Synergistic Rifabutin and Colistin Reduce Emergence of Resistance When Treating Acinetobacter baumannii.

Recently, we reported rifabutin hyperactivity against Acinetobacter baumannii We sought to characterize potential interactions between rifabutin and colistin, the last-resort drug for carbapenem-resistant infections. Rifabutin and colistin were synergistic in vitro and in vivo, and low-dose colistin significantly suppressed emergence of resistance to rifabutin. Thus, this combination is a promising therapeutic option for highly resistant A. baumannii infections.

Pharmacokinetic study of two different rifabutin doses co-administered with lopinavir/ritonavir in African HIV and tuberculosis co-infected adult patients.

BACKGROUND: This study aimed to assess the pharmacokinetic profile of 150 mg rifabutin (RBT) taken every other day (every 48 h) versus 300 mg RBT taken every other day (E.O.D), both in combination with lopinavir/ritonavir (LPV/r), in adult patients with human immunodeficiency virus (HIV) and tuberculosis (TB) co-infection. METHODS: This is a two-arm, open-label, pharmacokinetic, randomised study conducted in Burkina Faso between May 2013 and December 2015. Enrolled patients were randomised to receive either 150 mg RBT EOD (arm A, 9 subjects) or 300 mg RBT EOD (arm B, 7 subjects), both associated with LPV/r taken twice daily. RBT plasma concentrations were evaluated after 2 weeks of combined HIV and TB treatment. Samples were collected just before drug ingestion and at 1, 2, 3, 4, 6, 8, and 12 h after drug ingestion to measure plasma drug concentration using an HPLC-MS/MS assay. RESULTS: The Cmax and AUC0-12h medians in arm A (Cmax = 296 ng/mL, IQR: 205-45; AUC0-12h = 2528 ng.h/mL, IQR: 1684-2735) were lower than those in arm B (Cmax = 600 ng/mL, IQR: 403-717; AUC0-12h = 4042.5 ng.h/mL, IQR: 3469-5761), with a statistically significant difference in AUC0-12h (p = 0.044) but not in Cmax (p = 0.313). No significant differences were observed in Tmax (3 h versus 4 h). Five patients had a Cmax below the plasma therapeutic limit (< 300 ng/mL) in the 150 mg RBT arm, while the Cmax was above this threshold for all patients in the 300 mg RBT arm. Additionally, at 48 h after drug ingestion, all patients had a mycobacterial minimum inhibitory concentration (MIC) above the limit (> 64 ng/mL) in the 300 mg RBT arm, while 4/9 patients had such values in the 150 mg RBT arm. CONCLUSION: This study confirmed that the 150 mg dose of rifabutin ingested EOD in combination with LPV/r is inadequate and could lead to selection of rifamycin-resistant mycobacteria. TRIAL REGISTRATION: PACTR201310000629390, 28th October 2013.

In Vitro Activity of Rifampin, Rifabutin, Rifapentine, and Rifaximin against Planktonic and Biofilm States of Staphylococci Isolated from Periprosthetic Joint Infection.

The in vitro activities of rifampin, rifabutin, rifapentine, and rifaximin were tested against 200 periprosthetic joint infection (PJI)-associated staphylococci. Seven rifampin-resistant isolates had MICs of ≥4 µg/ml. Three isolates had rifampin MICs of 0.25 to 1 µg/ml and harbored an Asp471Gly RpoB variant, suggesting that the CLSI rifampin-susceptible staphylococcal breakpoint of ≤1 µg/ml may be too high. The remaining isolates had rifampin MICs of ≤0.016 µg/ml, and the rifampin, rifabutin, rifapentine, and rifaximin minimum biofilm bactericidal concentrations (MBBC) for ≥50% of isolates were 8, 1, 2, and 4 µg/ml (for S. aureus) and 2, 0.06, 0.25, and 0.5 µg/ml (for S. epidermidis), respectively, for rifampin-susceptible isolates. Nonrifampin rifamycins have promising staphylococcal activity, including antibiofilm activity.

Reconciliation of Recent Helicobacter pylori Treatment Guidelines in a Time of Increasing Resistance to Antibiotics.

