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Factores que afectan la disolución: tamaño de partícula y área superficial efectiva
La cinética de disolución, un aspecto esencial de la administración oral de fármacos, está significativamente influenciada por el tamaño de las partíc…
Recordemos la ecuación de Noyes-Whitney, que sugiere una correlación directa entre la velocidad de disolución y el área de superficie de un medicamento.
El área superficial de un fármaco sólido está inversamente relacionada con su tamaño de partícula.
El tamaño de partícula más pequeño de un fármaco aumenta su superficie efectiva y mejora la interacción fármaco-disolvente, lo que conduce a una rápida disolución del fármaco.
Ciertos fármacos, como la griseofulvina, la nitrofurantoína y los esteroides, como la hidrocortisona, presentan una mala absorción oral debido a la baja solubilidad acuosa.
Dichos medicamentos se micronizan para reducir el tamaño de las partículas. Esto aumenta el área de superficie del fármaco, mejorando la velocidad de disolución y elevando la absorción oral, al tiempo que disminuye la frecuencia de dosificación en ciertos fármacos.
La micronización hidrofóbica de fármacos puede beneficiarse de la adición de tensioactivos, como el polisorbato 80, que favorece la humectación y la solubilidad al reducir la tensión superficial entre los ingredientes.
A veces, la micronización no resuelve los problemas de biodisponibilidad relacionados con la solubilidad. Por lo tanto, el nanodimensionamiento, una técnica alternativa, se utiliza para producir partículas de fármaco en tamaño nanométrico, que pueden administrarse por vía oral o inyectarse por vía intravenosa como nanosuspensiones.
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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.