3.13
Modelos de compartimento: Modelo de compartimento único
O modelo de compartimento único serve como uma representação simplificada do corpo humano. Este modelo pressupõe que o corpo funciona como um único co…
O modelo de compartimento único assume que o corpo humano é um único compartimento aberto bem mexido.
Quando um medicamento administrado por meio de bolus intravenoso entra no corpo, ele se distribui instantaneamente sem barreiras e sai do corpo por meio de biotransformação e eliminação.
O volume do compartimento é o volume aparente de distribuição - um volume teórico no qual a dose administrada pode se distribuir rápida e uniformemente.
A depuração do medicamento do corpo segue a cinética de primeira ordem, onde a taxa de eliminação é diretamente proporcional à concentração do medicamento no corpo.
Com o tempo, a concentração plasmática do medicamento diminui exponencialmente com um declínio proporcional na concentração do medicamento tecidual.
Uma infusão contínua de uma determinada dose atinge exponencialmente um valor de estado estacionário. Se a infusão parar, a concentração cai exponencialmente.
Se a mesma dose for administrada em várias doses iguais, a concentração média no estado estacionário e o tempo necessário para atingir o estado estacionário são semelhantes aos de uma infusão contínua.
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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.