3.23
影响溶解的因素：颗粒大小和有效表面积
溶解动力学是口服药物输送的一个重要方面，它受药物粒径的显著影响。根据 Noyes-Whitney 溶解模型，溶解速率与药物的表面积直接相关。表面积越大，药物在水中的溶解度越高，从而导致药物溶解速率更快。减小粒径会增加有效表面积，从而增强溶解过程。微粉化和纳米化可用于减小药物产品的粒径。
微粉化可减小…
回顾Noyes-Whitney方程，该方程表明溶解速率与药物的表面积之间存在直接相关性。
固体药物的表面积与其粒径成反比。
药物的粒径越小，其有效表面积越大，可增强药物与溶剂的相互作用，从而加快药物的溶出速度。
某些药物，例如灰黄霉素、呋喃妥因以及皮质类固醇如氢化可的松，由于水溶性低，口服吸收效果较差。
此类药物经过微粉化处理以减小颗粒尺寸。这会增加药物的表面积，提高其溶出速率，增强口服吸收，并在某些药物中减少给药频率。
疏水性药物微粉化过程中可受益于添加表面活性剂（如吐温80），后者通过降低组分间的表面张力，促进润湿性和溶解性。
有时， 微粉化无法解决与溶解度相关的生物利用度问题。因此，采用另一种技术——纳米化，制备出纳米级药物颗粒，可作为纳米混悬液口服或静脉注射给药。
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Q1: How does the Noyes-Whitney equation relate particle size to drug dissolution?
The Noyes-Whitney equation establishes a direct correlation between dissolution rate and a drug's surface area. Since surface area is inversely related to particle size, smaller particles increase effective surface area and enhance drug-solvent interaction, leading to rapid dissolution. This relationship is fundamental to understanding how particle size modifications improve drug bioavailability.
Q2: Why are poorly soluble drugs like griseofulvin and hydrocortisone micronized?
Drugs with low aqueous solubility, such as griseofulvin, nitrofurantoin, and hydrocortisone, are micronized to reduce particle size and increase effective surface area. This enhancement improves the dissolution rate and elevates oral absorption while potentially decreasing dosing frequency. Micronization is a practical pharmaceutical strategy to overcome solubility-related bioavailability limitations.
Q3: What role do surfactants play in improving hydrophobic drug dissolution?
Surfactants like polysorbate 80 promote wetting and solubility of hydrophobic drugs by lowering surface tension between ingredients. When added to micronized formulations, surfactants enhance drug-solvent interaction and facilitate faster dissolution. This combination of micronization and surfactant addition addresses solubility challenges in poorly water-soluble pharmaceutical compounds.
Q4: When is nanosizing used instead of micronization for drug formulation?
Nanosizing is employed when micronization fails to resolve solubility-related bioavailability issues. This technique produces drug particles in nanometer size, which can be administered orally or injected intravenously as nanosuspensions. Nanosizing enhances dissolution, absorption, and therapeutic effectiveness for difficult-to-deliver drugs that do not respond adequately to conventional micronization.
Q5: What happens to nanosized particles after intravenous administration?
Nanosized particles may aggregate in the bloodstream and be sequestered by the reticuloendothelial system after IV administration, preventing immediate dissolution. However, they eventually dissolve and permeate into the cytoplasm, contributing to systemic drug exposure in a pseudo-extended-release pharmacokinetic profile. This delayed dissolution pattern can provide sustained therapeutic effects.
Q6: How does reducing particle size increase a drug's effective surface area?
A solid drug's surface area is inversely related to its particle size. When particle size decreases, the total surface area available for drug-solvent contact increases proportionally. This larger effective surface area maximizes molecular interactions at the solid-liquid interface, accelerating the dissolution process and improving the rate at which drug molecules enter solution.
Q7: What pharmaceutical parameters can be optimized alongside particle size reduction?
Beyond particle size reduction, excipients such as disintegrants and surfactants can be added to further boost dissolution by promoting tablet disintegration and wetting. These pharmaceutical parameters work synergistically with micronization or nanosizing to overcome solubility barriers. Strategic excipient selection complements particle size modifications to maximize oral bioavailability and therapeutic outcomes.