 Patients with human immunodeficiency virus HIV and respiratory disease commonly require protease inhibitors PIs and orally inhaled corticosteroids. Inhaled corticosteroids alone do not generally cause systemic adverse effects because of low systemic bioavailability, but the combination of inhaled fluticasone and various PIs has led to increased systemic fluticasone levels and multiple cases of secondary adrenal insufficiency. A study in healthy volunteers showed 350-fold increase in fluticasone area under the curve when ritonavir RTV 100mg twice daily was coadministered with intranasal fluticasone compared to intranasal fluticasone alone. The mechanism of this drug interaction is presumably secondary to PI inhibition of cytochrome P450 3A4, the enzyme responsible for fluticasone metabolism. As a result, inhaled fluticasone is not recommended in combination with most PIs unless the benefit outweighs the risk. One possible alternative to fluticasone is inhaled beclomethasone, which has not been studied in combination with PIs. Although beclomethasone also undergoes metabolism via CYP3A4 in vitro to its more active metabolite, beclomethasone-17-monopropionate, it appears to be largely hydrolyzed by esterases in vivo. Furthermore, the pharmacokinetic properties of beclomethasone-17-monopropionate, such as relatively short half-life, low maximum plasma concentration, and low volume of distribution, suggest that systemic accumulation leading to significant adverse effects is unlikely even in the presence of a CYP3A4 inhibitor such as a PI. 