Various Route of Drug Administration

Most of drugs can be administered by a variety of routes. The choice of appropriate route of drug administration in a given situation depends both on drugs as well as patient related factors.

Factors Governing Choice of Routes:

  • Physical and chemical properties of drug like state(solid, liquid, gas), solubility, stability, irritancy,  ph .
  • Site of desired action-localized and accessible or generalized and not accessible.
  • Rate and extent of absorption of the drug from different routes.
  • Effect of digestive juice and first pass metabolism of the drug.
  • Rapidity with which the response is desired.
  • Accuracy of dosage required–Specially in case of very potent drugs.
  • Condition of patient – Like unconsciousness, vomiting and emergencies.

Classification of Various Route of Drug Administration:  

Routes of drug administration can be broadly classified into –

  1. Local action
  2. Systemic action
Rote of Drug Administration

Local Routes of Drug Administration: 

These routes can only be used for localized lesions at accessible sites. Systemic absorption of the drug is minimal or absent. Thus high concentrations are attaining at desired site. Side effects or toxicity are absent or minimal.

1. Topical

These refer to external application of the drug to the surface for localized action.

Skin: Ointment, cream, lotion, paste, powder, dressings, spray etc.
Mucous membranes:
  • Mouth & pharynx ——-As paints, lozenges, mouth washes, gargles.
  • Eyes, ears and nose——As drops, ointments, irrigation, nasal spray.
  • Gastrointestinal tract—-As non-absorable drugs given orally e.g. magnesium hydroxide, sucralfate, neomycin.
  • Bronchi & lungs———As inhalation, aerosols (salbutamol).
  • Urethra ——————As jellies (lidocaine), irrigating solutions.
  • Vagina ——————-As pessaries, vaginal tablets, cream, powder etc.
  • Anal canal—————-As ointment, suppositories.
2. Deeper Tissues

Certain deeper areas can be approached by using a syringe and needle, but the drug should be such that systemic action is slow. E.g intrathecal injection (lignocaine).

3. Arterial Supply

Close intra-arterial injection is used for contrast media in angiography. Anticancer drugs can be infused in femoral or bronchial artery to localized the effect for limb malignancies

Systemic Routes of Drug Administration:

The drug administered through systemic routes is intended to be absorbed in to blood and distributed all over the body, including the site of action.

1. Oral Routes

Oral route is the oldest, safest, cheapest and commonest mode of drug administration. The dosage forms for oral route include tablets, capsules, mixtures, powders, syrup, elixirs, emulsion, gels etc.

Advantages
  • It is safer and more convenient.
  • Does not need assistance.
  • The medicament need not be sterile so is cheaper.
Disadvantages
  • Action is slower and thus not suitable for emergencies.
  • May cause nausea and vomiting.
  • Can not be used for un cooperative/unconsciousness/vomiting patient.
  • Certain drugs are not absorbed orally.e.g streptomycin.
  • Some drugs are destroyed by digestive juices (penicillin G, insulin) or in liver(nitro glycerine, lignocaine).
2. Sublingual or Buccal Routes

The tablet containing the drug is placed under the tongue or crushed in the mouth and spread over the buccal mucosa. Only lipid soluble and non-irritating drugs can be administered. Action is very rapid. e.g Nitroglycerine for angina pain, clonidine for hypertension.

Advantages:
  • The chief advantage is that liver is by passed and drugs with high first pass metabolism can be absorbed directly into systemic circulation.
Disadvantages:
  • It is somewhat inconvenient, one can spit the drug before the desired effect has been obtained.
3. Rectal Routes

Certain irritant and unpleasant drugs can be put into rectum as suppositories or retention enema for systemic effect. E.g. Bissacodyl (purgative), Indomethacin(analgesic), Diazepam(sedative & hypnotics).

Advantages:
  •  The chief advantage is that when the patient is having recurrent vomiting.
Disadvantage:
  • It is rather inconvenient. Absorption is slower and irregular. Rectal inflammation can result from irritant drugs e.g. Aminophylline and Ergotamine.
 4. Cutaneous Routes

Highly lipid soluble drugs can be applied over the skin for slow and prolonged absorption. The liver is also bypass.

The drug can be incorporated in an ointment and applied over specified area of skin.

TTS (Trans dermal Therapeutic System) are recently developed devices in the form of adhesive patches of varies shape and sizes. Which deliver the contained drug at a constant rate into systemic circulation.

