Drug Dose Regimens Flashcards
What four things influence dosing regimens?
- Amount of drug to be administered
- Route of administration
- Dosing frequency
- Length of time drug will be administered
How are these things determined:
- Amount of drug to be administered
- Route of administration
- Dosing frequency
- Length of time drug will be administered
- Pharmacokinetic properties
- Pharmacokinetic properties of drug and intended site of action
- Pharmacokinetic properties
- Time needed to affect treatment
- What is bioavailability?
2. How is it determined?
- Fraction of administered drug reaching the systemic circulation in its active form.
- How much is given vs. how much in circulation
* *IV = 1 (100% bioavailable)
* *Oral is less based on absorption and metabolism
Rate of availability
- What is it?
- What does it affect?
- What factors affect it?
- Rate at which drug enters systemic circulation
- Onset of action, apparent efficacy, and duration of action
- Dissolution of drug into absorbable form and blood flow
Volume of Distribution (Vd)
- What is it?
- How is it determined?
- What factors affect it?
- The blood volume in which a drug distributes (where the drug goes in the body)
- Vd = Amount of drug in the body/ plasma concentration (Cp)
- Body weight, composition, age, disease
Clearance (CL)
- What is it?
- How is it determined?
- What factors affect it?
- Elimination of active drug from the plasma after its distribution
- CL = rate of elimination/ plasma concentration (Cp)
* *CLtotal = CLrenal +CLliver+ CLx+ CLy+…. - Blood flow, capacity of elimination mechanism (metabolic and excretion), body weight, age, disease
What are the two factors that could be rate limiting to clearance and what do they depend on?
Capacity-limited elimination:
Capacity is saturated, so increased plasma concentration does not affect elimination. **Constant AMOUNT of what’s in the plasma being eliminated per unit time
Delivery-limited elimination:
Capacity is not saturated, so rate of elimination is dependent on plasma concentration. **Constant PERCENTAGE of what’s in plasma being eliminated per unit time
Maintenance Dose (Dm)
- What is the goal?
- What is it dependent on?
- To maintain Css (steady state plasma concentration) by replacing loss due to elimination
- Elimination
Loading Dose (DL)
- What is the goal?
- What is it dependent on?
- To quickly attain Css by filling Vd
2. Volume distribution (Vd) –> which is proportional to body weight
Dosing Frequency
- What is it dependent on?
- What is a good interval to use for dosing frequency?
- When is steady state level achieved?
- Clearance, which relates to drug half-life (t1/2)
- t1/2 –> good interval, but then alter to convenience
- 4-5x t1/2 for a “Plateau effect”
What effect does renal disease have on dosing?
Decreases CL, prolongs t1/2
What effect does hepatic disease have on dosing?
Decreases CL, prolongs t1/2, increases oral bioavailability, decreases plasma proteins (less albumin to bind to)
