Biopharmaceutics & Pharmacokinetics Lecture Notes PDF

BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD FACTORS FACTORS AFFECTING ABSORPTION AND BIOAVAILABILITY OF DRUG PHYSIOLOGICAL PHYSICOCHEMICAL DOSAGE FORM FORMULATION...

BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD FACTORS FACTORS AFFECTING ABSORPTION AND BIOAVAILABILITY OF DRUG PHYSIOLOGICAL PHYSICOCHEMICAL DOSAGE FORM FORMULATION PHYSICOCHEMICAL, DOSAGE FORM & FORMULATION BY: SALMAN ASHFAQ AHMAD FACTORS FACTORS PHYSICOCHEMICAL, DOSAGE FORM & FORMULATION FACTORS BY: SALMAN ASHFAQ AHMAD MECHANISM & NOYES-WHITNEY EQUATION  Dissolu on → Transfer of solute in solu on  Difference between solubility and dissolution  Mechanism of dissolu on → Diffusion layer + bulk of solu on  Dissolu on process → Noyes – Whitney equa on → Different parameters are connected mathematically in an equation  Noyes-Whitney equa on → dm / dt = (DAΔC) / h → ΔC = Cs – C  Noyes-Whitney equa on → Rate of diffusion of solute through boundary layers → Surrounding the spherical particle DISSOLUTI BY: SALMAN ASHFAQ AHMAD ON MECHANISM & NOYES-WHITNEY EQUATION MECHANISM OF DISSOLUTION DISSOLUTI BY: SALMAN ASHFAQ AHMAD ON PHYSIOLOGICAL FACTORS DISSOLUTI BY: SALMAN ASHFAQ AHMAD ON DRUG FACTORS SURFACE AREA WETTABILITY DRUG FACTORS SOLUBILITY IN DIFFUSION LAYER EXTENT OF IONIZATION CRYSTAL FORM DISSOLUTI BY: SALMAN ASHFAQ AHMAD ON DRUG FACTORS (SURFACE AREA)  ↑ surface area, ↑ we.ability → ↑ dissolu on  Increased effec ve surface area → Faster dissolu on  ↑ Dissolu on → ↑ Bioavailability (Absorp on → dissolu on rate limited)  ↑ bioavailability → ↑ plasma concentra on  Griseofulvin → Poorly soluble → 10 micron to 2.7 microns → 2x drug absorp on  Hydrophobic drug → Size reduc on → Aggrega on of drug par cles → ↓ Bioavailability → Aspirin, Phenacetin, Phenobarbital, etc.  Milling → Hydrophilic carrier, we>ng agent, or stabilizers DISSOLUTI BY: SALMAN ASHFAQ AHMAD ON DRUG FACTORS (SURFACE AREA)  Several drug delivery systems → Stabilize in nanometers → ↑ Bioavailability  Immunosuppressant Rapamune® (Sirolimus), Antiemetic Emend® (Aprepitant), lipid – regulating agent TriCor® (Fenofibrate), Megace® ES (Megesterol Acetate)  Sirolimus → ↑ bioavailability for Rapamune® tablets → Owing to nanopar cles  Megace® ES → Appe te loss / weight loss → AIDS → nanosuspension vs standard suspension → ↓ viscosity and ¼ of the volume to be dosed FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG FACTORS (WETTABILITY)  We>ng agents are added → Improves bioavailability  Phenace n → 75 µm → Polysorbate 80 added → ↑ rate and extent of drug absorp on  ↓ drug par cle size → No improvement in absorp on → Dissolu on is not rate limi ng factor FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG FACTORS (SOLUBILITY IN THE DIFFUSION LAYER)  Aqueous drug solubility → Cri cal factor for determina on of dissolu on rate  Slow dissolu on → Poor drug bioavailability  Relationship of rate of dissolution with the concentration in diffusion layer  Aqueous solubility of a drug → a) Crystallinity b) Drug molecule – solvent interaction  Solid par cles → Solubility limited due to solid state proper es → Brick dust molecules  ↑ log P values → ↑ lipophilicity → Grease ball molecules FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG FACTORS (EXTENT OF IONIZATION)  Weak electrolytes → Aqueous solubility dependent upon pH of the dissolving medium  Weak electrolyte → Rate of dissolu on dependent upon drug’s solubility and pH of diffusion layer  pH of diffusion layer → pka of drug and its solubility + pka and solubility of the buffers in bulk of GI fluids  PPIs → Increase gastric pH → ~ pH 5.5 → ↓ rate of dissolu on for triazole an fungals, an -cancer drugs  Posaconazole → ↑ dissolu on (~ 40%) → Administra on with acidic beverages  Unionized form of the drug → Absorp on → Replenishment of the unionized form due to equilibrium establishment FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG FACTORS (EXTENT OF IONIZATION)  Changing gastric pH → Pose problem for drugs with poor solubility FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG FACTORS (EXTENT OF