3 Flashcards
Wound definition
Defect or damage in skin caused by chemicals, physical forces, thermal causes or disease
2 broad classifications
Wound without tissue loss: eg surgeryWound with tissue loss: eg trauma or burn wounds
Incisions
Regular wound Caused by a clean sharp edged object
Laceration
Rough and irregular wound Caused by crushing or ripping
Abrasion (graze)
Superficial wound where top layers of skin are lost Caused by sliding on a rough surface
Puncture
Caused by sharp pointed object punching skinChance of anaerobic bacteria infection
Penetration wounds
Caused by entering the body
Avulsion
When the integrity of any tissue in the body is compromised Where something is basically torn off
Contusions
A bruise Caused by blunt force trauma
Haematoma
Caused by damage to blood vessel Blood then accumulates under the skin
3 phases of healing
1) Inflammatory 2)Proliferative 3) Remodelling
Inflammatory phase
Bleeding first to remove toxins Vasoconstriction begins to stop bleeding Coagulation initiated by platelets forming fibrin network Phagocytes engulf dead cells in the wound
Proliferative phase
Granulation tissue builds up in wound space due to fibroblasts and macrophages providing growth factors. (Occurs 2-3 days after wound occurs) This stimulates fibroplasia and angiogenesis (new blood vessels)Fibroplasia causes a bed of collagen to fill defect, pulling wound edges together
Remodelling phase
3 weeks after wound occurs Fibroblasts spur on greater collagen formation which forms a helical structure with inter and intra X links The tissue will not regain the properties of uninjured tissue
What pericytes?
Pericytes can differentiate into myofibroblasts Vascular pericytes can enter the wound bed and can assume a more contractile and matrix depositing phenotype
Petroleum impregnated dressing
For clean, healthy and shallow wounds Use at early stages of wound repair Use non adhering dressings for exuding wounds such as burns
Hydrogel dressings
Hydrogel sheets- for shallow wounds Can maintain moisture balance while absorbing exudates Hydrogel gels- for cavities, good for debriding and dislodging They donate moisture Promotes collagenase activity, granulation, epithelisation and contraction
Hypercolloid dressings
For early to mid repair wounds Reduces pain and promotes angiogenesis Used where granulation is necessary For minimal to moderate exudation Promotes moist wound healing and granulation
Foam dressings
Non adherent Absorbs large amounts of exudates For deep wounds with mild to moderate exudates Best used after granulation to encourage epithelisation and contraction
Alginate dressings
Made brown algae Good gel/film forming properties Calcium alginate promotes clotting cascade (10x faster compared to petroleum dressings)For burns, shearing/avulsion, cavity wounds Best for moderate to highly exuding wounds
Film dressings
Semi permeable allowing fluid to evaporate whilst still keeping wound moist Comfortable and resistant to wear/tearPrevents bacterial colonisation but does not absorb exudate
Natural polymers
Usually protein or polysaccharide in nature Bio-compatible, degradable and hydrophilic Does however vary batch to batch and can degrade way too fast
Collagen dressings
The protein is made of three peptide chains with triple helical domains Promotes healing via attachment and migration Dry collagen physically absorbs blood and traps them which adheres them to the wound site giving mechanical strength
Chitosan dressings
Made by acetylating chitin Active in slightly acidic media and releases beta 1-4 linked-D-glucosamine (used for hemorrhage control)Promotes fibroblasts, collagen deposition and platelet/RBC mobilisation as well as vasoconstriction Good film forming properties
What is an Aerosol?
