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Facteurs affectant la dissolution : taille des particules et surface effective
La cinétique de dissolution, un aspect essentiel de l'administration orale de médicaments, est fortement influencée par la taille des particules du mé…
Rappelez-vous l'équation de Noyes-Whitney, qui suggère une corrélation directe entre le taux de dissolution et la surface d'un médicament.
Lasurface d'un médicament solide est inversement proportionnelle à la taille de ses particules.
La taille plus petite des particules d'un médicament augmente sa surface effective et améliore l'interaction médicament-solvant, ce qui permet une dissolution rapide du médicament.
Certains médicaments, tels que la griséofulvine, la nitrofurantoïne et les stéroïdes, tels que l’hydrocortisone, présentent une mauvaise absorption orale en raison de leur faible solubilité aqueuse.
Ces médicaments sont micronisés pour réduire la taille des particules. Cela augmente la surface du médicament, améliore le taux de dissolution et augmente l'absorption orale tout en diminuant la fréquence de dosage de certains médicaments.
La micronisation hydrophobe des médicaments peut bénéficier de l’ajout de tensioactifs, comme le polysorbate 80, qui favorise le mouillage et la solubilité en abaissant la tension superficielle entre les ingrédients.
Parfois, la micronisation ne résout pas les problèmes de biodisponibilité liés à la solubilité. Ainsi, la nanodimensionnement, une technique alternative, est utilisée pour produire des particules de médicament de taille nanométrique, qui peuvent être administrées par voie orale ou injectées par voie intraveineuse sous forme de nanosuspensions.
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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.