10 Questions
What is the main factor affecting the dissolution rate of non-water soluble drugs?
Surface area of drug particles in contact with gastrointestinal fluids
Which parameter is described by the Noyes Whitney Dissolution Model?
Concentration of drug in diffusion layer
What does the pH range 1-3.5 in gastric fluid indicate?
Secretion of pepsin
What can affect the bioavailability of a drug?
Dissolution rate
Which step is affected by the solubility of a drug in water?
$Dissolution$
Which method is not discussed in the text for drug dissolution and absorption?
Filtration Method
Why are weak acids more easily absorbed in the stomach?
Due to the predominance of the unionized form (HA) at low pH
What does the pH partition model consider the GI membrane as?
A lipid barrier
Where are weak bases best absorbed according to the text?
In regions of higher pH, such as the small intestine
What is used to determine a drug's ability to partition between water and cellular membranes?
Chromatography
Study Notes
- The text discusses various methods for drug dissolution and absorption, including the Beaker Method, Stirrer Method, Rotating Disk Method, Rotating Basket Method, and Paddle Method.
- The text explains that weak acids are more easily absorbed in the stomach due to the predominance of the unionized form (HA) at low pH, whereas weak bases are not easily absorbed due to the presence of the charged form (BH+).
- The text introduces the pH partition model, which considers the GI membrane as a lipid barrier that only allows the absorption of unionized molecules.
- Weak acids with a pKa of around 3.0 are optimally absorbed in the stomach, while weak bases are best absorbed in regions of higher pH, such as the small intestine.
- The text discusses the importance of the octanol-water partition coefficient (P) in determining a drug's ability to partition between water and cellular membranes.
- The text describes how the drug solubility in a mixed solvent (water and a co-solvent) can be calculated using the equation log S = m x + c, where x is the volume fraction of the co-solvent.
- The text mentions that metal ions can catalyze the oxidation of drugs and that this effect can be prevented by adding chelating agents like disodium edetate.
- The text lists some common antioxidants used in pharmaceuticals, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and nordihydroguariaretic acid (NDGA).
- The text provides references and further reading for those interested in learning more about the topics discussed in the text.
Test your knowledge on the importance of drug solutions for absorption and action in the body. Understand the process from drug dissolution in the gastrointestinal tract to absorption into the bloodstream.
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