ROUTES OF DRUG ADMINISTRATION

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ROUTES OF DRUG ADMINISTRATION

• Often there is a great choice in selecting the
  route by which a drug should be given to
  patients. However, the condition of the patient
  and knowledge of advantages and disadvantages of
  various routes are of prime importance in making
  the selection of best suiting route.

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• Following are the different ways by which
• a therapeutic agent could be given to
• patients.
• 1 Enteral
• 2 Parenteral
• 3 Inhalation
• 4 Topical or Local

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• ENTERAL
• ORAL OR PER OS (P.O.)
• Oral route is the most common route of
  administration. It is safe, convenient, cheap
  and does not require the services of a skilled
  personnel. However, it has certain
  disadvantages.
• a) Some drugs are unpalatable and cause
  irritation of the intestinal tract resulting in
  nausea, vomiting and diarrhea, in particular if
  these are given before meal.

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1. Some drugs are destroyed by intestinal enzymes
   e.g. insulin is destroyed by intestinal enzymes.
2. In case of emergency, when quick action of a drug
   is desired this route is not suitable.
3. This route is not suitable in the cases of
   unconscious patients.
4. There is a necessity for cooperation on the part
   of patient.

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• f) Absorption may be slow, unpredictable and
  irregular because of the presence of variable
  amounts of food at various stages of digestion
  and acidity and alkalinity of the digestive
  juices might have a great impact on absorption of
  drugs.

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• g) A very important factor is that blood from
  intestinal tract passes via portal vein to the
  liver where the drug may be metabolized to a
  great extent before being distributed to the site
  of action. Thus oral route is not recommended
  for drug undergoing extensive FIRST PASS EFFECT.

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FIRST PASS EFFECT

• First Pass Effect may be defined as the loss of
  drug as it passes through the gastrointestinal
  membranes and the liver, for the first time,
  during the absorption process after oral
  administration. This is also known Pre-Systemic
  elimination.
• h) Drugs interaction may occur if two drugs are
  given cocurrently.

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• ii SUBLINGUAL
• The tablet is placed under the tongue and
  absorption form oral mucosa is rapid and uniform.
  This route has special importance for certain
  drugs. For example nitroglycerine is effective
  when given sublingually but ineffective when
  administered orally. The reason is that the drug
  has very high lipid solubility.

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• Also the drug being very potent needs few
  molecules to be absorbed in order to produce the
  therapeutic effect. The major advantage of this
  route is that venous drainage from mouth (bucal
  cavity) is poured into the superior vena cava and
  the drug is saved from first-pass effect. It
  nitroglycerine is given by oral route, the
  hepatic first-pass effect is sufficient to
  preclude the appearance of any intact
  nitroglycerine in the systemic circulation.

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• RECTAL ADMINISTRATION
• The drug may be given rectally for systemic
  effect when the patient is either unconscious or
  vomiting. However, absorption from rectum is
  irregular and incomplete and may cause irritation
  of rectal mucosa Also 50 of the drug absorbed
  from rectum passes through liver before entering
  the systemic circulation thus first-pass effect
  cannot be fully avoided.

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• The drugs administered reactally are in the form
  of suppositories e.g. Ergotamine for the
  treatment of migraine. Another form of
  preparation for rectal administration is the
  ENEMA i.e. a solution or suspension of the drug
  in water or some other vehicle. Suppositories
  may also be given for local treatment of rectal
  conditions e.g. benzocain is used to relieve pain
  and itching caused by haemorrhoids

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• Advantages of rectal Administration-
• Drugs could be given by this route in vomiting,
  motion sickness, migraine or when the patients is
  unable to swallow the medication. This route is
  also suitable for drugs that are irritant to the
  stomach e.g. aminophylline, indomethacin. This
  route is of particular value in case of children.

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• Disadvantages of Rectal Administration-
• The patient may be embarrassed.
• Inflammation of rectum may occur due to repeated
  administration.
• The absorption is irregular specially when rectum
  is not empty.

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• 2- PARENTERAL
• (Par-beyond enteral-intestine)
• The term parenteral administration implies the
  routes through which the drug directly reaches
  the body fluids, by passing the preliminary
  process of transport through the intestinal wall
  or pulmonary alveoli which is an essential
  process when drugs are taken orally, inhaled or
  administered reactally. Following are the
  Parenteral routes

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• Subcutaneous (S/C)
• Intramuscular (I/M)
• Intravenous (I/V)
• Intraperitoneal (I/P)
• Intradermal
• f) Intra Medullary
• g) Intrathecal
• h) Intraarticular
• i) Intra-cardiac
• j) Intra arterial

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• The Parenteral administration has certain
  advantages over oral route.
• Drug is neither invaded nor destroyed by
  digestive enzymes.
• A higher concentration of drug in blood may be
  achieved because the hepatic metabolism of drug
  due to First-Pass effect is avoided.

