D5-D6 Liquid medicines Flashcards
state 3 types of liquid medicines
- suspensions
- solutions
- emulsions
describe a solution
all ingredients are dissolved and therefore present as single molecules within the liquid
describe a suspension
insoluble solid particles dispersed in the liquid
describe an emulsion
- insoluble liquid droplets dispersed in another liquid
- eg. oil soluble and water soluble products together
in liquid medicines, describe the excipient: the vehicle
- the most common vehicle is water (must be BP quality)
- thick sweet liquids eg. syrup, sorbitol solution, glycerol
- more appetising and easier to pour and measure in a spoon
- other liquids eg. alcohol, ether, propylene glycol (mainly for external medicines eg. wart remover, acne treatment etc.)
what is the difference between the 2 liquid medicine vehicles of purified water BP and water for injection BP?
purified water BP
- used in liquid medicines
- low level of salts and impurities
water for injection BP
- sterile and particle-free
- used in injections and eye drops as you don’t want particles in these because they could block small blood vessels or irritate the eyes
in liquid medicines, describe the excipient: preservatives
- type of stabiliser
- inhibit microorganism growth
- added to water-containing medicines to prevent food poisoning, contamination of the medicine causing reinfection and microorganisms degrading the medicine
what are some issues with preservatives in liquid medicines?
- patients may react to them eg. allergy to skin products
- pharmacist must select an appropriate product
- ‘specials’ manufactured without the preservative that the patient may react to
state some ingredients that can act as preservatives
- internal: sorbates, benzoates, benzyl alcohol, methyl, ethyl, propyl parahydroxybenzoate
- external: benzalkonium chloride, benzethonium chloride, thiomersal, borates, chlorocresol, chlorobutanol
other:
- dehydrate microorganisms so they’re unable to multiply: glycerol, sorbitol, syrup (only at high concentrations)
- alcohol >10%
- diluted chloroform (toxic at high concentrations)
in liquid medicines, describe the excipient: antioxidants
- type of stabiliser
- react with dissolved oxygen
- oxidised more easily than the drug or other excipients so they terminate oxidation and free radical reactions
- oxygen then won’t be available to react with what you want to protect
- can be water-soluble or oil-soluble
examples of water-soluble antioxidants
- ascorbic acid (vitamin C)
- sulphites
- sulphur dioxide
examples of oil-soluble antioxidants
- tocopherol (vitamin E)
- butylated hydroxyanisole (BHA)
- butylated hydroxytoluene (BHT)
what are chelating agents?
- form complexes with heavy metal ions
- reduces their ability to catalyse oxidation reactions
- eg. EDTA
in liquid medicines, describe the excipient: buffers
- type of stabiliser
- mixture of weak acid and its salt or a weak base and its salt
- helps the conc of protons in solution (and pH) remains the same
explain what happens when a base or acid is added to a buffered solution
- if small conc of base is added, hydroxide ions react with weak acid to form salt and water
- if small conc of acid is added, protons react with salt to form acid and water
what pH range must medicines be in?
3-9
what is the pKa of a buffer?
the pH at which the concentration of the 2 buffering species are equal
eg. the weak acid and its salt
why are buffers important in liquid medicines?
- pH can affect the tastes of medicines
- alkaline will taste soapy
- acidic will taste sour
what are the 4 different types of sweeteners that can be used in liquid medicines?
- sugars
- glycerol
- sugar alcohols
- artificial sweeteners
describe the common form and characteristics of sugars being used as sweeteners in liquid medicines. what can they be if undiluted?
- syrup BP (67% of sucrose in water)
- causes tooth decay
- preservative if undiluted
describe the common form and characteristics of glycerol being used as a sweetener in liquid medicines. what liquid medicine is it often used in and why?
- glycerol BP
- often used in cough medicines (demulcent: helps with irritation)
describe the common form and characteristics of sugar alcohols being used as sweeteners in liquid medicines.
where are they often used? who are they suitable for? what can they cause?
