Liquid Dosage Forms Flashcards

General Overview of Liquid Dosage Forms

• Definition: Dosage forms are pharmaceutical products involving a mixture of active drug components and nondrug components (excipients). A liquid dosage form (LDF) is a medication intended for administration or consumption in liquid state.

• Preparation Methods:     * Dissolving active drug substances in aqueous or non-aqueous solvents (e.g., alcohol, ether, glycerin).     * Suspending the drug in an appropriate medium.     * Incorporating the drug substance into oil or water phases.

• Advantages of LDF:     * Easier to swallow for patients who have trouble with solid dosage forms.     * Faster absorption rate compared to solids.     * Greater flexibility in dose adjustment.     * Palatability (pleasant taste).     * Ideal for pediatric (children) and geriatric (elderly) populations.

• Disadvantages of LDF:     * Shorter shelf life (less stable) than solid forms.     * Accuracy of measurement can be difficult for the patient.     * Requires special storage conditions.     * Susceptible to microbial contamination.     * Bulky and inconvenient for transport.     * Loss of product possible through container breakage.

• Routes of Administration:     * Topical: Applied to the skin (lotions, suspensions) or mucous membranes (nasal drops, ear drops, eye solutions).     * Oral (p.o.): Suspensions, emulsions, and solutions consumed by mouth.     * Parenteral: Injections, including subcutaneous ($s.c.$), intramuscular ($i.m.$), and intravenous ($i.v.$).

Classification of Liquid Dosage Forms

• Monophasic Liquid Dosage Forms: Homogeneous systems where components are completely dissolved.     * Internal Use: Syrups, Mixtures, Elixirs, Linctuses, Drops, Draughts.     * External Use (Skin): Liniments, Lotions, Collodions, Paints.     * External Use (Mouth/Throat): Gargles, Mouthwashes, Throat paints, Throat sprays.     * External Use (Body Cavities): Eye drops, Nasal drops, Ear drops, Douches, Enemas.

• Biphasic Liquid Dosage Forms: Heterogeneous systems consisting of two phases.     * Emulsion: Liquid-in-liquid dispersion.     * Suspension: Solid-in-liquid dispersion.

Detailed Study of Syrups

• Definition: Concentrated aqueous preparations of sugars (usually sucrose) with or without flavoring and medicinal substances.

• Sucrose Concentration: Syrups contain approximately $60\%$ to $85\%$ sucrose.     * Simple Syrup (I.P.): Contains $667\,g$ sucrose per $1000\,g$ of preparation.     * Self-Preservation: Syrups with a density of $1.313$ or a sucrose content of $65\%$ by weight or more resist bacterial growth due to osmotic effect.

• Types of Syrups:     * Simple Syrup: Water used alone to dissolve sucrose.     * Medicated Syrup: Contains added medicinal substances (e.g., Codeine Phosphate Syrup as a cough suppressant).     * Flavored Syrup: Contains aromatic/pleasant substances; used as a vehicle for prescriptions.

• Preparation Methods:     1. Solution with Heat: Water is heated to $80$ to $85\,^{\circ}C$, sucrose is added. This may cause inversion (hydrolysis of sucrose into dextrose and fructose). Inversion leads to darkening (caramelization).     2. Agitation without Heat: Used for heat-sensitive materials; stainless steel or glass vessels are used.     3. Addition of Sucrose to Liquid Medicament: Sucrose is added directly to medicated liquids (like fluid extracts).     4. Percolation: Water or medicated liquids are passed slowly through a column of crystalline sucrose.

• Preservation and Storage:     * Stored at temperatures not exceeding $25\,^{\circ}C$.     * Preservatives used: Glycerin, methylparaben, benzoic acid, or sodium benzoate.

• Substitutes for Sucrose:     * Dextrose: Used with strong acids to avoid discoloration from inversion; forms saturated solution at $70\%\,w/v$. Requires preservatives like glycerin ($30\%$ to $45\%\,v/v$).     * Artificial/Non-Nutritive Syrups: For diabetic patients. Examples include "Diabetic Simple Syrup" containing cyclamate or saccharin. Aspartame is approximately $200$ times sweeter than sucrose.     * Sorbitol-Based: $70\%\,w/w$ aqueous solution; non-cariogenic (no dental caries) and chemically stable.

Detailed Study of Elixirs

• Definition: Clear, sweetened, hydroalcoholic solutions for oral use.

• Alcohol Content: Usually ranges from $5\%$ to $40\%$.

• Self-Preservative Properties: Elixirs containing at least $10\%$ to $12\%$ alcohol do not require additional antimicrobial preservatives.

• Types:     1. Non-Medicated: Used as vehicles (e.g., Aromatic Elixir NF, Isoalcoholic Elixir).     2. Medicated: Contains therapeutic agents (e.g., Phenobarbital Elixir, Digoxin Elixir, Piperazine citrate elixir).

• Advantages: Stable, easy to prepare, can dissolve both water-soluble and alcohol-soluble ingredients.

• Disadvantages: Harder to mask the taste of drugs compared to syrups; alcohol content is unsuitable for children; higher cost due to excise processing.

Oral Cavity and Throat Liquids

• Mouthwashes: Aqueous solutions used to clean/deodorize the buccal cavity. Often contain antiseptics (phenol derivatives) and astringents (Zinc Chloride).     * Classification: Fluoride (strengthens teeth), Cosmetic (masks halitosis), Antiseptic (Chlorhexidine gluconate).