Increasing resistance to antibiotics worldwide has adverse effects on the effectiveness of standard therapies to eradicate Helicobacter pylori infection. We reviewed guidelines developed by expert groups in Europe, Canada, and the United States for the treatment of H pylori infection. We compared the recommendations of these guidelines, reconciled them, and addressed the increasing resistance of H pylori to antibiotic therapy regimens. The guidelines recommend bismuth quadruple therapy for first-line treatment, replacing clarithromycin-based triple therapy. There is consensus for concomitant 4-drug therapy as an alternative, especially when bismuth is not available. When therapy is unsuccessful, it is likely due to resistance to clarithromycin, levofloxacin, and/or metronidazole; these drugs, if used previously, should be avoided in subsequent eradication attempts. Second-line therapies should be bismuth quadruple therapy or levofloxacin triple therapy, depending on suspected resistance, reserving rifabutin-based triple and high-dose dual amoxicillin proton pump inhibitor therapy for subsequent treatment attempts. The increasing resistance of H pylori to antibiotic therapy necessitates local availability of susceptibility tests for individuals, and establishment of regional and national monitoring programs to develop evidence-based locally relevant eradication strategies. Further studies into the development of more easily accessible methods of resistance testing, such as biomarker analysis of stool samples, are required. Options under investigation include substituting vonoprazan for proton pump inhibitors, adding probiotics, and vaccine development. Narrow-spectrum antibiotics and new therapeutic targets could be identified based on genomic, proteomic, and metabolomic analyses of H pylori.

Effective therapeutic regimens in two South Asian countries with high resistance to major Helicobacter pylori antibiotics.

Background: Nepal and Bangladesh have a high prevalence of Helicobacter pylori with high resistance rates to clarithromycin, metronidazole, and levofloxacin. Here, we evaluated the susceptibility and genetic mutations of 5 alternative antibiotics against isolates from both countries to obtain an effective treatment regimen for H. pylori eradication. Methods: We used the agar dilution method to determine the minimal inhibitory concentration of 5 alternative antibiotics against 42 strains from Nepal and 56 from Bangladesh and performed whole genome mutation analysis. Results: No resistance to furazolidone or rifabutin and a high susceptibility of sitafloxacin (95.2% in Nepal and 98.2% in Bangladesh) were observed. In contrast, resistance to rifaximin (52.4% in Nepal and 64.3% in Bangladesh) was high. Moreover, resistance to garenoxacin was higher in Bangladesh (51.6%) than in Nepal (28.6%, P = 0.041), most likely due to its correlation with levofloxacin resistance (P = 0.03). Garenoxacin and rifaximin were significantly correlated in Bangladesh (P = 0.014) and occurred together with all sitafloxacin-resistant strains. Mutations of gyrA could play a significant role in garenoxacin resistance, and double mutations of A87 and D91 were associated with sitafloxacin resistance. Analysis of the rpoB gene demonstrated well-known mutations, such as V657I, and several novel mutations, including I2619V, V2592 L, T2537A, and F2538 L. Conclusions: Rifabutin can be cautiously implemented as therapy for H. pylori infection due to its interaction with the tuberculosis endemic in Bangladesh. The high susceptibility of furazolidone and sitafloxacin suggests their possible future application in Nepal and Bangladesh.

The potential use of rifabutin for treatment of patients diagnosed with rifampicin-resistant tuberculosis.

