Due to the possible occurrence of uveitis, patients should also be carefully monitored when MYCOBUTIN 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 MYCOBUTIN should be suspended (see also ADVERSE REACTIONS).
Clostridioides difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including MYCOBUTIN (rifabutin) Capsules, USP, 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.
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 MYCOBUTIN (see ADVERSE REACTIONS).
If patients develop a skin rash they should be monitored closely, and MYCOBUTIN 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 MYCOBUTIN is essential because of the syndrome’s mortality and visceral involvement (e.g., liver, bone marrow or kidney).
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).
MYCOBUTIN is a CYP3A inducer. Co-administration with antiretroviral drugs metabolized by CYP3A, including but not limited to products containing bictegravir, rilpivirine, or doravirine may decrease plasma concentrations of those antiretroviral drugs, which may lead to loss of virologic response and possible development of resistance. Therefore, co-administration with antiretroviral drugs metabolized by CYP3A is not recommended or there may be a need to increase the dose of antiretroviral drugs (see PRECAUTIONS-Drug Interactions).
For further recommendations, please refer to the most recent prescribing information of the antiretrovirals or contact the specific manufacturer.
Because treatment with MYCOBUTIN Capsules may be associated with neutropenia, and more rarely thrombocytopenia, physicians should consider obtaining hematologic studies periodically in patients receiving prophylaxis with MYCOBUTIN.
Patients should be advised of the signs and symptoms of both MAC and tuberculosis, and should be instructed to consult their physicians if they develop new complaints consistent with either of these diseases. In addition, since MYCOBUTIN may rarely be associated with myositis and uveitis, patients should be advised to notify their physicians if they develop signs or symptoms suggesting either of these disorders.
Urine, feces, saliva, sputum, perspiration, tears, and skin may be colored brown-orange with rifabutin and some of its metabolites. Soft contact lenses may be permanently stained. Patients to be treated with MYCOBUTIN should be made aware of these possibilities.
Diarrhea is a common problem caused by antibacterials which usually ends when the antibacterial is discontinued. Sometimes, after starting treatment with antibacterials, patients can develop watery and bloody stools (with or without stomach cramps and fever) even as late as two or more months after having taken the last dose of the antibacterial. If this occurs, patients should contact their physician as soon as possible.
Rifabutin induces CYP3A enzymes and therefore may reduce the plasma concentrations of drugs metabolized by those enzymes. This effect may reduce the efficacy of standard doses of such drugs, which include itraconazole, clarithromycin, and saquinavir.
Some drugs that inhibit CYP3A may significantly increase the plasma concentration of rifabutin. Therefore, carefully monitor for rifabutin associated adverse events in those patients also receiving CYP3A inhibitors, which include fluconazole and clarithromycin. In some cases, the dosage of MYCOBUTIN may need to be reduced when it is coadministered with CYP3A inhibitors.
Table 2 summarizes the results and magnitude of the pertinent drug interactions assessed with rifabutin. The clinical relevance of these interactions and subsequent dose modifications should be judged in light of the population studied, severity of the disease, patient’s drug profile, and the likely impact on the risk/benefit ratio.
