Antibiotic complications during the treatment of Mycobacterium ulcerans disease in Australian patients

Management of Mycobacterium ulcerans infection (Buruli ulcer) in Australia: consensus statement

INTRODUCTION

Buruli ulcer, caused by Mycobacterium ulcerans, is increasing in incidence and spreading to new areas in southeast Australia. With increasing experience and emerging evidence, this consensus statement considers contemporary data to provide up-to-date recommendations to clinicians who may encounter this disease. The emergence of Buruli ulcer in previously non-endemic areas highlights the importance of increasing clinician and community awareness of this disease. Main recommendations and changes in management as a result of this consensus statement: Buruli ulcer is a notifiable disease in Victoria, the Northern Territory and Queensland. Cases identified in other states or territories should be discussed with relevant health authorities. We call for Buruli ulcer to be made nationally notifiable to monitor for its potential emergence in non-endemic regions. Diagnosis using polymerase chain reaction is sensitive and specific if performed correctly; a dry swab under the undermined edge of ulcers or a tissue sample via punch biopsy if the lesion is not ulcerated is recommended. If swabs are incorrectly performed or performed on non-ulcerated skin, they can give a false negative result. There is high quality evidence to support treatment of eight weeks' duration using rifampicin-based dual oral antibiotic therapy, in combination with clarithromycin or a fluoroquinolone; relapse is very rare but can occur in people with risk factors. There is emerging evidence for shorter durations of treatment (six weeks) in individuals with small lesions who are at low risk of relapse and in those who have undergone surgical excision of the lesion (four weeks). Patients should be warned that ulcers typically enlarge with antibiotic treatment, will not have healed by completion of antibiotics, and take a median of four to five months to heal. Surgical management is usually not required, but may be beneficial to reduce healing times, avoid or reduce the duration of antibiotics, and manage paradoxical reactions. Early identification and treatment of paradoxical reactions is important, as they are associated with increased tissue necrosis and delayed wound healing. Good wound care is critical in successful treatment of Buruli ulcer, as it enhances healing and prevents secondary bacterial infection. Compared with adults, children have a higher proportion of non-ulcerative and severe lesions, are less likely to experience adverse antibiotic effects, but have higher rates of paradoxical reactions; specialist referral is recommended.

A human model of Buruli ulcer: Provisional protocol for a Mycobacterium ulcerans controlled human infection study

Critical knowledge gaps have impeded progress towards reducing the global burden of disease due to Mycobacterium ulcerans, the cause of the neglected tropical disease Buruli ulcer (BU). Development of a controlled human infection model of BU has been proposed as an experimental platform to explore host-pathogen interactions and evaluate tools for prevention, diagnosis, and treatment. We have previously introduced the use case for a new human model and identified M. ulcerans JKD8049 as a suitable challenge strain. Here, we present a provisional protocol for an initial study, for transparent peer review during the earliest stages of protocol development. Following simultaneous scientific peer review and community/stakeholder consultation of this provisional protocol, we aim to present a refined protocol for institutional review board (IRB) evaluation.

A human model of Buruli ulcer: The case for controlled human infection and considerations for selecting a Mycobacterium ulcerans challenge strain

Critical knowledge gaps regarding infection with Mycobacterium ulcerans, the cause of Buruli ulcer (BU), have impeded development of new therapeutic approaches and vaccines for prevention of this neglected tropical disease. Here, we review the current understanding of host-pathogen interactions and correlates of immune protection to explore the case for establishing a controlled human infection model of M. ulcerans infection. We also summarise the overarching safety considerations and present a rationale for selecting a suitable challenge strain.

