Formulations

Question 1

How are suppositories / pessaries formed

Answer 1

1. Melt moulding
   
   • melt components together
   • pour melted mixture into mould
   • allow mould to cool
2. Compression moulding
   
   • paste mixture of base + drug is forced into a mould under pressure
   • does NOT require heat = advantage for heat sensitive drugs

Question 2

List the type of bases available for suppositories / pessaries

Answer 2

API is disolved or dispersed in base
Dissolution of base controls release of drug
- ↑ viscosity of base = ↓ drug release
- ↑ viscosity by adding fat or wax

1. Fatty base
   
   • used for hydrophillic drugs = will leave vechile easier + quicker (base is opposite to drug = repel)
   • once fatty base melts hydrophillic drug will move into aqueous environment
   • base melts at body temp. within 3-7 min
   • inc. triglycerides, synthetic veg. oil, fatty acids, fatty alcohol
2. Water-soluble base
   
   • used for lipophilic / hydrophobic drugs = will leave vechile easier + quicker
     1. Glycerinated Gelatin
     - dissolves slowly in mucus = prolonged release of drug
     - can cause dryness as it draws water out of mucuosal layer
     2. Polyethylene Glycol
     - note: can irritate muscusal membrane = dip suppository in water before inserting to ↓ irritation

Question 3

How do you store suppositories / pessaries

Answer 3

At room temp. / cool temp. (< 30ºC)
- this prevents it from melting / softening

In correct humidity
- low humidty = becomes dry + brittle (lose water to environemnet)
- high humidity = becomes moist (absorbs moisture)

Question 4

Vaginal tablets

Answer 4

• Need to be inserted as high as possible in vagina
• use LACTOSE as filler an to maintain pH as its a natural substrate for vaginal microflora
  - its converted into lactic acid which retains vaginal pH
  -

Question 5

Vaginal rings

USE: hormonal contraception

Answer 5

• Made from non-biodegradeble elastomeric polymers (return to normal shape when stretched)
  - e.g. silicone
  - non-biodegradeble are more flexible / less rigid
• Have a drug reservoir (within the polymer network) which controls drug release
  - drug stored in core
  - core surrounded by matrix
• Use applicator to insert
• ## Manufactured by melting

Question 6

What are semi-solid dosage forms

Answer 6

• Creams
  - more spreadable, less occlusive
  - less greasy than ointment = easy to wash off
  - can be used on weepy skin
  - water content is biggest volume in cream
  - have W/O or O/W
• Ointments
  
  • occlusive, keep moisture in (stop evaporation of water from skin = hydrates skin)
  • water-resistant = hard to wash off
  • greasy, hard to spread = patient compliance is poor
  • have little to no water
  • cant use on weepy / infected skin
• Gels
  
  • have thickeners added which ↑ viscosity by forming a network throughout the gel = make it a gel
  • non-greasy, not occluisive, not an emollient
  • easy to apply + wash off
  • alcohol based (sting when apply) BUT have cooling effect due to (evaporation of alcohol)
• Pastes

Question 7

What bases can be used in ointment

Answer 7

1. Absorption bases
   
   • have emulsifying agent which allows ointment to soak up water
2. Emulsifying base
   
   • can be easily washed off
   • is a water-misccible ointment
3. Water-soluble base
   
   • use PEG
   • melt when applied to skin = spreads easily
   • can be washed off easily

Question 8

How are creams prepared

Easier to make O/W creams

Answer 8

Creams are white becuase when light is shone through it, white light is scattered in all directions due to presence of large oil droplets

Use emulsifiers (choice of emuslifier depends on if making O/W or W/O emulsion)

surfactant bilayer is formed in aqueous phase

surfactant and co-surfactant coat oil particles in disperesed phase = barrier formed between oil and water droplets
- if both molecules are charged = electrostatic repulsion = stabilisation
- uncharged molecules have steric repulsion due to long hydrophillic chain

Low HLB = molecule prefers lipophilic conditions
- e.g. span has low HLb = makes W/O emulsion

High HLB = molecule prefers hydrophillic conditions
- e.g. tween has high HLB = makes O/W

Question 9

Transdermal (patches) drug delivery structure

Answer 9

1. Protective layer
2. Adhesvive layer
3. Drug release membrane
4. Drug reservoir
5. Pigmented backing