IONIZATION) FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG FACTORS (CRYSTAL FORM)  Drugs exist in polymorphic forms → Metastable and stable polymorphic forms  Metastable form → Quicker dissolu on  Chloramphenicol palmitate → Polymorphic form A, B and C → Normal temperature and pressure → Polymorph A is stable, Polymorph B is metastable, and Polymorph C is unstable  Amorphous solids → Quick dissolu on  Hydrates → Anhydrous form dissolves quickly (anhydrous Ampicillin) → Opposite also true (Erythromycin) FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD FACTORS AFFECTING DRUG CONCENTRATION IN BULK OF GI FLUIDS COMPLEXATION DRUG DISSOCIATION AND LIPID SOLUBILITY MICELLAR SOLUBILIZATION FACTORS PRODRUGS ADSORPTION OF DRUGS CHEMICAL STABILITY IN GI FLUIDS FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD COMPLEXATION  Complexa on → Beneficial or detrimental  Streptomycin + Mucin → ↓ bioavailability  Tetracyclines + Calcium → Insoluble complexes  Bisphosphonates + Food → Insoluble complexes  Tetracyclines + Diluent (DCP)→ Insoluble complexes  Amphetamine + CMC  Phenobarbital + PEG 400  Complexa on in liquid formula ons → ↑ stability FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD MICELLAR SOLUBILIZATION  Micellar solubiliza on → Substance or drug incorporated into micelle → ↑ solubility  Bile salts → Ability to solubilize drug → Depends upon lipophilicity of the drug  Food → S mula on of bile → Mechanism of solubility for number of drugs → BCS Class II drugs → E.g., Albendazole, Griseofulvin FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD ADSORPTION OF DRUGS  Concurrent drug administra on → Adsorp on  Extent of adsorp on → Reversibility of drug–adsorbent interaction  Promazine + Ac vated charcoal → Drug–adsorbent interaction  Cyanocobalamin + Glidant → Drug–adsorbent interaction FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD CHEMICAL STABILITY IN GI FLUIDS  Stability of dug in GI fluids → Essen al for absorp on of drug in appropriate quan ty → Therapeutic response  Acidic and enzymatic hydrolysis  Gastro-resistant formula ons → Designed to improve drug bioavailability → E.g., Erythromycin  Prodrugs → Limited solubility → Minimal dissolu on → Drug release at appropriate site → E.g., Erythromycin Stearate FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG DISSOCIATION AND LIPID SOLUBILITY  Drug dissocia on constant & its lipid solubility + pH of absorp on site → Absorp on  Degree of ioniza on + Extent of absorp on → Covered in pH – par on hypothesis → Overton (1899)  GI epithelium → Lipid barrier → Passive diffusion → Lipophilic molecule → Unionized drug penetrates membrane  Extent of ioniza on → Henderson Hasselbalch equa on → log [A-] / [HA] = pH – pKa (acidic drug) → log [BH+] / [B] = pKa – pH  Drug X → pKa = 3.0 → At pH 1.2 (98.4% un – ionized) → At pH 6.8 (99.98% ionized)  Drug Y → pKa = 5.0 → At pH 1.2 (99.98% ionized) → At pH 6.8 (98.4% un – ionized) FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DRUG DISSOCIATION AND LIPID SOLUBILITY  Large surface area, Longer small intes nal residence me, ↓ pH of microclimate → Absorp on of weakly acidic drug  Uns rred water layer → Barrier to drug absorp on for lipophilic drug  Convec ve flow → Increased in jejunum → Water and lipid soluble drugs  Number of drugs → ↑ Unionized form → ↓ Absorp on → Lipid solubility to be determined → Barbiturates → ↓ Barbitone (pka = 7.8) & ↑ Thiopentone (pka = 7.6)  Polar molecules (log P < 0), large molecules → Injectables → Gentamycin, Heparin, CeZriaxone, etc. → Lipid soluble drugs (log P > 3) → Well absorbed orally → ↑ Suscep bility to biliary clearance → Less lipid soluble, smaller molecule absorbed via Paracellular route (e.g., Atenolol) FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD PRODRUGS  Prodrugs → ↑ lipid solubility → ↑ absorp on  Ester group is introduced → Prodrug → Re convert into parent co,mpound  Examples: Pivampicillin (Ampicillin + Pivaloyloxymethy), Cefuroxime axetil (Cefuroxime + Acetylethyl), Enalapril (Enalaprilat + 1-carboxylic acid), Ibuterol (Terbutaline + Dibutyl) FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD IMPROVING BIOAVAILABILITY OF POOR AQUEOUS SOLUBLE DRUGS SALT FORMATION METHODS SDDS FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD SALT FORMATION  Drugs are available in salt form → Acidic or basic salt  Tolbutamide + Sodium → Dissolu on 5000x in acidic medium as compared with free acid  Naproxen + Sodium → Faster dissolu on  Chlorpromazine + HCl → Faster dissolu on in gastric and intes nal pH  Other salts form also exist  Some salt forms → Decreased dissolu on as compared with free drug → Sustained release formula on → Aluminum salts of weak acids and Pamoate salts of weak base  Acidic or basic excipients also used → Chemical instability → Sodium salt of Aspirin FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD SDDS SPRING – PARACHUTE MODEL FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD SDDS  SDDS → Improves bioavailability  It follows Spring – Parachute Model.  SDDS → Drug presented at supersaturated concentra on → GI fluids  SDDS → Drug springs into system → Slowly returns (parachute effect)  Polymers included → Prevent precipita on FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD IMPROVING BIOAVAILABILITY OF POORLY SOLUBLE DRUGS DUE TO LIPOPHILICITY COSOLVENTS SEDDs METHODS CYCLODEXTRIN MICELLAR SOLUBILIZATION FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD COSOLVENTS  Co-solvents → Low molecular weight → PEGs, PG, Glycerol → Drugs dissolved → Filled in so: gel capsules  Bexarotene (Targre n®) → An cancer drug + PEG 400  Etoposide (VePesid®) → Anticancer drug + PEG 400 + Glycerol + Citric acid + Water  Ethosuximide (Zarontin®) → Anticonvulsant drug + PEG 400  Drug precipitation → Large variability in bioavailability → E.g., Nifedipine FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD CYCLODEXTRINS  Cyclodextrins (CDs) → Cyclic oligosaccharides → Glucopyranose units  Lipophilic molecules → Trapped inside CDs → Increase aqueous solubility  CDs → Solubility enhancers  Example: Voriconazole → An fungal drug FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD MICELLAR SOLUBILIZATION  Micellar solubiliza on → Improves solubility of drug → ↑ bioavailability  Surfactants used for micellar solubilization.  Used for both liquid and solid formulations. FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD SEDDS  SEDDS → Drug solubilized in oil/surfactant vehicle  Filled in a soft gelatin capsule.  Micro-emulsion or nano-emulsion results.  Drug diffuses into the aqueous medium. FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD IMPROVING THE BIOAVAILABILTY OF DRUGS WITH POOR PERMEABILITY  Drug absorp on → Affected by number of factors  Drug pka, lipid solubility, molecular weight, hydrogen bonding, chemical stability FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD MOLECULAR SIZE & HYDROGEN BONDING  Paracellular absorp on → < 200 Da → Shape is also important  Transcellular passive diffusion → < 500 Da  ↑ Hydrogen bonding → ↓ Absorp on  Pep de drugs → Less well absorbed FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD PERMEATION ENHANCERS  Permea on enhancers → Added in formula on → To improve permeability  Improve permeability → Paracellular route by reversibly opening the ght junc ons or transcellular route by altering integrity  Surfactants, bile salts, medium chain fatty acids, chelating agents  FaHy acids and bile salts → Fluidizing the lipid membrane  EDTA chelates calcium FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD PERMEATION ENHANCERS  Semaglutide → Polypep de analogue of human glucagon like pep de 1 (GLP-1) → Type 2 diabetes → Use small faHy acid deriva ve → Permea on enhancer to ↑ transcellular transport across gastric mucosa → ↓ TEER (transepithelial electrical resistance) and ↑ membrane fluidity  SNAC + Vitamin B12 → ↑ absorp on of vitamin B12 FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DOSAGE FORM FACTORS  Rate and extent of drug absorp on → Affected by number of physiological and physicochemical factors  The rate and extent of drug absorp on → Affected by dosage form factors → Type of dosage form, manufacturing method, etc.  