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