Active ingredient: Rifabutin Chemical name: (12E,22E,24Z)-(9S,14S,15R,16S,17R,18R,19R,20S,21S)-3,5,9,10- Tetrahydro-6,18,20-trihydroxy-1'-isobutyl-14-methoxy- 7,9,15,17,19,21,25-heptamethyl-5,10,26-trioxospiro[9,4- (epoxypentadeca[1,11,13]trienimino)-2H-furo[2',3':7,8]naphtho [1,2-d]imidazole-2,4-piperidine]-16-yl acetate CAS Number: 72559-06-9
Mycobutin (rifabutin) is a wide spectrum, semi-synthetic ansamycin antibiotic particularly active on acid-fast bacilli, including atypical and multidrug-resistant mycobacteria. The empirical formula is C46H62N4O11 and the structural formula is as follows: Each Mycobutin capsule for oral administration contains 150 mg of rifabutin. The hard gelatin capsules are opaque and red-brown in colour. Inactive ingredients are cellulose-microcrystalline, sodium lauryl sulfate, magnesium stearate, silicon dioxide, iron oxide red CI77491, titanium dioxide CI77891, Opacode S-1-7020 HV White and gelatin.
Rifabutin has activity in vitro against laboratory strains and clinical isolates of M. tuberculosis. To date, in vitro studies have shown that from one-third to half of M.
tuberculosis
strains resistant to rifampicin are susceptible to rifabutin, indicating that cross- resistance between the two antibiotics is incomplete.
The in vivo activity of rifabutin on experimental infections caused by M. tuberculosis is about 3 to 10 times greater than that of rifampicin in agreement with the in vitro findings. Rifabutin has been shown to be active against non-tuberculous (atypical) mycobacteria including M. avium-intracellulare complex (MAC), in vitro as well as in vivo on experimental infections caused by these pathogens in mice with induced immunodeficiency.
In vitro
susceptibility testing methods and diagnostic procedures used for determining minimum inhibitory concentration (MIC) values against MAC organisms and other mycobacterial species have not been standardised.
In humans, rifabutin maximum plasma concentrations are reached around 2-4 hours after oral administration. The pharmacokinetics of rifabutin is linear after single dosing of 300, 450, and 600 mg to healthy volunteers. With these doses, Cmax is in the range of 0.4-0.7 ug/mL. Although systemic levels of rifabutin following multiple dosing decreased by 38%, its terminal half-life remained unchanged. Rifabutin, due to its high lipophilicity, demonstrates a high propensity for distribution and intracellular tissue uptake. It is widely distributed in various animal organs with the exception of the brain. In particular, in human lung tissue the concentrations measured up to 24 hours after dosing are about 5-10 times higher than the plasma levels. Substantially higher intracellular tissue levels than those seen in plasma have been observed in both rat and man. About 85% of the drug is bound to plasma proteins. Binding does not appear to be influenced by renal or hepatic dysfunction. Renal and biliary clearance of unchanged drug each contribute approximately 5% to CLs/F. About 30% of the dose is excreted in the faeces. Rifabutin and its metabolites are eliminated mainly by the urinary route. The t1/2b of Mycobutin in humans is approximately 35-40 hours. The bioavailability of rifabutin from the capsule dosage form, relative to a solution, was 85% in healthy adult volunteers. High fat meals slow the rate without influencing the extent of absorption from the capsule.
Mycobutin is indicated for: The prophylaxis of M. avium-intracellulare complex (MAC) infections in patients with advanced HIV infection (CD4 counts lower than 200/mL). The treatment of infections caused by MAC and other atypical mycobacteria, including in immunocompromised patients. The treatment of chronic multidrug-resistant pulmonary tuberculosis in the presence of rifampicin resistant, rifabutin-sensitive M. tuberculosis strains. The treatment of newly diagnosed pulmonary tuberculosis in the presence of rifampicin resistant, rifabutin-sensitive M. tuberculosis strains. In accordance with the commonly accepted criteria for the treatment of mycobacterial infections, Mycobutin should always be given in combination with other anti-mycobacterial drugs not belonging to the family of rifamycins.
