Dravyaguna is interpreted as clinical pharmacology since the most o the Ayurvedic drugs were initially evaluated only in human beings. Seers of Ayurveda have collected the information regarding the clinical usage of several herbs from cowherds, shepherds, tribals and other forest dwellers and they never felt the necessity of evaluating their activity in animals.
Dravyaguna encompasses the information of all other allied fields of pharmacology like:
- Namarupa Vijnanam-Pharmacognosy (the science of identification of drugs).
- Gunakarma Vijnanam-Pharmacodynamics (mechanism of drugs action) & Pharmacokinetics (study of absorption, distribution, metabolims and excretion of drugs)
- Amayikaprayoga Vijnanam-Therapeutics (branch of medicine concerned with cure of disease or relief of symptoms).
- Kalpana Vijnanam-Pharmacy (science of selection, preservation & compounding of drug)
The major object of teaching Dravyaguna to the medical students of Ayurveda is to provide a rational basis for choosing or using drugs skillfully to relieve ailments of the patient population. The modern pharmacology is traditionally associated with the study of drugs in different animals like dogs, monkeys, cats, rabbits, rats etc. Whereas the clinical pharmacology involves the study of various aspects of drug action and metabolism in humans, both in health and disease. The ultimate aim of pharmacological studies in animals is to find out a therapeutic agent suitable for clinical evalutation in man. The animal models (cat, rat etc.) cannot act as an ideal model of human being. The drug has to be carefully evaluated in human being for its safety and efficacy before it is accepted for therapeutic use.
Majority of the drugs that are currently used in modern medicine are synthetic where as the Ayurvedic therapeutics mainly employ plant-based medicines (oudbhija) along with metals & mineral (parthiva) and animal products (jagama drawya). Among the plant products, the important pharmacologically active principles (utkrishta guna-sampanna dravyamsha) are- (a) alkaloids (basic substances containing cyclic nitrogen) (b) glycosides (a combination of sugars with other organic structures) (c) glucosides (glycoside which yields glucose on acid hydrolysis) (d) oils (fixed or volatile) (e) resins (formed by oxidation of volatile) oils which are insoluble in water but soluble in alcohal) (f) gums (dispersible in water) (g) tannins (precipitate proteins from the cells and are non-nitrogenous).
Scientists of modern pharmacy generally argue that plant based medicines should be processed in the medium of alcohal as the majority of active principles (mainly alkaloids) are made available and according to them water extracts of plants are useless as they are devoid of maximum alkaloid content. The review of various bheshaja-kalpanas (pharmaceutical processes), namely kwatha, phanta, hima, taila, ghrita, arishta except asava-kalpana clearly indicates that water was suggested as the medium of extraction. Some of the scholars of Ayurveda following the concept of modern pharmaceutical scientists suggest to prefer kanjikam (contains self generated alcohal) as the medium for extracting the active portion of the drugs. But a careful review of different formulations indicates that kanjikam was not mentioned for majority of formulations. To achieve the maximum therapeutic action it is always preferable to administer the swarasa (fresh juice) or kalka (paste) or churna (powder) of fresh herb or dried herb. The human gut, which is highly sophisticated, and also the selective chemical laboratory can synthesize the required portion o the active principle and makes in available to various bodily organs and tissues. Ayurvedic pharmacology delineates five important principles namely rasa, guna, virya, vipaka and prabhava (Rasapanchaka) which are responsible for any drug action. Many times the terms 'action' and 'effects' of a drug are being used as synonyms. However, it is useful to term the initial consequences of drug-cell interactions as the action (karma) of the drug, the remaining events that follow are called drug effects (phala). In practice, no drug produces only a single effect but has spectrum of effects or actions. Further, a drug may be selective in one respect but non-selective in another. With this view only the most of the Ayurvedic Nighantus attributed a spectrum of actions and therapeutic indications to the majority of drugs. Most of the actions of drugs are attributed to the potent gunas which are given virya status. Most of the action of drugs are attributed to the potent gunas which are given virya status. Ayurvedic classics firmly established the relationship between the various pharmacological actions and the principles of drug action like rasa, vipaka and guna/virya. In my view rasa, which is identified, by nipata (contact with the tongue) and vipaka by nishtha karma (final action) serve as indices of guna at the tongue level and at the stage of biotransformation (alteration of drug within living organism) respectively. After absorption, drugs could undergo three possible fates, namely, that could be metabolized by enzymes (dhatwagni paka), they could change into other substances without intervention of enzymes (it happens in the case of vyavayi drugs) or they could be excreted unchanged and in the case of Samana pratyayarabdha dravyas. In the case of Samana pratyayarabdha dravyas through rasa, it becomes easy to draw the profiles of other principles of drug action and in the case of vichitra pratyayarabdha dravyas the pharmacological principles barring rasa (which is perceivable) are identified by inference basing on pharmacological action/therapeutic (karma & phala). The drugs metabolized by enzymes (vipaka) result in their activation, inactivation or modification. Vipaka alone engenders virya (activated drug energy) and it alone-
(i) activates the gunas like ushna to become ushnatara/ushnatama or
(ii) inactivates the action of gunas like sheeta which is unable to produce vata vriddhi (as in the case of ksheera (milk) (iii) modifies gunas originally attributed to rasa eg. Sheeta virya or madhura rasa becomes ushna virya after vipaka (such drugs are categorized as vichitra pratyayarabdha dravyas).
It is generally observed that most of the Ayurvedic scholars are inclined to interpret virya of a dravya as the active principle. Acharya Priyavrat Sharma has disagreed with this concept and rightly suggested that active principle is the adhisthana of virya, Sushruta alone initiated a debate to discuss the relative importance of all the principles of drug action and finally concluded that dravya is the only prime one among all the principles. If the active principle or active drug molecule (drayva) is attributed with drug action, it can also be safely interpreted that rasa (taste) serves as one of the indices to identify pharmacological behaviour of active principle and vipaka indicates the metabolic process to synthesize the active drug molecules and virya indicates the release of energy from the active drug molecule (active principle).
Drayvaguna in some respects as a bridge between basis medical sciences on one hand and clinical medicine on the other. An attempt is made in this book to give all the relevant details of the entire Dravyaguna subject in accordance with CCIM curriculum and students will get all the necessary information by reading this book. Students should not 'cram' this book to get through the examination successfully but I expect them to learn the basic pharmacology of drugs in common clinical use and their rational application in therapeutics. The CCIM syllabus in the subject of Dravyaguna consists of two papers-first paper contains the fundamental principles of Dravyaguna and second paper deals with the details of 365 herbs and the subject of modern pharmacology in brief. I with to acknowledge the help taken form the works of great scholars of Dravyguna late Acharya Yadavji Trikamji, late Acharya Bapalal Vaidya, late C. Dwarakanath, Acharya Priyavrata Sharma and Achrya K. C. Chunekar, which have rendered important guidelines in the preparation of this hand book. My heartfelt thanks are due to Sri K. Arunee Kumar, Lecturer in Botany, P. R. Govt. College, Kakinada for his ablest guidance in all my academic pursuits. I specially thank Mr. Naveen Gupta, Chaukhamba Surbharati Prakashan for taking up the task of publication.