Solutions

Question 1

What is the difference between a solvent and a solute?

Answer 1

A solvent is the liquid in which the solute is dissolved in to form a solution (and so a solute is the minor component)

Question 2

What are the types of aqueous solvents used in solution?

Answer 2

Water (potable, purified) or co solvents (these aid dissolution if the components aren’t totally soluble in water e.g. ethanol, glycerol)

Question 3

What are the different solubilities of drugs?

Answer 3

• very soluble (1g in 1ml)
• freely soluble (1 in 1 to 1 in 10)
• soluble
• sparingly soluble
• slightly soluble
• very slightly soluble
• practically insoluble (1 in more than 10,000)

Question 4

What factors affect solubility?

Answer 4

Temperature, molecular structure, solvent, particle size, pH

Question 5

What are the formulations of solutions?

Answer 5

oral, drops, sprays, aerosols, lotions, mouthwashes, enemas, injections

Question 6

What are the types of oral solution?

Answer 6

Syrup (85% sucrose/sugars), Elixir (contains alcohol, sugar), Linctus (viscous liquid for coughs)

Question 7

What are the advantages of oral solutions?

Answer 7

• easier to swallow
• fast GIT absorption
• even mix (don’t need shake)
• more stable than suspensions

Question 8

What are the disadvantages of oral solutions?

Answer 8

• less stable than solids
• may taste unpleasant and may be hard to mask this
• accuracy of dosing can be difficult

Question 9

How are doses given for oral solutions above and below 5ml?

Answer 9

For 5ml or above, a measured spoon is provided but for below 5ml, an oral syringe must be provided.

Question 10

What excipients are needed in oral solutions?

Answer 10

• vehicle (water, syrup, alcohol, glycerol, oils, propylene glycol)
• preservatives (can use syrup if above 65%)
• sweeteners
• colouring agents
• stabilisers (such as antioxidants)
• thickeners
• buffers

Question 11

What are the number of drops required for each dose of eye, nose and ear drops?

Answer 11

Eyes 1-2 drops
Nose 2-3 drops
Ears 3-4 drops

Question 12

1ml contains how many drops?

Answer 12

20

Question 13

Eye drops must be sterile, how is this achieved?

Answer 13

By adding preservatives and providing single use vials

Question 14

What are the excipients needed in eye drops?

Answer 14

• sodium hydroxide for 0.9% tonicity
• viscosity enhancers such as hypromellose to prolong contact with the eye
• buffers for stabilise pH at 7.2-7.4
• antioxidants to prevent oxidation
• preservatives (benzalkonium chloride is the most common but it isn’t compatible with contacts so chlorhexidine is used)

Question 15

What are nasal drops used for?

Answer 15

Local: congestion, inflammation, infection
Systemic: nicorette nasal spray

Question 16

What are ear drops used for?

Answer 16

Local: softening ear wax, infection, inflammation

Question 17

What are the advantages of drops and sprays?

Answer 17

• convenient
• reduced systemic side effects
• fast effects
• drops can be given to children

Question 18

What are disadvantages of drops and sprays?

Answer 18

• inaccurate dosing
• needs manual dexterity
• patient preference
• short shelf life once opened