P12 - topical drug delievery 2

what are the 5 challenges to consider in developing topical formulation

1. drug-vehicle interactions

2. formulation matching

3. vehicle-skin interactions

4. balancing efficacy and safety

5. mechancical effects

what are the 5 steps in formulation strategies

1. characterise the drug - MW, LogP

2. estimate theoretical delivery

3. learn from existing data

4. select candidate vehicles

5. evaluate safety

what is prefered for chronic skin diseases

hydrocarbon based formulations for their occlusive and protective properties

drug solubility can be improved in these systems using hydrocarbon miscible solvents

what are water free formulations typically used for

psorisasis, chronic eczema, mycoses

whie or off white colour and occlusive

what are polar gel formulations

single phase, semi solid systems usually based on water and or alcohol with low or no lipid content

what characteristics do polar gel formulations have an what are they used for

• cosmetically elegant, non-greasy, rapidly absorbed but provide little occlusion

• commonly used for anti-inflammatories, anti-allergic, acne

• variants include hydrogels, emulgels, suspension gels

whats a hydrogel

water based gel matrix

drug is dissolved

low occlusivity

anti-inflmmatories, anti-allergics

whats an emulgel

• hydrogel + dispersed lipid phase

• moderate occlusivity

• enables delivery of hydrophobic drugs through dual release

• drugs needing elegance and occlusion

whats a suspension gel

• hydrogel with suspended drug particles

• low occlusivity

• poorly water soluble drugs

what are creams

• disperse two phase systems and represent the majority of aqueous topical formulations

• they require emulsifiers to stabilise mixtures of oil and water phases

• oil droplets in water (O/W) or water droplets in oil (W/O)

What does the internal microstructure of creams directly influence

1. physical stability

2. drug release

3. skin feel and cosmetic properties

whats good about W/O emulsions

• has oil as the continous phase

• blends easily with SC lipids

• improving BA of lipid soluble drugs and moisturising the skin through a sligh occlusive effect

whats good about O/W emulsions

• has water as the continuous phase

• more cosmetically appeakling as formulation is less sticky and greasy

what does contact of the outer aquoeus phase in O/W emulsions with skin increase

water evaporation, producing a cooling effect affter application

however may withdraw moisture from the skin due to surfactant like emulsifiers that can extract or perturb SC lipids

what is W/O lotion

hydrophobic, semi liquid, two phase system with water dispersed in a continuous lipid phase

whats a W/O cream

hydrophobic ,semi solid system

whats O/W lotion

hydrophillic, semi liquid, two phase system with lipids dispersed in a continuous phase stabalised with O/W emulsifiers

whats O/W cream

hydrophillic, semi solid two phase system

continuous aq pahse reuslts in low occlusion - so suitable for inflammed skin while promoting comfort and cooling effect

if two cream formulations and one ointment all containing the same steriod concentration deliver signifcantly different quantaties of drug across the skin what does this mean?

formulations are therapeutically inequivalent

whats absorption base

• apolar

• single phase

• semi-solid system of hydrocarbons with complex emulsifiers

whats liposome formulations

• bi or multilamellar phospholipid vesicles with a hydrophillic core for drug entrapement

what are nanoemulsions

vesicles of phospholopids, surfactants and lipids dispersed in water

whats a microemulsion

transparent O/W or W/O colloidal emulsions of lipophillic and hydrophillic surfactants and water

whats an emulsifier free system

• two phase

• semi solid

• hydrophillic formulations with lipids

• continuous aq phase

• polymers/co polymers

whats a multiple emulsion

• three phase semi solid systems

• hydrophilllic -W/O/W

• hydrophobic - O/W/O

What spray emulsions

• stable

• sprayable

• two phase semi-liquid emulsions

whats foam/mousse formualations

gas dispersed in lipid-water mixtures, stabilised with surfactants

whats a water free two phase system

semi-solid physical mixture of two non-miscible organic phases stabalised with polymers/co polymers

whats a lacquer

polymeric film-builders in volatile solvents with plasticisers, forming transparent, elastic, adhesive films on skin or nails

what can rubbing or loss of volatile excipients cause

an increase in viscosity of the formulation

what can mechanical action cause

produce emulsifying effects

what does evaporation of volatile solvents cause

changes drug soluability in the remaining formulation altering thermodynamic activity and skin penetration

loss of solvent often increases thermodynamic activity until the drug reaches saturation