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Teorias de dissolução: o Modelo de Danckwerts e o modelo de barreira interfacial
Várias teorias de dissolução fornecem uma visão sobre os fatores que influenciam a taxa de dissolução. O Modelo de Danckwerts sugere que a turbulência…
Várias teorias de dissolução elucidam os fatores que afetam a taxa de dissolução.
O modelo de Danckwert postula que o meio de dissolução mostra turbulência na interface sólido-líquido em vez de uma camada estagnada.
O solvente agitado contendo pacotes macroscópicos se move para a interface por meio de correntes parasitas, absorvendo e entregando o medicamento à solução a granel.
O reabastecimento regular de pacotes de solvente mantém o gradiente de concentração.
Aqui, o transporte do medicamento para a solução a granel é a etapa limitante da taxa.
O modelo de barreira interfacial considera uma partícula de droga como um cristal com barreiras interfaciais distintas em cada face. Uma concentração intermediária, uma função de solubilidade, existe na interface devido à solvatação.
A taxa de dissolução é calculada por unidade de área e depende da constante de transporte interfacial e das concentrações na camada estática e na solução a granel.
A taxa de solubilização do medicamento na camada estática é a etapa limitante da taxa.
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Q1: What is Danckwerts' model of dissolution?
Danckwerts' model proposes that the dissolution medium exhibits turbulence at the solid-liquid interface rather than a stagnant layer. Macroscopic packets of agitated solvent move to the interface via eddy currents, absorbing and delivering the drug to the bulk solution. Regular replenishment of solvent packets maintains the concentration gradient, with drug transport to the bulk solution serving as the rate-limiting step.
Q2: How does the interfacial barrier model explain drug dissolution?
The interfacial barrier model describes a drug particle as a crystal with distinct interfacial barriers on each face. Solvation at the interface creates an intermediate concentration, a solubility function. The dissolution rate is calculated per unit area based on the interfacial transport constant and concentrations in the static layer and bulk solution, with solubilization rate in the static layer as the rate-limiting step.
Q3: What is the rate-limiting step in Danckwerts' model?
In Danckwerts' model, the rate-limiting step is the transport of the drug to the bulk solution. The model emphasizes that turbulent eddy currents continuously replenish solvent packets at the solid-liquid interface, maintaining the concentration gradient and controlling how quickly dissolved drug reaches the bulk solution.
Q4: What is the rate-limiting step in the interfacial barrier model?
In the interfacial barrier model, the rate-limiting step is the solubilization rate of the drug in the static layer. This differs from Danckwerts' model because the interfacial barrier model focuses on the solvation process at the crystal surface and the intermediate concentration established at the interface.
Q5: How do eddy currents function in Danckwerts' dissolution model?
Eddy currents in Danckwerts' model transport macroscopic packets of agitated solvent to the solid-liquid interface. These currents facilitate the absorption and delivery of dissolved drug to the bulk solution while continuously replenishing the solvent at the interface, maintaining a dynamic concentration gradient essential for sustained dissolution.
Q6: What role does the interfacial transport constant play in the interfacial barrier model?
The interfacial transport constant in the interfacial barrier model determines the dissolution rate per unit area. Combined with the concentrations in the static layer and bulk solution, this constant quantifies how efficiently the drug crosses the interfacial barrier and enters the static layer during the dissolution process.
Q7: How do Danckwerts' and interfacial barrier models differ in their approach to dissolution?
Danckwerts' model emphasizes turbulent solvent transport and bulk solution delivery as the rate-limiting step, while the interfacial barrier model focuses on solvation at the crystal surface and solubilization in the static layer as the rate-limiting step. Both models explain dissolution through different mechanisms of drug transport and concentration gradients.