A relatively stable suspension of solid/liquid particles in a gaseous medium (0.001mcm-100mcm)
Aerosol behaviour is affected by…
Interaction with surrounding air molecules and gravityIt’s own size, shape and density
The target site of aerosolised drugs is …
Respiratory bronchioles and alveoli
The pattern of deposition in the lungs…
The larger the particle the further up the airways it is deposited with any particle >10mcm getting trapped in the back of the throat
Advantages of inhaled drugs (local delivery)
-Drugs delivered directly to site of action -The onset of action is rapid -Less drug gets into systemic circulation (For local delivery)-Less of the drug is necessary for a therapeutic effect
Advantages of inhaled drugs (systemic delivery)
-Extensive blood supply allows for rapid absorption into systemic circulation -Avoids 1st pass metabolism -Therefore increased availability
Factors controlling deposition
Aerosol properties- size and distributionMode of inhalation- volume inhaled, flow rate and breath holding pausePatient factors- anatomy/physiology differences, respiratory disease But primarily affected by size and flow rate
Primary deposition mechanisms in the lung
Inertial impact (90%)- kinda just smacks into epithelium because they’re moving in a straight line. Mostly large particlesSedimentation (9%)- the particle moves along slowly, loses energy and plops down. Important for depositing in bronchiDiffusion (1%)- Particle happily floats along an settles down at a dead end, Earns lots of frequent flyer points. Important for deposition in bronchi/alveoliThe smaller the diameter the further along the resp. tract it gets. Small bois fly far. Oropharynx>bronchi>alveoli
Secondary deposition mechanisms
Interception- where particles contact walls (especially fibres at airway bifurcations Electrostatic deposition- charged particles can repel each other towards walls
5 essential components of a MDI
DrugPropellent Aerosol canister Metering valve Atomising nozzle
Suspension based formulation
Suspensions preferred due to chemical stability and is capable of delivering high powder loads Drug must be milled to respirable size <5mcm and must be insoluble Shaking required to redisperse drug to ensure suspension is homogenous
Role of adjuvant
To ensure physical stability of suspension Must be capable of dispersing and redispersing the drug Minimise segregation before administration of the drug
Common surfactants
SPAN 85, oleic acid and soya lecithins in CFC’sOleic acid, magnesium stearate, PEG/PVP in HFA’s
Solution based formulations
Suitable if solubility/stability is adequate Amount of emitted dose is directly related to solubility therefore usually requires a cosolvents as propellants are usually poor solvents Potential for drugs to recrystallise due to changing temperatures
Problems of solution based formulations
Polar co solvent can cause corrosion of Al cannister Co solvent lowers internal propellant pressure therefore atomisation less effective Modifying drug to be more soluble is most effective solution
Liquid propellant
Good because no loss of pressure after actuations This because the loss in pressure causes vapourisation of the propellant which restores the pressure within the cannister
Advantages of pMDI’s
Consistent dose Cheap Resistant to moisture Compact
Disadvantages
Patient coordination required Cold freon effect results in inconsistent deliveryTail off at the end of a can High deposition in throatVery little intellectual property protection for pharm R and D
DPI’s (Dry powder inhalers)
Driven by patient inspiration Easy to use Patient/environment friendly Long term replacement for pMDI’s
DPI mechanism of action
Inspiration creates energy for fluidisation and entrainment of formulation Energy caused by pressure drop (deltaP) that s due to inhalation flow (Q) and internal resistance of device (R)A minimum inhalation flow must be created (Qmin) before dose can be released
Relationship between device and airflow
R effects speed/acceleration of airflow through the device Acceleration effects DPI efficacySpeed affects the amount deposited in the lungs
Factors affecting respirable dose
R, Q and the powder formulation
Particle interactions are dictated by…
Van der waals forces Electrostatic forces Capillary forces Contribution of each of these depends on interacting materials and humidity
Van der waals forces
Dominant at short range in low humidity where there is no electrostatic forces
Capillary forces
Water condenses between to particles and forms a liquid bridge Force directly related to humidity and hydrophobicity Dominant at ambient conditions
Electrostatic forces
Due to friction between different materials Long range force Can be attractive or repulsive and increase at low humidity
3 interactions that must be controlled
Drug-drug (Cohesion)Drug-excipient (Adhesion)Drug-device (Segregation)
2 formulation strategies
Carrier based- uses adhesion to bind drug to a carrier Agglomerated- uses cohesion to form an agglomerate which is broken up during inspiration
Advantages of carrier based formulations
Accurate dosing of small quantities of a potent drug Improved handling and processing Carrier size, shape and morphology can be changed to influence fine particle friction (FPF)
Advantages of agglomerated powder systems
