Rifabutin (Page 3 of 4)

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term carcinogenicity studies were conducted with rifabutin in mice and in rats. Rifabutin was not carcinogenic in mice at doses up to 180 mg/kg/day, or approximately 36 times the recommended human daily dose. Rifabutin was not carcinogenic in the rat at doses up to 60 mg/kg/day, about 12 times the recommended human dose.

Rifabutin was not mutagenic in the bacterial mutation assay (Ames Test) using both rifabutin-susceptible and resistant strains. Rifabutin was not mutagenic in Schizosaccharomyces pombe P1 and was not genotoxic in V-79 Chinese hamster cells, human lymphocytes in vitro , or mouse bone marrow cells in vivo.

Fertility was impaired in male rats given 160 mg/kg (32 times the recommended human daily dose).

Pregnancy

Pregnancy Category B

Rifabutin should be used in pregnant women only if the potential benefit justifies the potential risk to the fetus. There are no adequate and well-controlled studies in pregnant or breastfeeding women.

Reproduction studies have been carried out in rats and rabbits given rifabutin using dose levels up to 200 mg/kg (about 6 to 13 times the recommended human daily dose based on body surface area comparisons). No teratogenicity was observed in either species. In rats, given 200 mg/kg/day, (about 6 times the recommended human daily dose based on body surface area comparisons), there was a decrease in fetal viability. In rats, at 40 mg/kg/day (approximately equivalent to the recommended human daily dose based on body surface area comparisons), rifabutin caused an increase in fetal skeletal variants. In rabbits, at 80 mg/kg/day (about 5 times the recommended human daily dose based on body surface area comparisons), rifabutin caused maternotoxicity and increase in fetal skeletal anomalies. Because animal reproduction studies are not always predictive of human response, rifabutin should be used in pregnant women only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

It is not known whether rifabutin is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

Safety and effectiveness of rifabutin for prophylaxis of MAC in children have not been established. Limited safety data are available from treatment use in 22 HIV-positive children with MAC who received rifabutin in combination with at least two other antimycobacterials for periods from 1 to 183 weeks. Mean doses (mg/kg) for these children were: 18.5 (range 15.0 to 25.0) for infants 1 year of age, 8.6 (range 4.4 to 18.8) for children 2 to 10 years of age, and 4.0 (range 2.8 to 5.4) for adolescents 14 to 16 years of age. There is no evidence that doses greater than 5 mg/kg daily are useful. Adverse experiences were similar to those observed in the adult population, and included leukopenia, neutropenia and rash. In addition, corneal deposits have been observed in some patients during routine ophthalmologic surveillance of HIV-positive pediatric patients receiving rifabutin as part of a multiple-drug regimen for MAC prophylaxis. These are tiny, almost transparent, asymptomatic peripheral and central corneal deposits which do not impair vision. Doses of rifabutin may be administered mixed with foods such as applesauce.

Geriatric Use

Clinical studies of rifabutin did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy (see CLINICAL PHARMACOLOGY).

ADVERSE REACTIONS

Adverse Reactions from Clinical Trials

Rifabutin capsules were generally well tolerated in the controlled clinical trials. Discontinuation of therapy due to an adverse event was required in 16% of patients receiving rifabutin, compared to 8% of patients receiving placebo in these trials. Primary reasons for discontinuation of rifabutin were rash (4% of treated patients), gastrointestinal intolerance (3%), and neutropenia (2%).

The following table enumerates adverse experiences that occurred at a frequency of 1% or greater, among the patients treated with rifabutin in studies 023 and 027.

Table 3 : Clinical Adverse Experiences Reported in 1 % of Patients Treated With Rifabutin
Adverse event Rifabutin ( N = 566 ) % Placebo ( N = 580 ) %
Body as a whole
Abdominal pain 4 3
Asthenia 1 1
Chest pain 1 1
Fever 2 1
Headache 3 5
Pain 1 2
Blood and lymphatic system
Leucopenia 10 7
Anemia 1 2
Digestive system
Anorexia 2 2
Diarrhea 3 3
Dyspepsia 3 1
Eructation 3 1
Flatulence 2 1
Nausea 6 5
Nausea and vomiting 3 2
Vomiting 1 1
Musculoskeletal system
Myalgia 2 1
Nervous system
Insomnia 1 1
Skin and appendages
Rash 11 8
Special senses
Taste perversion 3 1
Urogenital system
Discolored urine 30 6

Clinical Adverse Events Reported In <1% of Patients Who Received Rifabutin

Considering data from the 023 and 027 pivotal trials, and from other clinical studies, rifabutin appears to be a likely cause of the following adverse events which occurred in less than 1% of treated patients: flu-like syndrome, hepatitis, hemolysis, arthralgia, myositis, chest pressure or pain with dyspnea, skin discoloration, thrombocytopenia, pancytopenia and jaundice.

