Some drugs appear to be more quickly absorbed by the body with smaller particle size while some undergo better sustained release with larger particles. Why?
Is it related to the absorption mechanism (capillary action for smaller particles vs. lymphatic system for larger) by any means?
Particle size distribution is correlated with the surface area, thus dissolution rate. Bioavailability is a function of solubility and permeability.
Surface area is directly proportional with dissolution of the drug. So, smaller particles have larger surface area than the bigger particle. So that most researchers believe the nanoparticles service the drug dissolution and bioavailability of drug.
As the particle size decreases, Surface area increases , and simultaneously dissolution rate increases. It causes increase in solubility and so more quickly absorbed by the body. As accordingly larger particles have slow dissolution rate and gives sustained release effects.
Intramuscular injections mostly contains insoluble particles in aqueous solvent or soluble drug in non aqueous solvent. Prolonged release also occurs due to other factors like blood supply, drug properties. Larger particles provide maintenance dose.
Particle size distribution affects the absorption of drugs. Smaller the particle size, higher is the surface area and better is the absorption and bioavailability of the drug. It applies to all drug formulations, including modified release formulations.
Drug absorption is affected by particle size distribution, surface area and and the hydrophobicity and hydrophilic content of the particles. so the smaller the particles, the larger the surface area and more lipophilic content the better the penetration, absorption and bioavailability of the drug and its components and this is applicable in various drug formulations.
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