More suitable for high dose drugs However efficient deaggregation of agglomerate must occur so that drug is presented as discrete particles in the lung
Advantages of DPI’s
Propellant free No or very little excipientsLarge doses can delivered In dry form Breath actuated
Disadvantages of DPI’s
Dependant on patients inspiration force Due to higher velocity there is increased chance of inertial impaction Exposure to ambient conditions can reduce stability Less efficient at delivery than a pMDI
Nebulisers
A drug contained within a sterile solution Significant variation occurs a lot drug being left within the device, in expiration and many particles are to small or large As little as 10% of the target dose maybe delivered
Pneumatic nebuliser
Works by using a high velocity air jet to blow air very quickly causing them to break into small particles A baffle (inertial filter) traps oversized particles
Pneumatic nebuliser pros and cons
Cheap and can achieve small particle sizes But: has variable performanceDead (stagnant) volume Lower outputNot very portable
Ultrasonic nebulisers
Uses a piezoelectric ceramic disc which oscillates and causes droplet production
Ultrasonic nebuliser pros and cons
Consistent Produces small particles High output Small and quiet But: low inertiaparticle size increases at end of life expensive heats solution to 40 degrees celsius Unsuitable for suspensions
Soft mist inhalers (SMI’s) and Liquid dose inhalers (LDI’s)
Based on a drug dissolved in non volatile liquid Volumetric dosing Breath actuated Dose emitted as a slow moving cloud
AERx LDI
A hand held nebuliser Uses an actuater to extrude drug, held in 50mcl through tiny micron sized holes Microelectronics guide patient for optimum inspiration
Respimat mechanism
Drug stored in solution Solution is forced through micro nozzle as patient inhales
Respimat advantages
Avoids moisture problems and powder aggregation that can occur with DPI’s Can deliver a metered dose
Advantages of nasal systemic delivery
Avoids 1st pass effect and intestinal metabolism Acid sensitive drugs can be used Polar compounds with poor absorption can be used Small lipophilic drugs can be used Easy to use
Functions of the nose
Major: AC-temperature -humidity -filtration Minor: Smell
Structural features of nose
Volume: 20ml Surface area: 150cm cubed Rich blood supply Lots of turbulence
Nasal epithelium: Ciliated cells
200 cilia per cell Movement slightly out of phase with neighbors
Nasal epithelium: Pseudostratified columnar epithelium
Has a large surface area due to microvilli Protective mucus layer and cilia for clearance
Mucus consists of…
90-95% water 1-2% salts3% lipids 0.5-5% proteins
Functions of mucus
Traps particulates Physical barrier between epithelium and outside Can bind to drugs preventing diffuse of drugs Contains enzymes which may degrade drugs
Clearance in the nose
If particles are deposited on:Ciliated regions: quick clearance Non ciliated: slower clearance Nasopharyngeal region: gets swallowed and therefore not available Mucus clearance ~ 10-20mins Spray usually better than drops unless v. rapid absorption
How much of the drug delivered nasally is deposited in lungs?
None.The major is in nose, pharynx and stomach
Effect of molecular weight on absorption
Small MW=well absorbed Absorption >500= much worse MW>1000= 1-3% at most
Nasal formulations
Aqueous based so as not to effect clearance of cilia Generally used to treat congesion, allergic rhinitis and infection
Requirements for nasal formulation
pH between 5.5 and 6.5Must be isotonicViscosity should be similar to that of mucousMust has preservative as it is multidose Antioxidants for those drugs at risk of degradation
Delivery to brain through nose
Olfactory epithelium is one small area (4 cm2) where BBB is not present Drugs can enter via paracellular paths/axonal paths through olfactory nerves
Ways to improve nasal delivery
Surfactants/bile salts reduce viscosity of mucus which can increase drug absorption Use mucoadhesives to increase contact time with epithelium Primary purpose is to increase uptake of peptides
ViaNase and Optinose
Devices that alter turbulence in nose thereby increasing the dose delivered and minimising lung deposition
Anatomy of ear: external auditory canal
Around 23.5 mm in length 4.8-9.3mm wide
Anatomy of ear: Middle ear
(Not to be confused with my home, middle earth)Tympanic membrane separates external and middle ear The cavity is small and contains 3 auditory ossicles Infections can spread here
Anatomy of ear: Inner ear (Labyrinth)
Contains cochlea (hearing) and vestibular system (balance)Pretty inaccessible, difficult to pop in drugs (also due to blood-cochlea barrier)
Inner ear drug delivery: intra tympanic
High amounts of drug must diffuse into scali tympani across round window membrane from middle earRWM permeability is variable so drug accuracy not very good Drug can also be lost into pharynx via eustachian tube
Inner ear drug delivery: intra cochlear
Can implant drugs directly into cochlear per-ilymphatic spaces Such drugs have direct access to cells of inner ear Delivered via micro/osmotic pumps
Emulsions and suspensions
Liquid or solid phase in external liquid phase Disperse phase=the phase that is split up Continuous phase=the phase in which the disperse phase is split into
Why do emulsions/suspensions require stabilisers?