Background: Use of the Xpert MTB/RIF assay has increased the number of people diagnosed with rifampicin-resistant tuberculosis (RR-TB), especially in South Africa where Xpert is now the initial diagnostic for individuals with TB symptoms. We hypothesized that a proportion of RR-TB patients determined by Xpert can be treated with a rifabutin-containing regimen. Methods: Rifabutin susceptibility by rpoB mutation was assessed in 349 individuals from South Africa and 172 from Belgium. rpoB polymorphisms were identified by Sanger sequencing. Rifampicin and rifabutin susceptibility was assessed phenotypically. A systematic review was performed to comprehensively collate information on rifabutin susceptibility by rpoB polymorphism. Rifabutin susceptibility was assigned to rpoB polymorphisms based on their positive likelihood ratios and ORs. Results: One hundred and twelve rpoB polymorphisms (67.9% from literature) were identified from all 2045 RR-TB patients, of which 17 polymorphisms could be classified as susceptible/resistant to rifabutin. Eleven polymorphisms were associated with rifabutin susceptibility. The 516GTC mutation was the most common, representing 70% (South Africa) and 76% (Belgium) of all rifabutin-susceptible isolates. At a population level, the 11 polymorphisms associated with rifabutin susceptibility occurred in 33.2% and 16.6% of all South African and Belgian patients diagnosed with RR-TB, respectively. Conclusions: Identification of the exact rpoB polymorphism leading to the diagnosis of RR-TB has the potential to allow inclusion of rifabutin in the treatment regimen of a substantial proportion of RR-TB patients. A randomized controlled trial evaluating the efficacy of a rifabutin-containing TB treatment regimen in these selected patients is needed to provide the evidence required for a change in policy.

World trends for H. pylori eradication therapy and gastric cancer prevention strategy by H. pylori test-and-treat.

Helicobacter pylori-associated gastritis leads to the development of gastric cancer. Kyoto global consensus report on H. pylori gastritis recommended H. pylori eradication therapy to prevent gastric cancer. To manage H. pylori infection, it is important to choose the appropriate regimen considering regional differences in resistance to clarithromycin and metronidazole. Quinolones and rifabutin-containing regimens are useful as third- and fourth-line rescue therapies.

Novel and Effective Therapeutic Regimens for Helicobacter pylori in an Era of Increasing Antibiotic Resistance.

Helicobacter pylori (H. pylori) is a common gastrointestinal bacterial strain closely associated with the incidence of chronic gastritis, peptic ulcers, gastric mucosa-associated lymphoid tissue lymphoma, and gastric cancer. A current research and clinical challenge is the increased rate of antibiotic resistance in H. pylori, which has led to a decreased H. pylori eradication rate. In this article, we review recent H. pylori infection and reinfection rates and H. pylori resistance to antibiotics, and we discuss the pertinent treatments. A PubMed literature search was performed using the following keywords: Helicobacter pylori, infection, reinfection, antibiotic resistance, bismuth, proton pump inhibitors, vonoprazan, susceptibility, quintuple therapy, dual therapy, and probiotic. The prevalence of H. pylori has remained high in some areas despite the decreasing trend of H. pylori prevalence observed over time. Additionally, the H. pylori reinfection rate has varied in different countries due to socioeconomic and hygienic conditions. Helicobacter pylori monoresistance to clarithromycin, metronidazole or levofloxacin was common in most countries. However, the prevalence of amoxicillin and tetracycline resistance has remained low. Because H. pylori infection and reinfection present serious challenges and because H. pylori resistance to clarithromycin, metronidazole or levofloxacin remains high in most countries, the selection of an efficient regimen to eradicate H. pylori is critical. Currently, bismuth-containing quadruple therapies still achieve high eradication rates. Moreover, susceptibility-based therapies are alternatives because they may avoid the use of unnecessary antibiotics. Novel regimens, e.g., vonoprazan-containing triple therapies, quintuple therapies, high-dose dual therapies, and standard triple therapies with probiotics, require further studies concerning their efficiency and safety for treating H. pylori.

Rifabutin-based Fourth and Fifth-line Rescue Therapy in Patients with for Helicobacter pylori Eradication Failure.

