Mycobutin (rifabutin) Antibiotic Side Effects, Dosage, & Interactions

What is Mycobutin, and how does it work?

Generic drug: rifabutin

Brand name: Mycobutin

Mycobutin (rifabutin) is an antibiotic used to prevent mycobacterium avium complex (MAC) in people with HIV (human immunodeficiency virus) infection.
Mycobutin is also used with other medications to treat tuberculosis in people with HIV.

What are the side effects of Mycobutin?

Common side effects of Mycobutin include:

diarrhea,
stomach upset or pain,
changes in taste,
nausea,
vomiting,
belching,
bloating,
loss of appetite,
headache,
skin rash,
itching, or
red, orange, or brown discoloration of your skin, tears, sweat, saliva, urine, or stools (this side effect is harmless and will disappear when the medication is stopped).

What is the dosage for Mycobutin?

It is recommended that Mycobutin Capsules be administered at a dose of 300 mg once daily. For those patients with propensity to nausea, vomiting, or other gastrointestinal upset, administration of
Mycobutin at doses of 150 mg twice daily taken with food may be useful.
For patients with severe renal impairment (creatinine clearance less than 30
mL/min), consider reducing the dose of Mycobutin by 50%, if toxicity is
suspected. No dosage adjustment is required for patients with mild to moderate
renal impairment. Reduction of the dose of Mycobutin may also be needed for
patients receiving concomitant treatment with certain other drugs.
Mild hepatic impairment does not require a dose modification. The pharmacokinetics of rifabutin in patients with moderate and severe hepatic impairment is not known.

What drugs interact with Mycobutin?

Effect Of Rifabutin On The Pharmacokinetics Of Other Drugs

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.

Effect Of Other Drugs On Rifabutin Pharmacokinetics

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.

Table 2 Rifabutin Interaction Studies

Coadministered drugDosing regimen of coadministered drugDosing regimen of rifabutinStudy population (n)Effect on rifabutinEffect on coadministered drugRecommendationANTIVIRALSAmprenavir1200 mg BID × 10 days300 mg QD × 10 daysHealthy male subjects (6)↑ AUC by 193%,
↑ Cmax by 119%↔Reduce rifabutin dose by at least 50%. Monitor closely for adverse reactions.Delavirdine400 mg TID300 mg QDHIV-infected patients (7)↑ AUC by 230%,
↑ Cmax by 128%↓ AUC by 80%,
↓ Cmax by 75%,
↓ Cmin by 17%CONTRAINDICATEDDidanosine167 or 250 mg BID × 12 days300 or 600 mg QD × 1HIV-infected patients (11)↔↔Fosamprenavir/ ritonavir700 mg BID plus ritonavir 100 mg BID × 2 weeks150 mg every other day × 2 weeksHealthy 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.Indinavir800 mg TID × 10 days300 mg QD × 10 daysHealthy 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 TID.Lopinavir/ ritonavir400/100 mg BID × 20 days150 mg QD × 10 daysHealthy 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/ ritonavir1000/100 mg BID × 14 or 22 days150 mg every 3 days × 21–22 daysHealthy 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.Ritonavir500 mg BID × 10 days150 mg QD × 16 daysHealthy subjects (5)↑ AUC by 300%,
↑ Cmax by 150%NDReduce 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/ ritonavir500/200 BID × 15 doses150 mg single doseHealthy 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.Nelfinavir1250 mg BID × 7–8 days150 mg QD × 8 daysHIV-infected patients (11)↑ AUC by 83%,^¶
↑ Cmax by 19%↔Reduce rifabutin dose by 50% (to 150 mg QD) and increase the nelfinavir dose to 1250 mg BIDZidovudine100 or 200 mg q4h300 or 450 mg QDHIV-infected patients (16)↔↓ AUC by 32%,
↓ Cmax by 48%,Because zidovudine levels remained within the therapeutic range during coadministration of rifabutin, dosage adjustments are not necessary.ANTIFUNGALSFluconazole200 mg QD × 2 weeks300 mg QD × 2 weeksHIV-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.Posaconazole200 mg QD × 10 days300 mg QD × 17 daysHealthy 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.Itraconazole200 mg QD300 mg QDHIV-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 coadministration of rifabutin (300 mg QD) with itraconazole (600– 900 mg QD).Voriconazole400 mg BID × 7 days (maintenance dose)300 mg QD × 7 daysHealthy male subjects (12)↑ AUC by 331%,
↑ Cmax by 195%↑ AUC by ~100%,
↑ Cmax by ~100%^ÞCONTRAINDICATEDANTI-PCP (Pneumocystis carinii pneumonia)Dapsone50 mg QD300 mg QDHIV-infected patients (16)ND↓ AUC by 27 – 40%Sulfamethoxazole- Trimethoprim800/160 mg300 mg QDHIV-infected patients (12)↔↓ AUC by 15– 20%ANTI-MAC (Mycobacterium avium intracellulare complex)Azithromycin500 mg QD × 1 day, then 250 mg QD × 9 days300 mg QDHealthy subjects (6)↔↔Clarithromycin500 mg BID300 mg QDHIV-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 rifabutinANTI-TB (Tuberculosis)Ethambutol1200 mg300 mg QD × 7 daysHealthy subjects (10)ND↔Isoniazid300 mg300 mg QD × 7 daysHealthy subjects (6)ND↔OTHERMethadone20 – 100 mg QD300 mg QD × 13 daysHIV-infected patients (24)ND↔Ethinylestradiol (EE)/Norethindrone (NE)35 mg EE / 1 mg NE × 21 days300 mg QD × 10 daysHealthy female subjects (22)NDEE: ↓ AUC by 35%, ↓ Cmax by 20%
NE: ↓ AUC by 46%Patients should be advised to use additional or alternative methods of contraception.Theophylline5 mg/kg300 mg × 14 daysHealthy subjects (11)ND↔↑ indicates increase; ↓ indicates decrease; ↔ indicates no significant change
QD- once daily; BID- twice daily; TID – thrice daily
ND – No Data
AUC – Area under the Concentration vs. Time Curve; Cmax – Maximum serum concentration
* compared to rifabutin 300 mg QD alone
^† compared to historical control (fosamprenavir/ritonavir 700/100 mg BID)
^‡ also taking zidovudine 500 mg QD
^§ compared to rifabutin 150 mg QD alone
^¶ compared to rifabutin 300 mg QD alone
^# data from a case report
^Þ compared to voriconazole 200 mg BID alone

Other Drugs

The structurally similar drug, rifampin, is known to reduce the plasma concentrations of a number of other drugs (see prescribing information for rifampin).
Although a weaker enzyme inducer than rifampin, rifabutin may be expected to have some effect on those drugs as well.

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Is Mycobutin safe to use while pregnant or breastfeeding?

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.
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.