Oral dosage form → Solu on, suspension or solid dosage form → Affects the number of intervening steps  Generally, aqueous solution > aqueous suspension > solid dosage forms  Other factors beside bioavailability → Influence the type of dosage form prepared for administration FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD DOSAGE FORM FACTORS FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD AQUEOUS SOLUTIONS  Water soluble drug formula on → Eliminates the in vivo drug dissolu on  ↑ Solubility → Using techniques → Precipita on in gastric pH  Salt of weak acidic drug → Precipita on at gastric pH  Experimental drug → 3 formula ons → Bioavailability determined → Polyethylene glycol (19%), Hydroxypropyl β – cyclodextrin (57%) & Hydroxypropyl β – cyclodextrin (89%) → Difference of precipitation  Factors associated with aqueous solu on → Affect bioavailability → Chemical stability, complexation, solubilization & viscosity of the formulation FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD AQUEOUS SUSPENSIONS  Aqueous suspension → Poorly or insoluble drug administra on → Dissolu on rate limited  Administration results in availability of large surface area.  Aqueous suspension → Second to non – precipitating aqueous solution  Drug in hard gela n capsule or tablet → Ul mately achieve condi on of aqueous suspension  Factors associated with aqueous suspension → Affect bioavailability → Par cle size, crystal form, complexation, inclusion of surfactants, viscosity of formulation FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD LIQUID FILLED CAPSULES  Liquid filled capsules → SoA / hard gela n or HPMC  Drug inside capsule → Dissolved or dispersed in non – toxic, non – aqueous vehicles  Water miscible vehicle → Content of capsule released → Vehicle disperse / dissolve → Drug released → Solu on / suspension → Absorp on  Water immiscible vehicle → Content of capsule released → Vehicle dispersion → Facilitated by dispersing agents → Drug released as solu on / suspension / emulsion / nano – emulsion / micro – emulsion → Absorp on  Lipophilic vehicle → Diges ble oil → Drug highly soluble in vehicle → Fat absorp on process FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD LIQUID FILLED CAPSULES  Lipophilic vehicle → Non – diges ble oil → Drug highly soluble in vehicle → Par oning of drug in GI fluids  Drug suspended in oily vehicle → Dissolu on → Diffusion → Par oning  Digoxin → Poorly soluble drug → Mixture of PEG + Ethanol + PG → ↑ Absorp on than tablet  Ciclosporin → SANDIMMUNE®→ Large hydrophobic drug → ↓ Permeability → FaIy diet → Variable bioavailability → Formula on containing mixture of hydrophilic and lipophilic phases, surfactants, cosurfactants, cosolvents → Non – precipita ng microemulsion on dilu on → NEORAL®  Protease inhibitors → Saquinavir → Formulated as soA gela n capsule → ↑ Bioavailability FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD LIQUID FILLED CAPSULES  Factors associated with making of liquid soA gels→ Affect bioavailability → Solubility of drug, particle size, nature of vehicle, inclusion of surfactants, inclusion of suspending agent, complexation FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD POWDER FILLED CAPSULES  Bioavailability from a powder filled hard gela n / HPMC capsule → Similar to compacted tablet → Provided factors are controlled  Rate of drug dissolu on from capsule → Complex func on of different processes  Excipients in capsule dosage form → Influence the rate of dissolu on → Poorly soluble drugs → Hydrophilic excipients → ↑ Penetra on → ↑ Dispersion → Dissolu on of drug  No adsorption of drug by excipients  Formula on & type of process of filling → Affect packing density and liquid penetra on FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD POWDER FILLED CAPSULES  Factors associated with making of powder filled capsules → Affect bioavailability → Surface area & particle size, Use of salt form of drug, crystal form, stability of drug, drug – excipient interaction, nature & quantity of excipients, type and condition of filling process, packing density, composition & properties of capsule shell, interaction