Routes of Drug Administration


Routes of Drug Administration

The purpose of the administration of the drug is to make it available at its site of action. A drug must be either inserted into the body or applied to the body. There are several routes of drug administration that are broadly divided into two categories

  1. Local routes
  2. Systemic routes

Local routes 

When the site of the action is directly accessible, the drug could be applied directly. For example, topical application of an antibiotic cream at the site of the injury for preventing the infection of the wound. 

Advantages of local routes are

  • A high concentration of the drug is attained at the desired site without exposing the rest of the body to the drug.
  • Minimal or absence of systemic side effects or toxicities.

The local routes are: 

a.) Topical route: The drug is directly applied at the desired site of action. It includes application to localized lesions on the skin, mucous membrane, bronchi, eyes, ear canal, anal canal, or vagina. 

b.) Deeper Tissue: Drugs could be applied to deeper tissue via a syringe or needle for producing local effects. For example, intrathecal injection of lignocaine for blocking the sensation in certain neurons in the spinal cord by producing a local anesthetic effect.

c.) Arterial Supply: Intra-arterial injections of contrast media during angiography.

Systemic routes 

When the site of the drug action is not accessible, the drug is made available at the site via a transportation mechanism i.e., systemic blood circulation. In this case, the drug is administered into the systemic routes so that it will reach the plasma and ultimately, will reach the site of action. The systemic routes are:

a.) Oral route: The drug is taken orally. It is the oldest and most common route of drug administration.

Advantages

  • It is safer and more convenient than the parenteral routes.
  • No need for assistance is required.
  • Non-invasive in nature.
  • Medicament need not be sterile.
  • Both solid and liquid dosage forms could be administered.

Limitations

  • The delayed effect of drugs, therefore, is not suitable for emergencies.
  • Unpalatable drugs are difficult to be administered.
  • Nausea and vomiting are frequently observed.
  • Not suitable for uncooperative/ unconscious patients.
  • Certain drugs get destroyed by digestive juices, for example, Penicillin G, Insulin, etc.
  • The first pass effect leads to inconsistent drug absorption and is not suitable for certain drugs (streptomycin).

b.) Sublingual or buccal route: The tablet is placed under the tongue or in the buccal cavity for absorption through the mucosa.

Advantages

  • Absorption is rapid
  • The first pass effect is avoided

Limitations

  • Suitable for lipid-soluble and non-irritating drugs only.

c.) Rectal route: Certain irritant and unpalatable drugs can be administered via rectum for systemic effect. For example, retention enema or suppositories. 

Advantages

  • Suitable for unconscious patients or patients having recurrent vomiting.
  • About 50% chances of avoiding the first-pass effect.

Limitations

  • Inconvenient and embarrassing.
  • Irregular and unpredictable absorption.
  • Irritating drugs can cause rectal inflammation.

d.) Cutaneous route: Highly lipophilic drugs can be applied to the skin for slow and prolonged systemic absorption.

Advantages

  • Bypass the first-pass effect.
  • The drug is delivered at a constant and predictable rate.
  • Better patient compliances.

Limitations

  • Local irritation and erythema.

e.) Inhalation route: Volatile liquids and gases are administered by inhalation for systemic action. For example, general anesthetics. 

Advantages

  • Rapid absorption due to the large surface area of alveoli.

Limitations

  • Irritating vapors can cause inflammation of the respiratory tract.

f.) Nasal route: the nasal mucosa can absorb many drugs.

Advantages

  • The first-pass effect is avoided.

g.) Parenteral route: This route refers to the administration of drugs by injection directly into the tissue fluid or blood without having to cross the intestinal mucosa.

Advantages

  • Limitations of oral routes are avoided.
  • Rapid action of the drug
  • Gastric irritation and vomiting not provoked
  • Suitable for unconscious or uncooperative patients.
  • The first-pass effect is avoided

Limitations

  • Only sterilized preparation could be administered.
  • The technique is invasive and painful.
  • The assistance of another person is needed (though in certain cases self-injection is possible, e.g. insulin by diabetics) 
  • Chances of local tissue injury are high.

The important parenteral routes are:

(I) Subcutaneous route: The drug is deposited in the loose subcutaneous tissue.

Advantages

  • Self-injection is possible

Limitations

  • Only a small volume can be administered
  • Irritant drugs can’t be administered
  • Should be avoided in shock patients, delayed absorption

(ii) Intramuscular route: The drug is injected in one of the large skeletal muscles-deltoid, triceps, gluteus maximus, rectus femoris, etc. 

Advantages

  • Mild irritants can be injected.
  • Absorption of drugs in an aqueous solution is faster as compared to the subcutaneous route.

Limitations

  • Should be avoided in patients treated with an anticoagulant drug, can cause a local hematoma.

(iii) Intravenous route: The drug is injected as a bolus or infused slowly over hours in superficial veins.

Advantages

  • Rapid onset of action
  • Highly irritant drugs can also be given
  • The response is accurately measurable.

Limitations

  • Thrombophlebitis of injected vein
  • Necrosis of adjacent tissue in case of extravasation of the drug
  • Only aqueous solutions can be administered
  • Major risk as the vital organs are exposed to the higher concentrations of the drug.

(iv) Intradermal route: The drug is injected into the skin raising a bleb. For example, the BCG vaccine. 


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