Parenteral Route

Introduction

A drug administered parenterally is one injected via a hollow needle into the body at various sites and to various depths.

• Subcutaneous or hypodermic (under the skin)
• Intramuscular (muscle)
• Intravenous (vein)
• Intradermal (skin)
• Intraspinal (spinal column)
• Intrathecal (spinal fluid)
• Intracardiac (heart)
• Intraarticular (joint)
• Intrasynovial (joint fluid area)
• Intraocular (eye)

NOTE: All parenteral products must be sterile.

Indications

The parenteral route is preferred when

• Rapid absorption is essential, as in emergency situations
• Intravenous injection delivers the drug directly into the circulatory system, where it is then rapidly distributed around the body.
• Conversely, if a drug is administered by intramuscular injection, the release of the medicine from the injection site into the circulation can be delayed and prolonged.
• When patients are unconscious or unable to accept oral medication
• To provide a highly localized effect
• e.g. Intra-articular steroids
• Drugs are destroyed, inactivated or poorly absorbed following oral administration.
• e.g. Insulin injections, aminoglycosides gentamicin,

In general, the blood levels attained are more predictable than those achieved by oral dosage forms.

Disadvantages

• Primarily associated with pain and inconvenience.

Intravenous Administration

IV administration delivers the medication into the blood stream through 2 methods.

• Direct Push (IV Bolus)
• Lasting a few seconds to minutes, with the intent of producing a high drug concentration rapidly. However, most injections should normally be administered over 2 to 5 minutes.
• It is impractical if a drug needs to be given slowly or in a large volume.
• Intermittent or Continuous Infusion
• Involves administration over a longer time period often using larger volumes.
• Continuous infusion over 24 hours is indicated for drugs with short half-life (e.g. glyceryl trinitrate) and/or when a constant therapeutic drug level is required (e.g. insulin).

Incompatibility issues can arise during parenteral medication administration.

• Chemical incompatibility
• Causes drug degradation due to a hydrolysis, oxidation or decomposition reaction.
• Physical incompatibilities occur between a drug and one of the following:
• The container (e.g. polyvinyl chloride containers - leaching of diethylhexyl phthalate (DEHP) from the container or drug absorption into the PVC containers)
• The diluent (solution) (e.g. dextrose or saline)
• Another drug - e.g. when mixing drugs in the same container or Y-site administration.

Subcutaneous Routes

The subcutaneous route results in slow, steady drug absorption.

• Examples: Insulin, enoxaparin.

Intramuscular Routes

IM injections require a longer needle to access the muscle tissue, hence is more uncomfortable for the patient.

• The volume of medication is determined by the age of the patient and the muscle selected, but typically not more than 3 ml.