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This article throws light upon the three main routes of drug administration. The routes are: 1. Topical or External Application 2. Oral or Enteral Route 3. Parenteral Route (Injection).
Route # 1. Topical or External Application:
The drugs administration by this route generally affects to the part to which they are applied. However, some drugs applied topically are absorbed from the site of application and reach in systemic circulation. Drugs are externally applied on skin, mucous or serous membranes. Lotion, liniment, cream or ointment are applied externally to affect the part they come in contact with or surrounding and underlying region.
Local application of drugs on the skin may be:
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(i) Inunction-simple application of drugs by rubbing.
(ii) Epidermic-application of the drug on the skin.
(iii) Iontophoresis-electrolyte transmission of the drug through skin. In this process the drug is soaked in a wet cotton pad and kept at the site where it is to be absorbed. An electrode having similar polarity to drug is kept over it. The drug ions are repelled and enters through the skin. This process of drug administration is very useful in arthritis.
Examples of local or topical application are given below:
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(i) Instillation of drugs in nose.
(ii) Inhalation of drugs in nasopharynx.
(iii) Benzoin vapour inhalation.
(iv) Systemic use of drugs through lungs e.g., chloroform, ether etc.
(v) Application of drugs in eye, ear, throat, rectum, vagina and intrauterine administration of drugs in case of metritis and pyometra.
(vi) Administration of liquid medicament per rectum (enema).
Route # 2. Oral or Enteral Route:
This is the most convenient route of drug administration when patients cooperate with the physicians. In veterinary profession, we have a number of species of animals and birds. Some of the animals cooperate with us but many of them do not and are frenzied.
Sometimes, it becomes very difficult to administer the drug through oral route especially in wild and zoo animals. Even if the animal cooperates, the physician has to take the help of owner or the attendant of the animal.
(a) Advantages:
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(i) Safe and economical.
(ii) Minimum adverse reactions.
(b) Disadvantages:
(i) Some drugs are destroyed in the stomach or rumen e.g., chloramphenicol.
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(ii) Slow absorption and blood level can not be predicted.
(iii) Irritant drugs may cause vomiting especially in dogs.
(iv) In non cooperative it creates trouble.
Route # 3. Parenteral Route (Injection):
(i) Intravenous:
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Intravenous injections are recommended in following conditions:
(i) In emergency, when a rapid response is needed e.g., calcium borogluconate in milk fever.
(ii) When a precise and control drug effect is needed.
(iii) To maintain blood reaction e.g., sodium lactate in acidocis.
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(iv) To restore blood volume e.g., transfusion of blood.
(a) Precaution:
(i) Insoluble suspension, oily injections, acidic solutions and air bubbles should be avoided.
(b) Advantages:
(i) Speed of action.
(ii) Effective control
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(iii) Large quantities can be given.
(iv) Plasma plateau can be maintained by means of regulated continuous infusion.
(v) It is a safest route for drugs having a narrow margin of safety between therapeutic and toxic blood levels. For example, (effective blood level range 1 to 4 mg/ml) if effective range is not there and maintained, there is risk of potentially fatal arrhythmia. If range exceeds convulsive seizures may be produced.
(c) Sites of i.v. Injection:
(i) Cow, horse, sheep, goat-jugular vein.
(ii) Pig-ear vein.
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(iii) Dog, cat-cephalic and recurrent tarsal veins.
(d) Disadvantages:
(i) A bolus of concentrated solute suddenly reaches the myocardium and the chemoreceptors in the aortic arch and carotid sinus.
(ii) Anaphylactoid reactions.
(iii) Embolism.
(ii) Intramuscular Route:
(i) It is advantageous with drugs that are rapidly excreted.
(ii) It is difficult in frenzied and furious animals.
(iii) Drug absorption is delayed.
(iv) Risk of nerve damage.
(iii) Subcutaneous Route:
Drugs through this route are injected under the skin.
Salient features are mentioned below:
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(i) Absorption is slow and action prolonged.
(ii) Effect is slow and sustained.
(iii) Rate of absorption may be manipulated.
(iv) Intradermal Route:
Drugs are given within the skin layers (dermis). This route is used for testing the hypersensitivity of drugs.
(v) Intra Cardiac Route:
Drugs are directly injected into the heart muscles e.g., injection of adrenaline in sudden stoppage of a healthy heart and performing euthanesia on small animals.
(vi) Intramedullary:
Drugs are injected in medullary cavity of the bone when i.v. injection is not possible.
(vii) Serous Cavity Injection:
Drugs are injected in serous cavities, peritoneal, pleural, pericardial and articular cavities. While injecting intraperitoneally it should be taken care that the needle should not penetrate the visceral organs. Antibiotics and corticosteroids are injected intraarticularly in inflammed joints cavities and rheumatoid arthritis.
(viii) Epidural Injection:
Local anaesthetic is injected between first and second coccygeal vertebrae during parturition of cattle when it is required to abolish straining.
(ix) Intra mammary Infusion:
The medicinal contents are infused in the mammary gland canal in cases of mastitis.
