WHO Definition of Drug “Any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient”
Sources of Drugs
1. Natural Sources
i. Vegetable Sources: They are obtained from Plants
a) Alkaloids: Nitrogenous heterocyclic bases derived from plants.
ü They are insoluble in water but forms salts with water which are water soluble
ü Eg: Atropine from Atropa belladonna, Quinine from Cinchona bark, Morphine from Papavarum somniferum, Reserpine from Rauwolfia serpentine, Nicotine from Tobacco leaves
b) Glycosides: in these compounds a sugar moiety is joined to a non-sugar moiety with a ether linkage (-O-)
ü The pharmacological action lies in its non-sugar residues (aglycon)
ü The sugar portion guides the pharmacokinetic characteristics
ü Eg: Cardiac Glycosides used in CHF (Digitoxin, Digoxin obtained from Fox Glove leaves (Digitalis Purpurea) )
c) Oils:
Essential Oils (or Volatile oils) | Fixed Oils | Mineral Oils |
· They are obtained from leaves or flowers · They are used as Carminatives, Astringents in Mouth washes or as Flavoring agents eg: Eucalypus Oil, Clove Oil, Peppermint Oil, Ginger Oil | · These are non volatile oils. · They are obtained from Seeds · Eg: Groundnut Oil, Coconut Oil, Olive Oil | · These are petroleum products and obtained from dry distillation of wood. · These are mainly used as vehicles for preparation of ointments · Eg: Hard and Soft paraffin |
d) Tannins: These are non-nitrogenous phenolic derivatives from plant sources and are soluble in water
ü They are mainly used a Astringents
ü Eg: Tinct. Catechu, Tinct. Rhubarb
e) Gums: These are colloidal exudates of he plants
ü These are mainly used as emulsifying or suspending agents
f) Resins: These are polymers of volatile oil and are insoluble in water
ü Eg: Benzoin ( used as inhalation in common cold), Tinct.Benzoin ( as antiseptic protective sealing over bruises)
ii. Animal Sources: They are obtained from living or dead animals or from their parts
ü These comprise hormones, Vitamins, Vaccines and Sera
ü Eg: Insulin from Pancreas, Vit B12 from Liver Extract, Thyroxin from Thyroid
iii. Microbial Sources: Mostly they are obtained from Fungi, Moulds & Bacteria
ü These are mostly life saving drugs
ü Eg: Penicillin from Penicilium notatum, Chloramphenicol from Streptomyes venezuelae, Griseofulvin from Penicilium griseofulvum
iv. Mineral Sources: They are naturally available minerals used for therapeutic purpose
ü Eg: Ferrous Sulfate (in anemia), Magnesium Sulfate (as Purgative), Aluminium Hydroxide & Sodium Bicarbonate (as antacids), Radioactive isotopes like I131 for the diagnosis & treatment of Thyrotoxicosis & Thyroid malignancy and P32 for Polycythaemia vera
2. Semi-Synthetic Sources: The naturally obtained dreg has been chemically modified in laboratory for better pharmacokinetic profile and also to reduce the toxicity.
Example: Desferrioxamine – Antidote for Iron poisoning. Ferrioxamine is isolated from Streptomyces pilosus and degraded chemically to obtain iron free ligand Desferrioxamine.
3. Synthetic Sources: These drugs are completely synthesized in the laboratory
ü Majority of the drugs are synthetic drugs
ü They are having better efficacy, efficiency, and less toxic effects compare with naturally obtained drugs
ü Their chemical structure can be modified for getting better speicificity
ü Eg; Aspirin, Paracetamol
4. Genetically Engineered Drugs: These are obtained from new methodology involves the blending of discoveries from Molecular biology, Recombinant DNA technology, DNA alteration, Gene Splicing, Immnology & Immuno Pharmacology
ü Eg: Recombinex HB – a hepatitis-B vaccine, Humulin – human insulin of recombinant DNA origin, Interferon-alpha-2a & Interferon-alpha-2b for hairy cell leukaemia
Routes of Drug Administration (Enteral, Parenteral, Topical)
I. Enteral Routes: Placement of drug directly into any part of the GIT is called an ‘enteral’ mode of administration
a) Oral: Swallowing a drug through mouth
Advantages | Disadvantages |
ü Most commonly used method as it is safe, convenient & painless procedure ü Economical as sterilization of drug products is not essential ü No need of any assistant | ü Onset of action is slower ü Polar drugs can’t be given as they are not absorbed (eg: Streptomycin) ü Drugs are destroyed by the digestive juices (Eg: Penicillin-G, Insulin, Oxytocin) ü 1st pass effect (those destroyed in liver before reaching systemic circulation) (eg: Morphine, Isoprenaline) ü Bad test & Bad smell & irritant drugs can’t be given ü Drugs can’t be given to unconscious & uncooperative patients ü Drugs can’t be given during emesis |
b) Sublingual / Buccal
ü The drug is place beneath the tongue (sublingual) or crushed in mouth and spread over the buccal mucosa (Buccal).
