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Questions and Answers
Which solvent is most commonly preferred for oral, ophthalmic, or parenteral pharmaceutical solutions?
Which solvent is most commonly preferred for oral, ophthalmic, or parenteral pharmaceutical solutions?
What is the role of excipients in liquid pharmaceutical preparations?
What is the role of excipients in liquid pharmaceutical preparations?
Which of the following is not a type of aqueous pharmaceutical solution?
Which of the following is not a type of aqueous pharmaceutical solution?
What characteristic makes water an ideal vehicle for pharmaceutical solutions?
What characteristic makes water an ideal vehicle for pharmaceutical solutions?
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Which of the following solvents is considered too toxic for oral pharmaceutical preparations?
Which of the following solvents is considered too toxic for oral pharmaceutical preparations?
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What is the primary purpose of sterile water for injection?
What is the primary purpose of sterile water for injection?
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Which type of water contains antimicrobial agents?
Which type of water contains antimicrobial agents?
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Which of the following statements about purified water is accurate?
Which of the following statements about purified water is accurate?
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What type of alcohol is commonly used in pharmacy as a solvent?
What type of alcohol is commonly used in pharmacy as a solvent?
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What is the role of surface-active agents in pharmaceutical formulations?
What is the role of surface-active agents in pharmaceutical formulations?
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Study Notes
Solubility and Dissolution
- Solubility is defined as the concentration of a solute in a saturated solution at a specific temperature.
- Solubility of the API, particularly in the context of pharmaceutical preparations, is often a crucial factor for preparing aqueous solutions.
- For drugs with poor water solubility, a mix of water and a water-miscible solvent (such as alcohol, glycerol, polyethylene glycol, or propylene glycol) is typically used.
- A drug must be in solution before it can be absorbed by the body and exert its intended biological effect.
Factors Affecting Solubility
- Physicochemical Properties of the Therapeutic Agent: Includes molecular weight, volume, density, number of hydrogen bonds, and particle size.
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Solubility in Water:
- High Solubility: The pharmaceutical drug can be readily incorporated into a vehicle and formulated as an oral solution.
- Moderate Solubility: Co-solvents may be needed to enhance solubility if the desired concentration exceeds the inherent solubility of the drug.
- Low Solubility: Suspensions are the preferred formulation if co-solvents or surfactants are not viable options due to their detrimental effects on the drug’s safety.
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Dissolution Rate: The Noyes-Whitney Equation describes the rate of dissolution:
dc/ dt = K * S * (Cs - Ct)- Where
dc/ dtrepresents the rate of dissolution,Kis the dissolution rate constant,Sis the surface area of the dissolving solid,Csis the concentration of the drug near the dissolving particle (solubility), andCtis the concentration of the drug in the bulk fluid. - The dissolution process involves several steps: initial mechanical lag, wetting, penetration of the dissolution medium, disintegration, deaggregation, and dissolution of individual particles.
- Wetting is often a critical factor in the dissolution rate, as it governs the liquid's access to the solid surface.
- Surfactants can improve wettability, which in turn enhances dissolution.
- Air bubbles trapped in pores act as barriers, hindering dissolution.
- Where
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Factors Affecting Dissolution Rate:
- Surface Area/Particle Size: A larger surface area promotes faster dissolution.
- Temperature: Higher temperatures generally result in faster dissolution rates.
- Agitation: Stirring or shaking speeds up the dissolution process.
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Saturation:
- Unsaturated Solution: Can dissolve more solute.
- Saturated Solution: Contains the maximum amount of solute that can be dissolved at a given temperature.
- Supersaturated Solution: Contains more dissolved solute than a saturated solution (achieved at a higher temperature).
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Dissolution vs. Solubility:
- Dissolution is a kinetic process, describing the rate at which a substance dissolves.
- Solubility is a dynamic equilibrium state, where the rate of dissolution equals the rate of precipitation.
Solubility Expression
- Quantity per Quantity: mg/mL, g/L
- Percentage: % w/w (weight/weight), % w/v (weight/volume), % v/v (volume/volume)
- Molarity: mol/L (of solution)
- Molality: mol/kg (of solvent)
- Mole Fraction
- Normality
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Description
This quiz explores the fundamental concepts of solubility and dissolution in pharmaceuticals. Understand the physicochemical properties that affect solubility and learn about the importance of solubility for drug absorption and formulation. Ideal for students in pharmaceutical sciences.
