Drug formulation and design

Question 1

what are the routes of drug administration?

Answer 1

-eye drops
-eye ointments
-oral
-topical
-ballistic: drug delivery via micro bullet
-iontophoresis: using small electric charge to deliver drug through skin
-injection
-other systemic methods like inhalation

Question 2

what are the advantages of oral drug administration?

Answer 2

-convenient
-relatively cheap
-fairly safe

Question 3

what are the disadvantages of oral drug administration?

Answer 3

-absorption rate is variable
-drug can be inactivated by digestive acids and enzymes
-requires patient cooperation

Question 4

what are the advantages and disadvantages of intravenous injection of drug administration

Answer 4

adv:
-no barriers to absorption
-rapid onset

disadv:
-irreversibility
-potential for infection

Question 5

what are the advantages and disadvantages to intramuscular drug administration?

Answer 5

adv:
-sustained release so longer lasting drug action

disadvantage:
can be painful

Question 6

how are some drugs more stable than others?

Answer 6

more stable drugs are designed to make sure there is no bioactivity until they enter the body which therefor increases drug stability

Question 7

What are the steps to instil eye drops?

Answer 7

1. wash hands
2. check the drug, dose and date
3. ask px to look upwards tilting head back
4. pull lower lid down and forwards exposing lower conjunctival sac
5. instruct patient to blink gently when they feel the drop
6. instill a single drop without touching lids or lashes
7. apply some pressure on the lower punctum with a tissue to prevent drug escaping via the lacrimal system

Question 8

what structures in the eye absorb drugs?

Answer 8

-cornea
-conjunctiva
-punctae

Question 9

what can cause the percentage of eye drops to actually get absorbed by the eye to decrease?

Answer 9

-blinking
-loss from aqueous humour via normal drainage system

Question 10

what is the main way eye drops get absorbed into the eye?

Answer 10

via the cornea in trans corneal diffusion

Question 11

what is the limiting factor of trans corneal diffusion?

Answer 11

the epithelium

Question 12

what are the requirements for a drug to undergo trans corneal diffusion?

Answer 12

-has to have a conc. gradient, steeper = faster diffusion
-must be lipophilic to cross the corneal epithelium and endothelium
-must be hydrophilic to cross the corneal stroma

Question 13

why does fluorescein highlight corneal damages?

Answer 13

because it is too highly charged to diffuse through the corneal endothelium so the only way it can enter the cornea is by the endothelium to be damaged

Question 14

what is pKa in terms of drugs?

Answer 14

it is a drugs unchanging property and is equal to to he pH at which the concentrations of the charged and uncharged forms are equal the lower the pH, the lower the pKa

Question 15

how can you determine pKa ?

Answer 15

using the Henderson-Hasselbalch equation where

pH = pKa + log(conc of uncharged drug/conc of charged drug)

Question 16

What are the steps to a drug undergoing trans-corneal diffsion?

Answer 16

1. most optometric drugs start as weak bases w pKa >8.0 and are charged at pH 7.4
2. the small percent or drug in the uncharged form can cross the epithelium
3. the depletion of the uncharged form in the tear film causes more of the charged molecules to lose their charge maintaining the same ratio of charged to uncharged
4. after crossing the epithelium, some of the drug will become charged again as in maintaining the ratio so the charged form is able to cross the corneal stroma
5. at the endothelium, some of the drug is able to cross as it did at the epithelium

Question 17

what is biovaliability?

Answer 17

the amount of drug absorption/ amount of drug present at the receptor site

Question 18

name 5 factors affecting eye drop bioavaliability

Answer 18

-drug formulation and design
-corneal integrity
-topical anaesthetic administration
-iris pigmentation (pigment non-specifically absorbs drugs)
-patient-specific factors like age

Question 19

name 4 factors affected by drug formulation

Answer 19

-pH as determining determining ratio of charged to uncharged drug, affect stability during storage, and the fact drops may sting outside range 6.6-8.8 pH
-Tonicity as drops may sting outside range of 0.5-2% NaCL
-Oxidation which may be triggered by exposure to temperature, light or air
-Sterility so if not single use, preservatives need to be added

Question 20

give 4 ways eye drop delivery can be enhanced

Answer 20

-instil multiple drops waiting about 5 mins between each
-prior use of local anaesthetic
-ointments
-slow delivery inserts such as gels, contact lenses, collagen shields etc

Question 21

what kind of people are more prone to adverse drug reactions (ADRs)?

Answer 21

-pregnant women
-breastfeeding women
-elderly people
-children
-patients with underlying illnesses