Routes of Drug Admin
Dosage forms
Pharmacy Techniques
Drug Interactions
Classification of Drugs
PharmaExcipients

The route of administration (ROA) that is chosen may have a profound effect upon the speed and efficiency with which the drug acts .Drugs are introduced into the body by several routes. They may be taken by mouth (orally); given by injection into a vein (intravenously), into a muscle (intramuscularly), into the space around the spinal cord (intrathecally), or beneath the skin (subcutaneously); placed under the tongue (sublingually);inserted in the rectum (rectally) or vagina (vaginally); instilled in the eye (by the ocular route);sprayed into the nose and absorbed through the nasal membranes (nasally); breathed into the lungs, usually through the mouth (by inhalation); applied to the skin (cutaneously) for a local (topical) or bodywide (systemic) effect; or delivered through the skin by a patch (transdermally) for a systemic effect. Each route has specific purposes, advantages, and disadvantages.An alternate method of classifying these routes of administration is ENTERAL and PARENTERAL. Enteral means to do with the GI tract and includes oral, buccal, and rectal. Parenteral means not through the alimentary canal and commonly refers to injections such as IV, IM, and SC; but could also include topical and inhalation. The possible routes of drug entry into the body may be divided into four classes:

Routes of Drug Adminstration
Parenteral Enteral
Intravenous
Oral
Intramuscular
Sublingual
Subcutaneous
Buccal
Intra-arterial
Rectal
Pulmonary Topical
Metered Dose Inhaler
Percutaneous
Dry Powder Inhaler
Ocular
Nebulizer
Nasal
 
Parenteral

There are several different routes by which parenteral products may be administered and indeed there are very few, if any, organs into which parenteral dosage forms may not be injected. However, there are three routes by which parenterals are most frequently administered: (1) intravenous (IV); (2) intramuscular (IM); and (3) subcutaneous (SC). These sites are located beneath the epidermis/dermis within the skin.

Advantages

  • An immediate physiological response may be achieved (usually by the IV route). This is important in acute medical situations, e.g. cardiac arrest, anaphylactic shock, asthma.
  • Parenteral formulations are essential for drugs that offer poor bioavailability or those that are rapidly degraded within the gastrointestinal tract (e.g. insulin and other peptides).
  • They offer a method to administer drugs to patients who are unconscious or uncooperative or for patients with nausea and vomiting (and additionally dysphagia).
  • Local effects may be achieved using parenteral formulations, e.g. local anaesthesia.
  • Parenteral formulations provide a means by which serious imbalances in electrolytes may be corrected (using infusion solutions).

  • In patients who cannot consume food, total parenteral nutrition offers a means by which nutrition may be provided using specially formulated solutions that are infused into the patient.
 

Disadvantages

  • The manufacturing process is more complicated than for other formulations due to the requirement for aseptic technique. The level of training of staff involved in the manufacture of parenteral formulations is high and often specialist equipment is required to ensure that the finished product specification is achieved.
  • Skill of administration is required to ensure that the dosage form is administered by the correct route. If a parenteral suspension, which is designed for administration by the IM or SC route, is incorrectly administered by the IV route, a pulmonary microcapillary blockage may occur leading to a blockage in the flow of blood at that site.
  • Parenteral formulations are associated with pain on administration.
  • If the patient is allergic to the formulation (the therapeutic agents and/or the excipients), parenteral administration will
    result in both rapid and intense allergic reactions.
  • It is difficult to reverse the effects of drugs that have been administered parenterally, even immediately after administration. This is not strictly the case with other routes of administration, e.g. oral, transdermal.
Classification of Parentral Routes

Intravenous route (IV)

  • This involves administration of the parenteral formulation into a vein, usually a large proximal vein. The veins are located beneath the subcutaneous tissue, embedded within the muscle.
  • IV administration achieves a rapid and predictable response.
  • It ensures 100% drug bioavailability.

Intramuscular route (IM)

  • This involves administration into a muscle, usually the gluteal (buttocks), vastus lateralis (lateral thigh) or deltoid (upper arm) muscles. The musculature resides below the subcutaneous tissue (which itself lies beneath the epidermis and the dermis).
  • The volume of injection is small, usually 1–3 ml or up to 10 ml in divided doses.
  • Faulty injection technique may lead to local muscle damage.

Subcutaneous route (SC)

  • This involves administration into the subcutaneous tissue, a layer of fat located below the dermis.
  • Viscous formulations are not generally administered subcutaneously.
  • Typical sites of SC injection include the arms, legs and abdomen.
  • SC administration is the route of choice for the administration of insulin.

Intra-arterial route (IA)

  • The parenteral formulation is injected into an accessible artery.
  • This route requires specialist training to administer therapeutic agents as if the artery is missed, possible damage to adjacent nerves may result.
  • The IA route is used to administer radiopaque media to visualise organs, e.g. heart, kidney.

