The noncompartmental approach is a widely used method in pharmacokinetics to assess drugs' behaviors in the body. It considers several factors, including clearance, bioavailability, and total volume of distribution.

One key aspect of the noncompartmental approach is determining a drug's total clearance. This can be done by dividing the drug dose by the area under the concentration-time curve from zero to infinity. The area under the concentration-time curve represents the drug's overall exposure in the body over time. The trapezoidal method is commonly employed to calculate this area.

Bioavailability, denoted as F, is another important factor in the noncompartmental approach. It refers to the fraction of an administered dose that reaches the systemic circulation unchanged. Bioavailability can be determined by analyzing drug concentration data, providing insights into the drug's absorption and systemic availability.

The total volume of distribution, represented as V_ss, is a parameter that reflects the extent of drug distribution throughout the body. It is calculated by multiplying the drug's clearance by the mean residence time, which refers to the average time a drug molecule spends in the body.

However, calculating the mean residence time using the noncompartmental approach does have one limitation. It can only be readily calculated after a single intravenous (IV) dose. This restriction sets the noncompartmental approach apart from the compartmental approach, which allows more flexibility in estimating pharmacokinetic parameters.

In summary, the noncompartmental approach in pharmacokinetics utilizes clearance, bioavailability, and total volume of distribution to assess the behavior of drugs in the body. It involves calculating the total clearance by dividing the drug dose by the area under the concentration-time curve, determining bioavailability using drug concentration data, and estimating the total volume of distribution by multiplying clearance and mean residence time. However, the noncompartmental approach is limited in calculating mean residence time, as it requires a single dose of IV administration.