The following adverse events have occurred in more than one patient receiving rifabutin, but an etiologic role has not been established: seizure, paresthesia, aphasia, confusion, and non-specific T wave changes on electrocardiogram.

When rifabutin was administered at doses from 1050 mg/day to 2400 mg/day, generalized arthralgia and uveitis were reported. These adverse experiences abated when rifabutin was discontinued.

Mild to severe, reversible uveitis has been reported less frequently when rifabutin is used at 300 mg as monotherapy in MAC prophylaxis versus rifabutin in combination with clarithromycin for MAC treatment (see also WARNINGS).

Uveitis has been infrequently reported when rifabutin is used at 300 mg/day as monotherapy in MAC prophylaxis of HIV-infected persons, even with the concomitant use of fluconazole and/or macrolide antibacterials. However, if higher doses of rifabutin are administered in combination with these agents, the incidence of uveitis is higher. FDA proposes moving this paragraph from below with some revisions.

Patients who developed uveitis had mild to severe symptoms that resolved after treatment with corticosteroids and/or mydriatic eye drops; in some severe cases, however, resolution of symptoms occurred after several weeks.

When uveitis occurs, temporary discontinuance of rifabutin and ophthalmologic evaluation are recommended. In most mild cases, rifabutin may be restarted; however, if signs or symptoms recur, use of rifabutin should be discontinued (Morbidity and Mortality Weekly Report, September 9, 1994).

Corneal deposits have been reported during routine ophthalmologic surveillance of some HIV-positive pediatric patients receiving rifabutin as part of a multiple drug regimen for MAC prophylaxis. The deposits are tiny, almost transparent, asymptomatic peripheral and central corneal deposits, and do not impair vision.

The following table enumerates the changes in laboratory values that were considered as laboratory abnormalities in Studies 023 and 027.

Includes grades 3 or 4 toxicities as specified:

1 All values >450 U/L

2 All values >150 U/L

3 All hemoglobin values < 8.0 g/dL

4 All WBC values < 1,500/mm³

5 All ANC values < 750/mm³

6 All platelet count values < 50,000/mm³

Table 4 : Percentage of Patients With Laboratory Abnormalities
Laboratory abnormalities Rifabutin ( n = 566 ) % Placebo ( n = 580 ) %
Chemistry
Increased alkaline phosphatase1 <1 3
Increased SGOT2 7 12
Increased SGPT2 9 11
Hematology
Anemia3 6 7
Eosinophilia 1 1
Leukopenia4 17 16
Neutropenia 5 25 20
Thrombocytopenia6 5 4

The incidence of neutropenia in patients treated with rifabutin was significantly greater than in patients treated with placebo (p = 0.03). Although thrombocytopenia was not significantly more common among patients treated with rifabutin in these trials, rifabutin has been clearly linked to thrombocytopenia in rare cases. One patient in Study 023 developed thrombotic thrombocytopenic purpura, which was attributed to rifabutin.

Adverse Reactions from Post-Marketing Experience

Adverse reactions identified through post-marketing surveillance by system organ class (SOC) are listed below:

Blood and lymphatic system disorders

White blood cell disorders (including agranulocytosis, lymphopenia, granulocytopenia, neutropenia, white blood cell count decreased, neutrophil count decreased), platelet count decreased.

Immune system disorders

Hypersensitivity, bronchospasm, rash, and eosinophilia.

Gastrointestinal disorders

Clostridium difficile colitis/ Clostridium difficile associated diarrhea.

Pyrexia, rash and other hypersensitivity reactions such as eosinophilia and bronchospasm might occur, as has been seen with other antibacterials.

A limited number of skin discoloration have been reported.

Rifamycin hypersensitivity reactions

Hypersensitivity to rifamycins have been reported including flu-like symptoms, bronchospasm, hypotension, urticaria, angioedema, conjunctivitis, thrombocytopenia or neutropenia.

To report SUSPECTED ADVERSE REACTIONS, contact Lupin Pharmaceuticals, Inc. at 1-800-399-2561 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

ANIMAL TOXICOLOGY

Liver abnormalities (increased bilirubin and liver weight) occurred in mice, rats and monkeys at doses (respectively) 0.5, 1 and 3-times the recommended human daily dose based on body surface area comparisons). Testicular atrophy occurred in baboons at doses 2 times the recommended human dose based on body surface area comparisons and in rats at doses 6 times the recommended human daily dose based on body surface area comparisons.

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