Pharmacokinetic studies to assess bioequivalence The plasma concentration-time curves for two different products containing the same active drug following oral dosing are illustrated in Fig. 21.14. These formulations differ in terms of their rates of absorption (tmax and Cmax are different); however, for both formulations the drug concentration is below the maximum safe concentration, so no big difference in tolerability would be expected and the two formulations are above the minimum effective concentration for a similar period so would be expected to perform similarly. To declare bioequivalence between these two formulations, however, the ratio of the geometric means of Cmax and AUC for the test and reference products from a number of participants needs to be within predetermined statistical criteria (normally 80.00 % to 125.00 % ). Fig. 21.14 cdot Plasma concentration-time curves for two chemically equivalent drug products administered in equal single doses by the oral route.

## Step 1: Understanding the Graph<br />### The graph illustrates the plasma concentration of a drug over time for two formulations, Y (test) and X (standard). Formulation Y reaches a higher peak concentration quickly but declines faster, while Formulation X has a slower rise to a lower peak but stays within the therapeutic range longer.<br /><br />## Step 2: Bioequivalence Criteria<br />### To declare bioequivalence, the ratio of the geometric means of the maximum concentration ($C_{\text{max}}$) and the area under the curve (AUC) for both formulations must fall within the range of 80.00% to 125.00%.<br /><br />## Step 3: Analysis of Tolerability and Effectiveness<br />### Both formulations stay below the maximum safe concentration, indicating similar tolerability. They also remain above the minimum effective concentration for a comparable duration, suggesting similar effectiveness.<br /><br />## Step 4: Conclusion on Bioequivalence<br />### Despite differences in $t_{\text{max}}$ and $C_{\text{max}}$, if the statistical criteria for the ratios of $C_{\text{max}}$ and AUC are met, the formulations can be considered bioequivalent.