They are inherently unstable systems therefore to give an acceptable shelf life stabilisers are necessary
Emulsions attain equilibrium when…
When internal droplet join up to form one micro phase with the smallest possible surface area
3 ways in which particles encounter one another in suspension
Brownian movement Creaming/sedimentation Convection
Sedimentation rate (Vsed) is affected by…
Particle diameter= increase cause increase in Vsed Particle density= increase causes increase in Vsed Viscousity= increase cause decreases in Vsed
Vtotal=Va+VrExplain this equation
Calculates total energy of interaction Va=attractive potential energy Vr=electrostatic repulsive energy
Where do different forces dominate?
Primary minimum-At v.short distances attraction dominates causing particles to agglomerate Primary Maximum-At medium distance repulsive forces dominate and particles remain in suspension Secondary minimum-At larger distances repulsive force lessens and particles have weak attraction
Effect of electrolytes on stability
Low conc gives a larger primary maximum but no 2ndry minimum Moderate conc gives a 2ndry min allowing flocculation to occur as well as a primary max. preventing coagulation High conc. gives no primary max or min
Flocculation
Forms loose aggregates preventing caking Held together with weak interparticulate forces forming a lattice type structure.
How does caking occur?
Where particles are deflocculated they aren’t associated and so settle on top of one another The pressure from the particles on top pushes to the bottom particle into the primary minimum This irreversibly binds the particles
Microemulsions
Homogenous, transparent and low viscosity Low interfacial tension but v. high interfacial areaLots of surfactant necessary (surfactant+2nd cosurfactant usually)
Semi-solid emulsions
Stable o/w cream with:dispersed oil phase crystalline gel phase crystalline hydrate phasebulk phase containing dilute surfactant solution
What is a liposome?
Vesicular structure made of a bilayer around a aqueous coreConsidered as a liquid crystal
Functions of liposomes
Carries strongly hydrophobic drugs within bilayerCarries strongly hydrophilic drugs in aqueous coreCarries intermediate logP drugs somewhere between
Rigidity and permeability of lipsomes is determined by…
Alkyl chain length and unsaturationCholesterol for rigidity
Why use liposomes as carriers?
Biocompatible and degradableBiologically inert and low toxicity
Conventional lipsomes are…
Neutral -vely charged Passively targets MPS cells in liver spleenThey are rapidly taken up by phagocytes and taken from blood circulationeg. carries amphotericin B, doxorubicin and hep A vaccines
Sterically stabilised liposomes are…
Covered in a hydrophilic coating allowing for a prolonged circulation timeThe hydrophilic PEG group creates barrier against interaction with cellular componentsCan cause transient reactions in a subset of patients
Immunoliposomes are…
sterically stabilised or convetionalThey have specific antibodies on their surface and are targeted at cancerThe steric PEG chain can interfere with antigen binding
Cationic liposomes are…
+vly charged and carry genetic material. Thischarge interacts with -ve DNA condensing it into a more compact structureCan activate complement and cause adverse effects
Three layers of the skin and their thickness
Epidermis- 100 micronsStratun Corneum- 10 micronsDermis- 1000 microns
What is the Stratum corneum (SC)?