between capsule shell and its content FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD TABLETS (UNCOATED)  Tablets → Reduc on in surface area → Excipients added → Bring drug in pre – compacted state  Poorly soluble drug → Rapid disintegra on and release → Fine & well dispersed suspension in GI fluids → Dissolu on and absorp on  Disintegra on → Affected by concentra on and type of drug, excipients & compac on pressure  Dissolu on of poorly soluble drug in tablet → Comparable with dissolu on of drug in fine, well dispersed suspension  Factors associated with making of uncoated tablet → Affect bioavailability → Physico – chemical property of drug, nature & quantity of excipients, drug – excipients interaction, size and method of making granule, compaction pressure and compaction speed, storage condition & age of tablet FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD TABLETS (COATED)  Coa ng applied on tablets → Possess bioavailability related problems (uncoated tablets) + addi onal problems → Physicochemical nature and thickness of coa ng  Sugar coated tablets → Sealing the coat (Shellac & CAP) → Annealing agents (PEGs, CaCO3) added to reduce water impermeability  Film coated tablets → HPMC → Soluble at GI pH  Film coated tablets → Acrylic resins or EC → Hydrophobic → Reduces drug release  Gastro – resistant tablets → CAP, HPMC Phthalate, Co – polymers of methacrylic acid and their esters & Polyvinyl acetate Phthalate → Dissolve at pH 5  Gastro – resistant coa ngs → Offer ↓ onset of ac on FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD TABLETS (COATED)  Gastro – resistant formula ons → Pellets or intact tablet → Affect the release pa8ern of drug and hence onset of action  Gastro – resistant pellets → < 1 mm FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD INFLUENCE OF EXCIPIENTS  Excipients added in formula ons → To facilitate prepara on, pa ent acceptability and func oning of dosage form as DDS.  Excipients → Interact with the ac ve → Have poten al to influence the release, absorp on and other characteris cs of drug → Tetracycline + DCP, Amphetamine + Sodium CMC, Phenobarbital + PEG 4000, etc.  Excipients → Large variety → Example: Diluents, Surfactants, Lubricants, Disintegrants, Viscosity enhancers, Binders, Lubricants, Colorants, Stabilizers, Flavoring agents, Suspending agents, Emulsifiers, etc. FACTORS AFFECTING BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD BIOPHARMACEUTICAL CHARACTERISTICS  Biopharmaceu cs → Factors affec ng rate and extent of drug absorp on  Factors → Release of drug, dissolu on, stability, ability to cross & pre – systemic metabolism → Influence absorption  Key biopharmaceu cal proper es → Quan fied → Give insight about absorp on  Bioavailability → Overall measurement of availability of drug in systemic circula on → Need to be assessed RELEASE FROM STABILITY OF TRANSPORT PRE – SYSTEMIC DOSAGE FORM DRUG OF DRUG METABOLISM ASSESSMENT BY: SALMAN ASHFAQ AHMAD RELEASE OF DRUG  Dosage form design → Controls the release of the drug  Solubility of the drug at GI pH → First indicator → Dissolu on is rate limi ng process  Rate of dissolu on determined → Intrinsic + dosage form  In vitro dissolu on tes ng → Reflects in vivo dissolu on performance  Scientists nowadays focus on in vitro – in vivo correla ons → Useful in number of ways  In vitro – in vivo correla ons → Useful for drugs where dissolu on is rate limi ng → Dissolu on profile of drug studied in various physiological media  Dilute HCl based solu on of pH 1.2 → Simulate gastric pH ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD RELEASE OF DRUG  Phosphate buffer pH 6.8 → Simulate intes nal pH  For in vitro – in vivo correla ons → To mimic gastric fed state → Homogenize the meal to be used and dilute with water → Milk also used for fed state  Dura on of dissolu on test → Depends upon site of absorp on of drug + ming of administra on  Volume of dissolu on media + Degree of agita on → Difficult to decide  Immediate release → 500, 900 or 1000 ml → Gentle agita on ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD STABILITY IN PHYSIOLOGICAL FLUIDS  