Mycobutin is contraindicated in patients with a history of hypersensitivity to rifabutin or other rifamycins (e.g. rifampicin). Due to insufficient clinical experience in children, Mycobutin should not be used in these patients. Concomitant use of ritonavir and rifabutin is contraindicated. Delavirdine should not be coadministered with rifabutin.
Mycobutin may impart a red-orange colour to the urine and possibly to skin and body secretions. Contact lenses, especially the soft variety, may be permanently stained. In accordance with the commonly accepted criteria for the treatment of mycobacterial infections, Mycobutin should always be given in combination with other anti-mycobacterial drugs not belonging to the family of rifamycins. It is recommended that white blood cell and platelet counts and liver enzymes be monitored during long term treatment with multidrug regimens that include Mycobutin because Mycobutin may be associated with neutropenia and, more rarely, thrombocytopenia. Rifamycins have been associated with drug-induced hepatic breakdown of vitamin K in pregnant women and their offspring (see Use in Pregnancy). There have been no reports of adverse effects of Mycobutin on ability to drive and use machines.
Clostridium difficile associated diarrhoea (CDAD) has been reported with use of nearly all antibacterial agents, including rifabutin, and may range in severity from mild diarrhoea 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 diarrhoea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.
Mycobutin should be used with caution in cases of liver insufficiency. For patients with severe liver insufficiency a dose reduction should be considered. Mild hepatic impairment does not require a dose modification.
Mild to moderate renal impairment does not require any dosage adjustment. Severe renal impairment (creatinine clearance below 30 mL/min) requires a dosage reduction of 50%.
When Mycobutin is given in association with clarithromycin, the dosage of Mycobutin should be reduced to 300 mg (see Adverse Reactions). Because of the possibility of occurrence of uveitis, patients should be carefully monitored when Mycobutin is given in combination with clarithromycin (or other macrolides) and/or fluconazole (and related compounds). If uveitis occurs, the patient should be referred to an ophthalmologist. If considered necessary Mycobutin treatment should be discontinued and appropriate treatment given (see Interactions, Adverse Reactions).
Category C
Reproduction studies have been carried out in rats and rabbits given rifabutin at oral dose levels up to 200 and 80 mg/kg/day, respectively. Teratogenicity was not observed in either species. In rats, at an oral dose of 40 mg/kg/day, rifabutin caused an increase in skeletal variants. In rabbits, at an oral dose of 80 mg/kg/day, rifabutin caused maternotoxicity and an increase in foetal skeletal anomalies. There are no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of a human response, rifabutin should be used in pregnant women only if the potential benefit justifies the potential risk to the foetus. During the late stages of pregnancy, rifampicin has been associated with serious vitamin K deficiency in mother and neonate, resulting in haemorrhagic disturbances. Mycobutin has not been studied in pregnancy. This should be borne in mind if, in exceptional cases, the physician considers the benefit of treatment outweighs the risk and wishes to treat a pregnant woman with Mycobutin.
It is not known whether rifabutin is excreted in human breast milk. Because many drugs are excreted in human milk and 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.
Long-term carcinogenicity studies were conducted with rifabutin in mice and rats. Rifabutin was not carcinogenic in mice at oral doses up to 180 mg/kg/day, giving rise to rifabutin plasma levels of 2.6 ug/mL and 1.8 ug/mL in female and male mice, respectively. Rifabutin was not carcinogenic in rats at oral doses up to 60 mg/kg/day, giving rise to rifabutin plasma levels of 9.2 ug/mL and 7.1 ug/mL in male and female rats, respectively. Serum levels in humans after dosing with 600 mg rifabutin were in the order of ug/mL. Rifabutin was not mutagenic in a standard series of assays for gene mutations and chromosomal damage.
Studies in rats at oral doses of rifabutin at 160 mg/kg/day have shown impairment of spermatogenesis and effects on the gonads without any significant effect on the numbers of live offspring.