|Coadministered drug||Dosing regimen of coadministered drug||Dosing regimen of rifabutin||Study population (n)||Effect on rifabutin||Effect on coadministered drug||Recommendation|
|↑ indicates increase; ↓ indicates decrease; ↔ indicates no significant changeND — No DataAUC — Area under the Concentration vs. Time Curve; Cmax — Maximum serum concentration; Cmin – Minimum serum concentration|
|Amprenavir||1200 mg twice a day for 10 days||300 mg once a day for 10 days||Healthy male subjects (6)||↑ AUC by 193%,↑ Cmax by 119%||↔||Reduce rifabutin dose by at least 50%. Monitor closely for adverse reactions.|
|Bictegravir||75 mg once a day||300 mg once a day (fasted)||Healthy subjects||ND||↓ AUC 38% ↓ Cmin 56% ↓ Cmax 20%||Co-administration of rifabutin with Biktarvy (bictegravir/emtricitabine/tenofovir alafenamide) is not recommended due to an expected decrease in tenofovir alafenamide in addition to the reported reduction in bictegravir. Refer to Biktarvy prescribing information for additional information|
|Delavirdine||400 mg three times a day||300 mg once a day||HIV-infected patients (7)||↑ AUC by 230%,↑ Cmax by 128%||↓ AUC by 80%,↓ Cmax by 75%,↓ Cmin by 17%||CONTRAINDICATED|
|Didanosine||167 or 250 mg twice a day for 12 days||300 or 600 mg once a day for 12 days||HIV-infected patients (11)||↔||↔|
|Doravirine||100 mg single dose||300 mg once a day for 16 days||Healthy subjects (12)||ND||↓ 50% in AUC, ↓ 68% in C24 ↔ in Cmax||If concomitant use is necessary, increase the doravirine dosage as instructed in doravirine-containing product prescribing information.|
|Fosamprenavir/ ritonavir||700 mg twice a day plus ritonavir 100 mg twice a day for 2 weeks||150 mg every other day for 2 weeks||Healthy subjects (15)||↔ AUC *↓ Cmax by 15%||↑ AUC by 35%†,↑ Cmax by 36%,↑ Cmin by 36%||Reduce rifabutin dose by at least 75% (to a maximum 150 mg every other day or three times per week) when given with fosamprenavir/ritonavir combination.|
|Indinavir||800 mg three times a day for 10 days||300 mg once a day for 10 days||Healthy subjects (10)||↑ AUC by 173%,↑ Cmax by 134%||↓ AUC by 34%,↓ Cmax by 25%,↓ Cmin by 39%||Reduce rifabutin dose by 50%, and increase indinavir dose from 800 mg to 1000 mg three times a day.|
|Lopinavir/ ritonavir||400/100 mg twice a day for 20 days||150 mg once a day for 10 days||Healthy subjects (14)||↑ AUC by 203% ‡↓ Cmax by 112%||↔||Reduce rifabutin dose by at least 75% (to a maximum 150 mg every other day or three times per week) when given with lopinavir/ritonavir combination. Monitor closely for adverse reactions. Reduce rifabutin dosage further, as needed.|
|Saquinavir/ ritonavir||1000/100 mg twice a day for 14 or 22 days||150 mg every 3 days for 21–22 days||Healthy subjects||↑ AUC by 53% §↑ Cmax by 88%(n=11)||↓ AUC by 13%,↓ Cmax by 15%,(n=19)||Reduce rifabutin dose by at least 75% (to a maximum 150 mg every other day or three times per week) when given with saquinavir/ritonavir combination. Monitor closely for adverse reactions.|
|Rilpivirine||25 mg once a day||300 mg once a day||Healthy subjects (18)||ND||↓ AUC by 42% ↓ Cmin by 48% ↓ Cmax by 31%||Co-administration of rifabutin with Odefsey (rilpivirine/tenofovir alafenamide/emtricitabine) is not recommended, due to an expected decrease in tenofovir alafenamide in addition to the reported reduction in rilpivirine. Refer to Odefsey prescribing information for additional information.|
|Ritonavir||500 mg twice a day for 10 days||150 mg once a day for 16 days||Healthy subjects (5)||↑ AUC by 300%,↑ Cmax by 150%||ND||Reduce rifabutin dose by at least 75% (to a maximum 150 mg every other day or three times per week) when given with lopinavir/ritonavir combination. Monitor closely for adverse reactions.Reduce rifabutin dosage further, as needed.|