- sorbitol BP (70% sorbitol in water)
- often used in sugar-free medicines
- no tooth decay and suitable for diabetics
- not calorie-free
- can cause bloating, cramps, diarrhoea
describe the characteristics of artificial sweeteners being used as sweeteners in liquid medicines
- different taste
- no calories or tooth decay
- safety is unknown
in liquid medicines, describe the excipient: flavourings
- taste mask the drugs
- can be natural, natural identical or artificial
what is meant by a natural identical flavouring?
same chemical structure as a natural product but made in a lab
what flavouring should be used to combat a sour tasting medicine?
fruits
citrus
what flavouring should be used to combat a soapy tasting medicine?
chocolate
caramel
aniseed
what flavouring should be used to combat a salty tasting medicine?
vanilla
butterscotch
cinnamon
what flavouring should be used to combat a bitter tasting medicine?
chocolate
mint
liquorice
what flavouring should be used to combat a medicine with strong aftertaste?
liquorice
aniseed
state the 5 types of traditional flavourings
- oils
- spirits and tinctures
- concentrated waters
- waters
- syrups
describe the traditional flavouring: oils
give example
- the pure oil
- very concentrated
- straight from the plant
eg. peppermint oil
describe the traditional flavouring: spirits and tinctures
give example
who may they be unsuitable for?
- concentrated oil or flavour in alcohol
- not suitable for those who don’t drink
eg. peppermint spirit
describe the traditional flavouring: concentrated waters
give example
- concentrated solution or emulsion in water
eg. concentrated peppermint water, concentrated chloroform water
describe the traditional flavouring: waters
give example
- the most diluted form
eg. double strength chloroform water
describe the traditional flavouring: syrups
give example
- a flavour syrup
eg. orange syrup BP
what are the 3 different types of colours that can be used in liquid medicines?
- synthetic
- inorganic
- natural
describe synthetic colours used in liquid medicines
- thousands available
- commonly have an azo group (-N=N)
- more permitted for skin use, cosmetics and clothing (there are few that are safe to ingest)
describe inorganic colours used in liquid medicines
- iron oxides (yellow, red, black) used in tablet coats (to make them a different colour or more shiny)
- titanium dioxide (white): opacifant
what colour is betanin and where does it come from?
purple
beetroot
what colour is cochineal and where does it come from?
deep red
beetles
what colour is lycopene and where does it come from?
red
tomatoes
what colour is caramel and where does it come from?
brown
burnt sugar
what colour is curcumin and where does it come from?
yellow
turmeric root
what are the issues with colours as excipients in liquid medicines?
- not essential
- adverse effects
- gradually being withdrawn from food / medicines in the EU
- natural are usually safer but more likely to trigger allergy
state some example of adverse effects that have been caused by colours in liquid medicines
- azo dyes are linked to bronchoconstriction in those with asthma
- 6 food colourings have been linked to hyperactivity in children
- titanium dioxide may be linked to colorectal cancer
in liquid medicines, describe the excipient: solubility enhancers
- help solubilising the drug and excipients
eg. cosolvents, surfactants
describe surfactants
- long molecules that have hydrophilic head and a hydrophobic tail that self-assemble into micelles
- form micelles in water which helps dissolve hydrophobic drugs in water when they wouldn’t naturally do this
what are some issues with suspensions?
- poor physical stability
- prone to caking and separation
what is caking and separation?
- over time, undissolved particles fall to the bottom of the bottle due to gravity
- at an early stage, this is called separation and the particles can be redispersed by shaking the bottle
- after a prolonged time, the particles at the bottom start to stick together and ‘cake’
- this is difficult to redisperse
why is caking dangerous?
- bottom of bottle will have a very high concentration of drug
- may cause an overdose
how can separation and caking be prevented?
- tell patient to always shake the bottle before taking
- decrease size of suspended particles by grinding and sieving
- increase the viscosity of the vehicle (add thickening agent)
- flocculate
- improve ‘wetting’ of suspended particles (add surfactant)
in liquid medicines, describe the excipient: thickening agents
- increase the viscosity of the vehicle
- slow down the fall of suspended particles
- can be used to increase residence time of external medicines at site of action eg. eye drops
- tend to be long molecules
what are some common examples of thickening agents?
- cellulose ethers
- polysaccharides
- synthetic polymers
- proteins
what kinds of liquids can conical measures be used to measure?
- free-flowing liquids
- not viscous liquids
how can you measure viscous liquids?
- weigh them taking their density into account
- small amount: weighing boat
- large amount: beaker
- rinse vessel afterwards and add washings
do conical measures require rinsing?
no
