Drug interactions of thalidomide with midazolam and cyclosporine A: heterotropic cooperativity of human cytochrome P450 3A5.

There is growing clinical interest of thalidomide because of its immunomodulatory and antiangiogenic properties, despite its teratogenicity. However, little information about thalidomide has been reported regarding its precise effects on drug-metabolizing enzymes. We investigated the effects of thalidomide on cytochrome P450 (P450) enzymes in human liver microsomes to clarify the potential for possible drug interactions. Thalidomide inhibited S-mephenytoin 4'-hydroxylation activities of recombinant P450 2C19 and human liver microsomes: the apparent concentration of thalidomide producing 50% inhibition was approximately 270 microM for P450 2C19. Midazolam 4-hydroxylation activities were suppressed by thalidomide, but activities of 1'-hydroxylation and total midazolam oxidation and testosterone 6beta-hydroxylation were enhanced in the presence of thalidomide. Recombinant P450 3A5 was found to have altered kinetics at clinically relevant concentrations of thalidomide (10-30 microM). P450 3A4 was also affected, but only at higher thalidomide concentrations. Enhanced midazolam hydroxylation by thalidomide was also seen in liver microsomal samples harboring the CYP3A5*1 allele. Similarly enhanced rates of cyclosporine A clearance were observed in P450 3A5 and liver microsomes expressing P450 3A5 in the presence of thalidomide. A proposed effector constant for thalidomide corresponded roughly to its clinical plasma levels. Docking studies with a P450 3A5 homology model, based on the published structure of P450 3A4, revealed close interaction between thalidomide and the heme of P450 3A5. The present results suggest that total midazolam metabolism or cyclosporine A clearance may be increased by thalidomide in a dose-dependent manner. Unexpected drug interactions involving thalidomide might occur via heterotropic cooperativity of polymorphic P450 3A5.

An unusual case of Behcet disease with posterior scleritis: A case report.

RATIONALE: Posterior scleritis is an ocular inflammatory disorder that can be associated with both infectious and non-infectious immune reactions. Behcet disease is a chronic, relapsing, multisystemic inflammatory disorder with uveitis. There are no reported cases of posterior scleritis with Bechet disease. PATIENT CONCERNS: A 50-year-old man previously diagnosed with systemic Behcet disease presented with ocular pain and decreased vision in the left eye. DIAGNOSIS: Posterior scleritis associated with Behcet disease was diagnosed based on optical coherence tomography showing choroidal folds, as well as contrast computed tomography and ultrasound sonography demonstrating thickening of the posterior sclera. INTERVENTIONS: Treatment with systemic corticosteroids was initiated. Since inflammation relapsed during steroid tapering, anti-tumor necrosis factor-alpha (TNF-α) therapy was used in combination, and tapering of steroids was possible without recurrence of inflammation for 12 months. OUTCOMES: Posterior scleritis was resolved and visual acuity improved. With the continuation of TNF-α therapy, oral prednisolone was successfully tapered and discontinued. No relapse of inflammation was observed at follow-up 1 year after discontinuation of prednisolone. LESSONS: Ophthalmologists should be aware of the possibility of rare manifestation of posterior scleritis in patients with Behcet disease, and that combined use of systemic steroids and anti-TNF-α therapy may resolve the scleritis without recurrence of inflammation.