# PHRD5925 Pharmaceutics Lecture 12 - Drug Absorption (Part 2)

 3 main pharmaceutical factors affecting drug absorption 1) disintegration2) dissolution3) permeability relates the flux (rate) to the concentration gradient under steady state conditions Fick's First Law Fick's First Law (eqn) diffusion rate = diffusion coefficient * concentration gradient across the boundary predicts how diffusion causes the concentration to change with time Fick's Second Law (second derivative) 3 parameters permeability is depedent on 1) partition coefficient2) diffusion coefficient3) thickness/area of the membrane permeability (eqn) P=DK/h permeability coefficient = (diffusion coefficient * partition coefficient) / membrane thickness dW/dt diffusion rate process by which a solid enters into a solution dissolution parameters dissolution rate is dependent on (4) 1) time2) particle size3) solubility4) formulation factors equation that determines rate of dissolution based on the change in concentration over time (rapid formation of diffusion layer followed by slow dissolving step) Noyes-Whitney equation that determines rate of dissolution based on change in the amount of solid drug over time Nernst-Brunner equation that determines how the radius of the drug/mass changes as the particle dissolves (takes into account the change in particle size during dissolution) Hixon-Crowll Cube Root Law 2 factors affecting dissolution 1) particle size/surface area of drug particles2) solubility of a drug (salt vs nonsalt, crystalline vs amorphous) 3 ways to increase surface area 1) micronization2) nanocrystallization3) mortar & pestle sodium & potassium salts dissolve _____ than the free acid faster amorphous solids have ____ solubility compared to crystalline solids higher ability of solid material to exist in more than 1 crystal form polymorphism only 1 form is stable under a given set of conditions. all other forms are _____. metastable the stable crystalline form has _____ solubility than the metastable form. lower fraction of dosage form that reaches the site of action or biological fluid from which the drug has access to its site of action OR rate/extent to which the active ingredient is absorbed from a drug product & becomes available at the site of action bioavailability (BA) 4 factors bioavailability is dependent on 1) biopharm properties (dissolution/permeability)2) physicochemical properties 3) stability of drug in GIT4) 1st pass metabolism the absence of significant difference in the rate and extent of the bioavailability of the API in 2 formulations administered under similar conditions bioequivalence (BE) API active pharmaceutical ingredient BCS is based on... solubility & permeability 3 criteria that must be met for BCS to be used 1) solubility2) permeability3) dissolution high solubility = highest dosage strength is soluble in 250mL aqueous media over pH range 1.2-6.8 high permeability = extent of absorption in humans 90% of the administered dose BCS Class I high solubilityhigh permeability BCS Class II low solubilityhigh permeability BCS Class III high solubilitylow permeability BCS Class IV low solubilitylow permeability criteria for rapid dissolution, per the Dissolution Test >85% in <30min in pH 1.2, 4.5, 6.8 Criteria to be granted a biowaiver 1) immediate-release2) BCS Class I Authordaynuhmay ID271271 Card SetPHRD5925 Pharmaceutics Lecture 12 - Drug Absorption (Part 2) DescriptionDrug Absorption Updated2014-04-21T01:29:15Z Show Answers