The drug (in solution or bound to polymer) is held in a reservoir between an occlusive backing film and a rate controlling micro-pore membrane, the under surface of which is smeared with adhesive. The drug is delivered at the skin surface by diffusion for per cutaneous absorption into circulation. Site of applications are chest, abdomen, upper arm and lower back. E.g.  Nitroglycerine, Clonidine and Nicotine.

5. Inhalation Routes

Inhalants are drugs which because of their high vapor pressure can be carried into the nasal passages    with the inhaled air. Volatile liquids and gases are given by inhalation for systemic action. E.g. general anaesthetics (ether,nitrous oxide)

6. Nasal Routes

The mucous membrane of the nose can readily absorb many drugs. Digestive juices and liver are by passed. E.g. buserelin, goserelin (gonadotropin releasing hormone agonist) used in precocious puberty, prostatic carcinoma, premenopausal breast cancer and also used as contraceptive for both males and females.

7. Parental Routes

The term parental route refers to any route other than gastrointestinal (enteral), but is commonly used to indicate injection, which takes the drug directly into the tissue fluid or blood without having to cross the intestinal mucosa.

Advantages:
  • Absorption is rapid and quick.
  • Accurate dose of the drug can be given.
  • The drug enters into circulation in an active form.
  • It is useful in emergency and unconscious patient.
  • No chances for drug-food and drug-digestive juice interactions.
Disadvantages:
  • Pain may be produced by injection.
  • Abscess and inflammation at the site of injection.
  • Sterile procedures are required so it is expensive.
  • Self medication is not possible (except insulin inj.)

The important parenteral routes of drug administration are as follows-

  • Subcutaneous (s.c): The is deposited in the loose subcutaneous tissue which is richly supplied by nerves. This route is used to inject a small amount of the drug (2 ml or lesser). Irritant drugs can not be injected. Absorption is slower. Oily solutions or aqueous suspensions can be injected for prolonged action. e.g. insulin inj.
  • Intra-muscular (i.m): The drug is injected in one of the large skeletal muscles such as deltoid, triceps and gluteus maximus. Mild irritants and depot preparations can be injected. Absorption is faster. E.g. penicillin G, ranitidine, diazepam, diclofenac sodium etc.
  • Intra-venous (i.v): The drug is injected slowly in one of the superficial vein. The drug directly reaches in to the blood stream so bioavailability near about hundred percent. Quick and immediate effect is produced so useful in emergency and for unconscious patient. Irritant drug can be given. Large volume saline can be given by this route. Oily suspension can not be given.
  • Intra-dermal: The drug is injected into the outer layers of the skin. The amount of drug given is small and absorption is slow. This route is mainly used for diagnostic tests like Schick test for diphtheria, Dick test for scarlet fever and the tuberculin test. Also used for allergic sensitization testing in patients.
  • Intra-medullary: This route is also called bone marrow injection, and the material is injected into the bone marrow of the tibia and sternum. This route is used when the veins are not available in children. E.g.whole blood or normal saline.
  • Intra-peritoneal: A needle is inserted into the peritoneal space, and a special fluid is cyclically circulated through the space for removal of toxins or drugs in case of acute poisoning. This route is mostly useful for peritoneal dialysis and in renal failure.
  • Epidural: By this method the drug is deposited through a vertebral interspaces between the dura of the spinal cord and the periosteal lining of the spinal canal. It is used to produce epidural nerve block by depositing the local anaesthetic solution.
  • Intra-arterial: The needle is placed in an artery, through which an arterial blood sample may be withdrawn for blood gas studies or radio-opaque substances may be injected for arteriography. This technique is also used for the treatment of cancer.
  • Intra-thecal (intraspinal): The drug is injected into the subarachnoid space. This route is used to produce intense action of the drugs on the cerebrospinal system while treating infectious type of meningitis or to produce spinal anaesthesia. It is also used for myelography (to visualize the spinal cord).
  • Intra-cardiac: In some emergencies like sudden cardiac arrest, adrenaline directly into the heart may restart the heart beat. The injection is given by a long needle in the left fourth intercostal space close to the sternum.
  • Intra-articular: The drug (glucocorticoid) is injected into the joint space to attain high local concentrations within the inflamed joint, without much danger of systemic steroid toxicity.
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