Route of Drug Administration

By Abubakar salisu fago.

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 disadvantage

Most of the drugs can be given through number of routes.

Choice of proper route is depend on factors which are related to patient and drugs as well.

Important factors which govern the choice of route of drug administration area. Physical and chemical properties of drugs ( solid/liquide/gas/stability/PH /

irritancyb. Site of desire action- localized and approachable and generalized and

nonapproacheablec. Rate and extent of drug absorptiond. Effect of digestive juice and first pass metabolism of drugse. Rapidity at which response is desiredf. Accuracy of dose requiredg. Condition of patients

Grossly we can divide into those for a. Local actionb. Systemic action

Local routes of drug administration

a. Topicalb. Dipper tissuec. Arterial

Systemic routesOralSublingual (S.I) or buccalRectalCutaneousInhalationNasalParenteral a. Subcutaneous (S.C) – Dermojet, Pellet

Implantation, Sialistic (nonbiodegradable) and biodegradable

b. I.M c. I.V d. Intradermal injection

Local route sThese route can be use for localized lesions at accesible sites and drugs whose systemic absorption is minimal or absents. Thus higher concentration is attained at the site of desire without exposing the rest of the body.

Topical:Refers to external application of the drug to the surface of the body for their localized action. It is more encouraging and often convenient.Drugs can be efficiently delivered to the localized lesion on the skin, eye, ears, nose, oropharyngeal /nasal mucus, rectum , vagina in the form of powder, lotion, ointment, cream, suspension, emulsion, suppositories, logenzegs.

Non-absorbable drug can be given orally into the GI mucosa eg. Sucralfalte or Vancomycine .

Deeper tissue:Certain deep area can be approach through syringe and needle but drug should be such that systemic absorption is slow.Eg. Intra-articular injection (hydrocortisone) or intrathecal injection ( hydrocortisone)

Intra-Arterial route- Close intra-arterial injection used for contrast media in angiographyAnti-cancer drug can be infused in femoral or brachial artery to localized the effect for lower limb malignancy.

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 visualize organs, e.g. heart, kidney.

Intradural and extradural routesIntradural 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

Systemic RoutesOralOldest and common mode of drug administration Safer and more convenient and does not need any assistance Noninvasive and often painless Product need not to be sterile so drugs is cheaper Both solid and liquid dosage form can be administer

Oral route of drug administrationWhat is First pass metabolism?

First pass effect

Oral Route of drug administration

LimitationsAction is slow thus not suitable for emergency Unpalatable drugs are difficult to administer (Chloramphenicol) drug may be circumvent with capsule May causes nausea and vomiting Can not be used for noncooperative patients/ Unconscious and vomitous patients Absorption of drug is variable Others are destroyed the drug with digestive juice (pen) or in liver (GTN, testosterone, lidocaine)

Sublingual or BuccalThe tablet or pellet containing drugs placed under the tongue or crushed in mouth and spread over the buccal mucosa.Only lipid soluble non-irritating drugs can be give in this route. Absorption is relatively rapid-action can be produce in a minutesThough it is inconvenient one can spit the drug once the desired action of drug obtained.The cheap advantages is liver is by passed thus drugs are protected from fast pass metabolism and drugs are directly into the systemic circulation.Eg. GTN, desamino oxytocin.

Rectal:Certain irritating and unpleasant drug can be given through rectal route in the form of suppositories or retention enema for their systemic effects.

•It is rather inconvenient and embracing, absorption is slower, irregular and often unpredictable.

•Drug absorbed through external haemorrhoidal (50% by passed) and internal haemorrhoidal veins.Rectal inflammation and leaking can occur. eg.Diazepam, Indomethacine, paraldehyde.

Vaginal Route: Some drugs may be administered vaginally to women as a solution, tablet, cream, gel, suppository, or ring. The drug is slowly absorbed through the vaginal wall. This route is often used to give estrogen to women at menopause, because the drug helps prevent thinning of the vaginal wall, an effect of menopause (see Menopause: Hormone Therapy).

Cutaneous:Highly lipid soluble drug can be applied over the skin for slow, constant and prolong absorption. Drugs usually in the form of ointment , cream, or in the form of specially designed device like transdermal drug delivery system are given in this route. > The drug should be highly lipid soluble and non-irritant in nature.> Liver is by passed.

>Absorption can be enhanced by rubbing the drugs over the skin.

>Transdermal drug delivery system:

Inhalation:Volatile liquid and gases are given in this route for their systemic actions. Eg. General anesthesia. Absorption take place from the vast surface of alveoli- action is very rapid. When administration is discontinued the drug is defused back into the exhaled air and eliminate and action slowly subside. Thus control administration is possible in moment to moment by adjustment. Irritant vapor cause inflammation to respiratory tract and cause excessive secretion and may choke the air way.

Nasal Route: If a drug is to be breathed in and absorbed through the thin mucous membrane that lines the nasal passages, it must be transformed into tiny droplets in air (atomized). Once absorbed, the drug enters the bloodstream. Drugs administered by this route generally work quickly. Some of them irritate the nasal passages. Drugs that can be administered by the nasal route include nicotine (for smoking cessation), calcitonin (for osteoporosis), sumatriptan (for migraine headaches), and corticosteroids (for allergies).

Parentral route of drug administration

Subcutaneous (S.C)The drug is deposited into the loose subcutaneous tissue which is richly supplied by nerves (irritant drug can not be injected) but less vascular ( absorption is slower). Only small volume of drug can be injected through this route.Self injection is possible because deep penetration is not needed.The route should be avoided to shock patient who are vasoconstricted.

Some special forms of these routesa. Dermojetb. Pellet implantationc. Sialistic and biodegradable implants

Dermojet:In this method needle is not needed, a high velocity jet of solution is projected from the micro fine orifice of a gun like implements. The solution is cross the superficial layer and deposited into the subcutaneous tissue. It is usually painless.

Pellet Implantation:Drug in the form of solid pellet is introduce under the skin with a trocher and cannula. This provides sustained release of drugs over weeks together to few months. Eg. DOCA and testosterone.

A- Intravascular (IV, IA):- placing a drug directly into blood stream.-May be - Intravenous (into a vein) or - intraarterial (into an artery).

Advantages 1- precise, accurate and immediate onset of action, 100% bioavailability.

Disadvantages1- risk of embolism.2- high concentrations attained rapidly leading to greater risk of adverse effects

B-Intramuscular :(into the skeletal muscle).Advantages1- suitable for injection of drug in aqueous solution (rapid action) and drug in suspension or emulsion (sustained release).Disadvantages 1- Pain at injection sites for certain drugs.