BACKGROUND/AIMS: Optimized regimen has not yet been established for failures of multiple Helicobacter pylori (H. pylori) eradication. Hence, we aimed to evaluate the efficacy of rifabutin-based rescue therapy, at least after three eradication failures. METHODS: Twelve patients, who failed in the treatment for H. pylori eradication at least three times, were consecutively enrolled between 2007 and 2015 at Seoul National University Bundang Hospital. The rifabutin-based rescue regimen was consisted of proton pump inhibitor (PPI), rifabutin (150 mg b.i.d.), and amoxicillin (1 g b.i.d.), given for 7 or 14 days. MIC concentration test by the agar dilution method was performed on six patients prior to rifabutin-based rescue therapy. RESULTS: One patient did not take this regimen, and per-protocol (PP) analysis was performed in 11 patients. The overall eradication rate by intention-to-treat and PP analysis with rifabutin-based rescue therapy was 50.0% (6/12 patients) and 54.5% (6/11 patients), respectively. There was no difference of the eradication rate depending on the underlying disease, smoking, alcohol, number of previous eradication failures, and CYP2C19 genotype. All of the six patients were susceptible to rifabutin, but only three of them succeeded in eradicating with H. pylori. Side effects occurred in two patients (18.2%), and compliance was 90.9%. CONCLUSIONS: Even the eradication rate of rifabutin-based rescue therapy was not very good. Rifabutin-based rescue therapy could be considered as a rescue therapy, perhaps as the fourth or the fifth-line treatment option. No correlation of rifabutin sensitivity with eradication success rate of H. pylori suggests that frequent administration of high dose PPI and amoxicillin might be important.

Successful management of Mycobacterium haemophilum lower extremity cutaneous infection in a matched-unrelated donor stem cell transplant recipient.

Nontuberculous mycobacterial infections can often occur in individuals with adequate immune function. Such infections typically have cutaneous involvement and are caused by rapidly growing mycobacterium. Other nontuberculous mycobacteria species, like Mycobacterium haemophilum, almost always present as opportunistic infections occurring in severely immunocompromised hosts. Here, we present a complicated and protracted course of diagnosing M. haemophilum lower extremity cutaneous infection in a matched-unrelated donor stem cell transplant recipient.

[Determination of in vitro synergy by a checkerboard method when 3 core antimicrobial agents of the retreatment new scheme combined against MDR-MTB and XDR-MTB].

OBJECTIVE: In order to detect the in vitro synergistic effect of 4 drugs-pasiniazid (PA), moxifloxacin, rifabutin and rifapentini on multidrug-resistant mycobacterium tuberculosis (MDR-MTB) and extensively drug-resistant mycobacterium tuberculosis(XDR-MTB), which were core drugs of"The program of retreatment research of tuberculosis". METHOD: The checkerboard method was used to detect the minimum inhibitory concentration (MIC) of antituberculosis drug combination schemes (moxifloxacin-PA, moxifloxacin-PA-rifabutin and moxifloxacin-PA-rifapentini) to 40 strains of clinical drug resistant MTB(20 strains of MDR-MTB and 20 XDR-MTB) and the standard strain H37Rv, by calculating the fractional inhibitory concentration index of joint action in vitro to judge the combined effect, with fractional inhibitory concentration index(FICI)≤0.5 and FICI≤0.75 as the basis of 2 drugs and 3 drugs showing synergy. RESULTS: The FICI of moxifloxacin-PA scheme for DR-MTB was 0.125 to 1.000, only 5 strains with a FICI ≤0.5, showing synergistic effect. The FICI of moxifloxacin-Pa-rifabutin scheme with 20 strains of MDR-MTB ranged from 0.310 to 1.260, 10 strains with a FICI≤0.75, showing synergistic effect. The FICI of moxifloxacin-PA-rifabutin scheme with 20 strains of XDR-MTB ranged from 0.215 to 1.250, 11 strains with a FICI≤0.75, showing synergistic effect. The FICI of moxifloxacin-PA-rifapentini scheme with 20 strains of MDR-MTB ranged from 0.150 to 0.780, 19 strains with a FICI≤0.75, showing synergistic effect. The FICI of moxifloxacin-PA-rifapentini scheme with 20 strains of XDR-MTB ranged from 0.200 to 1.280, 16 strains with a FICI≤0.75, showing synergistic effect. CONCLUSIONS: The synergistic effect of moxifloxacin-PA scheme was poor, but showing better synergy when further combined with rifabutin or rifapentini. Rifabutin showed better effect than rifapentini, but the synergistic effect of moxifloxacin-PA-rifabutin combination scheme was poor than that of moxifloxacin-PA-rifapentini combination scheme.

