Routes of Drug Administration

Veer P. ChoollunRoll no. 127/02/15

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

Definition

• A route of administration 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 drug2. Site of desired action3. Rate and extent of absorption from different

routes4. Effect of digestive juices and first pass

metabolism on the drug5. Rapidity with which the response is desired6. Accuracy of dosage required7. Condition of patient

Classification

Route

Local

Topical

Deeper tissues

Arterial

supply

Systemic

Enteral Parenteral

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

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.

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.

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

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

Enteral Routes

• Definition:When drug is placed directly in the GI

tract. Enteral

Oral Buccal/ Sublingual Rectal

Oral Route

• Oral 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.

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 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

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

Sublingual/ Buccal

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

Rectal route

• Most commonly by suppository or enema.• 2 types of enema:

i) Evacuant - e.g. soap water in rectumii) Retention- e.g. prednisolone enema in ulcerative colitis

• ADVANTAGES1. 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%.

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, paracetamol, 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

Parenteral- Injections

Injections

Intradermal Intramu

scular

Subcutaneous

IntravenousIntraper

itoneal

Intrathecal

Intra-arterial

Intrarticular

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

E.g. Insulin, Heparin AdvantagesReliable Patients can be trained for self-administrationDisadvantagesIrritant drugs can cause severe pain- due to rich nerve supplyLess vascular tissue – slows absorption + if vasoconstriction is there then further decreases absorptionRepeated injections at same site lipoatrophy decreased absorption

Subcutaneous (s/c)

Intramuscular InjectionAdvantagesMore reliable Highly vascular↑ absorptionIrritants, depot preparations, suspensions, colloids can be injectedDisadvantagesPainful Nerve liable to injury or irritationLocal infection with necrosisSome drugs have decreased absorption by IM ( diazepam, phenytoin)Some drugs should be avoided (heparin)

Intravenous injection

Given as a) bolus- large dose dissolved in vehicle injected slowly e.g. Heparinb) Slow injection- over 15-20 mins e.g. Aminophyllinec) Slow infusion- for constant plasma conc. About 1 litre soln infused for about 3-4 hrs

depending drug and patient conditionsAdvantages- Immediate action ( useful in emergencies)- 100% bioavailability- Large volumes can be given- Irritants can be given- Rapid adjustments possibleDisadvantages- 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 anaestheticsAdvantagesUsed for long duration surgeries to prevent complications from general anaesthesiaDirect and Rapid Action N.B Strict aseptic conditions are required.

Inhalation

- Used for gaseous and volatile agents and aerosols.

AdvantagesA) Large surface areaB) Serves as local route in lung diseasesC) high blood flowD) Hepatic first pass met. Is avoidedE) Small dose since direct delivery – less toxicity- As result of that a rapid onset of action due to rapid

access to circulation.

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