Different Ways to Administer Drugs
Although LFA Tablet Presses specializes in Pill Presses and Tableting Equipment we understand that there are other methods of drug delivery. In this article we outline the more common means of administering pharmaceuticals and what your business needs to know in terms of the packaging and delivery of the drugs.
The method selected for administering drugs to a patient is dependent on the drug’s chemical and physical properties as well as the response desired and the patient’s demographics. Fundamentally drugs can be administered orally (by mouth), parenterally (by injection) or topically (by absorption through the skin). In some cases inhalation may be preferred to oral or parenteral administration and in recent years more drugs have been introduced that are administered by mucoadhesion. All of these forms of administration require different formulations of the pharmaceutical products.
Oral administration of medication is the most common method; it is the most convenient and safest way to give medicine. Administration is in the form of tablet, capsule, emulsion, mixture or as a gel. The body absorbs many of the oral drugs in the market today once they reach the small intestine; some medicines are absorbed from the colon and stomach area. Whilst oral administration is common, there are some medicines that cause irritation of the gastrointestinal tract and other methods may be preferred, as detailed below.
Drugs that are administered orally tend to have a slow onset, and release of drug into the body fluids may be prolonged, with less potent effects compared with drugs administered parenterally. Tablets for oral administration can also be placed under the tongue (sublingual) where the drug remains until it is dissolved completely by the saliva and is absorbed by the tissues. Medicines administered by the sublingual method are fast acting as the tissues under the tongue are a rich capillary network of blood vessels, enabling fast absorption of the drug. The sublingual method is also beneficial in that it helps prevent drugs from becoming destroyed by stomach acid, or by hepatic inactivation. In other words, sublingual drugs are absorbed into the circulatory system without having to pass through the gastrointestinal tract or the liver.
Parenteral drugs are administered through the patient’s subcutaneous or intramuscular glands. This method is preferred when the drug is poorly absorbed internally by the body or when it is deactivated by enzymes as it passes through the digestive tract. Parenteral administration is also offered when the patient cannot tolerate any oral medication but needs the medication to take effect quickly. To administer the medicine, the health care provider will use a needle or syringe or an intravenous infusion set.
- Intradermal – the administration of drugs is done at the outer layer of the skin. The quantity of drug administered is small and the rate of absorption is slow. This method is the usual choice for diagnostic tests or e.g., for BCG vaccines.
- Subcutaneous – the administration of drug is through the subcutaneous layer of the skin. The drug is injected in small amounts, usually less than 2.0 ml. Absorption of the drug is slow but the effect is longer lasting than other parenteral methods. The subcutaneous method is not recommended for patients who have suffered shock, as it reduces the peripheral circulation, which would then lead to a decreased absorption rate by the body. Irritant drugs are also not administered subcutaneously as these are painful and can cause tissue necrosis. Hypodermoclysis is a form of subcutaneous injection, that can be used where a slow rate of fluid uptake is required compared to intravenous infusion. Typically, it is limited to 1 ml per minute, although it is possible to increase this by using two sites simultaneously. The chief advantages of hypodermoclysis over intravenous infusion is that it is cheap and can be administered by non-medical personnel with minimal supervision. It is therefore particularly suitable for home care and common applications are the administration of glucose solution in the case of diabetic patients or saline solution to treat dehydration.
- Intramuscular – this kind of administration requires the use of large needles in order to penetrate the subcutaneous layer of the skin. The drug is deposited in between the layers of muscle mass. Intramuscular administration is ideal for administering suspensions and solutions.
- Intravenous – Intravenous administration of drugs is recommended when fast or immediate response is required or when absorption is compromised. This method enables the drug to reach the blood stream directly. A type of intravenous administration is that of infusion where large amounts of fluid are involved. The solution typically flows from a graduated bottle or sachet through the drip set. Infusion is used to address tissue dehydration, dilute toxic materials in the body, supply electrolytes as well as restore blood volume.
- Intramedullary – this method requires the drug to be injected in the patient’s sternum or tibia and directly into the latter’s bone marrow. The efficacy of the drug is the same as that achieved by an intravenous injection.
- Intra-arterial – when the patient’s vein is hard to locate and intravenous infusion is impractical, intra-arterial injection is employed. In this process, surgeons place a needle in the artery – it is used for taking blood samples for study. Intra-arterial injection is employed to inject dyes into the arteries so to enable sections of the artery to be visible when x-rayed.