Gastric pH alteration due to progressing HIV disease has been linked with malabsorption of some drugs used in HIV-positive patients (eg rifampin, isoniazid). Drug serum concentration data from AIDS patients with varying disease severity (based on CD4+ counts) suggest that rifabutin absorption is not influenced by progressing HIV disease.
Although structurally similar to rifampicin, rifabutin appears to induce enzymes of the P450 system to a lesser extent. Therefore, as rifabutin has been shown to induce the enzymes of the cytochrome P450 3A subfamily, treatment may affect the pharmacokinetic behaviour of drugs metabolised by the enzymes belonging to that subfamily (as is seen with rifampicin). Rifabutin accelerates the metabolism of: Fluconazole Oral contraceptives Methadone Phenytoin Rifabutin decreases the concentration of: Atovaquone Sulfamethoxazole Benzodiazepines Tacrolimus Opiate analgesics Trimethoprim Rifabutin accelerates the metabolism and may decrease plasma concentrations of: Astemizole Lovastatin Calcium channel blockers Midazolam Cisapride Nevirapine Clarithromycin Oestrogens Corticosteroids Quinidine Cyclosporin Ritonavir Delavirdine Saquinavir Erythromycin Terfenadine Indinavir Theophylline Itraconazole Triazolam Ketoconazole Warfarin Lidocaine Zidovudine Upward adjustment of the dosage of some of the drugs listed above may be required when administered with Mycobutin keeping in mind that some of the interactions show wide interindividual variability. The drugs normally subject to this include: dapsone, narcotic analgesics (including methadone), anticoagulants, corticosteroids, cardiac glycoside preparations (although not digitalis), quinidine, oral hypoglycaemic agents and oral contraceptives. It is important to note that during Mycobutin therapy oral contraception may not be adequate and patients should be advised to use other forms of contraception. There are insufficient data to assess whether dose adjustments are necessary when nevirapine and rifabutin are coadministered. Concomitant use of these drugs should be carefully monitored and the combination only used if clearly indicated. When rifabutin is used concomitantly with clarithromycin, a decreased dose of rifabutin is recommended due to the increase in plasma concentrations of rifabutin. Other macrolide antibiotics may also inhibit metabolism of rifabutin. When administered with indinavir, the dosage of rifabutin should be reduced by half. Protease inhibitors act as substrates or inhibitors of CYP450 3A4 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 patient specific drug profile. Other drugs such as ketoconazole, barbiturates, benzodiazepines, verapamil, b-blocking drugs, disopyramide, mexiletine, chloramphenicol and anticonvulsants may also require consideration for potential dose adjustment, during concomitant therapy based on the known effects of rifampicin. In contrast, no significant interactions may be expected with ethambutol, pyrazinamide, theophylline, sulfonamides and zalcitabine (DDC). Although pharmacokinetic data have shown that Mycobutin, when given in combination with zidovudine, reduces the plasma levels of the latter, a large, controlled clinical study has shown that these changes are of no clinical relevance. Clinical studies have shown that Mycobutin does not affect the pharmacokinetics of didanosine (DDI), isoniazid (for the latter refer also to Adverse Reactions) and fluconazole: fluconazole however increases rifabutin plasma levels. Zidovudine and DDI were shown not to affect the pharmacokinetics of rifabutin. In addition, some drugs increase the concentration of rifabutin and these include the following: Ciprofloxacin Indinavir Clarithromycin Itraconazole Enoxacin Ketoconazole Erythromycin Ritonavir Fluconazole Saquinavir Major interactions in this category leading to a significant increase in side effects, occur with clarithromycin, fluconazole, indinavir, ritonavir and, in particular, saquinavir. The following table summarizes the results and magnitude of the various drug interactions 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 1. Rifabutin Interaction Studies
| Coadministered Drugs | Effect on Rifabutin | Effect on Coadministered Drug | Comments |
| ANTIVIRALS | |||
| Delavirdine | ND | Oral clearance 5-fold resulting in significantly lower mean trough plasma concentrations (18 15 to 1.0 0.7 M) | Compared with historical data there was at least a 100 % increase in the AUC for rifabutin when given concomitantly with delavirdine. |