Treatment outcomes of refractory MAC pulmonary disease treated with drugs with unclear efficacy.

We aimed to investigate the treatment outcomes of patients with refractory Mycobacterium avium complex (MAC) lung disease treated with regimens containing drugs with unclear efficacy. Of all patients diagnosed with MAC lung disease between April 2004 and September 2012 at a tertiary referral center in South Korea, the outcomes of 51 patients treated with regimens containing drugs with unclear efficacy (clofazimine, moxifloxacin, rifabutin, and linezolid) because of treatment failure after receiving standard treatment were retrospectively analyzed. The mean age (standard deviation) of the 51 patients was 59.0 (10.3) years and 29 (56.9%) were male. The etiologic agent was M. avium in 17 patients (33.3%) and Mycobacterium intracellulare in 34 patients (66.7%); 42 patients (82.4%) had the fibrocavitary form of the disease. Of the 51 patients, 26, 28, 35, and 7 received clofazimine-, moxifloxacin-, rifabutin-, and linezolid-containing regimens (numbers are not mutually exclusive), with median drug administration durations of 147, 128, 209, and 88 days, respectively. Overall, 8 patients (15.7%) had a favorable response. Treatment outcomes did not differ by drug regimen or even by the combination of more than 2 drugs. The treatment outcomes of patients with refractory MAC lung disease were unsatisfactory with regimens containing possibly effective drugs such as clofazimine, moxifloxacin, rifabutin and linezolid.

Second and third line treatment options for Helicobacter pylori eradication.

Helicobacter pylori is a highly successful bacterium with a high global prevalence and the infection carries significant disease burden. It is also becoming increasingly difficult to eradicate and the main reason for this is growing primary antibiotic resistance rates in a world where antibiotics are frequently prescribed and readily available. Despite knowing much more about the bacterium since its discovery, such as its genomic makeup and pathogenesis, we have seen declining treatment success. Therefore, clinicians today must be prepared to face one, two or even multiple treatment failures, and should be equipped with sufficient knowledge to decide on the appropriate salvage therapy when this happens. This article discusses the factors contributing to treatment failure and reviews the second and third-line treatment strategies that have been investigated. Established empiric second line treatment options include both bismuth based quadruple therapy and levofloxacin based triple therapy. Antibiotic testing is recommended prior to initiating third line treatment. In the event that antibiotic susceptibility testing is unavailable, third line treatment options include rifabutin, rifaximin and sitafloxacin based therapies.

Inhalable microparticles of nitric oxide donors induce phagosome maturation and kill Mycobacterium tuberculosis.

Nitric oxide (NO) kills Mycobacterium tuberculosis (Mtb) in vitro, but gaseous NO is difficult to administer to patients. We evaluated the consequences of intracellular delivery of NO using inhalable microparticles (MP) containing NO donors. MP containing 10% w/w of NO donors alone, or in addition to 25% each of isoniazid (INH) and rifabutin (RFB) in a polylactide-co-glycolide (PLGA) matrix were prepared by spray drying. THP-1-derived macrophages infected with Mtb H37Rv were exposed to MP or soluble NO donors. Phagosome-lysosome fusion (PLF) and bacterial killing were monitored. Colony forming units (cfu) in lungs and spleen of mice infected with a low-dose aerosol and administered inhalations of MP were enumerated. Bacterial DNA in these tissues was estimated by real-time PCR. In vitro studies indicated a bacteriostatic effect of NO donors despite significant enhancement of PLF. Daily inhalation of MP containing 10% diethylenetriamine nitric oxide adduct (DETA/NO) alone reduced log10 cfu in the lungs from 6.1 to 4.4 at the highest dose in four weeks, but did not significantly affect cfu in the spleen. Inhalations of MP containing DETA/NO in combination with INH and RFB significantly (P < 10(-5), ANOVA) reduced cfu in lungs and spleens by 4 log. Gross morphology and histology of the lungs and spleen indicated that inhaled particles were well-tolerated. Inhalable MP containing NO donors need further investigation as an adjunct to standard anti-tuberculosis chemotherapy.

