Principles of Safe Drug Administration

Pharmacology

• The study of drugs: their uses, effects, and modes of action.

Pharmacokinetics

• How the body affects a drug (absorption, distribution, metabolism, and excretion).

Pharmacodynamics

• How a drug affects the body.

Absorption

• How a drug enters the body (route of administration).

Distribution

• Where a drug goes in the body and where it accumulates.

Metabolism

• How the body bio-transforms a drug to remove it.
• Involves chemical alteration of drug molecules to make them more water-soluble for excretion.

Elimination

• The process of a drug being bio-transformed from an active state to inactive metabolites.

Excretion

• The removal of drugs from the body, either as metabolites or unchanged drugs.
• Primarily performed by the kidneys.

Half-Life

• The time it takes for the concentration of a drug in the plasma or the total amount in the body to be reduced by 50%.

First Pass Metabolism

• Drugs administered orally are metabolized in the gut or liver before reaching systemic circulation.

Bioavailability

• The extent and rate at which the active drug or metabolite enters systemic circulation and reaches the site of action.

The R's of Drug Administration

• Right drug
  • Indications and contraindications
  • Appearance of the drug
• Right route
  • Correct pathway for drug administration
• Right patient
  • Age, other diseases, allergies, and potential side effects of the drug
• Right dose
  • Drug calculations
• Right time
  • Scheduled administration, rate of administration, and time for effect
• Right to refuse
  • Consent if appropriate
  • Action if incorrect drug administration is suspected
• Right response
  • Desired outcome of medication administration
• Right documentation
  • Accuracy records
• Right to question, advice, and knowledge
  • Confirm with partner
  • Advise patient of possible side effects

Patient Characteristics Affecting Medications

• Age
  • Children have less developed liver function, leading to quicker drug elimination.
  • Elderly may have compromised organ function or multiple co-morbidities, resulting in slower drug elimination.
• Body weight
  • Higher body weight require higher doses for effect due to changes in drug clearance.
• Pathophysiology
  • Disease, infection, and inflammation can decrease drug metabolism, affecting the duration of drug effect.
• Genetics
  • Impact on drug metabolism.
• Drug or food interactions
  • Certain drugs may be contraindicated if taken with other drugs, over-the-counter medications, or herbs.

Important Definitions

• Dose: The amount of medication to be given.
• Weight: The physical weight of the active dose of the medication.
• Volume: The physical volume of the fluid containing the medication.
• Expiry date: The latest date for safe administration of the medication.
• Route of administration: How the drug enters the body.
• Actions: The desired effect of the drug.
• Mechanism of action: How the drug works to create the effect.
• Indications: Conditions for which the medication is appropriate.
• Contraindications: Conditions where the medication is unsafe.
• Precautions: Conditions requiring close monitoring or cautious administration.
• Adverse effects: Negative or undesired effects of the medication.
• Side effects: Benign effects of the medication unrelated to its therapeutic effects.

Drug Dose & Volume

• Dose refers to the mass of drug required, regardless of preparation or form.

Paediatrics

• Paediatric drug dosage is based on patient weight.
• Three calculations for paediatric drug administration:
  • Patient weight
  • Drug dose based on weight
  • Volume based on drug dose

Calculating Doses

• Three formats for calculating drug doses:
  • mg/kg
  • µg/kg
  • mL/kg

Calculating Volume

• Drug preparation refers to the dosage and volume in the ampoule.
• Factors involved in volume calculation:
  • Volume of drug preparation required
  • Dosage (mass) of drug required
  • Concentration of the preparation provided

Drug Administration

Enteral Methods

• Drug is placed directly into the GI tract.
  • Sublingual: Under the tongue
  • Oral: Swallowed
  • Rectal: Administered as a suppository

Parenteral Methods

• Drug is delivered into systemic circulation bypassing the intestinal mucosa.
  • Topical: Used externally on skin, nose, eyes
  • Intradermal: Into the skin
  • Subcutaneous: Under the skin
  • Intramuscular: Into the skeletal muscle
  • Intravenous: Directly into the bloodstream
  • Endotracheal: Administered endotracheally through an ET tube
  • Intraosseous: Directly into bone marrow
  • Intranasal: Administered through nasal structures
  • Inhalation: Through airways and into alveoli
  • Vaginal: Administered into the vagina

Oral Administration

• Most common route in community settings.
• Primary drug absorption site: small intestine.
• Bioavailability is influenced by the first-pass effect.
• Examples: paracetamol, ibuprofen, aspirin

Sublingual Administration

• Under the tongue for absorption through the mucous membranes of the mouth.
• Bypasses first-pass metabolism, leading to higher bioavailability.
• Examples: glyceral trinitrate (GTN), anginine

Intranasal Administration

• Aerosol medication applied through the nose.
• Advantages: easily accessible and highly vascular.
• Contraindications:
  • Suspected nasal fractures
  • Obstructed nasal passage
• Complications:
  • Underdose if not administered properly
  • Mild, short-lasting discomfort (typically burning)

Nebuliser administration

• Converts liquid medication into an aerosol mist for inhalation.
• Rapidly absorbed across the respiratory tract epithelium.
• Administered through a mask with an oxygen flow rate of 6-8 L/min.
• Patient must be sitting.

Subcutaneous Injection

• Delivery of medication into the fat layer between the skin and muscle.
• Slower absorption than intramuscular route.
• Example: insulin, heparin
• Factors affecting absorption:
  • Exercise
  • Environmental temperature
• Contraindications:
  • Injection into scar tissue, bruises, infection, or broken skin.
• Precautions:
  • Pain
  • Bleeding

Intramuscular Injection

• Administration of medication into the muscle.
• Rapid setup and administration.
• Commonly used sites: deltoid muscle (shoulder) and vastus lateralis (outer side of thigh).
• Contraindications:
  • Evidence of infection or trauma at the injection site.
• Precautions:
  • Pain
  • Bleeding
  • Abscess
  • Cellulitis
  • Tissue necrosis