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METHODS OF ADMINISTRATION

Definition

• A is the path by which a drug or substance is brought into contact with the body.

Factors affecting the choice of route

1. Physical and chemical properties of the drug

2. Site of desired action

3. Rate and extent of from different routes

4. Effect of digestive juices and first pass metabolism on the drug

5. Rapidity with which the response is desired

6. Accuracy of dosage required

7. Condition of patient

Classification

Local Routes

• These can only be used for localised lesions at accessible sites & for 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

Topical route

• This refers to external application of the drug to the surface for localized action.

• (a) Skin: Drug is applied as ointment, , , , , dressing etc.

• (b) : The depends on the site :

• (i) Mouth and pharynx: Paints, lozenges, mouth washes, gargles.

• (ii) Eyes, and nose: As drops, ointments, irrigation, .

• (iii): As non-absorbable drugs given orally e.g. aluminium hydroxide, kaolin, neomycin.

• (iv)Bronchi and lungs: As , aerosols (nebulised or fine powder)- e.g. salbutamol, cromolyn sodium.

• (v) Urethra: As jellies e.g. , irrigating . • (vi): As , vaginal tablets, inserts, cream, , .

• (vii)Anal canal: As ointment, .

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 / retrobulbar

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 / brachial artery to localise malignancies in limbs

Enteral Routes

Definition:

When drug is placed directly in the GI tract.

Enteral types

 Oral  Buccal/ Sublingual  Rectal

Oral Route

is designated as per os (PO), which means to administer ‘by mouth’.

• The is swallowed, and the drug is absorbed from the and small intestines.

Advantages of Oral admin.

• Safest route

• Commonest

• Convenient

• No skill required, self medication

• Painless, & acceptable

• Cost effective

• No maximal/strict sterilization required

Disadvantages of Oral admin.

• Slow absorption® delayed 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

• Some drugs are destroyed by gastric secretions e.g. , ACTH

• Some drugs are undergo extensive first pass metabolism in the liver e.g. Lidocaine, GTN, testosterone

Sublingual/ Buccal

• Some drugs are taken as smaller tablets which are held in the mouth (buccal ) or under the (sublingual tablet).

Rectal route

• Most commonly by or .

• 2 types of enema:

i) Evacuant - e.g. soap water in

ii) Retention- e.g. prednisolone enema in ulcerative colitis

iii) ADVANTAGES

1. By-pass liver - Some of the draining the rectum lead directly to the general circulation, thus by-passing the liver. Reduced first-pass effect by 50%.

2. 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, , Ergotamine, Indomethacin

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

Intradermal

• Drug injected into the layers of skin raising a bleb

• e.g. BCG , allergy test

• Disadvantage

-small amount of drug injected

-may be painful

Subcutaneous (s/c)

E.g. Insulin, 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 is there then further decreases absorption

Repeated injections at same site ® lipoatrophy ® decreased absorption

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)

Intravenous injection

Given as

a) - large dissolved in vehicle injected slowly e.g. Heparin

b) Slow injection- over 15-20 mins e.g. Aminophylline c) 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%

- 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

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.

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.

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 .

• Drug may induce cough e.g. Cromolyn sodium

• Pulmonary secretion may get enhanced