Podcast
Questions and Answers
Which statement is true regarding the solubility of weak acids and bases?
Which statement is true regarding the solubility of weak acids and bases?
What is the ideal range of dielectric constant for a suitable cosolvent blend?
What is the ideal range of dielectric constant for a suitable cosolvent blend?
What is the purpose of using the Henderson-Hasselbalch equation?
What is the purpose of using the Henderson-Hasselbalch equation?
Which of the following is an essential factor when selecting a cosolvent?
Which of the following is an essential factor when selecting a cosolvent?
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What can occur if excessive amounts of surfactant are used in a drug formulation?
What can occur if excessive amounts of surfactant are used in a drug formulation?
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What is the effect of temperature on the solubilization of a drug?
What is the effect of temperature on the solubilization of a drug?
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In the process of cosolvency, what is necessary for a solvent to be effective?
In the process of cosolvency, what is necessary for a solvent to be effective?
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What characterizes surface-active agents (SAAs) in drug formulations?
What characterizes surface-active agents (SAAs) in drug formulations?
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Which of the following statements is true regarding weak electrolyte solubility?
Which of the following statements is true regarding weak electrolyte solubility?
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Which of the following is a common method for improving aqueous solubility?
Which of the following is a common method for improving aqueous solubility?
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Study Notes
Approaches to Aqueous Solubility Improvement
- Strongly ionized materials are often freely soluble in water.
- Weak acids and bases dissolve better at suitable pH values.
- The concentration of a material should not be close to its solubility limit (avoiding cooling or evaporation).
Cosolvency
- Increasing solubility of weak electrolytes or nonpolar compounds in water can be achieved by adding a second solvent.
- The second solvent should be miscible with water and dissolve the compound.
- This mixed solvent system often leads to higher solubility than predicted based on individual solvent solubility.
- The choice of cosolvent is crucial due to potential toxicity or irritation concerns.
- Ideal cosolvent blends have dielectric constants between 25 and 80.
- Common examples include water/ethanol blends, or combinations with sorbitol, glycerol, propylene glycol and syrup.
- Some specific examples are co-trimoxazole (PG/water) and paracetamol (alcohol/PG/syrup/water).
pH Control
- Many drugs are either weak acids or bases.
- The Henderson-Hasselbalch equation relates pH, pKa, and the solubility of unionized species.
- Lowering pH favors the solubility of weak bases.
- Increasing pH favors the solubility of weak acids.
- Choosing the optimal pH is crucial, as it must not interfere with other product requirements (like chemical stability).
Solubilization
- Adding a surface-active agent (SAA) can enhance solubility (SAA is non-toxic and non-irritating).
- SAAs form micelles, ranging from simple spheres to complex liposomes or liquid crystals.
- Nonpolar molecules dissolve within the lipophilic hydrocarbon section of the micelle in aqueous solutions.
- The amount of SAA must be carefully controlled to avoid unwanted cost and toxicity issues, and excessively high amounts can reduce drug bioavailability.
- The formulation should not have a phase transition boundary close to storage temperature.
- Generally, solubilization increases with increasing temperature.
- Examples include solubilizing fat-soluble vitamins (e.g., phytonadione using polysorbates), or iodine and macrogol ethers for creating iodophores.
- Another example includes phenolic compounds (like cresol/chloroxylenol) with soaps forming micelles; Lysol is one case in which 50% cresol is solubilized in an aqueous system using potassium soaps of oleic, linoleic and linolenic acids.
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Description
This quiz focuses on methods for enhancing aqueous solubility, including the effects of ionization, pH adjustments for weak acids and bases, and the role of cosolvency. Understand how to select appropriate cosolvents and the importance of solvent systems in achieving higher solubility. Test your knowledge on the principles behind these solubility strategies.
