Parenteral Administration

• Parenteral route refers to any route of administration that does not involve drug absorption via the gastrointestinal tract.
• Drugs are introduced directly across the body's barrier defenses into the systemic circulation or other vascular tissue through the parenteral route.
• Parenteral administration provides the most control over the actual dose of drug delivered to the body.
• Parenteral administration can be performed through bolus injection (small volumes), infusion (large volumes), or implant, aiming for rapid systemic effects.
• Useful locally on a given region, tissue, or organ by directly injecting the drug to achieve concentrated effects or minimize systemic adverse effects, such as intra-articular injection.
• Benefits to choosing a parenteral route over the oral route include better bioavailability, bypassing issues with oral medications, the need for immediate effect, or to control the rate of absorption and duration.
• Four main parenteral routes: Intravenous (IV), Intramuscular (IM), Subcutaneous (SC), and Intradermal (ID).

Intravenous Route (IV)

• Requires close monitoring.
• Bolus injection results in a very high concentration of drug initially in the right chambers of the heart and then the lungs.
• The peak concentration from the administered drug relies on the rate of injection.
• Can be performed in any superficial vein, but forearms or wrists are common.
• A central IV route with a catheter in the superior vena cava might be necessary.
• Central venous catheters (CVCs) facilitate rapid drug and fluid administration and allow for monitoring of central venous pressure in acute care settings or long-term in cancer care.
• Advantages include 100% bioavailability, a rapid action for emergency situations, and the ability to titrate the dose for drugs with a short duration of action.
• Very large volumes of infusion are possible and drugs can be delivered at a uniform rate to maintain a constant plasma level, like dopamine infusion in cardiogenic shock.
• Disadvantages include pain at the injection site, rapid allergic or adverse effects, extravasation leading to tissue damage, severe effects involving organs, local irritation from phlebitis, and a high probability of bacterial contamination requiring strict aseptic conditions.
• IV infusion allows for a slower infusion of drugs with less severe peak plasma concentration, useful for antiarrhythmic drugs (amiodarone) and antibiotics (vancomycin).

Intramuscular Route

• A common route for parenteral injections.
• Involves depositing medication deep into the muscle mass for rapid absorption via a rich blood supply.
• Absorption is more rapid than the oral route.
• Mild irritants, depot injections, soluble substances, and suspensions can be administered in this route.
• Effectiveness depends on muscle blood flow at the time of injection.
• Disadvantages include being not accessible for self-administration, painful, and irremovable if any effect occurs with depot preparation.

Subcutaneous Route (SC)

• Involves injecting a drug into the loose connective tissue between the dermis of the skin and the muscle layer.
• Drugs administered via this route must have low oral bioavailability.
• Absorbed well from subcutaneous fat, and may be suitable for self-injection, especially insulin and heparin.
• Provides a slow and constant effect.
• Disadvantages include potential irritation and sloughing of skin, suitability only for nonirritant drugs, slow absorption making it unsuitable for emergencies, and potential lipoatrophy and impaired absorption from repeated injections.

Intradermal (ID)

• Used for diagnostic tests such as tuberculin and allergy tests.
• Drug injected into the dermis and the more vascular layer of the skin.

Inhalation/nasal preparations

• Drugs are delivered via nasal mucosa or lung epithelium.
• Drugs rapidly pass across the large surface area of mucous membranes.
• Can use aerosol inhalations like salbutamol, and some anesthetics.