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AbsorptionAbsorptionOf Of

DrugsDrugs

Dr. Naveed Iqbal AnsariDr. Naveed Iqbal Ansari

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DefinitionDefinition

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Cell membraneCell membrane

StructureStructure

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Schematic diagram of an absorption membraneSchematic diagram of an absorption membrane

Lattice ofprotein

Lattice ofprotein

Inner lipoidalmatrix

Aqueous pores

Hydrophilic tail

Hydrophobic head

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The Process

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Simple TransportSimple diffusionFiltration

Facilitated TransportActive transportFacilitated diffusionPinocytosis

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Facilitated Diffusion

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Active Transport

Active Transport

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Endocytosis

Endocytosis

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Factors Affecting absorptionFactors Affecting absorption

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PharmacologyPharmacology

DrugsDrugs Tissue Tissue

1. Physico-chemical 1. Physico-chemical Routes of Routes of

PropertiesProperties Administration Administration

2. Quantity2. Quantity

(dose)(dose)

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Factors related to the drugFactors related to the drug

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Physico-Chemical PropertiesPhysico-Chemical Properties

1.1. Molecular weight/sizeMolecular weight/size

2.2. NatureNature

3.3. ValencyValency

4.4. Lipid/Water partition co-efficientLipid/Water partition co-efficient

5.5. IonizationIonization

PkaPka

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SolubilitySolubility

Lipid SolubilityLipid SolubilityPresence of benzene ringPresence of benzene ringHydrocarbon chainHydrocarbon chainHalogen (Bromine, Chlorine)Halogen (Bromine, Chlorine)

Water solubilityWater solubilityPresence of alcohol (-OH)Presence of alcohol (-OH)Amide (-CO.NHAmide (-CO.NH22))Carboxylic (-COOH)Carboxylic (-COOH)Formation of Glucuronide & Sulfate Formation of Glucuronide & Sulfate

conjugatesconjugates

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QuantityQuantity

DoseDose

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Factors related to the bodyFactors related to the bodyRoutes of administrationRoutes of administration

a.a. For local effectsFor local effectsa.a. SkinSkinb.b. GITGITc.c. Respiratory tractRespiratory tract

b.b. For systemic effectsFor systemic effectsa.a. SkinSkinb.b. GITGITc.c. Respiratory TractRespiratory Tractd.d. Par-enteralPar-enteral

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Routes of Drug DeliveryRoutes of Drug Delivery

Parenteral(IV)

Inhaled

Oral

Transdermal

Rectal

Topical

Parenteral(SC, IM)

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Absorption from the SkinAbsorption from the Skin

Must cross several cell layers Must cross several cell layers (stratum corneum, epidermis, (stratum corneum, epidermis, dermis) to reach blood vessels.dermis) to reach blood vessels.

Factors important here are:Factors important here are:

lipid solubilitylipid solubility

hydration of skinhydration of skin

site (e.g. sole of feet vs. site (e.g. sole of feet vs. scrotum)scrotum)

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Factors Affecting Absorption Factors Affecting Absorption from the GI Tractfrom the GI Tract

FORMULATIONFORMULATION Disintegration of dosage form and Disintegration of dosage form and

dissolution of particlesdissolution of particles Chemical stability of chemical in gastric Chemical stability of chemical in gastric

and intestinal juices and enzymesand intestinal juices and enzymes Motility and mixing in GI tractMotility and mixing in GI tract Presence and type of foodPresence and type of food Rate of gastric emptying Rate of gastric emptying Blood flow to GI tractBlood flow to GI tract Passage across GI tract wallPassage across GI tract wall

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Absorption from the LungsAbsorption from the Lungs

For gases, vapors and volatile liquids, For gases, vapors and volatile liquids, aerosols and particlesaerosols and particles

In general: large surface area, thin In general: large surface area, thin barrier, high blood flow rapid barrier, high blood flow rapid absorptionabsorption

Blood:air partition coefficient – Blood:air partition coefficient – influence of respiratory rate and influence of respiratory rate and blood flow blood flow

Blood:tissue partition coefficientBlood:tissue partition coefficient

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Par-enteral routePar-enteral route

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Bioavailability

for i.v.: 100%for i.v.: 100% for non i.v.: for non i.v.:

ranges from 0 to 100%ranges from 0 to 100%

lidocaine bioavailability 35% lidocaine bioavailability 35% due to destruction in gastric due to destruction in gastric acid and liver metabolismacid and liver metabolism

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Sustained release Sustained release preparationspreparations

depot injections depot injections (oily, viscous, particle size) (oily, viscous, particle size)

multilayer tablets multilayer tablets (enteric coated)(enteric coated)

sustained release capsules sustained release capsules (resins)(resins)

infusorsinfusors (with or without sensors)(with or without sensors)

skin patches skin patches (nicotine, GTN)(nicotine, GTN)

pro-drugspro-drugs liposomesliposomes

Targeted drugs , antibody-directedTargeted drugs , antibody-directed