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• Absorption is complete and predictable.
• In emergency this method is particularly useful.
  If the patient is unconscious, uncooperative or
  vomiting, the Parenteral therapy becomes
  necessary.
• However, there are certain disadvantages of the
  parenteral therapy which are as under
• i) It is expensive because all the parenteral
  preparations should be sterilized.

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• Asepsis must be maintained to avoid infection.
• An intravascular injection may accidentally occur
  when it is not actually intended.
• iv) Pain may accompany or follow the injection.
• v) It requires the services of a professionally
  skilled personnel because it is difficult for the
  patient to perform the injection himself.

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• Subcutaneous-
• The drug is dissolved in a small volume of
  vehicle and injected beneath the skin from where
  the absorption is slow and uniform. Substances
  causing irritation to the tissues should not be
  injected otherwise they will cause pain and
  necrosis (deadening of tissues) at the site of
  injection.

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A diabetic patient making subcutaneous injection
subcutaneous injection in the mouse
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• This method is particularly useful when
  continuous presence of the drug in the tissues is
  needed over a long period. The usefulness of
  this method is enhanced by the use of depot
  preparations from which the drug is released more
  slowly than it is from simple solution e.g.
  long-acting insulins. Another form of the depot
  preparation is subcutaneous implant.

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• In this case, a sterile pellet is implanted into
  subcutaneous tissue instead of injecting drug
  solution e.g. hormones are administered in this
  way. If a vasoconstrictor agent is incorporated
  in a drug solution, it retards the absorption
  e.g. adrenaline is combined with local
  anesthetics to prolong the local anesthesia.
• Intramuscular-
• Injection is made deep into the muscle tissue.

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• In humans, the best site is deltoid muscle in
  the shoulder or the gluteus muscle in the
  buttocks. This method is suitable for the
  irritating substances that cannot be given by
  subcutaneous route. The speed of absorption from
  site of injection is dependent on the vehicle
  used, absorption is quick from aqueous solutions
  and slow from oily preparations. Absorption is
  complete, predictable and faster than
  subcutaneous route.

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Intramuscular injection in deltoid and gluteal
muscles
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• Intravenous-
• Drug solution in injected directly into the
  lumen of a vein so that it is diluted in the
  venous blood. The drug is carried to the Heart
  and circulated to the tissues. Drugs in oily
  vehicle or those that cause haemolysis should not
  be given by this route. Since the drug is
  introduced directly into blood, the desired
  concentration of the drug is achieved immediately
  which is not possible by any other procedure.

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Intravenous Administration
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• This route is of prime importance in emergency.
  Also certain irritant drugs could be given by
  this route. Also this is the only route for
  giving large volume of drugs e.g. blood
  transfusion.
• However, there are certain disadvantages of this
  procedure.
• 1. Once the drug is injected nothing can be done
  to prevent its action.
• I/v injection requires technical skill to
  minimize the risk of leakage of irritant solution
  into the surrounding tissues.
• Air embolism may cause serious problems.

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• Intraperitoneal-
• The peritoneum offers a large absorbing surface
  area from which drugs enter circulation rapidly
  but primarily by way of portal vein. Hence
  First-Pass effect not avoided.
• This is probably the most widely used route of
  drug administration in laboratory animals. In
  human, it is very rarely employed due to the
  dangers of infection and injury to viscera and
  blood vessels.

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Inraperitoneal Injection
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• Intradermal-
• Drug are injected into papillary layer of skin.
  For example tuberculin injection for montoux test
  and BCG vaccination for active immunization
  against tuberculosis.
• BCG Bacille Calmette-Guerin

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• Administering Intradermal Injections-
• 1. Check physician's order
• 2. Prepare equipment
• Draw up 0.1ml of the medication in a 1cc syringe
  - ones called a TB/tuberculin syringe.
• Collect medication, procedure gloves, alcohol
  wipe, and cotton ball
• 3. Cleanse the site with an alcohol pad going
• in a circular motion
• 4. Hold the skin taut

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• 5. Hold the needle at a 15 degree angle to the
  skin with the bevel facing up.
• 6. Insert the needle through the skin, just
  below the epidermis into the dermis.
• 7. Inject the fluid, making a bubble just below
  the skin
• 8. Remove the needle
• 9. Dispose of used syringe and needle in a Sharps
  container

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Intradermal Injection
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• f) Intra Medullary-
• The needle is introduced into marrow cavity and
  effects are similar to those following
  intravenous injection. This route is used when
  veins are not available specially in children.
  In adults the injection is made into marrow
  cavity of sternum and under 3 years of age into
  that of tibia or femur.
• Intrathecal-
• Blood brain barrier often prevents the entry of
  certain drugs into the central nervous system.

