or tissue and acts.
Special action
A drug may have well marked selective action on a particular part of the body even in minute doses. Most of the alkaloids act in this way. A drug may either increase (Vriddhi) or diminish the altered physiological functions of a particular type of tissue in disease and the result is either stimulation or depression of its function.
Rasas have mostly local and some general effects till the digestion is completed. The Rasa, in the final form circulates through Rasa Dhatu all over the body and influences the doshas and metabolic processes. When it comes in contact with Doshas it increases or decreases them according to similar or dissimilar properties. Rasa, Guna and sometimes Virya have local action, while Vipaka and Virya have systematic action and Prabhava has got specific action. External administration (Bahiparimarjanam) of drugs are mostly directed towards local action while internal administration (Antah Parimarjam) towards systematic action.