Parenteral Routes

Parenteral Routes of Administration

Instructor Information

  • Dr. Atheer Awad

    • Email: a.awad@herts.ac.uk

    • Office: F157 Hillside House, University of Hertfordshire

Importance of Knowledge in Parenteral Products

  • Understanding parenteral products is essential not only for hospital pharmacists but also in various clinical settings.

  • Parenteral administration is often required for more complex, 'higher risk' patients.

  • Pharmacists can apply their scientific knowledge in areas such as:

    • Compatibility

    • Sterility

    • Formulations

    • Calculations

    • Manufacture/reconstitution

    • Dosing

    • Monitoring

Definition of Parenteral Products

  • Definition: 'Located outside the alimentary canal'

  • Parenteral products are substances taken into the body or administered by routes other than the digestive tract, such as intravenous or intramuscular injections.

Types of Parenteral Formulations

  • Examples of Parenteral Products:

    • Hydrocortisone Cream: Contains cetomacrogol, paraffin, cetostearyl alcohol, and chlorocresol; used for cutaneous application.

    • Eye Drops and Ear Drops: Various formulations aimed at specific therapeutic uses (e.g., Optrex for tired eyes; Sodium Bicarbonate for ear wax softening).

    • Clotrimazole: Used for the treatment of thrush in both pessary and cream forms.

    • Antifungal Treatment: Products like amorolfine for nail infections.

Parenteral Routes of Administration

Types of Injections

  • Intramuscular (IM)

  • Subcutaneous (SC)

  • Intravenous (IV)

  • Intradermal

  • Intra-arterial

  • Intrathecal

  • Intracavernosal

  • Intraosseous

  • Intra-articular

Advantages of Administration via Injection

  • Provides localized effects (e.g., steroids).

  • Produces rapid clinical effects, particularly with IV administration.

  • Allows for delayed/prolonged effects with IM injections.

  • Useful when the oral route is impractical, such as in drugs degraded in the gastrointestinal tract (e.g., gentamicin).

Intravenous (IV) Administration

  • Injections vs. Infusions: Different methods of delivering medication.

  • Peripheral vs. Central Administration: Use of devices like Peripherally Inserted Central Catheter (PICC).

  • Capable of rapid effect (bolus doses) or slow controlled effect (infusions).

  • Advantages:

    • 100% bioavailability; fastest route of drug administration.

    • Rate of administration can be controlled.

    • Useful for drugs that degrade orally.

  • Disadvantages:

    • Rapid onset of side effects.

    • Risk of infections/complications.

    • Requires aseptic technique and constant monitoring.

Intramuscular (IM) Administration

  • Administered in small volumes (1.5 mL - 5 mL).

  • Provides systemic effects typically within 15 to 30 minutes.

  • Used often for controlled release formulations.

  • Rate of Absorption Factors:

    • Vascularity of muscle site

    • Drug's lipid solubility

    • Vehicle of the drug

    • Injection technique

IM Depot Injections

  • Examples:

    • Depo-Provera: Medroxyprogesterone acetate (contraceptive).

    • Antipsychotic Depot: Flupentixol decanoate (administration every 2-4 weeks).

IM Administration Disadvantages

  • Potentially painful and difficult to self-administer.

  • Cannot retrieve once administered; risk of atrophy with repeated use.

Subcutaneous (SC) Administration

  • Also known as hypodermic; involves injection into loose connective and fatty tissues.

  • Typically smaller volumes (up to 1 mL).

  • Hypodermoclysis: Allows for larger volumes (up to 1000 mL) under rare circumstances.

  • Consideration for non-irritating drugs that require slower absorption.

SC Formulation Issues

  • Usually aqueous solutions or suspensions.

  • Rate of absorption affected by formulation and site vascularity.

  • Conditions like diabetes may affect absorption due to vascularity issues.

SC Formulation Examples

  • Insulin: For long and short-acting formulations.

  • Low Molecular Weight Heparins: Such as enoxaparin for DVT prophylaxis.

  • Zoladex: Goserelin for prostate and breast cancer, administered SC.

Intradermal Administration

  • Administered between epidermal and dermal layers.

  • Very small volume (up to 0.2 mL).

  • Primarily used for immunological testing (e.g., allergy tests).

Intrathecal Administration

  • Injection into cerebrospinal fluid (CSF).

  • Volumes up to 10 mL.

  • Useful for substances unable to cross the blood-brain barrier, cerebral infections, tumors, or anesthesia.

Other Direct Sites of Injection

  • Intraosseous: Into the bone marrow for emergency access.

  • Intra-articular: Into synovial fluid for joint conditions.

Specialist Administration Sites

  • Intracavernosal: Injection into the penis for erectile dysfunction.

  • Intra-urethral: Administration into the urethra for specific therapeutic agents.

Parenteral Formulations

  • Types: Injections available as ampoules or vials, including solutions, emulsions, and powders.

  • All formulations must meet certain criteria regarding sterility, isotonicity, and compatibility with other substances.

Needles and Administration

Needle Size and Diameter

  • Use the shortest and thinnest needle possible for administration.

  • Needle gauges: 30G (Yellow) to 18G (Pink).

Injection Angles

  • Intradermal: 10-15°

  • Subcutaneous: 45°

  • Intravenous: 25°

  • Intramuscular: 90°

Best Practices for Injection Techniques

Example: SC Injection

  • Instructions for proper technique to ensure patient safety.

Rates of Drug Absorption

  • Fastest to Slowest:

    1. Intravenous

    2. Inhalational

    3. Intramuscular

    4. Subcutaneous

    5. Intranasal

    6. Oral

    7. Cutaneous

    8. Rectal

Clinical Implications of Incorrect Administration

  • Examples of tragic outcomes due to improper injection techniques (e.g., incorrect administration of vincristine).

Pharmaceutical Considerations for IV Drugs

  • Critical points to consider regarding dosages, reconstitution, incompatibilities, and dilution factors.

Calculating Displacement Values

  • Know displacement values for accurate reconstitution of medication (e.g., diamorphine and bupivacaine).

  • Examples of calculations for ensuring accurate dosages.

Isotonicity in Parenteral Solutions

  • Isotonic Solution: Has the same osmotic pressure as body fluids.

  • Hypotonic and Hypertonic Solutions: Affect red blood cell morphology.

  • Freezing Point Depression is a method for calculating isotonicity; related equations provided for practical applications.

Recommended Reading

  • Aulton, M.E. and Taylor, K.M.G. (2021): "Aulton's Pharmaceutics", Chapter 38.

  • Adejare, A. (2020): "Remington: The Science and Practice of Pharmacy", Chapter 29.

  • Jones, D.S. (2016): "Pharmaceutics - Dosage Form and Design", Chapter 5.

Conclusion

  • Summary of important points regarding parenteral routes of administration and their applications in clinical practice.