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OP2205 > 5. Drug formulation and design > Flashcards

5. Drug formulation and design Flashcards

1
Q

Pharmacodynamics meaning

A

The study of actions, effects and interactions of drugs in the body -(What does the drug do to the body).

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2
Q

Pharmaceutics meaning

A

The mode of administration.

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3
Q

Pharmacokinetics meaning

A

Concerned with absorption, distribution, metabolism, and excretion.

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4
Q

Bioavailability meaning

A

The rate and extent of drug absorption.

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5
Q

Biotransformation meaning

A

The rate and extent of drug metabolism or degradation.

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6
Q

2 routes of administrations of drugs to the eye?

A

Eye drops & Eye ointments

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7
Q

Eye drops vs Eye ointments which one is present in the eye for longer?

A

Eye ointment- will be present in conjunctival sack for longer.

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8
Q

Pharmacological effects, intensity, duration and rate of onset for different drugs depending on route of admission ?

A

The pharmacological effects are the
same regardless of the routes of
admission. But the rate of onset,
intensity and duration are very
dependent on the route of
administration.

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9
Q

3 factors considered when determining the route of admission of a drug?

A
  1. Required site of action
  2. Required duration of action
  3. Stability of drug
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10
Q

Release of drugs in terms of tablets vs injections?

A

Tablets have a slow and sustained release. Injections have a fast and rapid release.

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11
Q

The physical and chemical stability of a drug relates to?

A

Relates to the chemical and physical integrity of the drug shelf life.

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12
Q

When drugs enter the body, they are metabolized by?

A

Metabolism by the liver

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13
Q

When you remove eyedrops from a package, what is checked?

A

Expiration date, if dose name matches the packet.

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14
Q

Is time noted for drug installation?

A

Yes, time is noted

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15
Q

Avoid touching lids and lashes when putting eyedrops, why?

A

To avoid contamination

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16
Q

What happens immediately as eyedrops are put in?

A

Immediate loss on blinking, drug concentration decreases rapidly. Because drug mixes with tears.

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17
Q

Eyedrops are systemically absorbed by?

A
  1. Conjunctiva
  2. Punctae
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18
Q

Eyedrops are ocullarly absorbed by?

A

Cornea

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19
Q

How is drug/ eyedrop lost from the eye?

A

Loss through aqueous humour through normal drainage system.

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20
Q

Major site of eyedrop absorption?

A

Cornea

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21
Q

Absorption of eyedrops is a passive process, what does this mean?

A

It needs a concentration gradient where the steeper the gradient, faster the diffusion will be.

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22
Q

To cross the cornea effectively what 2 properties are required by the drug?

A

The drug needs to have a balance of hydrophilic (water soluble) and lipophilic (lipid soluble) properties.

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23
Q

Lipophilic drugs easily cross the epithelium because?

A

The phospholipid membrane is uncharged

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24
Q

Which structure is the limiting factor when drugs are crossing the cornea?

A

Epithelium

25
Q

What charge is required for the drug to cross the following layers:
Epithelium
Stroma
Endothelium

A

Epithelium: Uncharged
Stroma: Charged
Endothelium: Uncharged

26
Q

Molecules in drugs gain or loss a charge depending on?

A

Depending on which barrier it is crossing

27
Q

Molecules in drugs gain or loss a charge depending on?

A

Depending on which barrier it is crossing

28
Q

Is fluorescein highly charged compared to tear film?

A

Yes- hence it does not enter the cornea unless corneal epithelium is damaged.

29
Q

Why is fluorescein not absorbed by healthy stroma?

A

Because of its charge

30
Q

The ratio of uncharged to charge in drugs depends on (eyedrop delivery)?

A
  1. The pH of tear-eyedrop mixture after instillation.
  2. The pKa (dissociation constant) of the drug.
31
Q

pKa meaning?

A

Dissociation constant.
This is the pH at which the concentrations of the charged and
uncharged forms are equal.
It is an unchanging property of a drug

32
Q

pKa is a measure of?

A

Measure of the strength of an acid in a solution
*Stronger the acid, lower the pKa value is

33
Q

Can pKa of a drug be changed?

