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CH4106 > Ophthalmic Dosage Forms > Flashcards

Ophthalmic Dosage Forms Flashcards

1
Q

Definition of Ophthalmics

A

Sterile products for instillation into the eye. Can be solutions, suspensions, ointments or ophthalmic inserts

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2
Q

Normal tear volume

A

7ul

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3
Q

Volume accommodated without spillage

A

30ul

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4
Q

After blinking, residual volume

A

10ul

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5
Q

Commercial eye drops volume

A

50ul

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6
Q

Optimal volume to administer for ophthalmics

A

5-10ul

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7
Q

Factors lowering bioavailability

A
  • Optimal volume of eye drops to administer - currently: optimal volume to administer is 5-10ul but commercial eye drops volume is 50 ul; ideally: high concentration/low volumes
  • Absorption primarily through the cornea - cornea structure: lipid-rich epithelium layer (outer), lipid-poor stroma layer, lipid-rich endothelium layer (inner)
  • Loss of drug: overflow and spillage; enzymatic degradation (lysosomes) and protein binding; removal by the naso-lacriminal apparatus - take place when reflex tearing causes volume to exceed 7-10ul, eventually goes to GI tract: potential systemic effects, salty/bitter taste; superficial adsorption by drug through the conjunctiva -> rapid removal by peripheral blood vessels
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8
Q

Administration considerations

A
  • the ophthalmic formulation delivers the drug: on the eye; into the eye; onto the conjunctiva
  • transcorneal transport is not an effective process. only 1/10 of a dose penetrates into the eye
  • to optimize ocular drug delivery systems, the following characteristics are required:
    1. a good corneal penetration
    2. a prolonged contact time with the corneal epithelium -> more drug absorption
    3. a simplicity of instillation for the patient -> design of the eye drop and and dropper
    4. a non-irritative and comfortable form. should not provoke lacrymation and reflex blinking
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9
Q

Ophthalmic dosage forms

A
  1. solutions
  2. suspensions
  3. ointments
  4. ophthalmic inserts
  5. biodegradable drug delivery (BDD)
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10
Q

Requirements for ophthalmic solutions

A
  • uniformity: all ingredients are in solution
  • sterility: autoclave at 121C or use bacterial filters; preservatives
  • buffers and pH: ideally formulate at pH 7.4
  • viscosity and thickening agents: consider lacrimal drainage
  • ocular bioavailability
  • isotonicity value - osmotic pressure must be similar to that of the tears; tonicity limits for eye preparations 0.6 - 2% NaCl or its osmotic equivalent
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11
Q

Manufacturing technique for ophthalmic solutions

A
  • Dissolve drug and all or part of excipients
  • Sterilize by heat or membrane filtration
  • If required, add the other sterilized excipients
  • Bring to volume with sterile water
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12
Q

What are ophthalmic suspensions

A

Dispersions of insoluble drugs using suspending agents.
Optimum particle size (<10um) to facilitate dissolution and prevent irritation.
Solid particles will dissolve to replenish the absorbed drug, increasing contact time and duration of action

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13
Q

Manufacturing technique for ophthalmic suspensions

A
  • Add the sterilized solid to the sterilized solution
  • the solid is sterilized with heat, ethylene oxide, or aseptic recrystallization

(particle size control: <10um)

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14
Q

What are ophthalmic ointments

A

Drug released is a function of concentration, diffusivity and solubility in the base.
Advantage: longer contact time -> greater bioavailability

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15
Q

Manufacturing techniques for ophthalmic ointments

A
  • Place the sterilized, filtered and molten base in a sterile, heated kettle
  • Add sterilized drug and excipients aseptically
  • Mill the melt to disperse insoluble components
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16
Q

What are ocular inserts

A

They are placed in the cul-de-sac between the eyeball and the eyelid (e.g. ocusert - non-eroding device designed to deliver pilocarpine for several drugs in the treatment of glaucoma) ; some are designed to dissolve in tear fluid (e.g. Lacrisert used to treat moderate to severe dry eye syndrome)

Biggest disadvantage: tendency to float on the eyeball

17
Q

What are biodegradable drug delivery

A

Controlled intraocular delivery that assures efficient delivery of medication to treat disease inside the eye.
Designed to provide continuous, controlled release drug therapy directly to the targeted site for a period from days to several years.
Placed in the eye at the time of elective surgery
Dissolve as they release drug

18
Q

Formulation factors to consider

A
  • General: sterilization - laminar flow hood using aseptic techniques, sterility is an absolute requirement, vehicle - generally sterile isotonic solutions, extemporaneous compounding is rare
  • Solution pH: pH of blood and tear is 7.4 -> pH range of solutions is maintained by buffer at 6.5 - 8.5 to prevent corneal damage as having pH 7.4 may not be possible considering solubility, stability or therapeutic activity
  • Solution buffers: needed for adjusting and maintaining the pH of the solution for optimal pH
  • Iso-osmoticity and isotonicity: NaCl equivalence (E) is used to measure the osmotic effect of solutions - blood and tears are iso-osmotic with 0.9% solution of NaCl; range of tonicities allowed from 0.6-1.8% NaCl solution
  • Preservatives: added to prevent bacterial contamination (e.g. benzalkonium chloride 0.013%, chlorobutanol 0.5%, benzethonium chloride 0.01%)
  • Antioxidants (e.g. EDTA-not often used in ophthalmic formulations due to low water solubility, sodium bisulfite, sodium metabisulfite, thiourea)
  • Viscosity and thickening agents - more residence time (e.g. cellulose derivative, polyvinyl alcohol)
19
Q

Packing of ophthalmic dosage forms

A
  • Easy administration and sterility maintenance
  • Packaged in low density polyethylene plastic with a fixed, built-in dropper to release medicine when in an inverted position
  • Protect from light and tightly closed
  • Stored at room temp. between 15 - 30C
  • An ocumeter ensures sterility of the drops when in a multi dose container
  • May require refrigeration to extend shelf life
20
Q

Classification for contact lenses

A
  • Soft - made from HEMA, cover the entire cornea, daily wear and extended wear
  • Hard - made from PMMA, cover part of the cornea, float not he tear layer overlying the cornea
  • Rigid gas permeable (RGP) lenses - oxygen permeable, durable and easy to handle

CH4106 (18 decks)

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