The Medicine - Semester 2 Flashcards
What is the difference between a drug or a medicine?
Drug - Active pharmacological agent
Medicine - API within its formulation
How does drug development start?
Drug tested in solution for interactions with isolated target cells
Why aren’t drugs administered as solutions?
Not administered in solution due to expense and impracticality
What are the aims of certain dosage forms?
Favourable manufacture, cost, stability
Sufficient amount of API must reach target cells
Define bioavailability and absolute bioavailability
Bioavailability - Absorption of drug as well as availability at site of action
Absolute Bioavailability - Amount of drug from the dosage form in the systemic circulation
Why is blood considered the central compartment?
Links all the tissues in the body
Describe the general routes of administration
Across epithelial layers (skin, GIT, bronchioles, pulmonary)
Bypassing epithelial layers (intra or extravascular injections)
When are parenteral administration routes used?
Patients who can’t take oral drugs
If quick response is required
If drug is unsuitable for oral administration
How do transdermal drug delivery systems work?
High concentration of drug in formulation - drug is low Mr and lipophilic
Excipients may enhance sc permeability
Rate controlling polymeric membrane controls drug release
Why may GI delivery be preferred over transdermal?
Higher SA and higher permeability (absence of stratum corneum)
What affects availability of absorption for a drug?
GIT Variables: intestinal transit time, properties of GIT fluid, properties of tissue at the absorption site
Drug/Dosage Form Variables: Chemical properties of the drug, formulation, pharmalogical effects of excipients
How does absorption differ at different points in the GIT?
Transit time increases as drug moves further down
Properties of the absorbing tissues changes
How do buccal/sublingual delivery systems work?
Mouth is more permeable than skin but smaller SA
Low Mr, lipophilic drugs
Convenient administration
Fast action and avoidance of first pass metabolism
How are drugs absorbed in the stomach?
Fairly low SA
Little absorption - tight junctions and no nutrient transporters
Weak acids and highly permeable drugs may be absorbed
How are drugs absorbed in the intestine?
High SA (microvilli)
Highly perfused
Nutrient transporters
Potential for paracellular transport
What are the three absorption pathways? Describe them
Transcellular: Small, lipophilic, unionised forms
Paracellular: Hydrophilic drugs with low Mr
Carrier Mediated: Protein transporters in membrane
Describe the absorption of gabapentin
Bioavailability decreases as dose increases due to need for active transport
Pro-Drug can be transported by a number of carriers, increasing bioavailability
How do drugs undergo first pass metabolism?
Drugs pass through liver before entering circulation by hepatic portal flow, may be broken down at this stage
How are excipients chosen and what is their purpose?
Generally dependent on indication
Enhance chemical properties of a medicine
What are the objectives of a dosage form?
Produce a predictable therapeutic response
A product that has capability for large scale manufacture
A quality of product that can be repeatably obtained
What aspects of novel drugs may present a problem during manufacturing?
High MW
Peptide, protein or viral components
What are the pharmaceutical considerations of dosage forms?
How different formulations will impact absorption
Physicochemical properties of drug itself
Therapeutic condition and the patient
Financial considerations
Describe pre formulation
Stage of development before drug is made into a medicine
Optimisation of a drug candidate to form a drug product
one is then picked for further development
What makes a good drug candidate to develop further?
Properties lead to an obvious formulation
Generally easiest to formulate
What aspects of a formulation determine bioavailability?
Stability
Dissolution
Drug-Excipient interactions
What are the intrinsic pre formulation considerations?
Solubility: 1mg/ml as liquid, 10mg/ml as oral product
Hygroscopicity: Increased water content can affect manufacturing processes/Water may result in degradation or interactions/Adsorption alone is not enough water to dissolve a substance
Define hygroscopicity and deliquescence
Hygroscopicity - Attraction of water through adsorption or absorption
Deliquescence - Molecule is so hygroscopic that it can dissolve in the volume of water
What are the macroscopic pre formulation considerations?
Melting point Particle size and shape Powder flow Compaction Amorphous materials Polymorphism
How does powder flow affect formulation?
Important for mixing and optimal filling of press
Angle of repose 15-25 degrees and particle size >50µm
How does compaction affect formulation?
Depends of bulk density and tapped density - bigger difference = better compaction
How do amorphous materials affect formulation?
More soluble than crystalline compounds but eventually become crystalline due to instability
How do polymorphs affect formulation?
