ROUTES OF DRUG ADMINISTRATION
The drugs can be administered by a variety of routes, either locally or administered orally and by injection. To produce local effects, drugs are applied topically to the skin or mucous membranes. To produce systemic effects drugs are administered orally, rectally, parenterally or by inhalation route.
The important routes of administration are:
The dosage forms applied locally to the skin are powders, paste, lotions, ointments, creams, plasters and jellies. They are used for their antiseptic, antipruritic, analgesic, local anaesthetic and other related effects.
The drug administered through systemic routes (orally or parenterally), is absorbed into the blood, distributed along through the circulation and produce their desired effects.
This is the most commonly used route for drug administration. It is also the safest, most convenient and economical. But, there are some limitation of this route:
• Drug action is slow, thus not suitable for emergencies.
• Incapability to absorb some drugs, due to their physical characteristics i.e. polarity of the drug.
• Unpalatable and other irritant drugs can not be administered.
• Can not be used for unconscious and uncooperative patient.
• May not be useful in the presence of vomiting and diarrhoea.
• Drugs, which can be destroyed by digestive juices (i.e. insulin, penicillin G) or in liver (i.e. testosterone, nitroglycerine) can not be administered orally.
• The absorption of certain drugs is negligible e.g. streptomycin.
Enteric Coated Tablets
The drugs which are destroyed by the gastric juices in the stomach, are coated with keratin, shellac and cellulose acid phosphate.
The highly lipid soluble and nonirritating drugs (i.e. nitroglycerine, isoprenaline, methyltestosterone) in the form of tablets or pellet is placed under the tongue, where they rapidly dissolve and are absorbed quickly in the general circulation.
(par = beyond, enteral = intestinal) The administration of drugs by injection directly into the tissue fluid or blood without having to cross the intestinal mucosa.
The non-irritant substances can be injected by this route.
The soluble substances, mild irritants and suspensions can be injected by this route in the large skeletal muscles (deltoid, triceps, gluteus maximus, rectus femoris etc.).
The drug is injected as a bolus or infused slowly directly into a vein to produce rapid action.
The drug is injected into the skin raising a bleb.
This route is useful in diagnostic studies, by which arterial blood sample may be withdrawn for blood gas studies.
Intrathecal or Intraspinal
For local and rapid effect of drugs on the meninges or cerebrospinal axis, drugs are injected directly into the spinal subarachnoid space.
By this method, the drug is introduced into the bone marrow of the sternum or tibia.
In sudden cardiac arrest and other cardiac emergencies, the adrenaline is directly injected into the heart by a long needle in the left fourth intercostal space close to the sternum.
This route is a common laboratory procedure, but it is seldom employed clinically in infants for giving fluids like glucose saline, as the peritoneum offers a large surface for absorption.
Certain drugs (i.e. glucocorticoids) can be administered directly into a joint space for the treatment of local condition i.e. rheumatoid arthritis.
The volatile liquids and gases are given by inhalation route.