Helicobacter pylori resistance rates for levofloxacin, tetracycline and rifabutin among Irish isolates at a reference centre.

INTRODUCTION: Helicobacter pylori eradication rates using conventional triple therapies are falling, making viable second-line and rescue regimens necessary. Levofloxacin, tetracycline and rifabutin are three efficacious antibiotics for rescue therapy. AIM: We aimed to assess the resistance rates for H. pylori against these antibiotics in an Irish cohort. METHODS: Gastric biopsies were collected from 85 patients infected with H. pylori (mean age 46 years) in the Adelaide and Meath Hospital, Dublin in 2008 and 2009. Susceptibility to antibiotics was tested using the Etest. Clinical information was obtained from endoscopy reports and chart review. RESULTS: 50.6 % of patients were females. Mean age was 47 years. Ten had prior attempts at eradication therapy with amoxicillin-clarithromycin-PPI, two had levofloxacin-based second-line therapy. 11.7 % [95 % CI (6.5-20.3 %)] (N = 10) had strains resistant to levofloxacin. There were no strains resistant to rifabutin or tetracycline. Levofloxacin resistance in the under 45 age group was 2.6 % (1/38) compared to 19.1 % (9/47) of above 45 age group (p = 0.02). DISCUSSION: The levofloxacin rates illustrated in this study are relatively low by European standards and in line with other studies from the United Kingdom and Germany, with younger patients having very low levels of resistance. Levofloxacin, tetracycline and rifabutin are all valid options for H. pylori eradication in Irish patients but the importance of compliance cannot be underestimated.

The efficacy of rifabutin for rifabutin-susceptible, multidrug-resistant tuberculosis.

OBJECTIVE: We investigated the efficacy of rifabutin (RFB)-containing regimens for the treatment of RFB-susceptible, multidrug-resistant tuberculosis (MDR-TB). METHODS: From 146 patients diagnosed with MDR-TB between January 2006 and December 2009 at Asan Medical Center in South Korea, 31 patients (21.2%) were found to have RFB-susceptible MDR-TB. Of these 31 patients, 14 patients who had been treated with RFB for more than one month were included. Forty-two patients with RFB-resistant MDR-TB were selected as a control group, and the outcomes of both groups were retrospectively compared. RESULTS: Of 14 patients with RFB-susceptible MDR-TB, the mean age was 44.4 years and the proportion of extensively drug-resistant TB (XDR-TB) was 35.7% (5/14). Baseline characteristics and the drug resistance pattern (except RFB) did not differ between the two groups. Treatment success was achieved in 12 (85.7%) patients in the RFB group: cure in 10 (71.4%) and treatment completion in two (14.3%). The treatment success rate was 52.4% (22/42) in the control group (p = 0.032). Treatment failure was more common in patients of the control group (40.5% vs. 14.3%; p = 0.106). CONCLUSIONS: RFB is useful as an additional drug in the treatment of MDR-TB in patients with RFB-susceptible MDR-TB.

Culture-based selection therapy for patients who did not respond to previous treatment for Helicobacter pylori infection.

BACKGROUND & AIMS: Eradication of Helicobacter pylori using empiric therapy has become difficult as a result of increasing resistance to antibiotics. We evaluated the efficacy of specific treatments, selected based on response of bacterial samples to culture with clarithromycin, levofloxacin, and metronidazole, for patients infected with resistant strains of H pylori. METHODS: We performed a prospective study at a single center of 236 consecutive patients with persistent H pylori infection, despite 1 or more treatment attempts, and documented resistance to at least 1 antimicrobial agent (based on bacterial culture tests). Biopsy samples were collected by endoscopy and cultured in selective media. Patients received either 10 days of levofloxacin (250 mg twice daily for 131 patients with susceptible infections) or 12 days of rifabutin (150 mg once daily for 105 patients resistant to levofloxacin) in combination with amoxicillin (1 g twice daily) and esomeprazole (40 mg twice daily). Efficacy of eradication was determined by the (13)C-urea breath test, 6 to 8 weeks after therapy. Compliance and side effects were determined via personal interviews at the end of therapy. Rifabutin toxicity was monitored by analysis of blood samples. RESULTS: H pylori infection was cured in 118 of the patients who received levofloxacin triple therapy (90%; 95% confidence interval, 85%-95%) and 93 of the patients who received rifabutin triple therapy (88.6%; 95% confidence interval, 82%-95%). In each group, the cure rate did not differ significantly between patients infected with H pylori strains resistant to single or multiple antibiotics. Mild side effects occurred in 15.5% and 14.9% of patients resistant to single or multiple antibiotics, respectively, and self-limiting neutropenia was observed in 1 (0.7%) case. CONCLUSIONS: Selection of triple therapy with either levofloxacin or rifabutin, based on results from bacterial culture tests, cures H pylori infection in about 90% who did not previously respond to antibiotics.

