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MBBS 4: Ophthalmology > Ocular Drug Administration > Flashcards

Ocular Drug Administration Flashcards

1
Q

What is a tear film?

A

The tear film is a thin fluid layer covering the ocular surface
- It is responsible for ocular surface comfort, mechanical, environmental and immune protection, epithelial health and it forms smooth refractive surface for vision.

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2
Q

What makes up the tear film?

A
  1. mucin layer
  2. aqueous layer
  3. lipid layer
    - going from the cornea outward to the
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3
Q

Function of the tear film?

A
  1. Providing ocular surface comfort
  2. Offering mechanical, environmental, and immune protection
  3. Maintaining epithelial cellular health
  4. Forming a smooth refracting surface for vision
  5. Flushing away debris and bacteria
  6. Containing antibodies and immune-boosting substances to protect the eyes from infection.
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4
Q

What are pharmacodynamics?

A

It is the biological and therapeutic effect of the drug
- mechanism of action

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5
Q

Describe the pharmacodynamics of drugs?

A

Most drugs act by binding to regulatory macromolecules, usually neurotransmitters or hormone receptors or enzymes
example;
1. If the drug is working at the receptor level, it can be agonist or antagonist
2. If the drug is working at the enzyme level, it can be activator or inhibitor

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6
Q

What are pharmacokinetics?

A

It is the absorption, distribution, metabolism, and excretion of the drug

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7
Q

How drugs can be delivered to the ocular tissue?

A
  1. Locally:
    - Eye drops
    - Ointments
    - Periocular injections
    - Intraocular injections
  2. Systemically:
    - Orally
    - IV
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8
Q

Describe pharmacokinetics of ocular drugs?

A
  • Topical route is the most commonly used
  • Drug penetration into the eye is approximately linearly related to its concentration in the tear film
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9
Q

The rate and extent of absorption of topically instilled drugs depends on?

A
  1. Elimination by nasolacrimal drainage
  2. Time the drug remains in the conjunctival cul-de-sac & precorneal tear film
  3. Drug binding to tear proteins
  4. Drug metabolism by tear & tissue proteins
  5. Rate of diffusion across the cornea & conjunctiva
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10
Q

Describe ocular drug ditribution?

A
  1. Transcorneal absorption
  2. Accumulation in aqueous humor
  3. Distribution to intraocular structures
  4. Trabecular meshwork pathway
  5. Distribution to systemic circulation
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11
Q

Describe ocular drug metabolism?

A

Enzymatic biotransformation of ocular drugs
Note: Esterases are of particular interest
Eg: Development of prodrugs for enhanced ocular permeability
1. Dipivefrin hydrochloride
2. Latanoprost

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12
Q

Topical drug delivery in eyes?

A
  1. drop
  2. ointment
  3. gel
  4. soft contact lenses
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13
Q

Periocular drug delivery in eyes?

A
  1. subconjuctival
  2. subtenon
  3. peribulbar
  4. retrobulbar
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14
Q

Intraocular drug delivery in eyes?

A
  1. intracameral
  2. intravitreal
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15
Q

Systemic drug delivery in eyes?

A
  1. oral
  2. intravenous
  3. intramuscular
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16
Q

What drug delivery route is used to apply anesthesia?

A
  1. peribulbar
    - Peribulbar anaesthesia is performed by injecting the anaesthetic drug in the orbit around the equator of the eyeball (globe).
  2. retrobulbar
    - Retrobulbar anaesthesia is performed by injecting the anaesthetic drug in the orbit further back behind the eye ball, which is near the nerves that control eye movement and sensation.
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17
Q

Advantages of topical route?

A
  1. Convenient
  2. Economical
  3. Relatively safe
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18
Q

Limitations and precautions of topical route?

A
  1. Compliance
  2. Corneal & conjunctival toxicity
  3. Nasal mucosal toxicity
  4. Systemic side effects from nasolacrimal absorption
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19
Q

Special utility of subconjunctival, sub tenons, and retrobulbar injections?

A
  1. Anterior segment infections
  2. Posterior uveitis
  3. Cystoid Macular Edema (CME)
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20
Q

Limitations and precautions of subconjunctival, sub tenons, and retrobulbar injections?

A
  1. Local Toxicity
  2. Globe perforation
  3. Optic nerve trauma
  4. Central retinal artery or vein occlusion
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21
Q

Limitations and precautions of intraocular injections?