| Didanosine | No significant change in kinetics. | No significant change in kinetics at steady state. | |
| Indinavir 13 | 55%-173% in AUC | 32% in AUC | There was a 60 % increase in rifabutin AUC with a 150 mg rifabutin dose and a 204% increase with a 300 mg once daily dose of rifabutin. When given in combination, the dosage of indinavir should be increased and that of rifabutin decreased. |
| Saquinavir | ND | 43% in AUC | |
| Ritonavir | 4 fold increase in AUC, 2.5 fold increase in Cmax | ND | In the presence of ritonavir the subsequent risk of side effects, including uveitis may be increased. If a protease inhibitor is required in a patient treated with rifabutin, agents other than ritonavir should be considered (see Precautions). |
| Tipranavir/ritonavir | Increase in AUC, Increase in Cmax | No significant change in tipranavir kinetics. | Therapeutic drug monitoring of rifabutin is recommended. |
| Zidovudine | No significant change in kinetics. | Approximately 32% in Cmax and AUC | A large controlled clinical study has shown that these changes are of no clinical relevance |
| ANTIFUNGALS | |||
| Fluconazole | 82% in AUC | No significant change in steady-state plasma concentrations | Uveitis was associated with the combination of rifabutin and fluconazole. |
| Itraconazole | ND | 70% to 75% in Cmax and AUC | One case report suggests a kinetic interaction resulting in an increase in serum rifabutin levels and a risk for developing uveitis in the presence of itraconazole. |
| ANTI-PCP (Pneumocystis carinii pneumonia) | |||
| Dapsone | ND | Approximately 27% to 40% in AUC | Study conducted in HIV infected patients (rapid and slow acetylators). |
| Sulfamethoxazole- Trimethoprim | No significant change in Cmax and AUC | Approximately 15% to 20% in AUC | There was a 19% in the AUC for trimethoprim and a 14% in the AUC for sulfamethoxazole when cotrimoxazole was given with rifabutin compared to when cotrimoxazole was given alone. |
| ANTI-MAC (Mycobacterium avium intracellulare complex) | |||
| Azithromycin | No PK interaction | No PK interaction | |
| Clarithromycin | Approximately 77% in AUC | Approximately 50% in AUC | Study conducted in HIV infected patients. Dose of rifabutin should be adjusted in the presence of clarithromycin. |
| ANTI-TB (Tuberculosis) | |||
| Ethambutol | ND | No significant change in AUC or Cmax | |
| Isoniazid | ND | Pharmacokinetics not affected | |
| OTHER | |||
| Methadone | ND | No significant effect | No apparent effect of rifabutin on either peak levels of methadone or systemic exposure based upon AUC. Rifabutin kinetics not evaluated. |
| Theophylline | ND | No significant change in AUC or Cmax compared with baseline. | |
ND - No data AUC - Area under the Concentration vs. Time Curve Cmax - Maximum serum concentration
The tolerability of Mycobutin in multiple drug regimens was assessed in both immunocompetent and immunocompromised patients suffering from tuberculosis and non- tuberculous mycobacteriosis in long-term studies with daily dosages up to 600 mg. Bearing in mind that Mycobutin was often given in these studies as part of a multidrug regimen, it is not possible to define with certainty a drug-event relationship. Adverse reactions identified through either clinical trials or post-marketing surveillance by system organ class (SOC) are listed below:
*
Adverse Reactions not observed in a clinical trial.
* *
Adverse Reactions neither observed in the clinical trials nor in the spontaneous reporting for rifabutin and are mandated for the pharmacological class.
Blood and lymphatic system: Pancytopenia, white blood cells disorder (including agranulocytosis *, leukopenia, lymphopenia *, granulocytopenia *, neutropenia *, white blood cell count decreased *, neutrophils count decreased *), thrombocytopenia, platelet count decreased * and anaemia (approximately 4-9%). The frequency and severity of haematological reactions may be increased by combined administration of isoniazid. Immune system disorders: Shock * *, hypersensitivity *, bronchospasm *, rash, eosinophilia. Eye disorders: Uvetis *, corneal deposits *. Gastrointestinal disorders: Clostridium difficile colitis * *, nausea, vomiting. Hepato-biliary disorders: Jaundice (approximately 8-12%), hepatic enzyme increased *.