Intradermal route (ID)

  • This is the injection into the dermal layer of the skin.
  • The ID route is generally used for diagnostic purposes, e.g. for the diagnosis of allergy and for the tuberculin test.
  • Only small volumes may be injected, circa 0.1 ml.

Intradural and extradural routes

  • Intradural and extradural administration is employed to achieve spinal anaesthesia.
  • Intradural administration involves injection of the therapeutic agent within the dural membrane surrounding the spinal cord.
  • Extradural administration involves injection of the therapeutic agent outside the dural membrane and within the spinal caudal canals.




Intrathecal (IT) route

  • This route is used to administer therapeutic agents to the cerebrospinal fluid to ensure that the appropriate concentration of drug is obtained at this site (e.g. for the treatment of infection).

Intracardiac (IC) route

  • The intracardiac route involves injection of the formulation directly into the muscles of the heart.
  • This route is normally used whenever there is a cardiac emergency.
 
Classification of Entral Routes
Oral - swallowing (p.o., per os)   Sublingual - placed under the  tonguel

Advantage

  • Convenient - can be self- administered, pain free, easy to take
  • Absorption - takes place along the whole length of the GI tract
  • Cheap - compared to most other parenteral routes

Disadvantages

  • Destruction of drugs by gastric acid and digestive juices
  • Effect too slow for emergencies
  • Unpleasant taste of some drugs
  • Unable to use in unconscious patient
 

Advantages

  • rapid absorption
  • drug stability
  • avoid first-pass effect

Disadvantages

  • inconvenient
  • Small doses
  • unpleasant taste of some drugs
Rectum - Absorption through the   rectum    

 

  • unconscious patients and children
  • if patient is nauseous or vomiting
  • easy to terminate exposure
  • absorption may be variable
  • good for drugs affecting the bowel such  as laxatives
  • irritating drugs contraindicated
   
 
Classification of Topical Routes
Occular   Percutaneous

For ocular drug delivery Conjunctiva, Cornea, Lacrimal fluid.

Advantages

  • The application of the therapeutic agents directly to the site of action ensures that the therapeutic agent is available at higher concentrations than may be achieved following oral administration.
  • Administration of the therapeutic agent locally ensures that the incidence of side-effects is minimised.
  • Following training, the administration of the dosage form locally to the eye may be easily performed by the patient.

Disadvantages

  • The retention of the drug at the site of action is relatively
    poor, due principally to the low tear volume
  • The application of ointment formulations to the eye may
    result in a temporary blurring of vision.
  • Ocular formulations are sterile and therefore specialist
    facilities are required for the manufacture of these dosage forms. patch   becomes to large

 

 

a- Dermal - rubbing in of oil or ointment  (local action)

b- Transdermal - absorption of drug through skin (systemic action)

             i. stable blood levels

             ii. no first pass metabolism

             iii. drug must be potent or

Nasal
The nasal route of administration provides a rapid systemic delivery of therapeutic agents (whilst avoiding first-pass metabolism). Examples of this approach include the treatment of migraine (ergot alkaloids, sumatriptin), diabetes insipidus (desmopressin), prostate cancer/endometriosis (gonadotrophin analogues) and smoking cessation (nicotine).
Otic(Ear)
Otic dosage forms are applied to the ear canal and are used for the treatment of infection, inflammation and/or pain.otic formulations may be formulated as aqueous or non-aqueous solutions and contain one (or more than one) category of therapeutic agent, e.g. local anaesthetics (benzocaine), steroids (prednisolone sodium phosphate, hydrocortisone), antimicrobial agents (polymixin B sulphate, chloramphenicol), in addition to agents that soften ear wax (e.g. carbamide peroxide).
 
Classification of Pulmonary Routes

1.Gaseous and volatile agents and aerosols

2.Rapid onset of action due to rapid access to circulation

        a.large surface area

        b.thin membranes separates alveoli from circulation

        c.high blood flow

Advantages

  • Fastest method, 7-10 seconds for the drug to reach the brain
  • User can titrate (regulate the amount of drug they are receiving)

Disadvantages

  • Most addictive route of administration because it hits the brain so quickly
  • Difficulties in regulating the exact amount of dosage
  • Patient having difficulties in giving themselves a drug by inhaler

Particles larger than 20 micron and the particles impact in the mouth and throat. Smaller than 0.5 micron and they aren't retained.

  • Respiratory system. Except for IN, risk hypoxia.
  • Intranasal (snorting) Snuff, cocaine may be partly oral via post-nasal dripping. Fairly fast to brain, local damage to septum. Some of the volatile gases also appear to cross nasal membranes
  • Smoke (Solids in air suspension, vapors) absorbed across lung alveoli: Nicotine, opium, THC, freebase and crack cocaine, crystal meth.Particles or vapors dissolve in lung fluids, then diffuse. Longer action than volatile gases. Tissue damage from particles, tars, CO
  • Volatile gases: Some anaesthetics (nitrous oxide, ether) [precise control], petroleum distillates. Diffusion and exhalation (alcohol).
  • Lung-based transfer may get drug to brain in as little as five seconds