Pharmacokinetics And Pharmacodynamics - NAPLEX

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.

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.

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

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

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

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.

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.

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

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

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

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

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

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

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

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

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.

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

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

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

$t_{1/2}=\frac{0.693}{k}$. 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.

$k=\frac{0.693}{t_{1/2}}$. 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.