Routes of drug administration: How to take your drug
Route of administration means the method by which you take your medicine. There are multiple ways of taking a drug. Whenever any symptom of pathological state is identified, medicine is given to treat the disorder. Medicines are available in various dosage forms and we intake them in different manner. To identify and choose a drug to treat an illness is basically a qualitative decision of the physician based on the physiological and patho-physiological status of the patient. To ensure the clinical efficacy of the prescribed medicine one should carefully consider the effective quantitative aspects of the drug such as minimum sufficient amount of the drug reaches at the target site to attain the desired therapeutic effect. Mode of administration plays very important role in the extent of absorption of the drug and effect produced by the drug. It mainly affects the absorption and distribution properties of a drug. Absorption of a drug refers to the travel of a drug from the site of administration to the site of action. Various factors such as, chemical nature, solubility, disintegration, dissolution, particle size, degree of ionization, physical forms, dosage forms, drug stability, formulation and first pass metabolism affects absorption, distribution, metabolism and excretion (ADME) properties of a drug.
Drugs are generally meant to diagnose and treat the illness. But if it is not taken in the correct manner it might prove ineffective and sometimes produce unwanted side effects. So it is very important to know how to ingest the medicine. For each medicine there are multiple ways of taking them depending upon the dosage form, chemical ingredients, intended biological effect and patient status etc.
Classification of routes of administration based on area of application
Oral: when a drug is taken by mount it is classified as oral route of administration. It is the most convenient, safest, simple and widely used mode of administration. Various dosage forms such as liquids, capsules, tablets, or chewable tablets can be comfortably taken by this method.
Topical: External application of a drug on skin, eye etc is know as topical application. When a drug is applied topically it gets absorbed through skin. Various antiseptics creams are available for topical application. Other dosage form meant for topical application are ointment, gel, paste etc.
Parenteral: Parenteral administration means injection or infusion of a drug directly in the blood circulation with assistance of a needle or catheter. The term “Parenteral” derives from greek words Para and enteron. Para means outside, Enteron means intestine. Hence, parenteral administration refers outside the intestine. This route bypass the alimentary canal. Parenteral route is generally opted to avoid first pass metabolism of the ingested drug to enhance the bioavailability of the drug.
Classification of routes of administration based on site of action
When you take a medicine it is intended to show some biological effect at a particular site in the body. On the basis of the target area routes are classified as follow
Systemic route of administration: When drug reaches to the site of action through systemic circulation and the intended biological action of the drug affects the whole body. Systemic effect is achieved by enteral or parenteral route. Enteral route refers to the absorption and passage of drug through gastro intestinal tract. Enteral route is further subclassified as oral, buccal (held inside the cheek), sublingual (held under the tongue). Parenteral route circumvent the alimentary canal and involve the direct entry of the drug into blood stream through injection or infusions.
Local route of administration: Drug is generally applied externally/ topically on the surface of the area where the therapeutic effect of the drug is desired. Local route is preferred when the intended effect is desired at a particular localized part of the body. For example general anesthetics are given by inhalation or injections so as to produce the complete loss of consciousness whereas local anesthetic is generally applied topically to a localized area of the body.
Factors affecting the choice of route of administration:
Since there are a various dosage forms and numerous methods of administering them. So it is important to know which route to be opted. Various factors affect the selection of the route of ingesting drugs such as physical and chemical properties of a drug: Solid/liquid/gas, solubility, pH, stability etc. A solid/liquid dosage form such as tablet, capsule or syrup is generally ingested by mouth while a gaseous dosage form is taken by inhlation route. Further stability and pH of the drug alter the choice of the route. Sometimes a drug is not stable in the gastric acid environment (e.g., benzylpenicillin) or gets degraded in the GIT tract before reaching the site of action. Hence oral route is not suitable for such medicines. To be effective, many medications need to reach a certain level in your bloodstream. To avoid first pass metabolism and enhance the bioavailability of the drug parenteral route is chosen. Patient related factors such as age, condition, pathological state etc also matter while deciding the route of intake.
|ORAL||Easy, simple, most convenient
Safest and Non-invasive mode.
Preferred by children.
Various dosage form such as tablet, capsules, syrups, oral powder etc.
Film coated and sugar coated tablets are available for sustained release and to overcome bitter taste respectively.
|Not suited for the patients who have difficulty with swallowing.
Absorption is generally slow.
Degradation by salivary and pancreatic enzymes results in decreased bioavailability.
|TOPICAL||Easy, Simple application.
Avoid contact with digestive enzymes.
|Very slow absorption.
Low penetration through skin.
Leaves stains on cloths such as ointments.
Product partially wasted while application
|INJECTION||Rapid absorption. Rapid onset of action.
Circumvent first pass metabolism.
Dose can be accurately monitored and extent of absorption is predictable.
Prefered in emergency situation.
|Difficult and painful application.
Expensive and need assistance.
Children generally don’t prefer.
Require great skill and care while administering a drug
Targeted delivery. Metered dose inhalers now available.
|Bioavailability depends on patient’s inhaler technique and the size of drug particles generated by the delivery technique.|
To be effective, any medication need to reach a certain level in blood plasma and must be able to reach the site of action to produce the expected therapeutic effect. The choice of drug administration mode plays very critical role and depends on pharmacodynamic as well as pharmacokinetic properties of a drug. The amount of a drug and the rate at which the drug reaches the target site depend in part on the route taken to administer the drug. The mode of administration affects the rate, extent of absorption of a drug and amount of drug reaching the target site. If one chooses a incorrect manner of taking a drug, it might get metabolized or excreted out unchanged without displaying required biological effect. Sometimes unwanted side effects results due to mistaken selection of route of administration. Drugs can be administered by a wide variety of routes, each with its advantages and disadvantages. Therefore making a right choice of route might upshot the therapeutic value of certain medications and may be the start of a successful therapeutic intervention.
Dr. Suman Rohilla
SGTCP, SGT University, Gurgaon