Structural Biochemistry/Routes of Drug Administration

“Better medical treatments do not always require stronger medicine. The effectiveness of chemical agents depends on the method of administration. So treatment can often be improved by finding optimal drug formulation of delivery system.” (Professor Mark Saltzman) As the result, many chemists, biochemists, pharmacists, bioengineers, and chemical engineers work to improve the administration of the drugs instead of find the stronger medicine. There are three categories of drug administration, topical, parenteral, and enteral.

Drug Administration Routes refers to the various ways of inserting a drug or other chemical inside a patient or animal in order for the chemical to be absorbed into the blood and delivered to the target tissue. There are several known ways to administer drug into an organism, but the easiest and the most commonly used method is through injection.

Topical Administration
For topical drug administration, drugs are applied directly to the affected area. The effect reminds in the local area. The advantage of topical administration is that drugs can be given to the patient. No trained personnel are required for application. Usually, there is no pain involved in administration. Side effects are very minimal.

Epicutaneous
Drugs are applied directly onto the skin surface. This administration can be used to test if a patient is allergic to certain drugs or substance. Epicutaneous administration can also be used for local anesthesia to relieve minor pain for cuts or burns.

Eye Drops
Drugs are applied directly into the affected eye. Eye drops are saline-containing liquid. Examples of eye drops are rinse eye drops, Glaucoma eye drops, steroid and antibiotic eye drops.

Inhalational
Drugs are inhaled through the mouth by the patient. Inhalational administration drugs can be used to treat asthma or acute infection in upper airway. The advantage of inhalational administration is that the response of body is much faster than oral administration because the drug does not have to go through the gastrointestinal (GI) tract. Also, because the drug does not have to go though liver, so the damage to liver is minimized.

Intranasal Route
Intranasal route administration is also known as nasal spray. Examples of nasal spray are decongestant nasal spray or allergy relive.

Parenteral Drug Delivery
Parenteral drug delivery has systematic effect on the body, meaning that the drugs do not stay specifically at one area, but body as a whole. In parenteral drug delivery, substance is given by routes other than the gastrointestinal (GI) tract, including intravenous injection, subcutaneous injection, intraarterial injection, etc.

Intravenous Injection
The substance is injected into the vein. The substance can be drugs. The first intravenous injection every given to a patient was in 1667. The advantages of intravenous injection are that the response is very rapid, the dosage of the drug can be easily controlled, and veins are insensitive to irritation by irritant drugs at higher concentration. However, there are many disadvantages of intravenous injection. First of all, it is not always easy to find a suitable veins. Veins disappear when a patient is under high pressure or tension. Second of all, intravenous injection can be toxic due to its fast response from the body. Third of all, a trained personnel is required, and the drug cannot be given to the patients. Last of all, it is rather expensive to prepare sterilizing the needles.

Intramuscular Injection
The substance is injected into the muscle. The substance can be vaccines or antibiotics. The advantages of intramuscular injection are that large volume of drugs can be applied and a sustainable release of drugs is possible. Muscles can act as an adsorption compartment. When the concentration of drug inside of the body is low, the muscle can slowly release the drugs into the body. However, there are also many disadvantages of intramuscular injection. Trained personnel are required for intramuscular injection; the drug cannot be given to the patients. Absorption is sometimes erratic, especially for poorly soluble drugs. The solvent of the drug may be released faster than the drug, causing the drug to precipitate at the site of injection and therefore immobilizes the drug.

Subcutaneous Injection
The subcutaneous (SC, SQ) route is one of the most versatile routes of administration in that it can be used for both short term and very long term therapies. The injection of a drug or the implantation of a device beneath the surface of the skin is made in the loose interstitial tissues of the upper arm, the anterior surface of the thigh, or the lower portion of the abdomen. The upper back also can be used as a site of subcutaneous administration. The site of injection is usually rotated when injections are frequently given. The maximum amount of medication that can be subcutaneously injected is about 2 ml. Needles are generally 3/8 to 1 inch in length and 24 to 27 gauge.

Absorption of drugs from the subcutaneous tissue is influenced by the same factors that determine the rate of absorption from intramuscular sites; however, the vascularity in the subcutaneous tissue is less than that of muscle tissue, and therefore absorption may be slower than after intramuscular administration. But absorption after subcutaneous administration is generally more rapid and predictable than after oral administration

Subcutaneous injection is injection under the skin. Insulin is a good example for subcutaneous injection. The advantages of subcutaneous injection are that the drugs can be given to the patient because no trained personnel are needed, and the adsorption, even though slow, but is usually complete. The adsorption can be improved by applying massage or heat on the injected site. However, subcutaneous injections are very painful, irritating drugs can cause damage in the skin, and only a small dosage of drug can be applied.

Below is a picture illustrating the difference between different kinds of injections.

Intraarterial Injection
Intraarterial injection is injection into the artery. But it can be very dangerous because, the artery presence in very deep on body.

Intradermal Injection
Intradermal injection is injection into the skin itself. Examples are skin testing for some allergen or tattoo.

Transdermal
Transdermal patch utilizes diffusion through the skin to sustain drug released. Examples are transdermal patch. Picture below demonstrates the difference between traditional intramuscular injection and a transdermal patch. As can be seen from the illustration, intramuscular injection can be much more painful than transdermal patch.



Oral
Many drugs can be made into tablets or capsules. The advantages of oral administration is that it is portable, convenient, easy to take, and not painful. It is cheap because the tablets do not need to be sterilized and can be produced in large quantities. However, oral administration can be sometimes inefficient because high dosage or low soluble drugs suffer low bioavailability. The drug will also be metabolized in the liver during adsorption, which is known as the first-pass effect. Also, the food the patient consumes may also alter the effect of the drugs. The drug can also be damaging to the normal gut flora in the GI tract. Last of all, oral drugs cannot be given to unconscious patient.

Rectal
Various drugs are produced in suppository or enema form.

Gastric feeding tube
Many drugs or nutrition can be given to unconscious patients through gastric feeding tube.