Routes of Drug Administration and Parenteral Formulations

Comprehensive vocabulary flashcards covering enteral, parenteral, and topical routes of drug administration, ocular and skin anatomy, pharmacopoeial quality requirements, and methods of sterilization.

Route of Administration

The path by which a drug, fluid, or any substance is brought into contact with the human body.

Enteral Administration

Drug delivery routes that involve the gastrointestinal tract (stomach and small intestines), specifically encompassing oral, sublingual, and rectal methods.

Parenteral Administration

Drug delivery methods that bypass the gastrointestinal tract and mucous/skin membranes by directly injecting into the body (such as intravenous, intramuscular, and subcutaneous injections).

First-Pass Effect

The hepatic metabolism of a pharmacological agent following absorption from the gastrointestinal tract into the portal circulation, which reduces the concentration of active drug reaching systemic circulation.

Sublingual Route

An enteral route where the dosage form is placed under the tongue, allowing rapid absorption directly into the sublingual veins and blood circulation while bypassing hepatic first-pass metabolism.

Buccal Route

An enteral route where the dosage form is placed in the buccal pouch between the gums and the inner cheek lining to be absorbed directly across the buccal mucosa.

Nifedipine (Sublingual)

A calcium channel blocker administered in $5\,\text{mg}$ and $10\,\text{mg}$ sublingual doses that rapidly reaches circulation to reduce blood pressure, serving as a drug of choice for hypertensive emergencies.

Parenteral Injection Angles

The standard angles of needle insertion for parenteral administration: intramuscular at $90^\circ$, subcutaneous at $45^\circ$, intravenous at $15^\circ-20^\circ$, and intradermal at $10^\circ-15^\circ$.

Intravenous (IV) Injection

A parenteral administration route delivering drugs directly into the bloodstream at a $15^\circ-20^\circ$ angle, offering immediate onset of action, $100\%$ bioavailability, and no requirement for drug absorption.

Intramuscular (IM) Injection

A parenteral route where medication is injected into muscle (such as buttock, thigh, or shoulder) at a $90^\circ$ angle, typically using a $22$- to $25$-gauge needle ($\frac{1}{2}$ to $1\,\text{inch}$) with a maximum volume limit of $4\,\text{mL}$.

Intradermal (ID) Injection

A parenteral injection administered at a $10^\circ-15^\circ$ angle into the capillary-rich layer just beneath the epidermis and above the dermis, typically using volumes up to $0.5\,\text{mL}$ for slow absorption (e.g., BCG vaccine, allergen testing).

Subcutaneous (SC) Injection

A parenteral route where medication is injected into loose connective and fatty tissues beneath the dermis at a $45^\circ$ angle, utilizing a $25$- or $26$-gauge needle ($\frac{3}{8}$ to $\frac{5}{8}\,\text{inch}$) for volumes of $1-2\,\text{mL}$ (e.g., insulin).

Dermal Penetration Pathways (DDDS vs. TDDS)

The comparison between transepidermal drug delivery (DDDS), where drugs penetrate the stratum corneum for local action in the epidermis/dermis, and transdermal drug delivery (TDDS), where drugs pass into capillary vessels and fatty tissue for systemic distribution.

Transdermal Drug Delivery System (TDDS)

A non-invasive pharmaceutical delivery method that diffuses active substances from the surface of intact skin through tissue layers into systemic circulation for therapeutic effect.

Topical Administration

The direct application of medication—most often in semisolid forms such as creams, ointments, gels, or pastes—onto skin or mucous membranes (e.g., eye, nose, vagina, rectum) for localized effect.

Aqueous Humour

A transparent, watery, plasma-like fluid secreted by the ciliary processes at a rate of $2$ to $2.5\,\mu\text{L\,min}^{-1}$ into the posterior chamber of the anterior cavity, draining through the trabecular meshwork to nourish avascular tissues and maintain ocular pressure.

Intraocular Pressure (IOP)

The positive fluid pressure exerted by aqueous humour circulation that stabilizes the eyeball and ensures correct alignment of optical structures; normal levels remain below $21\,\text{mmHg}$.

Vitreous Humour

An immobile, colorless, gelatinous mass composed of $98\%$ water, type II collagen, sugars, and salts that fills the posterior segment between the lens and retina without blood vessels.

Corneal Structural Layers

The five distinct anatomical layers of the cornea: epithelium (pavement epithelium), Bowman's membrane, stroma, Descemet's membrane, and endothelium.

Corneal Epithelium

A hydrophobic tissue comprising $5-6$ cell layers ($50-100\,\mu\text{m}$ thick, representing $10\%$ of corneal thickness) that constitutes $90\%$ of the barrier to hydrophilic drugs and $10\%$ to hydrophobic drugs.

Bowman's Membrane

An $8-14\,\mu\text{m}$ thick homogeneous sheet in the cornea that does not regenerate if destroyed and does not act as a barrier to drug absorption.

Corneal Stroma

Modified connective tissue making up $90\%$ of corneal thickness ($70-80\%$ water by wet weight; $20-25\%$ collagen by dry weight) that serves as the principal barrier to hydrophobic drug permeation.

Pyrogens

Fever-inducing bacterial toxins (including exotoxins secreted by live bacteria and endotoxins released from lysed bacteria) that must be absent from parenteral preparations.

Bacterial Endotoxins

Pyrogenic lipopolysaccharide components derived from microbial cell walls during lysis; they are not fully removed by filtration or steam sterilization but can be degraded by dry heat at $250\,^\circ\text{C}$.

Steam (under pressure) Sterilization

The most universally applied terminal sterilization method (autoclaving), utilizing steam under pressure with a standard holding cycle of $15\,\text{min}$ at $121\,^\circ\text{C}$ and $15\,\text{psi}$ ($103\,\text{kPa}$).

Dry Heat Sterilization

A non-toxic terminal sterilization method using circulated heated air at atmospheric pressure (e.g., $180\,^\circ\text{C}$ for $0.5\,\text{hr}$ or $160\,^\circ\text{C}$ for $2\,\text{hr}$), suitable for non-aqueous oily injections, dry powders, and depyrogenation ($250\,^\circ\text{C}$).

Radiation Sterilization

A terminal 'cold sterilization' method using ionizing particulate ($\beta$-rays) or electromagnetic ($\gamma$-rays) radiation to destroy microbial DNA; commonly used for disposable medical devices like needles and syringes.

Ethylene Oxide Sterilization

A gaseous terminal sterilization process recommended for thermolabile materials (such as plastic containers, syringes, catheters, and dialysis tubing) that cannot withstand high autoclave temperatures.

Sterilization by Filtration

A non-terminal sterilization method that passes heat-sensitive solutions (biologicals, ophthalmic drops) through a $0.2\,\mu\text{m}$ membrane filter to remove viable bacteria and fungi (viruses are not removed).

Ophthalmic Ointment

A sterile, semisolid formulation prepared under aseptic conditions for ocular application, offering longer corneal contact time than eye drop solutions but causing temporary visual blurring.