Advantages | Disadvantages |
ü Quick onset of action because of rapid absorption due to more blood supply in that region ü Bypasses the portal circulation à no 1st pass metabolism ü Drug action can be terminated at any time when side effects are observed | ü Distasteful, irritant drugs can’t be given ü Higher molecular weight drugs can’t be absorbed (eg; insulin) |
Examples Isosorbide dinitrate tablets & Nitroglycerin tablets (for Angina), Isopranline sulfate tablets (for Bronchial Asthma), Nifedipine in powder form (in Hypertension) | |
c) Rectal: Through Rectum (Suppositories, Enema)
Advantages | Disadvantages |
ü Useful in patients with nausea and vomiting ü 1st pass metabolism is greatly bypassed as a major portion of the drg is absorbed from external haemorrhoidal veins ü Useful for gastric irritant drugs | ü Chances of rectal inflammation ü Absorption is irregular ü Inconvenient and embarrassing to the patient |
Examples ü Dulcolax & Glycerine suppositories, enemas, ointments for Local action ü Aminophylline (Bronchodillator) & Indomethacin (Anti-inflammatory agent) Suppositories for Systemic action | |
II. Parenteral Routes: Routes other than “Enteral” are called ‘Parenteral’ routes of administration. Administration of drugs by injection, by topical application to skin or by inhalation through the lungs are all parenteral.
a) Intravenous:Through lumen of the veins
Advantages | Disadvantages |
ü Directly enters into the systemic circulation à no 1st pass effect & quicker onset of action ü Less dose is needed to achieve greater therapeutic effects ü Valuable in emergency ü Can be given evening unconscious, uncooperative patients those are having nausea, vomiting & diarrhea ü Hypertonic solutions & GIT irritant drugs can be infused ü Large volume of fluids can be infused at a uniform rate ü Amount of the drug can be controlled with an accuracy | ü Strict aseptic conditions are needed ü Patient has to depend upon other person for administration of drug ü Painful ü Risky because once the is injected it can’t be recalled ü Introduction of any air or particulate matter produce embolism which is fatal ü Drugs in suspensions & Oily drugs can’t be given ü Depot injections can’s be given ü Venous thrombosis & Thrombophlebitis of the vein injected ü Necrosis around the site of action |
Examples: Glucose, Glucose normal saline, Dopamine & Norepinephrine drips | |
b) Intramuscular
ü Deltoid muscle or gluteal mass of left or right buttock
ü Vastus muscle underlying the lateral surface of the thigh
Advantages | Disadvantages |
ü Absorption is more predictable, less variable & rapid compared to Oral route ü Depot injections can be given | ü Perfect aseptic conditions are needed ü Chances of abscess at the site of injection ü Chances of nerve damage leading to paresis of muscle supplied by it ü Large volumes can’t be given (maximum 5 – 10 ml) |
Examples: Depot injection of Testosterone, Antibiotics, Antiemetics | |
c) Intraperitoneal | d) Intrathecal (Intraspinal) |
ü Into the peritoneal space ü Rapid absorption due to large surface area ü Painful, risky ü Antirabies injection can be given | ü Into the subarachnoid space ü They crosses BBB & Blood CSF barrier ü Strict aseptic conditions & grater expertise is needed ü Its painful & risky procedure ü Many radiopaque contrast media for myelography (to visualize spinal cord) are given through this route ü Xylocaine injection for providing Spinal Anesthesia |
e) Intramedullary: Injection into the tibial or sternal bone marrow | f) Intra-arterial: into the lumen of the desired artery |
g) Intra-articular: injection directly into the joint space | h) Subcutaneous: Injection into the subcutaneous tissue under the skin |
Inhalation: Inspiration through nose or mouth | |
III. Topical Routes
a) Transdermal
ü Transdermal Patches
ü In these adhesive patches, the drug is incorporated into a polymer (usually Polyisobutylene) which in turn is bonded to an adhesive plaster
ü The drug is delivered at the skin surface by diffusion, for percutaneous absorption into circulation
ü These preparations are designed to provide steady & smooth plasma concentration of the drug for a period ranging from 1-3 days from the site of their application
ü Site of application: Chest, Abdomen, Upper arm or Mastoid region
ü Examples: Transdermal Patches of Nitroglycerine, Scopalamine, Clonidine, Estradiol
ü For diagram refer KD Tripathi Text book
b) Conjuctival: into the conjuctiva for local effects eg: Sulfacetamide
c) Vaginal and Urethral: Pessaries are used for local actions
d) Inunction (Rubbing): rubbing onto the skin
Newer Drug Delivery Systems: To improve drug delivery and to prolong its duration of action, special drug delivery systems have recently been developed.
ü These include: Ocuserts, Progestaserts, Transdermal Adhesive Patches, Prodrugs, Computerised Miniature Pumps, Use of Monoclonal Antibodies and Liposomes as drug carriers.
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