FB - Clinical Pharmacokinetics Flashcards
What is the primary goal of clinical pharmacokinetics in medicine?
Enhance drug efficacy, Reduce drug toxicity
What factors are considered in determining the appropriate loading dose of a drug?
Desired plasma drug concentration, Drug’s apparent volume of distribution
How does the timing of drug administration relate to trough plasma drug concentration?
Drugs should be administered after the trough level is reached to maintain effective concentration and minimize toxicity.
Why is patient age important in drug administration?
Age affects organ functions that impact drug metabolism and excretion, influencing drug dosage and frequency.
What is the significance of achieving a steady state in drug therapy?
Steady state indicates a balance between drug dosing and elimination, ensuring consistent therapeutic effects.
How does multiple dosing affect the plasma drug concentration?
Multiple dosing leads to drug accumulation until a steady state is reached.
What role does drug mechanism of action play in dosage regimen?
It determines how the drug interacts with the body, influencing efficacy and safety of the dosage regimen.
Why is patient compliance important in pharmacotherapy?
Non-compliance can lead to (a) suboptimal therapeutic outcomes and increased risk of drug resistance, (b) overdosing and increased drug toxicity.
How can drug toxicity be minimized in clinical practice?
By monitoring plasma drug levels and adjusting the dosage accordingly.
What is the importance of the apparent volume of distribution in pharmacokinetics?
It provides an idea where the drug is likely to be distributed in the body; helps in calculating the correct loading dose to achieve the desired drug concentration in the body.
How does renal function impact drug dosing and selection?
Renal impairment can reduce drug clearance, necessitating dosage adjustments to prevent toxicity.
What is the relevance of pharmacokinetic principles to personalized medicine?
They enable individualization of drug therapy based on patient-specific factors for optimal efficacy and safety.
After how many half-lives does a drug reach steady state with multiple dosing?
Steady state is reached after 5 half-lives (T½) of the drug.
How is dosing modified for drugs with different half-lives?
If T½ is 8-24 hours, dosing could be three to onetimes daily. If T½ is short (eg. less than 3 hours), intravenous (IV) infusion or sustained released preparations can be used.
For drugs with low therapeutic index (TI), what is crucial for optimum therapeutics?
Considerations for pharmacokinetics (PK) are more important in drugs with low TI and in patients with altered absorption, distribution, metabolism, and excretion (ADME).
How long does it take for plasma drug concentration (PDC) to drop to ~3% of the original level?
It takes 5 half-lives (T½) for PDC to drop to ~3% of the original level. (work from first principle – each half-life reduces half: 100% à 50% à 25% à 12.5% à 6.25% à 3.125%)
How does pH affect the absorption of weak acids and bases?
Weak acids: Higher pH reduces absorption à high pH shifts the ionization equilibrium towards ionized species Weak bases: Higher pH increases absorption. [recall: the unionized species will be preferentially absorbed into the body]
What are the some factors affecting drug distribution?
Drug’s physico-chemical properties, Biological fluid pH differences, Organ blood flow, Drug transporters, Drug-plasma protein binding
What are some factors influence drug metabolism?
Enzyme activity (inhibition/induction), Pharmacogenetics (e.g., CYP2D6), Age (neonates to elderly)
How does urine pH affect drug excretion?
Acidic urine: Excretes weak bases, reabsorbs weak acids. Alkaline urine: Excretes weak acids, reabsorbs weak bases.
What does “STAT” and “PRN” mean in terms of single dosing?
“STAT” means immediate dosing, “PRN” means as needed.
What is the significance of peak plasma concentration (Cmax) in steady state dosing?
Cmax is the highest plasma concentration of a drug after dosing, important for efficacy and determining toxicity.
How is steady state achieved in multiple dosing?
Steady state is reached after 5 half-lives (T½) dosing
How does changing dosing intervals affect drug levels?
Altering dosing intervals (e.g., 100mg every 2h, 3h, 6h) changes peak and trough plasma drug concentration levels.
How is steady state concentration (Cssav) related to dosing frequency?
Cssav is the average plasma concentration at steady state, achieved uniformly with consistent dosing, e.g., continuous IV infusion or regular oral dosing.