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• Also the blood CSF barrier prevents the approach
  of drugs to the meninges. Thus when local and
  rapid effects of drugs on meninges are desired
  the drugs are injected into Subarachnoid (between
  arachnoid mater and pia mater)space and effects
  of the drugs are then localized to the spinal
  nerves and meninges e.g. intrathecal injection of
  streptomycin in tuberculosis and meningitis used
  to be used by this route but with the invention
  of third generation cephalosporins it is not used
  any more to treat these conditions. The injection
  of local anaesthetics for the induction of spinal
  anaesthesia is given by this route.

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• (the three membranes covering the brain and
  spinal cord from outside to inward are dura
  mater, arachnoid mater and pia mater)
• Intra articular-
• It is also known as intra synovial. Sometimes
  drugs are injected into the joint cavity to
  localize their action at the site of
  administration e.g. Hydrocortisone acetate in the
  treatment of rheumatoid arthritis. Local
  anesthetic is added to minimize pain of
  injection. Strict aspesis must be maintained to
  avoid joint-infection.

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• Intra Cardiac-
• In cardiac arrest intracardiac injection of
  adrenaline is made for resuscitation.
• Intra-arterial-
• Sometimes a drug is injected directly into an
  artery to localize its effects in a particular
  tissue or organ. However, the therapeutic value
  of such practice is doubtful.

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• Infact in human the use of this technique is
  restricted to the injection of radio-opaque media
  for diagnostic purposes. A competent person is
  required to inject the drug intra arterially.
  However, there is no fear of first-pass effect
  when the drug is given by this route.

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• 3- INHALATION
• Inhalation or Pulmonary Absorption Gaseous and
  volatile drugs may be inhaled. They are then
  absorbed by pulmonary endothelium and mucous
  membrane of the respiratory tract and reach
  circulation rapidly. Volatile or gaseous
  anaesthetics such as halothane, enflurane and
  nitrous oxide are administered by this route.

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• Bronchodilators are generally given from
  inhalers in aerosol form. Now inhalers have been
  developed which allow the supply of accurately
  metered doses of drugs. This development has
  greatly extended the scope of this technique.

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• 4 LOCAL OR TOPIOCAL APPLICATION
• a) Skin
• Drugs applied locally on the skin are poorly
  absorbed through the epidermis. However, dermis
  is permeable to many solutes. Thus systemic
  absorption of drugs occurs more readily through
  abraded, burned or denuded skin. Inflammation
  and other conditions that enhance cutaneous blood
  flow also promote absorption.

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• Drugs are applied in the form of ointments,
  pastes, poultice and cream to the skin for their
  local action. However, absorption through skin
  can be increased by suspending the drug in an
  oily vehicle and rubbing the preparation into the
  skin. This method of administration is called
  inunction.
• Mucous Membranes-
• Drugs are applied onto the various mucous
  membranes for their local action.

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• Mouth and Pharynx-
• Bitters are used for their reflex action to
  improve digestion. Boroglycerine and gentian
  violet paint (as astringent) are used for their
  effects on buccal mucosa.
• Stomach Intestine-
• Antacids (to neutralize secreted HCl) and
  emetics ( to induce emesis) are used for their
  local effect
• Rectum-
• Drugs are applied in the form of suppository
• or enemas e.g. glycerin suppository for their
• local action. Drugs are employed for relief of
• itching and pain in haemorrhoid.

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• iv) Respiratory Tract-
• In infections of respiratory tract, tincture
  benzoin co steam inhalations give relief from
  nasal congestion, phenyl ephrine nasal drops are
  also used for nasal congestion.
• v) Vagina-
• The drugs are used in the form of pessary or
  tablet to treat the vaginal infections. Although
  this method can be applied for the drugs that are
  absorbed through vaginal mucous membrane into the
  circulation, it is restricted to the local
  treatment of vaginal conditions

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• vi) Conjunctivae-
• Mydriatics ( to dilate pupil), miotics (to
  constrict the pupil), local anaesthetics
  antiseptics and antibiotics are applied to the
  conjunctivae for their local action.
• Conjunctiva The delicate membrane lining the
  eyelids and covering the eye ball.