Routes of Drug Delivery (K2)

Question 1

Why are these factors essential when considering drug delivery route?
- Surface area and contact time
- Limited Exposure of drug to metabolism
- Good blood supply

Answer 1

SA + Contact time: To enable maximal drug absorption
Exposure: Don’t want to break down the drug before its done the job
Blood supply: Drug diffusion is faster at sites with a good blood supply due to the conc gradient

Question 2

Why are these factors essential when considering drug delivery route?
- Accessibility to absorption site
- patient compliance
- Consistency
- Cost

Answer 2

Accessibility: For drug to work it must be able to reach the target site, eg blood brain barrier is hard to penetrate
Patient compliance: Drug is useless if patient cannot keep to the drug regime (Dementia)
Consistency: Amount of drug Absorption in the GI tract depends on if its eaten with food or not
cost: Low cost of manufacture and cost of final product are key to success

Question 3

List some other reasons that patients may struggle to comply with drug regimes:

Answer 3

• Dementia (Forgetting or confused or dont know)
• Small children struggle to swallow large pills
• Some people hate needles
• May taste bad or cause side effects

Question 4

What are some forms of oral drugs?

Answer 4

Tablets, cough syrups, capsules, solution painkillers

Question 5

What are some surface level advantages and disadvantages generally for oral drugs?

Answer 5

+ Good patient compliance, convenient, self administered, large surface area for absorption and cheap

• Doesnt skip first pass metabolism (large amount broken down in the gut by pH or enzymes), Sometimes they need to be eaten with food (Variability)

Question 6

What is the definition of first pass metabolism?

Answer 6

The chemical alteration or a drug by the action of an enzyme

Question 7

What happens to drugs once they have been absorbed by the GI tract?

Answer 7

• They enter the hepatic portal vein, which takes them to the liver
• The liver is another site of drug metabolism before entering the systemic circulation

Question 8

What is meant by topical, and give 3 examples

Answer 8

Treatment applied to the surface layer
- Creams, Gels, Patches, Ointments, eye drops

Question 9

What are some key advantages and disadvantages of topical treatments?

Answer 9

+ Localised delivery, avoids first pass metabolism, higher bioavailability, self administrable

• Limited applicability (localised and so cannot reach far tissues easily), typically limited to dermatological and ophthalmological applications

Question 10

What do these terms mean?
- Intravenous
- Subcutaneous
- Intraarterial
- Intrathecal
- Intraperitoneal
- Intramuscular
- Intravitreal

Answer 10

• Intravenous - into the vein
• Subcutaneous - fat layer under the skin
• Intraarterial - Into the artery
• Intrathecal - Into the spinal cord
• Intraperitoneal - Into the perineum cavity (Abdomen area)
• Intramuscular - Into the muscle
• Intravitreal - Into the eye

Question 11

What are the general advantages and disadvantages to using needles as a form of drug delivery?

Answer 11

+ High bioavailability, direct delivery to target site

• Patient discomfort/lack of compliance, requires professional administration, higher risk of overdose or toxicity, risk of infection

Question 12

What is an advantage and disadvantage of inhaled drugs

Answer 12

+ Localised delivery and fast acting

• Limited application

Question 13

What is meant by a transmucosal drug? with an example

Answer 13

• Absorbed through the mucosa (lining of skin) eg. Sublingual, innercheek, vaginal, rectal

Question 14

List some advantages and disadvantages of transmucosal drugs

Answer 14

+ Self administrable, avoids first pass metabolism

• Can be uncomfortable, limited applications

Question 15

Name a few forms of implanted drug delivery systems

Answer 15

• Contraceptive pill
• Insulin Pump
• Intrathecal pump

Question 16

List some advantages and disadvantages of implantable drug delivery systems

Answer 16

+ Provide long-term and controlled release of drug

• Requires professional to implant, can be serious dependent on implant type

Question 17

What is meant by Bioavailability?

Answer 17

The fraction of administered drug that reaches the blood stream or target site of action in an unchanged form (ie. not metabolised)

Question 18

How does the drug concentration in blood plasma vs time profile compare between IV injection and tablet

Answer 18

Both tail off as the drug is metabolised and distributed to the tissues

Question 19

This graph shows profiles of drugs delivered by injection and tablet once absorbed into the plasma. What might this fail to show?

Answer 19

• Some drugs bind to proteins in the plasma (so never diffuse out)
• Factors may affect concentration of drug in the blood for the oral dosage, eg whether they ate
• Not all drugs need to reach the blood stream, their target site may be earlier, eg antacids

Question 20

Bioavailability is sometimes written as F and is a fraction, eg 0.8., what would 1 and 0 mean?

Answer 20

1 - all the drug administered reached the target site, eg injection ideally

0 - No drug reached the target site, (no drug hopefully)

Question 21

What is relative and absolute bioavailability?

Answer 21

Relative Bioavailability: Compares test drug to a known standard

Absolute: Compares bioavailability of one route to bioavailability after injection of the same does (F =1)

AUC = area under curve