Hypopyon uveitis in patients with acquired immunodeficiency syndrome treated for systemic Mycobacterium avium complex infection with rifabutin

Metabolism of rifabutin in human enterocyte and liver microsomes: kinetic parameters, identification of enzyme systems, and drug interactions with macrolides and antifungal agents

Biotransformation of rifabutin, an antibiotic used for treatment of tuberculosis in patients infected with the human immunodeficiency virus (HIV), and its interactions with some macrolide and antifungal agents were studied in human intestinal and liver microsomes. Both liver and enterocyte microsomes metabolized rifabutin to 25-O-deacetylrifabutin, 27-O-demethylrifabutin, and 20-, 31-, and 32-hydroxyrifabutin. The same products (except 25-O-deacetylrifabutin) were formed by microsomes from lymphoblastoid cells that contained expressed CYP3A4. The apparent Michaelis-Menten constant (Km); approximately 10 to 12 mumol/L) and maximal velocity (Vmax; approximately 100 pmol/min/mg of protein) values for CYP-mediated metabolism were similar in liver and enterocyte microsomes. Deacetylation of rifabutin (Km approximately 16 to 20 mumol/L and Vmax approximately 50 to 100 pmol/min/mg of protein) was catalyzed by microsomal cholinesterase. Clarithromycin, ketoconazole, and fluconazole inhibited CYP-mediated metabolism of rifabutin in enterocyte microsomes equally or more potently than in liver microsomes but had no effect on cholinesterase activity. Azithromycin did not inhibit in vitro metabolism of rifabutin. This study provides evidence that CYP3A4 and cholinesterase are major enzymes that biotransform rifabutin in humans and that intestinal CYP3A4 contributes significantly to rifabutin presystemic first-pass metabolism and drug interactions with macrolide and antifungal agents.

Anterior nongranulomatous uveitis after intravitreal HPMPC (cidofovir) for the treatment of cytomegalovirus retinitis. Analysis and prevention

BACKGROUND AND OBJECTIVE

The authors characterize and analyze the incidence of a previously reported mild anterior nongranulomatous uveitis associated with intravitreal injections of (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC), also termed cidofovir (Vistide, Gilead Sciences, Foster City, CA). This is an acyclic nucleoside phosphonate analogue with a potent anticytomegalovirus effect. The authors also analyzed the effects of probenecid therapy, as well as prophylaxis with probenecid plus topical corticosteroids and cycloplegics on the course and outcome of the uveitis.

METHODS

Prospective case series from a tertiary referral center, which included 46 consecutive patients with acquired immune deficiency syndrome (AIDS) and cytomegalovirus (CMV) retinitis. There was a total of 130 injections in 69 eyes treated with 20 micrograms of intravitreal HPMPC. Forty-one patients (119 injections) received oral probenecid, 5 patients (11 injections) did not, and 21 patients (53 injections) received topical corticosteroids and cycloplegics as an adjuvant to probenecid in the prophylaxis of iritis.

RESULTS

Mild to moderate nongranulomatous iritis was seen in 26% of patients after their first injection (n = 12). Patients receiving probenecid prophylaxis after first injection had a significantly lower frequency of iritis versus patients who did not receive probenecid at the time of first injection (P = 0.0089). In contrast, treatment with topical corticosteroid and cycloplegics after injection did not statistically significantly affect the frequency of iritis in patients (P = 0.44). The development of iritis after a second injection of HPMPC was more likely if it had occurred after the initial injection (P = 0.015; Fisher's exact test). All cases of iritis were treated with topical corticosteroids and cycloplegics, and there was no permanent impairment of vision secondary to iritis after HPMPC injection in any eyes.

CONCLUSIONS

Anterior uveitis was seen in 26% of patients after first-time HPMPC injection. Concomitant use of probenecid appears to decrease the frequency of the iritis from 71% to 18% in patients with AIDS and CMV retinitis after the first intravitreal injection of HPMPC. Topical corticosteroid administration after injection (before iritis) was ineffective in preventing iritis treatment with topical corticosteroids and cycloplegics resulted in resolution of all iritis cases.

Uveitis associated with rifabutin and macrolide therapy for Mycobacterium avium intracellulare infection in AIDS patients

OBJECTIVE

Uveitis has been increasingly recognised as a side effect of rifabutin regimens in the prophylaxis and treatment of Mycobacterium avium intracellulare (MAI) infection. This study describes the clinical features and analyses the factors associated with rifabutin induced uveitis.

DESIGN

Retrospective observational study.

SETTING

Tertiary care institution, The Royal Hospitals NHS Trust, London.

PATIENTS

68 HIV seropositive individuals receiving rifabutin for prophylaxis or treatment of MAI infection.

RESULTS

11 episodes of uveitis occurred in 10 different individuals at a median of 62 days. The disease was bilateral in four and unilateral in the remainder. All subjects experienced ocular pain and photophobia and 9 individuals had a significant reduction in visual acuity. Uveitis was treated with mydriatics and topical steroids and resolved in all cases when rifabutin was stopped. The risk of uveitis was significantly increased with concurrent clarithromycin therapy, Odds Ratio 13.08, 95% Confidence Interval 1.98 to 83.12.

CONCLUSION

Rifabutin can cause a reversible uveitis. This risk is increased with concurrent clarithromycin therapy. Adverse drug interactions can be an important cause of morbidity in patients with advanced HIV disease.

Ophthalmic complications of HIV infection

HIV retinopathy, a noninfectious microangiopathy, is the most common ocular manifestation of HIV infection. Opportunistic infections, neoplasms, neuro-ophthalmic lesions, and drug-induced lesions may also cause ocular problems. Opportunistic ocular infections, particularly CMV retinitis, are a major cause of morbidity in patients with AIDS. Because of the underlying chronic and progressive immune dysfunction, the ocular symptoms, signs, clinical course, and treatment are often atypical and severe, requiring protracted medical therapy.

