Module 3.6 - Compartmental Models

Question 1

Pharmacokinetics

Answer 1

Knowing the rate and extent of drug absorption following administration

Question 2

Compartments

Answer 2

Systems that are continuous and nonhomogenous are replaced with compartments that are discrete and in which concentrations, and so on, are homogenous

Question 3

Why do we inject needles into veins?

Answer 3

P is extremely low in these vessels. Can kill someone if you puncture the wrong artery.

Question 4

What is the most common drug form?

Answer 4

Tablet

Question 5

Enteral vs. parenteral

Answer 5

Enteral = entry through GI tract
Parenteral = anything else (ie. transdermal)

Question 6

The therapeutic response following dosing is dependent on the ______ achieving an adequate _______ concentration.

Answer 6

drug

plasma

Question 7

What is the biggest challenge with IV injection?

Answer 7

Accidental overdose (hard to reverse dependent on how fast drug is absorbed), so needs to be done by a professional

Question 8

AUC

Answer 8

Area under curve: total amount of drug absorbed into blood circulation

Question 9

MTC vs MEC

Answer 9

MTC = minimum toxic concentration
MEC = minimum effective concentration

Question 10

When should you inject a second dosage into a patient?

Answer 10

Likely a while after the first dosage has reached the MEC, but it will depend on the drug

Question 11

How do you find out when to inject a second dose?

Answer 11

1. Find MTC and MEC
2. Calculate the maximum concentration at the first dosage
3. Guess a time for the second dosage past the MEC
4. Add the concentration from the first dosage at that time with the maximum concentration at the second dosage
5. If the concentration exceeds the MTC, then estimate a longer time and iterate

Question 12

Bioavailability

Answer 12

AUC for a dosage form / AUC from the IV

(This is because everything is absorbed in IV)

Question 13

Why is the majority of drugs administered orally? (2)

Answer 13

• Everybody eats
• Have high patient compliance

Question 14

What are the problems with drugs being ingested orally? (3)

Answer 14

Dosage has lots of barriers of absorption to go through:

• Dosage must survive acidic environment
• Avoid dosage bonding to mucus (-ve charge)
• Biosalts in SI emulsify fats (if drug has fats, can interact with biosalts)

Question 15

Oral absorption

Answer 15

There is an increase in SA in small intestine due to villi. Nutrients and material are absorbed in the small intestine, with a transit time for bolus of food to move through SI = 3-6h.

Question 16

Forms of oral drugs (3)

Answer 16

1. Tablet (bunch of powder mixed and condensed, but has to break apart)
2. Suspension
3. Capsule (hard gelatine coating, becomes viscous once hydrated)

Question 17

Onset (of drug)

Answer 17

Period of time before which you feel anything

Question 18

Concentration of the drug with respect to time depends on (5):

Answer 18

• Fraction of drug absorbed
• Initial mass of drug introduced
• Distribution volume (in body)
• Combo of absorption and elimination constants
• Exponential time functions

Question 19

Why is the behaviour of transdermal drugs follow the same model as orally administered drugs?

Answer 19

They need to diffuse through layers (ie. skin surface, skin, components of skin, enzymatically degraded, blood stream)

Question 20

How do we adjust the bioavailability (k_a) of a drug? (3)

Answer 20

• Alter its resistance to pH
• Change coating to dissolve more quickly
• Change coating so it sticks to walls