• Gargles: Aqueous or hydroalcoholic solutions for throat infections. Typically dispensed in concentrated form to be diluted with warm water.

• Throat Paints: Viscous liquid preparations using glycerin as a vehicle to ensure the medication adheres to the mucous membrane longer.     * Compound Iodine Paint (Mandl's Paint): Contains Potassium Iodide ($25\,g$), Iodine ($12.5\,g$), Alcohol $90\%$ ($40\,ml$), Water ($25\,ml$), Peppermint oil ($4\,ml$), and Glycerol (up to $1000\,ml$).

• Linctuses: Viscous oral liquids for cough relief (e.g., Codeine Linctus).

Liquids Instilled into Body Cavities

• Douches: Solutions directed into body cavities (eye, ear, nose, or vagina) for cleansing or antiseptic purposes.

• Enemas: Rectal injections used for bowel evacuation, systemic absorption (retention enemas), or local disease treatment. Retention volume is small (approx. $30\,ml$).

• Nasal Solutions: Usually aqueous drops or sprays. Nasal decongestants should only be used for $3$ to $5$ days to avoid chronic edema (rhinitis medicamentosa).

• Otic Solutions: Ear drops for local anesthesia, inflammation, or cerumen (wax) removal. Glycerin or propylene glycol is often used as a vehicle.

• Ophthalmic Preparations: Must be sterile and free from foreign particles. Includes eye drops, eye lotions (irrigation), eye ointments, and ophthalmic inserts.     * Lachrymal Fluid pH: Approximately $7.2$ to $7.4$.     * Tonicity: Ideally equivalent to $0.9\%\,w/v\,NaCl$. Eyes tolerate a range of $0.7$ to $1.5\%$.

Biphasic Liquid Dosage Forms: Emulsions

• Definition: A thermodynamically unstable system consisting of at least two immiscible liquid phases, where one is dispersed as globules ($0.01$ to $50\,\mu m$) within the other and stabilized by an emulsifying agent.

• Types:     * Oil in Water (O/W): Oil droplets in water transition (convenient for oral use).     * Water in Oil (W/O): Water droplets in oil.     * Multiple Emulsions: e.g., Water in Oil in Water ($W/O/W$).

• Identification Tests:     * Dye Test: Water-soluble dyes (Amaranth) color the O/W phase; oil-soluble (Scarlet) color the W/O phase.     * Dilution Test: Emulsions can be diluted only with their continuous phase.     * Electrical Conductivity: O/W emulsions conduct electricity; W/O do not.     * Fluorescence Test: Many oils fluoresce under UV light; W/O shows total fluorescence, O/W shows spotty patterns.

• Hydrophile-Lipophile Balance (HLB): A scale from $1$ to $18$ identifying surfactant characteristics.     * $1$ to $3$: Anti-foaming agents.     * $3$ to $6$: W/O emulsifying agents (e.g., Spans).     * $8$ to $18$: O/W emulsifying agents (e.g., Tweens).     * $13$ to $15$: Detergents.

• Stabilities Issues: Creaming (reversible separation), Coalescence/Cracking (irreversible), and Phase Inversion.

Biphasic Liquid Dosage Forms: Suspensions

• Definition: A coarse dispersion where insoluble solid particles (internal phase) are distributed throughout a liquid (external phase).

• Particle Size: Typically $0.5$ to $5\,\mu m$.

• Stokes' Equation for Sedimentation Velocity ($v_{sed}$):     * $v_{sed} = \frac{d^2(\rho_s - \rho_o)g}{18\eta_o}$     * Where $d$ = particle diameter, $\rho_s$ = density of dispersed phase, $\rho_o$ = density of medium, $g$ = gravity, $\eta_o$ = viscosity of medium.

• Sedimentation Volume ($F$):     * $F = \frac{V_u}{V_0}$     * Where $V_u$ = ultimate volume of sediment, $V_0$ = original volume.

• Classification based on Electrokinetic Nature:     * Flocculated: Particles form loose aggregates (flocs). Rapid sedimentation, but sediment is easy to re-disperse. Zeta potential is between $-20$ and $+20\,mV$.     * Deflocculated: Particles remain as individual units. Slow sedimentation, but forms a hard "cake" (claying) that is difficult to re-disperse.

• Zeta Potential: The difference in potential between the surface of the tightly bound layer (shear plane) and the electro-neutral region.

• Innovation: Nanosuspensions: Biphasic systems with pure drug particles sized less than $1\,\mu m$ ($1000\,nm$).

Dosage forms are pharmaceutical products with active and inactive components. Liquid dosage forms (LDF) are medications meant for liquid administration. Preparation Methods include dissolving the drug, suspending it, or incorporating it into oil or water. Advantages are better swallowing ability, faster absorption, flexible dosing, palatability, and suitability for children and the elderly. Disadvantages include shorter shelf life, measurement difficulty, special storage needs, microbial contamination, bulkiness, and breakage risk. Routes of Administration: Topical (lotions, drops), Oral (suspensions, solutions), and Parenteral (injections). Classification consists of Monophasic (homogeneous, e.g., syrups, elixirs) and Biphasic forms (heterogeneous, e.g., emulsions, suspensions).