Classification of Drugs

Classification of Drugs Drugs are classified into various classes on the basis of different factors. These factors directly or indirectly affect the therapeutic use and profile of a drug. Drugs can be classified on the basis of: 1. Availability to general public - Over the counter (OTC) drugs: These drugs can be obtained directly from the pharmacy without prescription. These drugs are used for minor ailments. Examples of OTC drugs are antacids (magnesium hydroxide), analgesics (paracetamol), decongestants etc. - Prescription drugs: These drugs can be obtained from the pharmacy only with prescription of a registered medical practitioner. These drugs are used for major ailments. Examples are antiepileptic drugs (carbamazepine), antibiotics, narcotics etc. 2. Classifications made according to legal requirements: Group ‘Ka’ Group ‘Kha’ Group ‘Ga’ (assignment) (refer drug act 2035) 3. Therapeutic use: Antibiotics - Empirical therapy - Definitive therapy - Prophylactic therapy (remember previous notes) 4. Mechanism of action: E.g. Drugs for peptic ulcer i. Reduction of gastric acid secretion - H2 antahistamines: ranitidine, cimetidine - Proton pump inhibitors: omeprazole, lansoprazole - Anticholinergics: pirenzepine, propantheline - Prostaglandin analogue: misoprostol ii. Neutralization of gastric acid - Systemic neutralizers: sodium bicarbonate, sodium citrate - Nonsystemic neutralizers: magnesium hydroxide, aluminium hydroxide iii. Ulcer protectives - Sucralfate, colloidal bismuth subcitrate iv. Anti-H pylori drugs - Amoxicilln, metronidazole, tinidazole 5. Clinical classification: E.g. Barbiturates - Ultra short acting barbiturates: thiopentone - Short acting barbiturates: pentobarbitone - Long acting barbiturates: phenobarbitone 6. Routes of administration - Local routes: Topical route (creams, ointments) - Systemic routes: oral (antibiotics), sublingual (glyceral trinitrate), rectal (suppository), parenteral (saline), nasal (corticosteroids nasal spray) 7. Chemical structures etc. Classification of drugs based on mechanism of action Anticholinergic drugs Anticholinergic drugs are those which block actions of ACh on autonomic effectors and in the CNS. Cholinergic actions: Heart: rate of impulse generation is reduced, bradycardia or even cardiac arrest may occur, ventricular contractility decreases. Blood vessels are dilated, flushing, fall in BP. Smooth muscles contract, peristaltic movement increases, bronchial muscle constrict Secretions: sweating, salivation, lacrimation, tracheobronchial and gastric secretion Eyes: miosis (contraction of pupils) occur 1) Natural alkaloids: atropine, hyoscine 2) Semi-synthetic derivatives: homatropine, hyoscine butylbromide 3) Synthetic compounds i) Mydriatics: cyclopentolate ii) Antisecretory-antispasmodic: propantheline, dicyclomine iii) Vasicoselective: oxybutynin, flavoxate iv) Antiparkinsonian: trihexyphenidyl, biperidine Autocoids and Related Drugs Antihistaminics Histamine is present mostly within storage granules of mast cells. Tissues rich in histamine are skin, gastric and intestinal mucosa, lungs, liver and placenta. Pharmacological actions of histamine: Dilation of small blood vessels and constriction of larger arteries and veins Force of contraction is increased in isolated heart. Bronchoconstriction and smooth muscle contraction Increase in gastric secretion Stimulates nerve endings (itching) Releases adrenaline causing rise in BP 1) Highly sedatives: diphenhydramine 2) Moderately sedative: pheniramine, cinnarizine 3) Mild sedative: chlorpheniramine, cyclizine 4) Second generation antihistaminics: cetrizine, fexofenadine Nonsteroidal Antiinflammatory Drugs (NSAIDs) and Antipyretic-Analgesics Inhibit production of PGs that induce hyperalgesia Block the action of pyrogens that induce PGs in hypothalamus which raise the temperature. Inhibit production of PGs at the site of injury to inhibit inflammation A. Nonselective COX inhibitors Salicylates: aspirin Propionic acid derivatives: ibuprofen Anthranillic acid derivatives: mephenamic acid Aryl-acetic acid derivatives: diclofenac Oxicam derivatives: piroxicam Pyrrolo-pyrrole derivative: ketorolac Indole derivative: indomethacin Pyrazolone derivatives: phenylbutazone B. Preferential COX-2 inhibitors Nimesulide, meloxicam C. Selective COX-2 inhibitors Celecoxib, parecoxib D. Analgesic-antipyretics with poor antiinflammatory action Paraaminophenol derivatives: paracetamol Pyrazolone derivatives: metamizol Benzoxaocine derivative: nefopam Antirheumatoid drugs Rheumatoid arthritis is an autoimmune disease in which there is joint inflammation, synovial proliferation and destruction of articular cartilage. Immune complexes composed of IgM activate complement and release cytokines which are chemotactic for neutrophils. These inflammatory cells secrete lysosomal enzymes which damage cartilage and erode bone while PGs produced in the process cause vasodilation and pain. A. Disease modifying antirheumatic drugs (DMARDs) Immunosuppresants: methotrexate, cyclosporin Sulfasalazine Chloroquine Leflunomide Gold sodium thiomalate d-penicillamine B. Biologic response modifiers (BRMs) TNF inhibitors: etanercept IL-1 antagonist: anakinra C. Adjuvant drugs Corticosteroids: prednisolone Drugs for cough Cough is a protective reflex its purpose being expulsion of respiratory secretions or foreign particles from air passages. Cough may be useful or useless. 1. Pharyngeal demulcent: lozenges, glycerine 2. Expectorants Bronchial secretion enhancers: sodium citrate Mucolytics: bromhexine 3. Antitussives Opoids: codeine Nonopoids: noscapine Antihistamines: chlorpheniramine 4. Adjuvant antitussive Bronchodilators: salbutamol, terbutalin Drugs for bronchial asthma Bronchial asthma is characterized by hyperresponsiveness of tracheobronchial smooth muscle to a variety of stimuli, resulting in narrowing of air tubes, often accompained by increased secretion, mucosal edema and mucosal plugging. Symptoms include dyspnoea, wheezing, cough and may be limitation of activity. 1. Bronchodilators 2-sympathomimetics: salbutamol, terbutaline methylxanthines: theophylline, aminophylline anticholinergics: ipratropium bromide 2. leukotriene antagonists montelucast, zafirlucast 3. mast cell stabilizers sodium cromoglycate 4. corticosteroids systemic: hydrocortisone, prednisolone inhalational: beclomethasone dipropionate, flticasone propionate 5. anti-IgE antibody omalizumab Refer clinical pharmacology for following classification of drugs - skeletal muscle relaxants - local anesthetics - general anesthetics - antiarrhythmic drugs - antihypertensive drugs - antiarrhythmic drugs - diuretics - hypolipidaemic drugs - drugs for peptic ulcer - drugs for emesis - drugs for constipation and diarrhora - antimicrobial drugs - -lactam antibiotics - antitubercular drugs - antileprotic drugs - antifungal drugs - antiviral drugs - antimalarial drugs - antiamoebic and antiprotozoal drugs - antihelmintic drugs - anticancer drugs