Most stable has the highest melting point however may not have the best bioavailability or manufacturing properties
How is solubility of an API measured?
Create saturated solution and filter
Analyse solution to determine solute conc. present
What are the rotating/static disc methods for measuring solubility?
Drug formulated in non-disintegrating disc - one face exposed to solvent
Maintain constant speed of rotation, position of disc/holder
Remove solvent and assay at fixed time intervals
How can solubility be modified?
Esterification reduces aqueous solubility
Co solvents can be used to alter solubility
Metastable polymorphs are less soluble
Addition of solvent molecules into crystalline structure reduces solubility (if solvent is aqueous)
How does ionisation affect solubility and what does it depend on?
More ionisation increases solubility
Depends of pH and pKa of molecule and pH of solvent
Why are oral drugs absorbed in the small intestine?
Usually weak bases so they remain unionised
How drug salts increase solubility of drugs?
Acid/base reacts to form salt - stronger = more complete reaction
Dissolution of salt may result in pH change which further aids dissolution of drug
What is wettability and what does it depend on?
Ability of a liquid to stay in contact with a surface - it is defined by the contact angle of droplet of liquid on a surface
Depends on adhesion and cohesion forces (adhesion improves wetting)
What is the contact angle?
Result of interfacial energies of surface tension of the liquid and the different interfacial energies
Wetting is favourable if contact angle is less than 90°
What is viscosity?
Resistance to movement
Describe properties exhibited by Newtonian Fluids
Rate of flow directly proportional to stress applied
What types of flow do pharmaceutical fluids exhibit?
Plastic flow - Needs a minimum amount of pressure to begin to flow, elastic at pressures before this
Pseudoplastic flow - Material flows with application of pressure, pressure disentangles long molecules to reduce flow resistance
What is dilatant flow?
Addition of pressure increases viscosity of the fluid
Particle disruption causes clumping and larger voids for fluid to fill
Increased in viscosity reversed with removal of shear
Why is dissolution important?
Drug has to be in solution in order to get into bloodstream, other fluids and tissues
What is the Notes-Whitney equation and what does it indicate?
Rate of dissolution
dm/dt = DA(Cs-C)/h
D = Diffusion coefficient, A = SA of particle, h = thickness of diffusion layer, Cs = saturation concentration in diffusion layer, C = concentration in GI fluid
What factors affect the rate of dissolution?
A - Depends on particle size, porosity, dispersibility and wettability
Cs - Depends on solubility in diffusion layer
C - Low conc. maximises Cs - C
D - Depends on the viscosity of the solution
What are the different crystal forms of APIs?
Polymorphs - Metastable or stable, most stable not necessarily most soluble
Amorphous/Crystal - Amorphous more soluble but eventually converts to crystalline structure
Solvates - Higher degree of solvation, lower solubility
How does drug concentration vary in GI fluid?
- Adsorption of the drug to other materials may prevent absorption
- If the drug is chemically unstable it may be broken down in the stomach so less is available for absorption in intestine (enteric coating and pro drug prevents this)
What is the intrinsic dissolution rate of a molecule?
Rate of mass transfer per area of dissoluting surface
What is the importance of in vitro testing?
Predict rate and extent of drug release in vivo to predict absorption
What is the effect of limited solubility?
Dissolution is the rate limiting step of the reaction
What are the experimental conditions used for testing intrinsic solubility?
0.1M HCl, 0.1M NaOH and water used
UV spectroscopy for analysis
Test in temperatures of 4°, 25° and 37°
pH and common ion effect
What are the steps of absorption?
Disintegration
Dissolution
Permeation
Pre-systemic metabolism
How do transit time and stability affect absorption of oral formulations?
If transit time is too fast, medicine is excreted before it is absorbed
Drug may be broken down in stomach/gut or by extensive 1st pass metabolism so low bioavailability
What are the solubility and permeability parameters for formulation?
Solubility - Max dose in 250mL or less over pH 1-8
Permeability - Predicted over 90% absorption
What are the limitations of testing drugs before formulation?
Stability varies in different conditions
Binding interactions of drugs and excipients are not considered
What are the BCS drug classes?
1: HP/HS
2: HP/LS
3: LP/HS
4: LP/LS
What is the main formulation consideration for classes 2 and 3?
2: Maximise dissolution rate
3: Maximise transit time in intestine
How may class 4 drugs be formulated?
Pro-drugs
New formulations
What are the physicochemical factors affecting rate and extent of absorption?
