Pharmacokinetic Parameters - NAPLEX

Fraction of drug eliminated per unit time. The elimination rate constant represents the proportion of drug removed per unit time in first-order kinetics.

$V = \frac{Dose}{C_0}$. After an IV bolus, volume of distribution equals the dose divided by the extrapolated initial plasma concentration.

$V = \frac{Amount\ in\ body}{C_p}$. Volume of distribution is calculated as the ratio of drug amount in the body to its plasma concentration at equilibrium.

$V = \frac{400}{10} = 40\ \text{L}$. Volume of distribution is dose divided by initial concentration after IV bolus in a one-compartment model.

$CL = \frac{500}{50} = 10\ \text{L}/\text{h}$. Clearance is dose divided by AUC, reflecting elimination efficiency for IV administration.

$t_{\frac{1}{2}} = \frac{0.693}{0.2} = 3.465\ \text{h}$. Half-life equals the natural log of 2 divided by the elimination rate constant in first-order elimination.

$k = \frac{0.693}{6\ \text{h}} = 0.1155\ \text{h}^{-1}$. The elimination rate constant is the natural log of 2 divided by half-life for first-order kinetics.

Apparent volume relating amount in body to plasma concentration. Volume of distribution is a proportionality constant linking the total drug amount in the body to its plasma concentration.

$CL = \frac{Dose}{AUC}$. For intravenous dosing, clearance is the ratio of dose to the area under the concentration-time curve, reflecting total drug exposure.

$CL = k \times V$. Clearance equals the product of the elimination rate constant and volume of distribution in a one-compartment model with first-order kinetics.

$t_{\frac{1}{2}} = \frac{0.693}{k}$. Half-life is derived from the natural log of 2 divided by the elimination rate constant for first-order processes.

$t_{\frac{1}{2}} = \frac{0.693\times V}{CL}$. Half-life integrates volume of distribution and clearance, using the natural log of 2 to express time for 50% elimination.

$\text{Dose rate} = \frac{CL\times C_{ss}}{F}$. Maintenance dose rate sustains steady-state concentration by matching clearance adjusted for bioavailability.

$LD = \frac{C_{target}\times V}{F}$. Loading dose achieves target concentration rapidly by accounting for volume of distribution and bioavailability.

$R = \frac{1}{1-e^{-k\tau}}$. The accumulation factor accounts for drug buildup at steady state based on elimination rate and dosing interval.

$F = \frac{AUC_{EV}\times Dose_{IV}}{AUC_{IV}\times Dose_{EV}}$. Bioavailability compares AUCs normalized by doses between extravascular and IV routes to assess absorption efficiency.

Volume of plasma cleared of drug per unit time. Clearance quantifies the efficiency of drug removal by measuring the plasma volume from which the drug is completely eliminated per unit time.

$MD = \frac{CL\times C_{ss,avg}\times \tau}{F}$. Maintenance dose ensures average steady-state concentration by incorporating clearance, interval, and bioavailability.

$C_{ss,avg} = \frac{F\times Dose}{CL\times \tau}$. Average steady-state concentration balances absorbed dose against clearance over the dosing interval.

Fraction of administered dose reaching systemic circulation unchanged. Bioavailability quantifies the extent of unchanged drug entering systemic circulation relative to the administered dose.

Approximately $4$ to $5$ half-lives. Steady state is achieved when input equals output, typically after 4-5 half-lives in first-order kinetics.

$C_t = C_0\times e^{-kt}$. Concentration declines exponentially from initial value based on the elimination rate constant in a one-compartment model.

Clearance. For IV dosing, AUC is inversely proportional to clearance, which governs the rate of drug elimination.

$\frac{C_t}{C_0} = e^{-kt}$. In first-order elimination, the fraction of drug remaining decays exponentially with time and rate constant.