Stability of drugs in physiological fluids → Chemical stability across GI pH range & suscep bility to enzymatic breakdown  Stability of drug in GI fluids → Simulated GI fluids or real GI fluids → Incuba on at 37°C for 3 hours → Loss of > 5% drug indicates poten al instability  Drugs when reach to colonic region → Resistance to the bacterial enzymes → Needed to be considered ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD PERMEABILITY  Number of methods to es mate permeability → Assessment of oral absorp on in humans  Methods → In silico to physicochemical and biological methods  Biological methods → In vitro, in situ, and in vivo methods ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD PARTITION COEFFICIENT  Par on coefficient of the molecule → Determined between oil and water phase (log P) → Lipophilicity of the molecule  n – octanol → Commonly used solvent → Oil phase  Shake flask method → Commonly used method  Aqueous phase saturated with oily phase & vice versa  Constant temperature is maintained → Drug is added and system is allowed to reach equilibrium (24 hours) → Concentra on is measured  Distribu on coefficient (log D) is determined → Weakly acidic or basic drug → BeJer predic on of drug’s ability to permeate ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) PARTITION COEFFICIENT SHAKE FLASK METHOD ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) PARTITION COEFFICIENT  Par on coefficient of the molecule → Computa onal methods → Correla on between calculated and measured values  Molecule fragmented and analyzed for lipophilicity → clog P  Moriguchi method → 13 parameters → mlog P  HPLC method → Used for es ma ng how well drug par ons into lipophilic phase ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) CELL CULTURE TECHNIQUES  Cell culture techniques → Widely used → Predict intes nal absorp on → Cell line widely used is Caco – 2  Caco – 2 → Human colon carcinoma cell line → First proposed model for absorp on by Hidalgo  In culture of Caco – 2 → Cells differen ate to form monolayer of polarized enterocytes → Resemble cells those in small intestine ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) CELL CULTURE TECHNIQUES Caco – 2 CELL CULTURE SYSTEM ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) TISSUE TECHNIQUES  Range of ssue techniques → Used as absorp on models  Two popular models → Isolated sheets of intes nal mucosa & use of everted intes nal rings ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) PERFUSION STUDIES  Rat model is preferred for perfusion studies → Ease of use and similarity to the permeability to human intestine  In situ intes nal model is used → Whole animal is used → Nerve , blood and lympha c supply intact ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) PERFUSION STUDIES  Rat model is preferred for perfusion studies → Ease of use and similarity to the permeability to human intestine  In situ intes nal model is used → Whole animal is used → Nerve , blood and lympha c supply intact ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD (PERMEABILITY) PRE – SYSTEMIC METABOLISM  Intes nal cell frac ons (brush border membrane prepara ons) → Homogenized prepara ons of rat intes nal segments → Used for pre – systemic metabolism  Incubation at 37°C.  Various liver prepara ons → Phase I and Phase II metabolism reac ons ASSESSMENT – KEY BIOPHARMACEUTICAL PROPERTIES BY: SALMAN ASHFAQ AHMAD BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD INTRODUCTION RELEASE OF DRUG CONCENTRATION STABILITY OF DRUG TIME PROFILE PERMEABILITY MEASUREMENT PRE – SYSTEMIC OF METABOLISM BIOAVAILABILITY ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD PLASMA CONCENTRATION – TIME CURVE PERORAL ADMINISTRATION (BLOOD SAMPLE) ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD PLASMA CONCENTRATION – TIME CURVE TERMINOLOGIES ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD PLASMA CONCENTRATION – TIME CURVE PLASMA CONCENTRATION TIME CURVE (3 FORMULATIONS) ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD PLASMA CONCENTRATION – TIME CURVE  Three different formula ons A, B, & C → Administered to