Size and wettability of particles
Solubility and pKa of drug molecule
Lipophilicity of drugs
Stability of drug
What are the biological factors affecting rate and extent of absorption?
Gut motility GIT transit time Local pH Enzymes/surfactants Epithelial SA and physiology Gut contents
How does pH influence drug absorption?
Solubility (esp. for WA/WB)
Stability (drug susceptible to acid hydrolysis)
Gastric pH increases after food
Intestinal pH is affected by food
How does food influence transit time?
Slower gastric emptying after food therefore longer transit time
How can food be used to improve stability of the drug?
Advise to take with or after a meal to increase gastric pH
How can the drug be altered to improve stability in the stomach?
Increase particle size to slow dissolution
Formulate as a salt to alter dissolution
Use enteric coatings to delay disintegration until intestine
What is a pro-drug?
API not released until medicine is absorbed, protects API
Increases solubility
What is the aim of drug absorption?
Peak concentration within therapeutic range
What decides bioavailability and dosage regimen?
Time taken for absorption and elimination
What are the practical issues with assessing bioavailability?
Drug amount has to measured as a conc. and scaled to approximate known volume of blood
Have to account for DME by using a control measurement of injecting the drug
What is the equation for absolute bioavailability?
AUCoral/AUCiv
What is the most common route of administration?
Oral
What are the advantages of tablets?
Increased patient compliance (convenience and aesthetics)
Easy to store and dispense
Better stability
Low cost, easy bulk manufacture
Drug release can be altered
Taste can be masked
Different forms of tablets available to suit patient need
What are the disadvantages of tablets?
Multi stage manufacture results in product loss
Absorption depends on gastric emptying
Powder properties affects compression
May be inappropriate for some patient groups
What is defined as a high dose or low dose API?
High: >80% of total tablet weight
Low: <5% of total tablet weight
How does the size of tablet vary?
Size of tablet is proportional to amount of API so low dose tablets will be smaller
What is the maximum total tablet weight and what is the normal range for an API?
<800mg total weight
5-500mg of API per tablet
How should tablet doses be considered in relation to compliance?
Dose should require no more than two tablets at any time to improve patient compliance
What is the minimum tablet weight and what may be used to achieve this? What properties does this excipient have?
Min. weight 50mg
Low dose tablets will require a filler/diluent to reach this
Fillers/diluents have good compression/solubility properties
What excipients aid disintegration and how?
What percentage of tablet makes up this excipient?
Disintegrants
Facilitate water uptake or rupture from within to break up tablet
1-10% per every 100g of tablet
What is the purpose of a binder? How are they added during manufacture?
What percentage of tablet is a binder?
Formation of tablets with adequate mechanical strength
Added as dry powder or solution
2-10% per every 100g of tablet
What is the difference between a glidant and a lubricant?
Glidants improve flowability of powder to improve compaction or granulation
Lubricants allow easy tablet formation and ejection from a tablet press
What percentage of tablet does lubricant consist of?
0.25-1% per every 100g of tablet
What is an anti adherent and what percentage of a tablet does it make up?
Reduce adherence between tablet and press to maintain even tablet surface
0.5% per every 100g of tablet
What are the purposes of colourants and flavourings?
Improve taste
Improve appearance
Identification
What properties are essential during the manufacturing process?
Powders must be compressible when mixed
Powders must cohere and maintain compaction when pressure is applied
Tablet must maintain structure when removed from the tablet press
Give a basic overview of the tablet manufacturing process
Die filled with contents from stationary hopper
Tablet compressed then ejected
What factors determine the site of drug absorption?
Ka
Lipid solubility
pH of absorption site
What affects dissolution and absorption of sparingly soluble drugs?
Particle size
Crystal form
What four main factors may affect the stability of a drug?
Hydrolysis
Oxidation
Heat
Light
What should be considered when deciding excipients for a formulation?
Interactions with the drug, drug and excipients should be compatible
What are the four unit processes for tableting?
Weighing: Each excipient is weighed according to final tablet weight
Mixing: Ensure uniform distribution of API and standardised powder properties
Tablet manufacture and compression
Quality testing
How are the aims of mixing achieved?
Powder mixed in a number of different planes
Why is powder flow important?
Affects movement from hopper to die cavity (same amount each time under gravity)
What could be the result of uneven flow?
Air trapped within powder
May result in capping or lamination
There may be excess fine powder around the tablet
Powder may be contaminated by dust
How do particle interactions affect powder flow?
