hi viewers welcome back to another video of biopharmaceutics and pharmacokinetics series and today we will discuss about area under the curve or auc and how to determine it with the help of trapezoidal rule so let's get started area under the curve or auc represents the total integrated area under the plasma level time profile and express the total amount of active drug which reaches the systemic circulation a uc is equals to dose over clearance a uc is expressed in microgram per ml hours it is independent of root of drug administration and elimination rate as long as it does not change and auc is directly proportional to dose of a drug if we talk about the importance of area under the curve in toxicology a uc can be used as a measure of drug exposure it is derived from drug concentration and time so it gives a measure how much and how long the drug stays in the body the efficacy of some antibiotics is related to auc or mic thus maintaining a concentration above a minimum inhibitory concentration or mic is more important than peak concentrations in biopharmaceutics the auc measured after administration of a drug product is an important parameter in the comparison of drug products it is the most important parameter in evaluating the bioavailability of a drug from different dosage forms as it represents the extent of absorption in pharmacokinetics drug auc values can be used to determine other pharmacokinetic parameters such as clearance or bioavailability similar techniques can be used to calculate area under the first moment curve or aumc and thus mean resident time area under the curve is also important for drugs that are administered repetitively for the treatment of chronic conditions like asthma or epilepsy there are various methods available to determine the area under the curve which includes plenty meter method cut and weight method trapezoidal rule which is basically a mathematical method and counting square method and in this lecture we just focus on trapezoidal rule to determine the auc the area under the plasma concentration time curve or auc is very useful for calculating the relative efficiency of different drug products it can use to calculate the total body clearance and the apparent volume of distribution we can calculate auc directly from the cp versus time data we need to use it different approaches but the simplest and most common approach is a numerical approximation method called as the trapezoidal rule there are following simple steps involving trapezoidal rule in step one first of all divide the whole auc into various small segments know as trapezoids in step two then calculate the area of each segment separately with the help of formula a u c one to two is equal to c p two plus c p one over two and multiply by t 2 minus t 1 in step 3 calculate area of all the segments in the same way and then add up all areas of all the segments to get the sum by following formula in step four to finish this calculation we have two more areas to consider the area of first and the last segments after a rapid iv bolus drug administration with a one compartment model the first segment can be calculated after determining the zero plasma concentration or cp knot by extrapolation that is done by plotting the cp versus time data on semi log graph paper and then extending the best fit line back to the y-axis after that the final segment can be calculated from the following equation then calculate the total area by adding all the required values in the following formula so that's all about area under the curve or a uc and its determination with the help of trapezoidal rule hope you like this video and for more cool content about biopharmaceutics and pharmacokinetics please like and share this video and subscribe to my channel pharmacyd thank you