Routes of drug administration

Pharmacology : Routes of administration

1. Routes of Drug Administration Veer P . Choollun Roll no. 1 27/02/15

2. Contents Definition Factors affecting route Classification Local Routes and their advantages and disadvantages Enteral Routes and their advantages and disadvantages Parenteral Routes and their advantages and disadvantages

3. Definition A route of administration is the path by which a drug or substance is brought into contact with the body.

4. Factors affecting the choice of route Physical and chemical properties of the drug Site of desired action Rate and extent of absorption from different routes Effect of digestive juices and first pass metabolism on the drug Rapidity with which the response is desired Accuracy of dosage required Condition of patient

5. Classification

6. Local Routes These can only be used for localised lesions at accessible sites & for drugs whose systemic absorption from these sites is minimal. E.g. GTN applied as ointment High concentrations are attained at desired site without exposing rest of body. The local routes are: 1. Topical 2. Deeper tissues 3. Arterial Supply

7. Topical route This refers to external application of the drug to the surface for localized action. (a) Skin: Drug is applied as ointment, cream, lotion, paste, powder, dressing etc.

8. Topical Route (b)  Mucous membrane : The dosage form depends on the site : ( i )     Mouth and pharynx : Paints, lozenges, mouth washes, gargles. (ii)   Eyes, ears and nose : As drops, ointments, irrigation, nasal spray. (iii) Gastrointestinal tract : As non-absorbable drugs given orally e.g. aluminium hydroxide, kaolin, neomycin. (iv) Bronchi and lungs : As inhalations, aerosols (nebulised solution or fine powder)- e.g. salbutamol, cromolyn sodium. (v)   Urethra : As jellies e.g. lidocaine, irrigating solutions. (vi) Vagina : As pessaries, vaginal tablets, inserts, cream, powders, douches. (vii) Anal canal : As ointment, suppositories .

9. Deeper tissues Another local/ Parenteral route of administration though invasive The drug is in such state that absorption is slow and systemic absorption is minimal e.g. Hydrocortisone acetate in knee joint/ retrobulbar injection

10. Arterial Supply Local but Parenteral route attained by drug with minimal systemic absorption E.g. 1) Intra-arterial injection for contrast media in angiography; 2)anti –cancer drugs in femoral artery/ brachial artery to localise malignancies in limbs

11. Enteral Routes Definition: When d rug is placed directly in the GI tract.

12. Oral Route O ral administration is designated as per os (PO), which means to administer ‘by mouth’. The medication is swallowed, and the drug is absorbed from the stomach and small intestines.

13. Advantages of Oral admin . Safest route Commonest Convenient No skill required, self medication Painless, & acceptable Cost effective No maximal/strict sterilization required

14. Disadvantages of Oral admin. Slow absorption  delayed onset of action Not suitable for emergencies Unpalatable and irritant drugs not administered e.g. Chloramphenicol May cause nausea and vomiting Absorption of drugs  variable and erratic e.g . Streptomycin not absorbed Interactions of prescribed drug with food and other drugs affects absorption Administration difficult in uncooperative & unconscious patients

15. Disadvantages of Oral admin. – cont’d Some drugs are destroyed by gastric secretions e.g. Insulin, ACTH Some drugs are undergo extensive first pass metabolism in the liver e.g. Lidocaine, GTN, testosterone

16. Sublingual/ Buccal Some drugs are taken as smaller tablets which are held in the mouth (buccal tablet) or under the tongue (sublingual tablet).

17. Rectal route Most commonly by suppository or enema. 2 types of enema: i) Evacuant - e.g. soap water in rectum ii) Retention- e.g. prednisolone enema in ulcerative colitis ADVANTAGES By-pass liver - Some of the veins draining the rectum lead directly to the general circulation, thus by-passing the liver. Reduced first-pass effect by 50%. Useful - This route may be most useful for patients unable to take drugs orally (unconscious patients) or with younger children Or in persons feeling nausea and vomiting. e.g. diazepam, paracetamol, Ergotamine, Indomethacin

18. Disadvantages of Rectal route Psychological, patient may be embarrassed and dislike this way Irritation of mucosa & inflammation may occur with repeated use Emergency (slow onset of action) Absorption unreliable, especially if rectum is full of fecal matter

19. Parenteral- Injections

20. Intradermal Drug injected into the layers of skin raising a bleb e.g. BCG vaccine, allergy test Disadvantage -small amount of drug injected -may be painful

21. E.g. Insulin, Heparin Advantages Reliable Patients can be trained for self-administration Disadvantages Irritant drugs can cause severe pain- due to rich nerve supply Less vascular tissue – slows absorption + if vasoconstriction is there then further decreases absorption Repeated injections at same site  lipoatrophy  decreased absorption Subcutaneous (s/c)

22. Intramuscular Injection Advantages More reliable Highly vascular  ↑ absorption Irritants, depot preparations, suspensions, colloids can be injected Disadvantages Painful Nerve liable to injury or irritation Local infection with necrosis Some drugs have decreased absorption by IM ( diazepam, phenytoin ) Some drugs should be avoided (heparin)

23. Intravenous injection Given as a) bolus- large dose dissolved in vehicle injected slowly e.g. Heparin b) Slow injection- over 15-20 mins e.g. Aminophylline Slow infusion- for constant plasma conc. About 1 litre soln infused for about 3-4 hrs depending drug and patient conditions Advantages Immediate action ( useful in emergencies) 100% bioavailability Large volumes can be given Irritants can be given Rapid adjustments possible Disadvantages Irritation of veins cause thrombophlebitis Extravasations of drug can cause irritation Only aqueous soln can given IV

24. Intrathecal Drug to be injected in the subarachnoid space for CNS action e.g. Spinal anaesthetics Advantages Used for long duration surgeries to prevent complications from general anaesthesia Direct and Rapid Action N.B Strict aseptic conditions are required.

25. Inhalation - Used for gaseous and volatile agents and aerosols. Advantages A) Large surface area B) Serves as local route in lung diseases C) high blood flow D) Hepatic first pass met. Is avoided E) Small dose since direct delivery – less toxicity As result of that a rapid onset of action due to rapid access to circulation.

26. Inhalation Disadvantages Most addictive route of administration because it hits the brain so quickly. Difficulties in regulating the exact amount of dosage. Sometimes patient having difficulties in giving themselves a drug by inhaler. Drug may induce cough e.g. Cromolyn sodium Pulmonary secretion may get enhanced