Adhesion causes powder to stick to container, free flowing if particle size <250µm
Cohesion reduces flow, gliding should be used or granulation to increase particle size (>50µm)
What characteristics of the powder increase adhesion and cohesion?
Particle size, shape, texture, hardness, surface and distribution
Moisture content (increases)
Particle/bulk density
Temperature
What characteristics of the container increase adhesion and cohesion?
Wall surface roughness Chemical composition Temperature Pressure Humidity Environmental factors
How is powder flow measured?
Tilting table method
Work out angle of repose (angle at which powder will strat to slide down tilted table)
Angle of repose of 15-25° is ideal for powder flow
What is the bulk density of a powder?
Difference between tapped and untapped powder - due to pores
Bigger bulk density increases flowability
How can powder flow be improved?
Uniform, sufficient particle size and shape
Addition of gliding, lubricant or anti adherent
Alter surface forces of particles
Change process conditions
What is granulation?
Powder particles adhere to form granules, increase particle size increases flowability
Also improves compaction
Describe wet granulation
Liquid binder added to powder Damp mass sieved into pellets/granules Drying Sieved again to separate granule sizes Dry lubricant/liquid binder added if required
Describe dry granulation
Large tablets produced by slugging
Material rolled into sheet and milled for desired particle size
What are the advantages of dry granulation?
Only requires two pieces of equipment
Useful for temp/moisture sensitive powders
More economical
Easy to scale for mass production
Tablet compaction not affected by roller compaction
At what stages are tablet properties checked?
Development, manufacture, quality control
What tablet properties are checked?
Uniformity Weight Disintegration Dissolution Friability Fracture resistance Appearance
What are the checks for tablet uniformity?
Check at least 5 tablets
Assay for API content - 90-110% acceptable
Use BP monograph tests
What are possible variations in tablet uniformity?
Non-homogenous powder
Segregation of powders
Compressability issues
How is tablet weight checked?
20 tablets collected from random containers
2 can be >10%
If any over 20% batch rejected
Describe the processes of wicking and swelling
Wicking: water pulled into pores, reducing physical bonding forces between particles
Swelling: particles swell and break matrix from within
How is disintegration tested?
6 small-medium or 3 large tablets tested
Drop one tablet into each tube containing aqueous medium and agitate
Monitor time taken for tablet to break up
If two or more tablets fail, batch is rejected
Define dissolution
The transfer of molecules or ions from the solid state into solution
What are the ways of testing dissolution?
Stirred vessel method (basket or paddle)
Continuous flow method (dissolution medium pumped through cell containing dosage form and controlled rate)
What factors affect dissolution testing?
Temperature and dissolution medium
What is the importance of mechanical strength?
Resistance to wearing and fracture
What does friability test for and how is it tested?
Tests resistance to forces during production, storage and administration
Measured as weight loss during 100 rotations over 4 minutes
What is resistance to crushing?
Force required to split tablet along diameter
Should not fracture
What problems may be associated with tablet appearance?
Chipping
Capping
Lamination
How are gastroretentive tablets absorbed?
In upper intestine Floating in stomach Adhesion to stomach wall Sedimentation in stomach Swelling of formulation in stomach
What are mucoadhesive tablets?
Placement on mucosal membrane for local drug delivery
Why are coatings used on tablets?
Improve physical properties Alter release of API Improve taste and appearance Identification, handling and packaging Protection
What are the two methods of coating? Describe them
Pan coating - Tablet bed sprayed with coating while rotating for even coverage
Fluidised bed coating - Top spray, bottom spray or rotational spray
What coatings usually use the fluidised bed coating method?
Granule coating
Film coating
MR coating
What are the aims of film coating?
Immediate release, improves physical properties of drugs
MR, alter release of API
What compounds are used for film coating?
Polymers
Plasticisers
Colourants
Solvated compounds
What are the desired polymer properties for film coating?
Solubility Low viscosity Permeability Strength and flexibility Adhesion to tablet
Why are short, repeated doses used for film coating? What type of solvent is used?
Short process producing well-distributed coating
Quick drying solvent
What factors affect coating efficiency? What effect can these have?
Shape of tablet and direction of spray
Some areas of the tablet may have a thicker coat than others
What are the problems surrounding film coating?
Erosion, peeling or breakage due to poor friability
Poor mechanical strength
Porous tablet - uneven coating
Peeling due to excess moisture in tablet
How are sugar coatings applied?
