3.13
Modelos de compartimientos: Modelo de un solo compartimiento
El modelo de un solo compartimiento sirve como una representación simplificada del cuerpo humano. Este modelo asume que el cuerpo funciona como un sol…
El modelo de un solo compartimento asume que el cuerpo humano es un solo compartimento abierto bien agitado.
Cuando un fármaco administrado a través de un bolo intravenoso entra en el cuerpo, se distribuye instantáneamente sin barreras y abandona el cuerpo a través de la biotransformación y la eliminación.
El volumen del compartimento es el volumen aparente de distribución, un volumen teórico en el que la dosis administrada puede distribuirse rápida y uniformemente.
La eliminación del fármaco del cuerpo sigue una cinética de primer orden, en la que la tasa de eliminación es directamente proporcional a la concentración del fármaco en el organismo.
Con el tiempo, la concentración plasmática del fármaco disminuye exponencialmente con una disminución proporcional de la concentración tisular del fármaco.
Una infusión continua de una dosis dada alcanza un valor de estado estacionario exponencialmente. Si la infusión se detiene, la concentración cae exponencialmente.
Si se administra la misma dosis en varias dosis iguales, la concentración media en estado estacionario y el tiempo necesario para alcanzar el estado estacionario son similares a los de una perfusión continua.
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Q1: What is the single-compartment model in pharmacokinetics?
The single-compartment model represents the human body as a single well-stirred open compartment where drugs distribute instantaneously without barriers. When administered intravenously, a drug rapidly distributes uniformly throughout this compartment and then undergoes biotransformation and elimination. This simplified model assumes uniform drug concentration across the body at any given time.
Q2: How does drug clearance work in the single-compartment model?
Drug clearance from the body follows first-order kinetics, meaning the elimination rate is directly proportional to the drug concentration present. As concentration decreases, the elimination rate also decreases proportionally. This results in exponential decline of both plasma and tissue drug concentrations over time, following drug elimination the concept of clearance.
Q3: What is the apparent volume of distribution?
The apparent volume of distribution is a theoretical volume into which an administered drug dose can rapidly and uniformly distribute within the single-compartment model. It represents the relationship between the amount of drug in the body and its plasma concentration. This volume helps predict how extensively a drug distributes throughout the body.
Q4: How does continuous infusion reach steady state in the single-compartment model?
During continuous infusion, drug concentration rises exponentially until reaching a steady-state value where the infusion rate equals the elimination rate. Once steady state is achieved, plasma concentration remains constant. If infusion stops, the concentration falls exponentially following first-order kinetics throughout the body.
Q5: How do multiple equal doses compare to continuous infusion?
When a drug is administered in multiple equal doses, the mean steady-state concentration and time required to reach steady state are similar to those achieved with continuous infusion. Both dosing approaches result in comparable pharmacokinetic profiles, though multiple dosing creates fluctuations around the mean concentration value.
Q6: Why is the single-compartment model considered a simplified representation?
The single-compartment model assumes the body functions as one well-mixed compartment with instantaneous, uniform drug distribution and no physiological barriers. In reality, drugs distribute at different rates into various tissues and organs. This simplification makes calculations manageable for basic pharmacokinetic predictions while acknowledging limitations.
Q7: What happens to drug concentration after an IV bolus in the single-compartment model?
After intravenous bolus administration, the drug distributes instantaneously and uniformly throughout the compartment. Plasma concentration then declines exponentially as the drug undergoes biotransformation and elimination. The tissue drug concentration follows a similar exponential decline pattern proportional to the plasma concentration changes.