The fundamentals behind drug regimes

Question 1

What factors need to be considered when determining a dosage regimen

Answer 1

Activity/toxicity
Clinical factors (compliance of patient, state of patient)
Pharmacokinetics
Other factors e.g., route, form of drug, drug interactions

Question 2

What pharmacokinetic factors determine dosage regimen?

Answer 2

Dose: potency and efficacy
Onset: Absorption & distribution
Loading dose: Vd
Maintenance dose: clearance
Time to steady-state: half-life

Question 3

What is dosage?

Answer 3

the administration of medicine in prescribed amounts over time

Question 4

What factors affect the dosage of a drug given

Answer 4

potency
absorption
Bioavailability and 1st pass metabolism
Distribution

Question 5

What factors affect the onset of action of a drug/Tmax?

Answer 5

Route of administration
Chemical structure and formulation (slow or fast release)
Clinical situations (pH change, shock, tissue blood perfusion)

Question 6

IF a drug is given orally, what factors affect the onset of action?

Answer 6

Polypharmacy (other drugs)
Gut content
Splanchnic blood flow

Question 7

What is the central compartment of all drugs?

Answer 7

Plasma

Question 8

What is a loading dose?

Answer 8

An initial higher dose to enable therapeutic concentrations sooner
Dose = Vd x plasma conc

Question 9

What is a maintenance dose?

Answer 9

The dose given to maintain drug conc at therapeutic conc
= clearance (CL) x steady state conc (Css)

Question 10

How can steady state concentrations be maintained?

Answer 10

Constant IV infusion (impractical)
Increased dose frequency (beware of owner compliance)

Question 11

What is normal kinetics in multiple dosing

Answer 11

Plasma concentrations (at Css) increase proportionally with dose.

Question 12

What are saturation kinetics in multiple dosing?

Answer 12

If dose is increased, then disproportionate increase in steady state concentrations.
Necessitates smaller dose increments

Question 13

Explain plasma protein binding

Answer 13

Most drugs are bound to plasma protein e.g., albumin
Bound and free drugs in equilibrium
Only free drugs are active and can be distributed, metabolised and excreted
Drugs with extensive protein binding are eliminated slower

Question 14

How can drug-drug interactions impact plasma protein binding?

Answer 14

Competition between drugs for protein binding can clinically causesignificant drug interactions but this is very uncommon