Successive applications of sucrose solution by pan coating
What is the purpose of sugar coating?
Mask taste, can be used with film coating for MR release
How long does sugar coating take and what effect does it have on the tablet weight?
> 8 hours
Weight increased by 30-50%
Describe the sugar coating process and the products used in each stage
Seal porous tablet (shellac, PVP, CAP)
Sub coating (bulking agent, binder, anti adherent)
Smoothing - additional sub coat (TiO2+sucrose)
Colouring (dyes)
Polishing (solvated wax)
Printing (edible ink)
What is compression coating?
Core formed from first compression
Core then placed in bigger dye which is filled and compressed
Second compression forms coating
What are the advantages of compression coating?
Dry process
Can be used for formulations containing 2 drugs (one in coating, one in core)
What are the disadvantages of compression coating?
Expensive
Complex
Requires specialist equipment
Cracks in coat may increase tablet porosity and decrease stability
What are the two types of capsules?
Hard capsule
Soft gelatin capsule (if not gelatine may be another animal protein or plant polysaccharide)
What is the advantage of soft gelatin capsules?
Can be used for delivery of poorly soluble oral drugs Useful for potent drugs Safer manufacture (no dust)
Briefly describe the preparation process of a soft gelatin capsule
Gelatin preparation Material preparation Encapsulation Drying Inspection Polishing Packaging
Describe the structure of a two-piece hard capsule
Tapered rim of body for easy closure
Matched locking rings on body and cap
Rounded ends increase mechanical strength
Aerodynamic air vents allow air to escape from cap
How are hard capsules formed?
Capsule supplied as closed unit, opened by vacuum
Capsule filled with powder
Recovery of unused powder
Process repeated
Define shelf life
How long a drug retains its chemical and physical properties without a loss of potency
In what conditions is drug stability determined?
Native form
As formulation during development
As formulation in storage
Why is drug degradation dangerous?
Could lead to formation of potentially toxic species
Describe hydrolysis
Give an example of a group susceptible to hydrolysis
Breakdown of drug due to presence of water
May be catalysed in acidic/basic conditions
Beta-lactam ring
Describe oxidation
Give examples of groups that are susceptible to oxidation
Addition of oxidation or removal of hydrogen Catechols Phenols Amines Thiols Thioethers
Give two examples of drugs that can undergo dimerisation
Ampicillin and amoxicillin
Give an example of a drug that undergoes polymerisation
Gluteraldehyde
How can isomeric changes lead to degradation?
Some stereoisomers may be inactive or have a different effect to other isomer
Give an example of a drug that shows different isomeric behaviour
Ibuprofen - R form has no activity but is converted to active S form in the body
What is photo degradation and what wavelength is most damaging?
Degradation catalysed by UV light
300-400nm
How can degradation of proteins occur?
Conformational changes due to changes in physical conditions
Give one source of non-chemical degradation
Interactions between incompatible excipients and drug
What is the Maillard reaction? What product is formed and how is it prevented?
Reaction between lactose and amide containing drug
Glycosylamine formed, rearranged to 1-amino-2-keto sugar
Use alternative diluent to lactose
Use mannitol as sweetener if required
How can stability be maximised?
Store in ideal temperatures (2-8°, 20°, room temp)
Use non aqueous solvents
Use buffers to maintain pH
Protect from light and oxygen
What is physical stability?
Stability of formulation rather than drug itself
What are the advantages of stress testing?
Deciding formulation approach
Deciding excipients
Determining protective additives
Determining packaging considerations
Why is stress testing used?
Can identify breakdown products
Can be used to determine appropriate storage
May identify excipient incompatibilities
What should be known to determine physical stability?
Drug details: Mr, purity, chemical structure, synthetic impurities, degradation products
Physicochemical properties: Solubility, pKa, partition coefficient
What are the various roles of pharmacists in paediatric treatment?
Industrial: Development of paediatric products
Community: Advising on use of products
Hospital: Advice on use and working with clinical team
Describe the process of paediatric development
Consider therapeutic effect
Consider information from adult clinical trials
What are the different paediatric patient groups?
Neonates: 1-27days Infants: 1-23months Child: 2-11years Adolescent: 12-17years Adult: >18years
How do paediatric formulations differ?
Depends on pharmacokinetics
Age group has to be considered
Dose range affects formulation
Define biopharmaceutics
Study of factors affecting bioavailability
What are the pharmacokinetic differences in children affecting absorption?
