D.1.3 Describe the different methods of administering drugs


A route of administration in pharmacology and toxicology is "the path by which a drug, fluid, poison, or other substance is brought into contact with the body".external image Curadermcream_.jpg

Methods specified by IB include:
  • Oral
  • Injection
  • Inhalation
  • Rectal

Some other methods include:
  • Ocular: in the eye
  • Topical: Applied on the skin (creams etc.)

Oral
  • Oral drugs are administered through the mouth, usually in a solid or liquid form, then absorbed through the small intestine.
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      Advantages:
      • Cheap
      • Convenient and easily obtained
      • Self-administrable
      • Non-invasive method of administration
      • A wide variety of available dosages
    • Disadvantages:
      • Patients might have difficulties swallowing the tablets
      • High action time
      • May be partially destroyed or metabolized by the human digestive and metabolic systems, mainly the small intestine and liver
      • Slow absorption
      • May act as catalysts for vomiting
  • The oral forms of drugs are always higher in doses than the injected forms.
  • They are affected by other food or drugs in the digestive tract, and in blood circulation.

Injection
Methods of administration
Methods of administration

(IB only specifies the first three in the diagram)
  • These drugs must be pure, sterile, and pyrogen-free (the products from bacterial growth).
  • Parenteral administration can be classified into several types: intravenous, intramuscular, intradermal, intrathecal/Intraspinal, subcutaneous, transdermal, and implantation.
    • Intravenous external image image2.jpg
      • Intravenous drugs are administered directly in a vein, commonly seen in an IV drip.
      • Intravenous administration is much quicker than other administration methods in delivering medication or fluids throughout the body.
      • Drugs administered intravenously often have a stronger effect than those administered using alternate types.
      • Certain drugs can only be administered intravenously, for example blood transfusions or lethal injections. It is also used above oral drugs for those drugs that contain protein, which would be broken down via the digestive tract.
      • The effects of the drugs wear off much quicker, thus patients are often kept on continuous infusion.
    • Intramuscular: Procaine Penicillin G
      • Intramuscular drugs are administered directly into a muscle.
      • For example, the deltoid. Intramuscular administration is usually used for drugs that are administered in amounts that cannot be feasibly injected subcutaneously.
    • Subcutaneous: Insulin
      • The drug is injected just below the skin's cutaneous layer
      • Subcutaneous drugs are administered in the form of a bolus, a compound meant to raise a drug’s concentration in blood to a specific level, into the subcutis.
      • Drugs such as insulin or morphine are administered most successfully through subcutaneous injection
  • Advantages
    • Fast effect (from few seconds to few minutes depending on the drug)
    • 100% absorbed
    • A direct way into the body (good for drugs that cannot be absorbed by alternate routes)
    • Can be made to last long (from few weeks to few months)
    • IV for continuous medication
  • Disadvantages
    • Belonephobia (fear of needles)
    • Risk of disease being transferred (such as HIV) if needles are shared or not sterilized
    • Normally people cannot administer themselves
    • Fatal risk of injecting air bubbles
    • Bypasses many defense mechanisms of the body
    • Dosage must be measured extremely carefully, mistakes may have fatal consequences
    • Many drugs cannot by-pass the blood-brain barrier

Inhalation
  • Drugs administered by inhalation through the mouth must be atomized into smaller particles than those administered by the nasal route, so that the drug can pass through the windpipe (trachea) and into the lungs. How deeply into the lungs they go depends on the size of the droplets. Smaller droplets go deeper, which increases the amount of drug absorbed. Inside the lungs, they are absorbed into the bloodstream.
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    • Types of inhalation:
      • Vaporization
        • This is when the drug is changed from a liquid or solid form into a gas or vapor through the use of heat. (ie. steam inhalation.)
      • Gas Inhalation
        • This is mostly used for anesthesia.
      • Nebulization
        • This is probably the most common form of drug inhalation. It is when the drug is converted into a fine spray using pressured gas. (ie. drugs associated with asthma that people carry around to spray.)
  • Advantages:
    • Inhaling is the fastest method. It only takes a few seconds(about 7-10) for the drug to reach the brain.
    • The user can regulate the amount of drug they are taking
  • Disadvantages:
    • It is impossible to get the exact amount of dosage.
    • The drug does not stay in the bloodstream for long.

Rectal:
  • Rectal drugs are administered by inserting them into the rectum through the anus.
  • Drug is absorbed by blood vessel's and to body's circulatory system, which distributes the drug to body's organs and etc.
  • This method is preferred when there is a emergency of vomiting, or when the patient is uncooperative, unconscious or mentally incapable.
  • e.g. Enemas and Suppositories
  • Many drugs that are administered orally can also be administered rectally as a suppository. In this form, a drug is mixed with a waxy substance that dissolves or liquefies after it is inserted into the rectum. A suppository is prescribed for people who cannot take a drug orally because they have nausea, cannot swallow, or have restrictions on eating. Suppositories are also commonly used with children who are not old enough to swallow pills or uncooperative children.
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