warnings
WARNINGS Tuberculosis Rifabutin capsules must not be administered for MAC prophylaxis to patients with active tuberculosis. Patients who develop complaints consistent with active tuberculosis while on prophylaxis with rifabutin should be evaluated immediately, so that those with active disease may be given an effective combination regimen of anti-tuberculosis medications. Administration of rifabutin as a single agent to patients with active tuberculosis is likely to lead to the development of tuberculosis that is resistant both to rifabutin and to rifampin. There is no evidence that rifabutin is an effective prophylaxis against M. tuberculosis . Patients requiring prophylaxis against both M. tuberculosis and Mycobacterium avium complex may be given isoniazid and rifabutin concurrently. Tuberculosis in HIV-positive patients is common and may present with atypical or extrapulmonary findings. Patients are likely to have a nonreactive purified protein derivative (PPD) despite active disease. In addition to chest X-ray and sputum culture, the following studies may be useful in the diagnosis of tuberculosis in the HIV-positive patient: blood culture, urine culture, or biopsy of a suspicious lymph node. MAC Treatment with Clarithromycin When rifabutin is used concomitantly with clarithromycin for MAC treatment, a decreased dose of rifabutin is recommended due to the increase in plasma concentrations of rifabutin (see Precautions - Drug Interactions , Table 2 ). Hypersensitivity and Related Reactions Hypersensitivity reactions may occur in patients receiving rifamycins. Signs and symptoms of these reactions may include hypotension, urticaria, angioedema, acute bronchospasm, conjunctivitis, thrombocytopenia, neutropenia or flu-like syndrome (weakness, fatigue, muscle pain, nausea, vomiting, headache, fever, chills, aches, rash, itching, sweats, dizziness, shortness of breath, chest pain, cough, syncope, palpitations). There have been reports of anaphylaxis with the use of rifamycins. Monitor patients receiving rifabutin therapy for signs and/or symptoms of hypersensitivity reactions. If these symptoms occur, administer supportive measures and discontinue rifabutin. Uveitis Due to the possible occurrence of uveitis, patients should also be carefully monitored when rifabutin is given in combination with clarithromycin (or other macrolides) and/or fluconazole and related compounds (see Precautions - Drug Interactions , Table 2 ). If uveitis is suspected, the patient should be referred to an ophthalmologist and, if considered necessary, treatment with rifabutin should be suspended (see also Adverse Reactions ). Clostridioides difficile Associated Diarrhea Clostridioides difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including rifabutin capsules, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of C. difficile . C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibacterial use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents. If CDAD is suspected or confirmed, ongoing antibacterial use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibacterial treatment of C. difficile , and surgical evaluation should be instituted as clinically indicated. Severe Cutaneous Adverse Reactions There have been reports of severe cutaneous adverse reactions (SCAR), such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP) associated with rifabutin (see ADVERSE REACTIONS ). If patients develop a skin rash they should be monitored closely, and rifabutin discontinued if lesions progress. Specifically, for DRESS, a multi-system potential life-threatening SCAR, time to onset of the first symptoms may be prolonged. DRESS is a clinical diagnosis, and its clinical presentation remains the basis for decision making. An early withdrawal of rifabutin is essential because of the syndrome's mortality and visceral involvement (e.g., liver, bone marrow or kidney). Antiretroviral and Anti-HCV Drug Interaction s Protease inhibitors act as substrates or inhibitors of CYP3A4 mediated metabolism. Therefore, due to significant drug-drug interactions between protease inhibitors and rifabutin, their concomitant use should be based on the overall assessment of the patient and a patient-specific drug profile. The concomitant use of protease inhibitors may require at least a 50% reduction in rifabutin dose, and depending on the protease inhibitor, an adjustment of the antiretroviral drug dose. Increased monitoring for adverse events is recommended when using these drug combinations (see Precautions-Drug Interactions) . Rifabutin is a CYP3A inducer. Co-administration with antiretroviral drugs metabolized by CYP3A, including but not limited to products containing bictegravir, elvitegravir, oral rilpivirine, or doravirine and anti-HCV drugs including but not limited to sofosbuvir (alone or incombination) may decrease plasma concentrations of those drugs, which may lead to loss of virologic response and possible development of resistance. Therefore, co-administration with antiretroviral and anti-HCV drugs metabolized by CYP3A is not recommended or there may be a need to increase the dose of antiretroviral or anti-HCV drugs (see Precautions-Drug Interactions) . For further recommendations, please refer to the most recent prescribing information of the antiretrovirals or anti-HCV drugs or contact the specific manufacturer.