A

pKa Of a drug can’t be changed but the pH of the eye drop formulation can be changed, within limits.

34
Q

Optometric drugs are bases or acids?

A

Weak bases with pKa greater than 8

35
Q

Natural pH of the tear film?

A

7.4

36
Q

Endothelium is a single layer of what type of cells?

A

Squamous cells

37
Q

Factors affecting eyedrops bioavailability?

A
  1. Drug formulation and design- drug ingredients.
  2. Corneal integrity- greater the corneal damage, more the drug is absorbed.
  3. Tropical anesthetic administration
  4. Iris pigment
  5. Patient specific factors- age, genetic background etc
38
Q

Eyedrops are absorbed along which 2 surafces?

A

Cornea and conjunctival surfaces

39
Q

Onset of Intravenous injections and 2 associated risks?

A

Rapid onset
Risks: Irreversibility and potential for risk

40
Q

3 disadvantages of oral admission of drugs?

A
  1. Absorption rate is variable.
  2. Drug can be inactivated by digestive enzymes and acids.
  3. Requires patient cooperation.
41
Q

Pressure on the inner canthus is applied after drops installment why?

A

to reduce escape of drug through lacrimal system

42
Q

When instilling drops px is asked to blink only when?

A

Gently only when they feel the drop

43
Q

Drug absorption in dark iris vs light iris?

A

Drugs less effective in darker pigmented iris

44
Q

Tropically applied eyedrops process of absorption?

A

Trans- corneal diffusion

45
Q

Describe the absorption of fluorescein in the eyes due to damaged corneal epithelium?

A

Superficial damage to cornea: staining is seen due to fluorescein pulling. With deep and more serious corneal damages, diffusion of the fluorescein is seen into the layers of the stroma.

46
Q

pKa is determined by Henderson- Hasselbalch equation, what is it?

A

pH= pKa+ {log[concentration of uncharged drug] / [concentration of charged drug] }

47
Q

In Trans- corneal depletion, the ratio of charged: uncharged is maintained by?

A

This depletion of the uncharged form in the tear film causes more of the charged molecules to lose their charge, so as to maintain the same ratio of charged :
uncharged.
After crossing the epithelium, some of the drug will become charged (again maintaining the charged :uncharged ratio). The charged form will be able to
cross the corneal stroma.

48
Q

Once a drug passes through endothelium, it next moves to?

A

Drug passes into aqueous humour before it is taken up by various ocular muscles like the iris.

49
Q

True or false: drugs are absorbed better in a cornea that is damaged?

A

True

50
Q

What is drug formulation?

A

Balance of components or eye drop ingredients- related to the combination of chemicals when they are mixed. It should be designed to give stability and cause minimal irritation.

51
Q

4 factors that affect drug formulation?

A
  1. pH: determines ratio of charged to uncharged in a drug.
  2. Tonicity: stings outside range 0.5-2% NaCl.
  3. Oxidation
  4. Sterility
52
Q

What factors in drug formulation affect stability and ratio of charged to uncharged?

A

pH

53
Q

4 ways to enhance drug delivery?

A
  1. Multiple drops - wait 5 minutes
  2. Prior use of local anesthetics
  3. Ointments- however, gives blurry vision
  4. Slow delivery inserts
54
Q

What do local anaesthtics due when put prior to eye drops?

A

Cause a mild punctate keratitis- that speeds up drug absorption

55
Q

3 ADRs (Adverse drug reactions)

A

Toxicity - liver and kidney at risk
Hypersensitivity
Allergy

56
Q

5 individuals with high risk to ADRs

A
  1. Pregnant women
  2. Breastfeeding women
  3. Elderly people
  4. Children
  5. Patients with underlying illness
57
Q

Immediate instruction given to Px after eyedrops are put in the eyes?

A

With a tissue Px should occlude the lower punctate by applying gentle pressure.

58
Q

Relationship between eye drop effectiveness and iris colour?

A

Drugs bind with pigments in the eye hence less effective in darker coloured iris. Hence, a higher concentration is used in PX’s with darker iris.

59
Q

Process of eyedrops absorption is known as?

A

Trans-corneal diffusion

OP2205 (8 decks)

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