Skin and subcutaneous tissue disorders:
Skin discolouration.
Musculoskeletal and connective tissue disorders:
Arthralgia, myalgia (approximately 3%).
General disorders and administration site condition:
Pyrexia (approximately 2-4%), rash (approximately 3-4%) and, rarely (<1%), other hypersensitivity reactions such as eosinophilia, bronchospasm and shock might occur, as has been seen with other antibiotics.
Dermatological:
Limited numbers of cases of skin discoloration have been reported.
Ocular:
Mild to severe, reversible uveitis has been reported. The risk is very low when Mycobutin is used at 300 mg as monotherapy in MAC prophylaxis versus Mycobutin in combination with clarithromycin for MAC treatment (see Precautions). Corneal deposits have been reported during routine ophthalmologic surveillance of some IIIV-positive paediatric patients receiving Mycobutin 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. Treatment discontinuation was necessary in approximately 13% of patients with HIV infection and 5% of patients with tuberculosis in clinical trials, related to gastrointestinal symptoms, liver function test abnormalities and blood or lymphatic system disorders.
Mycobutin can be administered as a single, daily, oral dose at any time independently of meals. Caution should be applied when rifabutin is coadministered with any of the other drugs listed in the "Interactions with Other Drugs" section. Dosages of either drug may need to be adjusted on a case-by-case basis.
Mycobutin as a single agent:
prophylaxis of MAC infection in immunodepressed patients: 300 mg (2 capsules) daily
Mycobutin in combination regimens: In non-tuberculosis mycobacterial disease: 300-600 mg (2 to 4 capsules) daily for up to 6 months after negative cultures are obtained. In chronic, multidrug-resistant pulmonary tuberculosis: 300-450 mg (2 to 3 capsules) daily for up to 6 months after negative sputum cultures are obtained. In newly-diagnosed pulmonary tuberculosis: 150-300 mg (1 to 2 capsules) daily for 6 months. When Mycobutin is given in association with clarithromycin, the dosage of Mycobutin should be reduced to 300 mg once daily. When Mycobutin and indinavir are coadministered, the dosage of Mycobutin should be halved and the dosage of indinavir increased to 1,000 mg qid.
There are inadequate data to support the use of Mycobutin in children at the present time.
No specific recommendations for dosage alterations in the elderly are suggested.
A specific toxic dose of rifabutin has not been established, although a syndrome of arthralgia/ arthritis has been reported following daily monotherapy of 1 gram or more. Other signs and symptoms of overdosage are likely to be similar to adverse effects from normal therapeutic doses. There is no specific antidote. Treatment is symptomatic and supportive, including respiratory and cardiovascular function. Plasma rifabutin levels may confirm overdosage but are not clinically useful. Monitor complete blood count, liver enzyme levels and fluid-electrolyte status as indicated, and perform an ophthalmologic examination if the patient exhibits ocular symptoms. An aqueous slurry of activated charcoal may be administered after a potentially toxic ingestion, but it is most effective within one hour of ingestion. In patients who are not fully conscious or have impaired gag reflex, consideration should be given to administering activated charcoal via nasogastric tube once the airway is protected. Rifabutin is approximately 85% protein-bound, is extensively distributed into various tissues and is not primarily excreted via the urinary route, therefore neither haemodialysis nor forced diuresis are expected to be of any benefit. Contact the Poisons Information Centre for advice on the management of an overdose.
Mycobutin is supplied as 150 mg capsules in:
PVC/Al blister packs of 30 (3 strips of 10 capsules) (AUST R 55038)
Glass bottles of 30 (AUST R 55048) - not marketed
The capsules are red-brown, with the words "Pharmacia & Upjohn" and "Mycobutin" imprinted on the capsule in white ink.
Pfizer Australia Pty Ltd ABN 50 008 422 348 38-42 Wharf Road West Ryde NSW 2114 Australia
6 MARCH 2000