Lecture 7: Routes of Administration PDF

LECTURE 7 Rout of Administration  Introduction A drug defined as an agent intended for use in diagnosis, treatment, cure, or prevention of disease in humans or other animals. After administration of a drug a successful therapeutic response will be achieved if the drug reac...

LECTURE 7 Rout of Administration  Introduction A drug defined as an agent intended for use in diagnosis, treatment, cure, or prevention of disease in humans or other animals. After administration of a drug a successful therapeutic response will be achieved if the drug reaches the suitable site of action or "receptor" site in sufficient concentration to exert its pharmacological action. This is achieved by the drug being absorbed into the body tissues from the site of administration. The choice of administration site depends on different factors such as whether a local or systemic action is required or how quickly a response to the drug is needed.  (1) The Oral Route The oral route is used to obtain either systemic or local effects The drug formulated in either solid or liquid form is absorbed from gastro intestinal tract (G.I.T.) It is the commonly used route for drug administration Advantages: – It is the simplest route of administration – Self administration of drugs can be carried out – It is the safest route of administration Disadvantages: – The onset of action is relatively slow – Absorption from G.I.T. may be irregular – Certain drugs are destroyed by enzymes and other secretions found in G.I.T. – Drug solubility can be altered by presence of other substances in G.I.T. e.g. Calcium – Slow gastric emptying drug inactivation by prolonged contact with gastric juices specially in elderly peoples – It is unsuitable route in unconscious or vomiting patients  (2) The Buccal Route: A drug administered by this route is formulated as tablet The high vascularity of the tongue and bucchal cavity and the presence of saliva facilitates the dissolution of drug making this route highly effective The tablets formulated for this route give quick onset of action Advantages: – Relatively quick onset of action – Drugs absorbed directly into the systemic circulation avoiding the first pass effect – Drugs can be administered to unconscious patients – Antiemetic drug can be given by this route  (3) The sublingual route: For sublingual absorption, the area under the tongue is used. This gives a very fast onset of action but the duration is usually short.  (4) The Rectal Route: For administration by this route, drugs are formulated as liquids (enemas) solid dosage forms (suppositories) and semisolids (creams – ointments) This route is used for both systemic and local effects The rectum is supplied by three veins namely the middle and inferior which drain directly to the general circulation and the upper rectal vein which drains into the portal vein and then flows to the liver. This means that some of the drugs absorbed from the rectum can be subjected to the first pass effected therefore bioavailability may be less than 100% Advantages: – Can be used when the oral route is unsuitable e.g. vomiting, unconscious patient, elderly or mentally disturbed patients – Useful when the drug causes G.I.T. irritation – Can be used for local action Disadvantage – Absorption can be irregular variable effect – Less convenient than oral route – Low patient acceptability  (5) The Vaginal Route For administration by this route, drugs are formulated as pessaries and oblong tablets (solid) or creams and ointments (semisolids) vaginal douches (liquid) These are inserted into the vagina This route can be used for both local and systemic effect Advantages: – Drugs from the vagina are not subject to the first pass effect – The higher fluid content in the vagina drugs dissolution is more efficient than by the rectal route  (6) The Inhalation Route In this route drugs are inhaled through the nose or mouth to produce either local or systemic effect This route is used mainly to treat respiratory conditions therefore drugs here are delivered to the site of action lungs Because of the large surface area rapid drug absorption Advantages – The drug dose required to produce a systemic effect is much smaller than for the oral route – Reduction in side effects  (7) The Topical Route This route means that the skin is used as the site of administration This route is mainly used for local effects The formulations used include ointments, Creams and pastes (semisolids) lotions (liquids) Recently specialized dosage forms are developed when applied to the skin give systemic action by passing through skin layers to the blood these called transdermal dosage forms (patches)  (8) The Parenteral Route This is the term used to describe drugs given by injection Injections administered by many routes, which are described as follows: Interavenous Route: i.v. – Drugs injected directly into the systemic circulation – This produces a very fast onset of action Interamuscular Route: i.m. – Drugs injected into the muscle layers – Used to produce a fairly fast onset of action specially when formulated in liquid forms – A slower or prolonged action well occur when the drug is presented as suspension or in oily form Subcutaneous Route: S.C. – Drugs are injected into the subcutaneous layer of the skin – Easiest and least painful type of injection – Slower onset of action but prolonged e.g. insulin  (8) The Parenteral Route: cont… Intera-dermal injections: I.D. – Injected into the skin between the dermis and epidermis – Small volumes are injected (0.1 – 0.2 ml) – Mainly used for diagnosis of allergy and immunity Intra-arterial injection: – Administered directly into an artery – Mainly used for diagnosis e.g. X- ray contrast Intra spinal Route: – Used to administer spinal anesthetics – Injection are made into the subarachnoid space (intrathecal) or peridural space (peridural) or into the cisterna magna (interacisternal) Intra articular route – Made into the synovial fluid of joint – Used for the localized administration of corticosteroids as anti- inflammatory agents