1. Local or Topical application:

For the local action on the skin and mucous membrane of the mouth, nose and eye, suitable medicinal preparations are used externally. The preparations like, liniments, lotions, drops, ointments, suppositories etc are used externally for local action.

2. Systemic Administration:

For systemic or internal action chiefly oral and parenteral routes are used. The choice of the route, however, depends on
(i) Physical & chemical characters of the drugs
(ii) Effect desired
(iii) Urgency and seriousness of the condition.

(a) Oral Administration (Enteral):

It is the easiest, safest, commonest and the most convenient route for internal administration of drugs. Medicines can not be, however, given to unconscious or non-cooperative patients or in patients with persistent vomiting and diarrhea. Drugs like adrenaline, insulin etc. cannot also be given by mouth due to their destruction by the digestive juice. Irritant drugs are not given by this route otherwise vomiting may be induced. Moreover, there is uncertainty and delay of absorption from this route and it should not be relied upon in serious patients. Mixtures, tablets, pills, capsules, linctus, emulsions etc, are given by this route.

Advantages: Easy, safe, and convenient route,


Disadvantages:

(i) Delayed action
(ii) Irritant drugs can not be given
(iii) Some drugs are destroyed by gastro- intestinal enzymes ex. insulin, penicillin etc.
(iv) Absorption may be uncertain
(v) Cannot be administered to an unconscious patient
(vi) Cannot be given to patients having gastrointestinal upset such as diarrhea and vomiting etc.

(b) Rectal (Enema):

When oral route is not suitable, rectal route may be used. Sometimes, it is preferred because of better and quicker absorption. Glucose, saline, barbiturate and paraldehyde preparations may be given by rectum with advantage.

(c) Parenteral (Injection):

Routes of internal drug administration other than oral are called parenteral but it generally refers to administration by injection.

Advantages:

A definite dose may be given for immediate action. It is also suitable for unconscious, non-cooperative and as well as for those patients with vomiting and diarrhea.

Disadvantages:

There is pain and chance of local sepsis and sometimes a risk of serious reactions and even death especially from intravenous administration and moreover it is costly. Technical skill & aseptic measures are necessary.

(3) Intravenous Injection (I.V.):

The drug is usually introduced directly into the blood vessel for immediate action. Blood, plasma, irritant drugs and large volume of saline and glucose etc. may be given by this route. Greater degree of skill and aseptic precautions are necessary to avoid fatal accidents from embolism, drug reaction & septicemia.

Advantages:

(i) Immediate effect
(ii) Large volume may be given
(iii) Irritant drugs may be administered
(iv) Desired dose may be given
(v) General anesthetic may be given by this route.

Disadvantages:

(i) High skill & experience are necessary.
(ii) More chance of venous thrombosis, air embolism and death.
(iii) High aseptic measures are necessary.

(4) Intramuscular route (I.M.):

Drugs are introduced into the mass of the voluntary muscle for more rapid action than the subcutaneous route. Insoluble, irritant and oily preparations are given only by this route. There may be local damage of the muscle fibers, nerve injury and accidental introduction of insoluble matters and air bubbles into the vein of the muscle causing embolism and even death.

(5) Sub-cutaneous route (S.C.):

By this route the, drug is pushed under the skin from where it is slowly absorbed for prolong action. Irritant drugs should not be used by this route otherwise necrosis may occur.

(6) Intradermal or Intracutaneous route:

By this route, the drug is injected into the layers of the skin, By this route allergic test, vaccination for small-pox and BCC vaccination, diagnostic tests like tuberculin test etc. are given.

(7) Intrathecal or Intraspinal Injection:

By this method a drug is injected into the cerebro-spinal fluid in the sub-arachnoids space by lumber puncture. Spinal anesthesia is done by this route. Antibiotics like penicillin or streptomycin does not reach the cerebrospinal fluid easily from I. M. injection so they are given by this method when needed urgently.

(8) Inhalation:

By this method, drugs are introduced through the inhalation into the respiratory tract. The absorption is rapid and the action is quick by this method. The volatile drugs like general anesthetics, oxygen, carbon dioxide etc. are given by inhalation. The non-volatile drugs like adrenaline, penicillin or isoprenaline are given in the form of fine spray called aerosol therapy for inhalation.

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