Pharmacokinetics Lecture

Comprehensive vocabulary flashcards defining core pharmacokinetic parameters, elimination models, dosing calculations, and therapeutic drug monitoring concepts.

ADME

An acronym for Absorption, Distribution, Metabolism, and Excretion, which describes the four key stages a drug goes through in the body.

AUC (Area Under the Curve)

A measurement of total drug exposure over time on a blood concentration-time curve, calculated as $\text{AUC} = \frac{\text{Dose}}{\text{CL}}$.

Clearance ($\text{CL}$)

The volume of body fluids from which a drug is completely removed per unit of time ($\text{ml/min}$ or $\text{L/h}$), relating the rate of elimination to plasma drug concentration via the formula $\text{CL} = \frac{V_d \times 0.693}{t_{1/2}}$.

$$C_{\max}$$

The maximum or peak plasma drug concentration achieved in the blood after administration.

$C_{ss}$ (Steady-State Concentration)

The drug concentration in the body reached when the rate of drug administration (intake) equals the rate of drug elimination, typically attained after $4\text{ to }5$ elimination half-lives ($t_{1/2}$).

Minimum Effective Concentration (MEC)

The lowest plasma drug concentration required to produce a therapeutic response.

Maximum Tolerated Concentration (MTC)

The upper plasma concentration threshold above which drug toxicity begins to occur (also known as minimum toxic concentration).

Elimination Half-Life ($t_{1/2}$)

The time required for plasma drug concentration to decrease by $50\%$, calculated in first-order processes using the formula $t_{1/2} = \frac{0.693}{k_e}$.

First-Order Kinetics

A kinetic process where a constant percentage of drug is eliminated per unit of time, causing the elimination rate to vary proportionally with drug concentration while the half-life remains constant.

Zero-Order Kinetics

A kinetic process where a constant amount of drug is eliminated per unit of time regardless of plasma concentration due to the saturation of elimination mechanisms.

Michaelis-Menten Kinetics

Also called saturable, mixed-order, or non-linear kinetics; describes drug metabolism when enzymatic pathways become saturated (observed with drugs such as phenytoin, theophylline, and voriconazole).

$$V_{\max}$$

The maximum rate of drug metabolism achieved when metabolizing enzymes are completely saturated.

$K_m$ (Michaelis-Menten Constant)

The plasma drug concentration at which the rate of metabolism is half-maximal ($\frac{1}{2}\,V_{\max}$).

Volume of Distribution ($V_d$)

The theoretical volume of body fluids in which the total amount of drug in the body would need to be dissolved to yield the observed plasma concentration ($V_d = \frac{D}{C}$).

Loading Dose (LD)

An initial dose administered (such as an IV bolus) to rapidly attain the desired therapeutic steady-state concentration ($C_{ss}$), calculated as $\text{LD} = \frac{C_p \times V_d}{F}$.

Maintenance Dose (MD)

The ongoing drug dose administered via continuous infusion or repeated intervals ($\tau$) to maintain steady-state concentration, calculated as $D = \frac{\text{CL} \times C_{ss}}{\tau}$.

Bioavailability ($F$)

The fraction or percentage of an administered drug dose that enters the systemic circulation unchanged ($100\%$ or $F = 1$ for intravenous administration).

Therapeutic Drug Monitoring (TDM)

The clinical practice of measuring drug levels to optimize therapy, maximize clinical efficacy, and minimize toxicities, especially for agents with narrow therapeutic indices.

Peak Level

The highest plasma drug concentration reached in the blood, typically drawn $30\,\text{minutes}$ after an intravenous infusion to allow for distribution, primarily correlating with drug efficacy and dose size.

Trough Level

The lowest plasma drug concentration reached right before the next scheduled dose, drawn immediately before or within $30\,\text{minutes}$ prior to administration, primarily correlating with toxicity and dosing intervals.

First-Pass Metabolism

The initial enzymatic hepatic breakdown or degradation of an orally administered drug before it reaches the systemic circulation, which decreases its oral bioavailability compared to IV dosing.