same person at different mes → Same route of administration  Assump ons: Sufficient me elapsed between administra on of each formula on → No residual concentra on and residual effects → Kine cs & pa"ern of distribu on, binding phenomenon, the kinetics of elimination and experimental conditions are all same  Differences exist → Rate and / or extent of absorp on of the drug from each formula on  Differences in bioavailability → Due to different formula ons → Pa ent can be over, under or correctly medicated  Plasma concentra on me curve → Beside biopharmaceu cal factors → Affected by other factors ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD BIOPHARMACEUTIC S: DRUG BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD URINARY DRUG EXCRETION CURVE  Urine method of analysis → Intact drug and / or metabolites  Drug assay method not available for urine → Drug assay method not sensi ve → Assay of metabolites done in urine  Assumptions: No drug metabolism before reaching systemic circulation  Assumption: The appearance of drug and / or metabolite in the urine is the function of the rate and extent of absorption  Urinary excre on studies → Cumula ve amount of intact drug and / or metabolite & rate of excre on → Urine samples are collected → Construct cumula ve urinary excre on curve → Urine samples collected till all drug and / or metabolites excreted ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD URINARY DRUG EXCRETION CURVE PLASMA CONCENTRATION TIME CURVE & URINARY EXCRETION CURVE ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD URINARY DRUG EXCRETION CURVE  Comparison of bioavailability → Three formula ons A, B, & C → Administered to same pa ent → Same dose → Oral route → Same plasma concentra on – time curve in previous example  Slope of curve → A > B > C → Rate of oral absorp on of drug → A > B > C  Plasma and urine concentration – me profile → Same drug → Indicate Tmax A < B < C  Tmax ∝ 1 / drug absorption rate ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD URINARY DRUG EXCRETION CURVE URINARY EXCRETION CURVE (3 FORMULATIONS) ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD ABSOLUTE BIOAVAILABILITY  Absolute bioavailability → Frac on / percentage of administered dose → Reaches systemic circulation  Comparison of total amount of intact drug from a particular route of administration to the amount that reaches via IV route (bolus administra on) → Same or different dose but different dosage forms  AUC of both routes are compared  Absolute bioavailability = (AUCT)abs / (AUCT)iv → Equivalent doses  Absolute bioavailability = [(AUCT)abs / (AUCT)iv] x (Div / Dabs) → Different doses ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD ABSOLUTE BIOAVAILABILITY  Absolute bioavailability = (XU)abs / (XU)iv → Equivalent doses  Absolute bioavailability = [(XU)abs / (XU)iv ] x (Div / Dabs) → Different doses  Calculated value of absolute bioavailability → Valid if: Kine cs of distribu on and elimina on → Independent of route & time of administration and size of the dose administered ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD ABSOLUTE BIOAVAILABILITY ABSOLUTE BIOAVAILABILITY OF A DRUG ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD RELATIVE BIOAVAILABILITY  Rela ve bioavailability → Drug cannot be administered IV bolus dose  Comparison of total amount of intact drug from a test dosage form to the amount that reaches via standard dosage form → Same or different dose but different dosage forms  Standard → Orally administered solu on or commercial formula on of proven efficacy  AUC of both routes are compared  Relative bioavailability = (AUCT)test / (AUCT)standard → Equivalent doses  Relative bioavailability = (AUCT)test / (AUCT)standard ] x (Div / Dabs) → Different doses ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD RELATIVE BIOAVAILABILITY  Relative bioavailability = (XU)test / (XU)standard → Equivalent doses  Relative bioavailability = [(XU)test / (XU)standard ] x (Div / Dabs) → Different doses  Numerous dosage form factors → Affect the bioavailability of drug ASSESSMENT OF BIOAVAILABILITY BY: SALMAN ASHFAQ AHMAD