Bioavailability and metabolism of mometasone furoate: pharmacology versus methodology.

The degree of systemic exposure ofter inhalation of corticosteroids is of great clinical concern. For optimum outcome, the pulmonary deposition should be sufficiently high to produce the desired anti-inflammatory effect in the lungs, whereas the plasma concentrations due to the absorption of the corticosteroid from the lung and the gut should be minimal. Recently, it has been reported that inhaled mometasone furoate has a systemic bioavailability of less than 1%, which is much lower than other corticosteroids currently available. However, critical evaluation of the study methodology and results does not support this finding. A major shortfall of the study was an insufficient analytical sensitivity, resulting in a calculated average plasma concentration profile that was entirely below the limit of quantification. These numbers were generated by replacing all concentrations below the limit of quantification byzero and then calculating an average value. This procedure can lead to erroneous results and misinterpretation. Furthermore, the potential contribution of active metabolites needs to be adequately addressed in comparisons of inhaled corticosteroids. Reliable estimates of systemic drug exposure are critical in evaluating the real safety profiles and therapeutic index for inhaled corticosteroids that are effective in treating chronic asthma.