Pharmacokinetics And Pharmacodynamics - NAPLEX

1. State the formula for AUC after a single IV bolus dose with first-order elimination.

   $AUC=\frac{\text{Dose}}{CL}$. For IV administration, AUC reflects total drug exposure as the ratio of dose to clearance in first-order elimination.

2. State the formula for maintenance dosing rate to achieve target $C_{ss}$ (IV infusion).

   $\text{Rate}_{in}=CL\times C_{ss}$. For continuous IV infusion, the input rate maintains steady-state concentration by equaling the product of clearance and desired level.

3. What is the definition of extraction ratio $E$ for an eliminating organ?

   Fraction removed from blood in one pass through the organ. Extraction ratio quantifies organ efficiency in drug removal, measuring the proportion cleared during single-pass blood flow.

4. What is the definition of steady state during chronic dosing?

   Rate in equals rate out; average concentration is stable. Steady state occurs when drug input balances elimination, resulting in constant average plasma concentrations over dosing intervals.

5. What does the pharmacodynamic parameter $EC_{50}$ represent?

   Concentration producing $50\%$ of maximum effect. EC50 denotes drug potency as the concentration eliciting half of the maximum possible effect in pharmacodynamic models.

6. State the formula for loading dose to rapidly achieve target concentration $C_{target}$.

   $LD=\frac{V_d\times C_{target}}{F}$. Loading dose accelerates achievement of target concentration by considering distribution volume and adjusting for bioavailability.

7. State the relationship between total concentration $C_{total}$ and unbound concentration $C_u$.

   $C_u=f_u\times C_{total}$. Unbound concentration, critical for pharmacological activity, is obtained by multiplying fraction unbound by total plasma concentration.

8. State the formula for absolute bioavailability $F$ using AUC and dose (extravascular vs IV).

   $F=\frac{AUC_{po}\times Dose_{iv}}{AUC_{iv}\times Dose_{po}}$. Absolute bioavailability compares exposure from extravascular and IV routes, adjusted for doses, to quantify systemic availability.

9. State the $E_{max}$ model equation for effect $E$ as a function of concentration $C$.

   $E=\frac{E_{max}\times C}{EC_{50}+C}$. The Emax model describes the hyperbolic relationship between drug concentration and effect, based on receptor occupancy theory.

10. What is the definition of bioavailability $F$?

    Fraction of dose reaching systemic circulation unchanged. Bioavailability accounts for absorption and first-pass effects, representing the proportion of administered dose entering systemic circulation intact.

11. State the formula for elimination rate constant $k$ using half-life $t_{1/2}$ (first-order).

    $k=\frac{0.693}{t_{1/2}}$. The elimination rate constant is derived from the half-life using the natural logarithm of 2, reflecting first-order kinetics where a constant fraction is eliminated.

12. Identify the key distinction between first-order and zero-order elimination kinetics.

    First-order: constant fraction; zero-order: constant amount per time. First-order kinetics eliminate a constant proportion of drug, while zero-order eliminates a fixed amount, independent of concentration.

13. State the Hill (sigmoid $E_{max}$) model equation using Hill coefficient $\gamma$.

    $E=\frac{E_{max}\times C^{\gamma}}{EC_{50}^{\gamma}+C^{\gamma}}$. The sigmoid Emax model incorporates the Hill coefficient to account for curve steepness, reflecting cooperative binding or multiple receptors.

14. State the formula for volume of distribution $V_d$ using amount in body and plasma concentration $C_p$.

    $V_d=\frac{\text{Amount in body}}{C_p}$. Volume of distribution quantifies drug dispersion by relating the total amount in the body to its measured plasma concentration.

15. What does the pharmacodynamic parameter $E_{max}$ represent?

    Maximum achievable drug effect. Emax represents intrinsic efficacy, the peak response achievable as concentration increases in dose-response relationships.

16. State the formula for maintenance dose per interval $\tau$ for oral dosing to achieve target $C_{ss,avg}$.

    $\text{Dose}=\frac{CL\times C_{ss,avg}\times \tau}{F}$. This formula determines the oral dose per interval to sustain average steady-state concentration, accounting for clearance, interval, and bioavailability.

17. State the formula for initial concentration $C_0$ after an IV bolus dose.

    $C_0=\frac{\text{Dose}}{V_d}$. Initial concentration post-IV bolus assumes instantaneous distribution, calculated as dose divided by volume of distribution.

18. State the formula for AUC after a single extravascular dose (first-order) using $F$.

    $AUC=\frac{F\times \text{Dose}}{CL}$. Incorporates bioavailability to adjust for incomplete absorption in extravascular dosing, relating total exposure to dose and clearance.

19. What is the definition of fraction unbound $f_u$ in plasma?

    Unbound concentration divided by total concentration. Fraction unbound indicates the portion of drug free in plasma, available for distribution, metabolism, and exerting effects.

20. State the formula for half-life $t_{1/2}$ using elimination rate constant $k$ (first-order).

    $t_{1/2}=\frac{0.693}{k}$. Half-life is calculated using the natural logarithm of 2 divided by the elimination rate constant, indicating the time for drug concentration to decrease by half in first-order kinetics.

21. State the relationship between clearance, volume of distribution, and $k$ for first-order elimination.

    $CL=k\times V_d$. This equation links clearance to the product of elimination rate and distribution volume, fundamental for understanding drug removal in first-order kinetics.

22. Approximately how many half-lives are required to reach about $95\%$ steady state for first-order kinetics?

    About $4$ to $5$ half-lives. In first-order kinetics, drug accumulation approaches plateau after 4-5 half-lives, achieving approximately 95% of steady-state levels.

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