Module 3.6 - Compartmental Models Flashcards
Pharmacokinetics
Knowing the rate and extent of drug absorption following administration
Compartments
Systems that are continuous and nonhomogenous are replaced with compartments that are discrete and in which concentrations, and so on, are homogenous
Why do we inject needles into veins?
P is extremely low in these vessels. Can kill someone if you puncture the wrong artery.
What is the most common drug form?
Tablet
Enteral vs. parenteral
Enteral = entry through GI tract
Parenteral = anything else (ie. transdermal)
The therapeutic response following dosing is dependent on the ______ achieving an adequate _______ concentration.
drug
plasma
What is the biggest challenge with IV injection?
Accidental overdose (hard to reverse dependent on how fast drug is absorbed), so needs to be done by a professional
AUC
Area under curve: total amount of drug absorbed into blood circulation
MTC vs MEC
MTC = minimum toxic concentration
MEC = minimum effective concentration
When should you inject a second dosage into a patient?
Likely a while after the first dosage has reached the MEC, but it will depend on the drug
How do you find out when to inject a second dose?
- Find MTC and MEC
- Calculate the maximum concentration at the first dosage
- Guess a time for the second dosage past the MEC
- Add the concentration from the first dosage at that time with the maximum concentration at the second dosage
- If the concentration exceeds the MTC, then estimate a longer time and iterate
Bioavailability
AUC for a dosage form / AUC from the IV
(This is because everything is absorbed in IV)
Why is the majority of drugs administered orally? (2)
- Everybody eats
- Have high patient compliance
What are the problems with drugs being ingested orally? (3)
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)
Oral absorption
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.
Forms of oral drugs (3)
- Tablet (bunch of powder mixed and condensed, but has to break apart)
- Suspension
- Capsule (hard gelatine coating, becomes viscous once hydrated)
Onset (of drug)
Period of time before which you feel anything
Concentration of the drug with respect to time depends on (5):
- Fraction of drug absorbed
- Initial mass of drug introduced
- Distribution volume (in body)
- Combo of absorption and elimination constants
- Exponential time functions
Why is the behaviour of transdermal drugs follow the same model as orally administered drugs?
They need to diffuse through layers (ie. skin surface, skin, components of skin, enzymatically degraded, blood stream)
How do we adjust the bioavailability (k_a) of a drug? (3)
- Alter its resistance to pH
- Change coating to dissolve more quickly
- Change coating so it sticks to walls