Inflammatory opacities of the vitreous in rifabutin-associated uveitis

PURPOSE

To describe rifabutin-associated uveitis with opacities in the inferior and posterior vitreous in three patients with acquired immunodeficiency syndrome.

METHOD

Case reports of the three patients are presented.

RESULTS

The patients, who were being treated with rifabutin and fluconazole, developed anterior and posterior uveitis. The posterior uveitis was characterized by white-yellow inflammatory opacities located in the inferior and posterior vitreous. Discontinuation of rifabutin and the start of topical corticosteroid therapy resulted in improvement of the uveitis and visual acuity.

CONCLUSION

Recognition of rifabutin-associated uveitis with opacities in the inferior and posterior vitreous may prevent unnecessary invasive diagnostic and therapeutic procedures.

AIDS and the eyes

The eye is affected in 50-75% of adult AIDS patients. This rate of ocular involvement is much higher than that in symptom-free HIV-seropositive patients, and seems to increase in incidence with severity of disease. These observations indicate that regular screening of HIV-positive patients is warranted to allow early identification of potential vision and life threatening disease.

Rifabutin induced vitritis in AIDS patients

The authors report three patients with the acquired immunodeficiency syndrome (AIDS) who developed uveitis while prophylactically taking rifabutin (300 mg/kg or more), clarithromycin and fluconazole. The uveitis presented unilaterally, but became bilateral within seven days in each patient. Inflammation was more severe in the vitreous than in the anterior chamber. Examination of the vitreous and blood from one patient with microbiological smears, bacterial and fungal culture and the polymerase chain reaction (PCR) to herpesviruses did not reveal an infectious etiology. Discontinuation or decreasing the dose of rifabutin to 300 mg/day and treatment with topical steroids and cycloplegics resulted in resolution of the uveitis within two weeks. Our findings support the observation that prophylactic doses of rifabutin, combined with clarithromycin, fluconazole or other agents which can increase rifabutin levels, can induce uveitis in patients with AIDS. It is important to recognize that a severe vitritis which can obscure visualization of the retina can be solely attributed to rifabutin in patients with AIDS. Therapy requires lowering the dose of rifabutin and the use of topical corticosteroids and cycloplegics.

Uveitis associated with rifabutin therapy

PURPOSE

To highlight the association of uveitis with the use of rifabutin.

METHODS

Retrospective study of two patients with acute anterior uveitis.

RESULTS

Both patients were receiving rifabutin for treatment of atypical Mycobacterium infection associated with AIDS when they developed unilateral acute anterior uveitis and arthritis. The inflammation resolved and vision improved with introduction of topical corticosteroids, mydriatics and cessation of rifabutin treatment.

CONCLUSION

Use of rifabutin with clarithromycin may precipitate acute uveitis in patients with AIDS being treated for systemic Mycobacterium avium complex infection. Uveitis produced by rifabutin may be analogous to Herxeimer reaction as seen in syphilis. Clarithromycin and fluconazole elevate levels of rifabutin due to inhibition of metabolism through cytochrome p-450 pathway. The differential diagnosis includes Reiter's syndrome, syphilis causing uveitis, metastatic endophthalmitis, and direct HIV-related uveitis.

Rifabutin-associated uveitis

OBJECTIVE

To review rifabutin-associated uveitis and discuss the mechanism and potential role of drug interactions with clarithromycin and fluconazole in contributing to this adverse event.

DATA SOURCES

A MEDLINE search (1991 through September 1994) of English-language literature using the main MeSH headings "rifabutin" and "uveitis" and the subheadings "adverse effects" and "chemically induced." Relevant articles also were selected from references of identified articles. Abstracts from recent medical conferences of infectious diseases, pharmacology, and HIV were screened for additional data.

STUDY SELECTION AND DATA EXTRACTION

All articles and abstracts reporting uveitis potentially related to rifabutin were considered for inclusion. Fifty-four cases were identified. Pertinent information from the case reports, as judged by the authors, was selected and synthesized for discussion.

DATA SYNTHESIS

Rifabutin is being prescribed increasingly for the treatment and prophylaxis of Mycobacterium avium complex (MAC) infection in the HIV-infected population. Uveitis was initially thought to be a rare, dose-limited complication of rifabutin therapy. In an early dose-ranging tolerance study, uveitis was associated with daily doses of 1200 mg or more. Because this toxicity appeared to be dose-related, lower dosages (300-600 mg/d) of rifabutin were selected for study in subsequent clinical trials. More recent reports noting the association of uveitis with these lower dosages of rifabutin have raised concerns about the prevalence of this adverse event. In the 54 identified cases, patients presented with symptoms of unilateral or bilateral uveitis from 2 weeks to more than 7 months following initiation of rifabutin therapy. In all reported cases, patients were receiving concurrent therapy with clarithromycin and/or fluconazole, both of which have inhibitory effects on rifabutin metabolism. In most cases, uveitis resolved within 1-2 months following discontinuation of rifabutin with or without administration of topical corticosteroids.

CONCLUSIONS

Rifabutin is prescribed frequently for the prophylaxis and treatment of MAC infection, especially in patients with HIV. Uveitis is a rare, dose-related toxicity of this therapy. The risk of rifabutin-associated uveitis may be increased in patients receiving concurrent therapy with clarithromycin or fluconazole because of drug interactions. Patients receiving therapy with combinations of any of these agents should be warned about signs and symptoms of uveitis and be monitored closely for the development of rifabutin toxicity. If uveitis develops, rifabutin therapy should be discontinued promptly.