Correlation between rpoB gene mutation in Mycobacterium avium subspecies paratuberculosis and clinical rifabutin and rifampicin resistance for treatment of Crohn's disease.

AIM: To investigate overlapping regions of the rpoB gene previously involved with rifamycin resistance in M. tuberculosis and seek correlation between rpoB mutations in clinical MAP strains with susceptibility to RIF and RFB. METHODS: We designed a molecular-based PCR method for the evaluation of rifabutin (RFB) and rifampicin (RIF) resistance based on probable determinant regions within the rpoB gene of MAP, including the 81 bp variable site located between nucleotides 1363 and 1443. The minimum inhibitory concentration (MIC) for RIF was also determined against 11 MAP isolates in attempt to seek correlation with rpoB sequences. RESULTS: We determined that MAP strain 18 had an MIC of > 30 mg/L and 30 mg/L and > 10 mg/L for RIF and RFB respectively. Sequencing of the entire rpoB gene in MAP strains UCF4, 18, and UCF5-RIF16r revealed an rpoB mutation A2284C further downstream of the 81 bp variable region in UCF4, accounting for observed slight increase in MIC. In addition, no other significant mutations were found in strains 18 and UCF-RIF16r. CONCLUSION: The data clearly illustrates that clinical and in vitro-selected MAP mutants with rpoB mutations result in resistance to RIF and RFB, and that a single amino acid change in the beta subunit may have a significant impact on RIF resistance. Unconventional drug susceptibility testing such as our molecular approach will be beneficial for evaluation of antibiotic effectiveness. This molecular approach may also serve as a model for other drugs used for treatment of MAP infections.

Osteomalacia in an HIV-infected man receiving rifabutin, a cytochrome P450 enzyme inducer: a case report.

INTRODUCTION: People infected with human immunodeficiency virus are frequently treated with medications that can induce or inhibit cytochrome P450 enzymes. CASE PRESENTATION: A 59 year old man treated with zidovudine, lamivudine, indinavir, and ritonavir for infection with human immunodeficiency virus volunteered to take part in a study of bone loss. He was found to have vitamin D insufficiency with secondary hyperparathyroidism and received vitamin D and calcium supplementation. He suffered a recurrence of infection with Mycobacterium avium intracellulare for which he received treatment with ciprofloxacin, rifabutin, and ethambutol. Subsequently, he developed worsening vitamin D deficiency with hypocalcaemia, secondary hyperparathyroidism and elevated markers of bone turnover culminating in an osteomalacic vertebral fracture. Correction of the vitamin D deficiency required 100,000 IU of cholecalciferol monthly. Rifabutin is a cytochrome P450 inducer, and vitamin D and its metabolites are catabolised by cytochrome P450 enzymes. We therefore propose that treatment with rifabutin led to the induction of cytochrome P450 enzymes catabolising vitamin D, thereby causing vitamin D deficiency and osteomalacia. This process might be mediated through the steroid and xenobiotic receptor (SXR). CONCLUSION: Treatment with rifabutin induces the cytochrome P450 enzymes that metabolise vitamin D and patients treated with rifabutin might be at increased risk of vitamin D deficiency. In complex medication regimens involving agents that induce or inhibit cytochrome P450 enzmyes, consultation with a clinical pharmacist or pharmacologist may be helpful in predicting and/or preventing potentially harmful interactions.