|Tipranavir/ ritonavir||500/200 twice a day for 15 doses||150 mg single dose||Healthy subjects (20)||↑ AUC by 190%,↑ Cmax by 70%||↔||Reduce rifabutin dose by at least 75% (to a maximum 150 mg every other day or three times per week) when given with tipranavir/ritonavir combination. Monitor closely for adverse reactions. Reduce rifabutin dosage further, as needed.|
|Nelfinavir||1250 mg twice a day for 7–8 days||150 mg once a day for 8 days||HIV-infected patients (11)||↑ AUC by 83%, ¶↑ Cmax by 19%||↔||Reduce rifabutin dose by 50% (to 150 mg once a day) and increase the nelfinavir dose to 1250 mg twice a day.|
|Zidovudine||100 or 200 mg every four hours||300 or 450 mg once a day||HIV-infected patients (16)||↔||↓ AUC by 32%,↓ Cmax by 48%,||Because zidovudine levels remained within the therapeutic range during co-administration of rifabutin, dosage adjustments are not necessary.|
|Fluconazole||200 mg once a day for 2 weeks||300 mg once a day for 2 weeks||HIV-infected patients (12)||↑ AUC by 82%,↑ Cmax by 88%||↔||Monitor for rifabutin associated adverse events. Reduce rifabutin dose or suspend MYCOBUTIN use if toxicity is suspected.|
|Posaconazole||200 mg once a day for 10 days||300 mg once a day for 17 days||Healthy subjects (8)||↑ AUC by 72%,↑ Cmax by 31%||↓ AUC by 49%,↓ Cmax by 43%||If co-administration of these two drugs cannot be avoided, patients should be monitored for adverse events associated with rifabutin administration, and lack of posaconazole efficacy.|
|Itraconazole||200 mg once a day||300 mg once a day||HIV-Infected patients (6)||↑#||↓ AUC by 70%,↓ Cmax by 75%,||If co-administration of these two drugs cannot be avoided, patients should be monitored for adverse events associated with rifabutin administration, and lack of itraconazole efficacy. In a separate study, one case of uveitis was associated with increased serum rifabutin levels following co-administration of rifabutin (300 mg once a day) with itraconazole (600–900 mg once a day).|
|Voriconazole||400 mg twice a day for 7 days (maintenance dose)||300 mg once a day for 7 days||Healthy male subjects (12)||↑ AUC by 331%,↑ Cmax by 195%||↑ AUC by ~100%,↑ Cmax by ~100%Þ||CONTRAINDICATED|
|ANTI-PCP (Pneumocystis carinii pneumonia)|
|Dapsone||50 mg once a day||300 mg once a day||HIV-infected patients (16)||ND||↓ AUC by 27 –40%|
|Sulfamethoxazole- Trimethoprim||800/160 mg||300 mg once a day||HIV-infected patients (12)||↔||↓ AUC by 15–20%|
|ANTI-MAC (Mycobacterium avium intracellulare complex)|
|Azithromycin||500 mg once a day for 1 day, then 250 mg once a day for 9 days||300 mg once a day||Healthy subjects (6)||↔||↔|
|Clarithromycin||500 mg twice a day||300 mg once a day||HIV-infected patients (12)||↑ AUC by 75%||↓ AUC by 50%||Monitor for rifabutin associated adverse events. Reduce dose or suspend use of MYCOBUTIN if toxicity is suspected. Alternative treatment for clarithromycin should be considered when treating patients receiving rifabutin|
|Ethambutol||1200 mg||300 mg once a day for 7 days||Healthy subjects (10)||ND||↔|
|Isoniazid||300 mg||300 mg once a day for 7 days||Healthy subjects (6)||ND||↔|
|Methadone||20 – 100 mg once a day||300 mg once a day for 13 days||HIV-infected patients (24)||ND||↔|
|Ethinylestradiol (EE)/Norethindrone (NE)||35 mg EE / 1 mg NE for 21 days||300 mg once a day for 10 days||Healthy female subjects (22)||ND||EE: ↓ AUC by35%, ↓ Cmax by 20%NE: ↓ AUC by 46%||Patients should be advised to use additional or alternative methods of contraception.|
|Theophylline||5 mg/kg||300 mg for 14 days||Healthy subjects (11)||ND||↔|
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