DDS_Fundamentals_1_Barriers&amp;MassTransport

# DDS_Fundamentals_1_Barriers&amp;MassTransport - Drug...

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Drug Transport Pharmaceutical and Biopharmaceutical Aspects of Mass Transport OR How do we move drugs out of their delivery systems, into the body, and to the place we want them to work?

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Drug Transport I. Barriers Synthetic Membranes and Barriers Controlled release dosage forms Tissue scaffolds Filters Containers/Packaging
Biological Membranes and Barriers Epithelial tissues (e.g. GI, corneal, nasal, renal) Skin Muscle Fat Vascular endothelium Basement membrane Tight junction Cell membrane Nuclear membrane

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Mass Transfer Driving Forces Passive Transport Osmosis Facilitated Transport Active Transport Convective Transport density gradients, temperature gradients mixing or pumping actions
Measuring Mass Transfer: Fick’s Laws

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Fick’s First Law (phenomenological) J = -D d C d x Where J = flux (mass transferred per unit time across a unit area) D = diffusion coefficient (a proportionality constant) d C/ d x = concentration gradient across barrier Assumptions ideal mixture closed system isothermal D is a function of T, C, and P
Fick’s Second Law Since dC/dx is experimentally difficult to measure, a mathematical relationship between C and another variable (e.g. t) is desired. From mass balance across a differential element :

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Derivation of Fick’s Second Law dC = (mass/time) in – (mass/time) out dt volume dC = J in – J out dt dx = -d (J) dx = -d (-D dC/dx) dx dC = D d 2 C dx dx 2
Solution under Steady State Conditions Steady State: dC/dt = 0 at all x

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DDS_Fundamentals_1_Barriers&amp;MassTransport - Drug...

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