Pharmacognosy: Crude Drugs, Phytochemistry and Quality
Core concepts
Pharmacognosy questions combine botanical identity, chemical class of active constituents, pharmacological use, and quality testing. Learn drugs by family and constituent: alkaloids (e.g. Atropa belladonna - tropane alkaloids), glycosides (cardiac glycosides from Digitalis; sennosides from Cassia), volatile oils (e.g. clove - eugenol), resins, tannins, gums and mucilages. Understand biosynthetic pathways at a broad level - shikimic acid for aromatic amino acids and many phenolics, mevalonate/deoxyxylulose for terpenes, and amino acid pathways for alkaloids. Know the pharmacopoeial identity tests, adulteration types (substitution, exhaustion, artificially damaged drugs), and evaluation methods: organoleptic, microscopic, physical, chemical and biological.
Traps examiners use
- Confusing primary metabolites (needed for growth) with secondary metabolites (ecological roles, usually the active constituents).
- Mixing the source of a constituent with a similar-sounding drug - always anchor the binomial name.
- Assuming all alkaloids are basic and water-soluble; some are neutral or amphoteric.
- Forgetting that exhaustion (drug partially extracted before sale) is a recognised adulteration.
Worked example
A sample is claimed to be Digitalis purpurea leaf. A candidate must state the constituent class (cardiac glycosides, e.g. digitoxin), the family (Plantaginaceae, formerly Scrophulariaceae), the pharmacological action (positive inotropy via Na⁺/K⁺-ATPase inhibition), and at least one identity test (e.g. Keller–Kiliani reaction for deoxy sugars). Structure your answer as name → family → constituent → action → test; examiners award marks per element.