Target concentration intervention

Question 1

Why do the PK and PD vary?

Answer 1

Systematic/ predictably: body size, disease state, genotype

Random/ not predictable: between subject variability, within subject variability

Question 2

What are the three ways we can dose?

Answer 2

Population: every one gets the same dose, most convenient

Group: Same dose for a similar group, e.g. same wight, CrCL, genotype

Individual: dose determined by an individuals response

Question 3

What are the two reasons for TCI?

Answer 3

1) usefulness of a drug is hard to measure (the drug is working when the clinical outcome is not easily observable). Examples: anti-arrythmics, anti-convulsants
2) Big unpredictable variability.

Question 4

TCI step 1

Answer 4

Choose target concentration

Question 5

TCI step 2

Answer 5

Determine V and CL
estimates?
V: size and body composition
CL: size, renal + hepatic function

Question 6

TCI step 3

Answer 6

Calculate LD(V) and maintenance dose (CL)

Question 7

TCI step 4 and when?

Answer 7

Measure response.

Question 8

TCI step 5

Answer 8

Measure conc. Goal is to estimate PK e.g CL

Take one sample typically (gentamicin 2), and take it during the middle of the dosing interval. (usually closer to the Css)
(gentamicin peak and trough) (The conc varies a lot over the day)

Question 9

Therapeutic drug monitoring

Answer 9

Is imprecise, and sub-optimal at borders of the range. Drugs concentrations are measured, and if within the normal range it is okay. leads to if towards bottom of range, more likely to be ineffective or vice versa, toxic

Question 10

TCI strong points

Answer 10

Is accurate and focuses on the individual. is accurate and focuses on the PK and PD principles to show how patients are different