A
  1. Corneal toxicity
  2. Relatively short duration of action
21
Q

Special utility of intraocular injections?

A

Anterior segment surgery or infections

21
Q

Special utility of intravitreal injections?

A

immediate local effect

22
Q

Limitations and precautions of intravitreal injections?

A

retinal toxicity

23
Factors influencing local drug penetration into ocular tissue?
1. drug concentration and solubility 2. Viscosity 3. Lipid solubility 4. surfactants 5. pH 6. drug toncity 7. molecular weight and size
24
How Drug concentration and solubility influence local penetration?
higher concentration - better penetration e.g pilocarpine 1-4% but limited by reflex tearing
25
How drug viscosity influences local penetration?
addition of methylcellulose and polyvinyl alcohol increases drug penetration by increasing contact time with cornea and altering corneal epithelium
26
How drug lipid solubility influences local penetration?
higher lipid solubility- more penetration
27
How drug surfactants influence local drug penetration?
preservatives alter cell membrane in cornea and increase drug permeability e.g. benzylkonium and thiomersal
28
How drug pH can influence local drug penetration?
the normal tear pH is 7.4 - If drug pH is much different, this will cause reflex tearing
28
How drug tonicity can influence local drug penetration?
when an alkaloid drug is put in relatively alkaloid medium, the proportion of the uncharged form will increase, thus more penetration
29
Describe drops treatment?
aka Gutta - simplest and most convenient method which is mainly for day time use - 1 drop = 50 microliter - Conjunctival sac capacity = 7-13 micro liter - So, even 1 drop is more than enough
30
How to use eye drops?
1. hold the skin below the lower eye lid 2. pull it forward slightly 3. INSTILL 1 drop
31
Measures to increase drop absorption?
1. wait 5-10 minutes between drops 2. compress lacrimal sac 3. keep lids closed for 5 minutes after instillation
32
Describe ointments?
- Increase the contact time of ocular medication to ocular surface, thus better effect - It has the disadvantage of blurring vision - The drug has to be highly lipid soluble with some water solubility to have maximum effect as ointment
33
Describe periocular injections?
- They reach behind the iris-lens diaphragm better than topical application E.g., subconjunctival, sub tenon, peribulbar, or retrobulbar - This route bypasses the conjunctival and corneal epithelium, which is good for drugs with low lipid solubility e.g. penicillin's - Also, steroids and local anesthetics can be applied this way
34
Uses of subconjuctival injections?
1. To achieve higher concentration 2. Drugs which cannot penetrate cornea due to large size 3. Penetration via sclera
35
Use of subtenon injections?
1. Ant. Subtenon – diseases anterior to the lens 2. Post. Subtenon – disease posterior to the lens
36
Use of retrobulbar injections?
1. Optic neuritis 2. Papillitis 3. Posterior uveitis 4. Anesthesia
37
Use of peribulbar injections?
anesthesia
38
Describe intraocular injections?
Intracameral or intravitreal E.g. 1. Intracameral acetylcholine (miochol) during cataract surgery 2. Intravitreal antibiotics in cases of endophthalmitis 3. Intravitreal steroids in macular edema 4. Intravitreal Anti-VEGF for DR
39
Describe sustained release devices?
These are devices that deliver an adequate supply of medication at a steady-state level E.g. 1. Ocusert delivering pilocarpine 2. Timoptic XE delivering timolol 3. Ganciclovir sustained-release intraocular device 4. Collagen shields
40
Describe factors influencing systemic drug penetration into ocular tissue?
1. lipid solubility of the drug - more penetration with high lipid solubility 2. Protein binding - more effect with low protein binding 3. Ocular inflammation - more penetration with ocular inflammation
41
What drug can be administered topically to the eye?
fluorometholone
42
What is the primary delivery system for ocular drugs?
topical
43
What is the most common technique for administering ocular drugs?
eye drops
44
What type of adverse reactions are associated with ocular drug administration?
1. Allergic reactions 2. Systemic reactions 3. Local reactions
45
What type of ocular drug administration is used when the drug needs to be absorbed into the intraocular tissues?
subtenon
45
What type of ocular drug administration is used when the drug cannot penetrate the cornea?
subconjuctival
45
What type of ocular drug administration is used when the drug needs to be absorbed into the systemic circulation?
intravenous
46
What type of ocular drug administration is used when the drug needs to be absorbed through the conjunctiva?
subconjuctival

MBBS 4: Ophthalmology (55 decks)

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