- Intrathecal – this term is used to describe injecting medicine in the vertebral interspinous space to the spinal fluid. The effect is rapid absorption of the medicine and is the method is often used for spinal anesthesia.
- Epidural – in this procedure, the drug is injected into the epidural space inside the bony spinal canal but just outside the dura mater ("dura"). In contact with the inner surface of the dura is another membrane called the arachnoid mater ("arachnoid"). The cerebrospinal fluid that surrounds the spinal cord is contained by the arachnoid mater. In adults, the spinal cord terminates around the level of the disc between L1 and L2 (in neonates it extends to L3 but can reach as low as L4), below which lies a bundle of nerves known as the cauda equina ("horse's tail"). Hence, lumbar epidural injections carry a low risk of injuring the spinal cord. Insertion of an epidural needle involves threading a needle between the bones, through the ligaments and into the epidural potential space taking great care to avoid puncturing the layer immediately below containing spinal fluid under pressure.
- Intra cardiac – used when a patient is suffering from cardiac arrest. The injection introduces the drug directly to the heart and help the heart start beating again.
Medicines can be introduced into the body by inhalation. There are two classes of substances that are commonly administered by inhaling – volatile and non-volatile.
- An example of volatile substances are anaesthetic agents that are liquid at room temperature but evaporate easily for administration by inhalation. All of these agents share the property of being quite hydrophobic (i.e., as liquids, they are not freely miscible with water, and as gases they dissolve in oils better than in water). Agents that we once widely used such as chloroethane, chloroform, cryofluorane, cyclopropane, diethyl ether, enflurane, ethylene, fluroxene and halothane have given way to modern agents desflurane, isoflurane, and sevoflurane. In the list of volatile materials could be added nitrous oxide and xenon, both of which are gases at normal temperature and pressure, and both of which can be used as anaesthetics, often when diluted with oxygen.
- Non-volatile substances include many liquids that can be administered in the form of aerosols, in which small droplets of liquid are suspended in a gas such as air or oxygen. Aerosols can be stable for long periods and since the droplets are very very small, they are able to penetrate deep into the lungs. The smaller the drops, the more deep can they go. Common devices for generating aerosols include nebulizers, humidifiers, inhalers and vaporizers. Brochodialators are administered for prompt absorption of the drug by the patient. A wide variety of fast-acting drug formulations can be administered such devices.
Topical medicines are those that are absorbed by the skin. As the skin or dermis is permeable to different liquids, drugs can be easily absorbed by topical application. Other medication can be applied to the skin include liniments, gels, creams, ointments and lotions.
Some drugs are designed to be administered through the patient’s rectum. This method is practised if the drug is unpalatable or too large to be administered orally, or when the stomach is non-retentive due to vomiting.
Mucosal administration or mucoadhesion, refers to the application of drugs through the mucosal glands in the body including those in the mouth, nose, throat, vagina and rectum. Mucus membranes (mucosae) are the moist surfaces lining the walls of various body cavities including the gastrointestinal and respiratory tracts. They consist of a connective tissue layer (the lamina propria) above which is an epithelial layer, the surface of which is made moist usually by the presence of a layer of mucus. The epithelia may be either single layered (e.g. the stomach, small and large intestines and bronchi) or multilayered/stratified (e.g. in the esophagus, vagina and cornea). Mucus is present either as a gel layer adherent to the mucosal surface or as a luminal soluble or suspended form. The major components of all mucus gels are mucin glycoproteins, lipids, inorganic salts and water, the latter accounting for more than 95% of their weight, making them a highly hydrated system. The major functions of mucus are that of protection and lubrication.
The concept of mucoadhesion has gained considerable interest in pharmaceutical technology since the early 1980s. Mucoadhesive drug delivery systems interact with the mucus layer covering the mucosal epithelial surface, and mucin molecules and increase the residence time of the dosage form at the site of absorption. Mucoadhesive drug delivery systems prolong the residence time of the dosage form at the site of application or absorption. They facilitate an intimate contact of the dosage form with the underlying absorption surface and thus improve the therapeutic performance of the drug. In recent years, many such mucoadhesive drug delivery systems have been developed for oral, buccal, nasal, rectal and vaginal routes for both systemic and local effects. Dosages maybe applied in the form of aerosols, nasal sprays, lozenges, tablets and suppositories.