Parenteral Drug Administration

### Parenteral Administration

Parenteral drug delivery refers to drug administration by routes other than the gastrointestinal tract, typically involving injections.
This method is commonly used in medical practice and is often the primary route for certain drugs.
Advantages of parenteral administration:
- Rapid onset of action.
- Predictable and almost complete bioavailability.
- Bypasses the gastrointestinal tract, avoiding issues associated with oral drug administration.
- Reliable route for drug administration in critically ill and comatose patients.
Disadvantages:
- Injections can be painful.
- Patient compliance can be a challenge.
- Limitations exist for the delivery of protein products, particularly those requiring sustained levels.

This involves the injection of drugs into the subcutaneous fatty tissue layer.
Suitable for self-administration, as seen in insulin injections for diabetes management.
Factors influencing drug delivery via the subcutaneous route:
- Molecular size: Larger molecules have slower absorption rates than smaller ones.
- Viscosity: High viscosity can impede drug diffusion into body fluids.
- Anatomical characteristics: Vascularity and the amount of fatty tissue at the injection site impact absorption rate.
Subcutaneous injections generally have a slower onset of action compared to intramuscular or intravenous injections.
Absorption rate can be enhanced using hyaluronidase, an enzyme that promotes tissue breakdown.
Disadvantages of subcutaneous injections:
- Difficult to control absorption rate.
- Local complications like irritation and pain at the injection site can occur.
- Frequent site changes are necessary to avoid drug accumulation and potential tissue damage.
Self-administration systems are available, including syringes, pre-filled syringes, autoinjectors, pen pumps, and needle-less injectors.
Remains a predictable and controllable route for peptides and macromolecules.

Injections given deep into skeletal muscles, commonly the deltoids or gluteal muscles.
Offer a faster onset of action than subcutaneous injections but slower than intravenous injections.
Absorption is diffusion-controlled and faster due to the high vascularity of muscle tissue.
Absorption rate is influenced by various factors, including:
- Physicochemical properties of the injected solution.
- Physiological variables like muscle blood circulation and muscular activity.
Disadvantages:
- Pain at the injection site.
- Limited injection volume due to muscle mass constraints.
- Potential for peptide degradation at the injection site.
- Complications include peripheral nerve injury, hematoma formation, and abscess development.
- Accidental puncture of a blood vessel can introduce the drug directly into the bloodstream.
A range of dosage forms are available for this route, including emulsions, suspensions, and reconstituted powders.
Undissolved drug products tend to result in slower, more gradual absorption with longer-lasting effects.
Intramuscularly administered drugs often form a depot in the muscle mass from which the drug is gradually absorbed.
Peak drug concentrations typically occur between 1 and 2 hours after injection.
Factors affecting drug release from the depot:
- Depot compactness: Less compact depots have faster release rates.
- Drug concentration and particle size.
- Solvent nature.
- Physical form of the product.
- Product flow characteristics.
- Injection volume.

Involves injection of an aqueous solution into a superficial vein or continuous infusion via a needle or catheter placed in a vein.
Essential for some drugs and preferred in emergencies due to its rapid onset of action.
Theoretically, no drug is lost, leading to smaller required doses compared to other routes.
Infusion rate control allows for prolonged and continuous administration.
Devices for timed administration of intermittent doses via intravenous catheters are available.
Intravenously administered particles distribute to various organs depending on their size:
- Particles larger than 7 μm are trapped in the lungs.
- Particles smaller than 0.1 μm accumulate in the bone marrow.
- Particles between 0.1 and 7 μm are taken up by the liver and spleen.
- This size-dependent distribution is helpful for targeted drug delivery.
Disadvantages:
- Potential for immune reactions to proteins and peptides.
- Trauma to veins can lead to thrombophlebitis.
- Extravasation of the drug solution into surrounding tissues can cause irritation and necrosis.
- Infections can occur at the catheter insertion site.
- Air embolism is possible due to air entering the intravenous line.
Techniques for modifying drug disposition and metabolism are available by encapsulating drugs within nanovesicles, such as liposomes.

Direct injection into arteries is not a commonly used therapeutic route.
Used for angiography with contrast materials.
Primarily employed for regional chemotherapy of specific organs and limbs, via catheters placed in arteries.
It has been used for treating malignant brain tumors.