The brick wall layer Made up of corneocytes (brick) and corneodesmosomes (rivets) and mortar (complex lipid mixture)Prevents water loss
Pathways through SC
Transcellular- striaght through cells Intercellular- around cells through ‘mortar’Follicular- through hair folliclesEccrine- through glands in the skin
Jmax=(Ksc/v D/h) x CsatvExplain this equation
Ficks law of maximum diffusionJmax=max diffusionKsc/v=SC/vehicle partition Coefficient of drugD=diffusivity in membraneh=diffusion path lengthCsatv=saturation concentration of drug in vehicle
Why is the previous equation shortened to Jmax=D/h x CsatSC?
Under ideal circumstances Jmax can be independant of vehicle so it is removed from equationThis however assumes vehicle does not alter SC properties or the drug conc in SC
logKp= -2.7+(0.71x logP)-0.00061x MW)What is this equation and why does Guy love it so much?
Him and his mate invented itIts predictive of the permeability coefficient
What does introducing a co solvent do?
Increases Csatv (solubility in vehicle) but decreases Ksc/v (the partition coefficient)Therefore it is predicted that there will be a decrease in flux when % of cosolvent> the level required to just completely dissolve the drug
Effects of physiochemical properties on bioavailability
Increasing lipophilicity gives greater flux (to an extent)Jmax decreases with increasing MW
Rtotal=Rsc +RedExplain this equation
This calculates total resistanceRsc= resistance of SCRed= resistance of epidermisRsc»Red therefore Rsc is rate determining factor
Effect of pH on percutaneous drug delivery
Skin is acidic so non ionised drugs most easily absorbedReally high/low pH is pretty damaging to skinTherefore pH is usually kept near neutral
Formulation preferred for chronic skin conditions
Hydrocarbon based formulations preferred for occlusive properties However not very good for topical drug delivery due to poor drug solubility Solubility can be enhanced with solvents like isopropyl myristate or propylene glycol
4 water free formulations
PEG gel- 1 phase, semi solid, polarLipogel- 1 phase, semi solid, polar, based on triglyceridesOleogel- 1 phase, semi solid, polar, triglyceride+ hydrocarbon+ inorganic fillerFatty ointment- 1 phase, semi solid, non polar, hydrocarbon based
Polar gel formulations
Water/alcohol based can low lipid or lipid freeCan be made into emulsions (emulsion gel) and suspension gels Not good for occlusive treatments (eczema/psoriasis)
2 types of gel formulations
Hydrogel- semi solid, made of large organic mlecules interpenetrated by water Emugel- 2 phase, semi solid similar to the above but with a small fraction of emulsified lipids
Creams (emulsions)
Adjustable Requires stabilisers Dispersion is effected by emulsifier films at the oil/water interface
Effect of w/o compared to o/w
w/o has higher F as it blends easier with SC lipids but o/w is preferred by patients as it isn’t sticky/greasyAlso provides cooling effect as aqueous continuous phase evaporates but can withdraw moisture from skin due to surfactant like emulsifiers
2 types of w/o creams
w/o lotion- hydrohobic, semi liquid, 2 phasew/o cream- hydrophobic, semi solid, 2 phase
Post administration formulation metamorphosis
Evaporation of solvent can change drug solubility in residual phase This usually leads to an increase in thermodynamic activity until saturation is reached At this point either supersaturation occurs or a reduction in permeability
Drug delivery to targets below the skin
Eg NSAID’s Has lower systemic circulation therefore less side effects
Parts of the eye (that i don’t know)
Conjunctiva- fleshy bit under eyeCornea- clear membrane that covers the eye ballChoroid- blood vessels that supplies the back of the eyeSclera- the white of the eye
Advantages of ocular administration
Drug delivered straight to target site Higher conc. at target site achieved than with oral forms Lesser side effectsRelatively easy for patient to self administer
Disadvantages of ocular administration
Poor drug retention and high clearance from eyeRequires frequent dosing therefore is inconvenient for patient Must be sterile Ointments can cause blurring and other forms can cause local irritation