Different rate of saliva production
Altered gastric emptying and pH
Altered intestinal transit time, SA and motility
Different metabolic enzymes and transporters
How does neonatal acid secretion differ and what effects does this have?
Reduced secretion
Increased bioavailability of acid labile drugs
Solubility of basic drugs decreased
Drugs with pH sensitive coatings may not be broken down in the correct place
How does paediatric stomach volume affect pharmacokinetics?
Liquid intake smaller so dissolution volume and gastric concentration is altered
Why does permeability decrease with age?
P-gp transporter expression increases
What is the impact of a larger liver in children?
Increased clearance and first pass metabolism
What is formulation bridging?
Comparing the rate and extent of absorption of different formulations
What is the purpose of formulation bridging in paeds?
Determine appropriate dose
Dose adjustment in chronic treatment
Comparison of adult and paediatric formulations
Why do adult and paediatric doses need to be compared?
Medication has to be tested in adults due to ethical reasons
What is in silico physiologically based pharmacokinetic modelling?
Simulates absorption and pharmacokinetics to predict formulation performance
Why is IS physiologically based PKs useful for paediatric formulations?
Physiological parameters can be altered
Why are liquid preparations flavoured or sweetened?
Come into direct contact with taste buds
What group is responsible for sweetness in a compound?
Hydroxyl groups
Organic esters, alcohols, aldehydes
How do coatings influence taste?
Prevent direct contact of the powder with tastebuds
What is the function of a diluent and what are its desired properties?
Bulking agent to enable accurate dosing of potent drugs Unreactive Non-hygroscopic Biocompatible Cheap Well compactible Water soluble Palatable
How do hydrophilic diluents increase dissolution rate?
Create pores in tablet to allow water to enter - breakdown of drug
What type of molecule is a disintegrant?
Polymer
What are the four mechanisms of disintegration?
Wicking - Water pulled into pores
Swelling - Particles swell
Deformation - Particles swell to recompression size
Repulsion - Electrostatic forces from water entering causes particles to repel
Describe the structures of non-ionic and anionic disintegration polymers
Non-ionic: Polysaccharides
Anionic: Chemically modified cellulose or low weight cross linked polyacrylates
How do lubricants work?
Frictional forces between particles and surfaces are reduced
Describe the two types of lubricants
Give an example
Fluid film lubricants: melt under pressure to create a film, resolidify when pressure is removed (hydrogenated vegetable oil)
Liquid lubricants: Released from granules with application of pressure, reabsorbed with removal of pressure
What is the purpose of a binder?
Agglomeration of powder particles by alteration of inter particle adhesion
Mixed with granulation fluid in wet granulation process
What molecules are used as binders? Give some examples
Natural/synthetic polymers
Sugars
PVP, gelatin, polyethylene glycol
Give some examples of chemical antioxidants and when they are used
Sodium Sulfite: High pH aq. solutions
Sodium Bisulfite: Neutral pH aq. solutions
Sodium Metasulfite/Ascorbic Acid: Low pH aq. preparations
Alpha-tocopherol/Ascorbyl palmitate: Lipid preparations
Give an example of a chelator and state its purpose
EDTA, prevent precipitation of metals or reaction with other excipients
What is a buffer and what is its purpose?
WA and its salt
Maintain pH of aq. solutions
When are buffers used in suspensions?
When pH is important for route of administration or if solubility induces pH change
What may be affected by the ionic nature of a buffer?
Flocculation properties or ionisation states
When are antimicrobial preservatives required?
When water is present in a formulation
Describe benzalkonium chloride
Cationic surfactant
Dissociates to form Cl- and long chain ionised surfactant moiety
Not a pure substance due to molecules of varying length
What is controlled by viscosity enhancing agents?
Palatability
Ease of pouring
Rate of particle sedimentation
Why may viscosity enhancing agents reduce absorption?
Interactions between drug and hydrophilic polymer
What should be balanced in a suspension?
Maintenance of suspended state with ease of use (controlled viscosity)
Give some examples of insoluble inorganic viscosity enhancers
Tragacanth
Gum arabic
Bentonite (clay)
What viscosity enhancers can be used to prevent interference with flocculation?
Cellulose ethers
What is the issue with drug incorporation into a micelle?
Micelles are excreted so drug will not be absorbed
How do chemical/physical reactions between excipients and APIs affect pharmacokinetics?
Physical: Alters dissolution and bioavailability
Chemical: Alters stability and bioavailability