Mycobacterium ulcerans culture results according to duration of prior antibiotic treatment: A cohort study

Mycobacterium ulcerans disease is a necrotising disease of the skin and subcutaneous tissue and is effectively treated with eight-weeks antibiotic therapy. Significant toxicities, however, are experienced under this prolonged regimen. Here, we investigated the length of antibiotic duration required to achieve negative cultures of M. ulcerans disease lesions and evaluated the influence of patient characteristics on this outcome. M. ulcerans cases from an observational cohort that underwent antibiotic treatment prior to surgery and had post-excision culture assessment at Barwon Health, Victoria, from May 25 1998 to June 30 2019, were included. Antibiotic duration before surgery was grouped as <2 weeks, ≥2-<4 weeks, ≥4-<6 weeks, ≥6-<8 weeks, ≥8-<10 weeks and ≥10-20 weeks. Cox regression analyses were performed to assess the association between variables and culture positive results. Ninety-two patients fitted the inclusion criteria. The median age was 60 years (IQR 28-74.5) and 51 (55.4%) were male. Rifampicin-based regimens were predominantly used in combination with clarithromycin (47.8%) and ciprofloxacin (46.7%), and the median duration of antibiotic treatment before surgery was 23 days (IQR, 8.0-45.5). There were no culture positive results after 19 days of antibiotic treatment and there was a significant association between antibiotic duration before surgery and a culture positive outcome (p<0.001). The World Health Organisation category of the lesion and the antibiotic regimen used had no association with the culture outcome. Antibiotics appear to be effective at achieving negative cultures of M. ulcerans disease lesions in less than the currently recommended eight-week duration.

Neglected tropical diseases in Australia: a narrative review

•Neglected tropical diseases (NTDs) represent a threat to the health, wellbeing and economic prosperity of billions of people worldwide, often causing serious disease or death. •Commonly considered diseases of low and middle-income nations, the presence of NTDs in high income countries such as Australia is often overlooked. •Seven of the 20 recognised NTDs are endemic in Australia: scabies, soil-transmitted helminths and strongyloidiasis, echinococcosis, Buruli ulcer, leprosy, trachoma, and snakebite envenoming. •Dengue, while not currently endemic, poses a risk of establishment in Australia. There are occasional outbreaks of dengue fever, with local transmission, due to introductions in travellers from endemic regions. •Similarly, the risk of introduction of other NTDs from neighbouring countries is a concern. Many NTDs are only seen in Australia in individuals travelling from endemic areas, but they need to be recognised in health settings as the potential consequences of infection can be severe. •In this review, we consider the status of NTDs in Australia, explore the risk of introducing and contracting these infections, and emphasise the negative impact they have on the health of Australians, especially Aboriginal and Torres Strait Islander peoples.

Systematic review of M. Bovis BCG and other candidate vaccines for Buruli ulcer prophylaxis

Buruli ulcer, caused by Mycobacterium ulcerans, is a neglected tropical disease endemic to over 30 countries, with increasing incidence in temperate, coastal Victoria, Australia. Strategies to control transmission are urgently required. This study systematically reviews the literature to identify and describe candidate prophylactic Buruli ulcer vaccines. This review highlights that Mycobacterium bovis Bacillus Calmette-Guérin (BCG) vaccine is the only vaccine studied in randomised controlled trials and confirms its importance as a benchmark for comparison against putative vaccines in pre-clinical studies. Nevertheless, BCG alone is unable to offer long-term protection in humans. A number of experimental vaccines that exceed the protection provided by BCG in mice have emerged, particularly those utilising recombinant BCG expressing immunogenic M. ulcerans proteins. Although progress is promising, there remain key questions about the optimal approach to characterising the immunological correlates of protection in humans and strategies to investigate the safety and efficacy of such vaccines in humans.

Impact of Dose, Duration, and Immune Status on Efficacy of Ultrashort Telacebec Regimens in Mouse Models of Buruli Ulcer

Telacebec (Q203) is a new antituberculosis drug in clinical development that has extremely potent activity against Mycobacterium ulcerans, the causative agent of Buruli ulcer (BU). The potency of Q203 has prompted investigation of its potential role in ultrashort, even single-dose, treatment regimens for BU in mouse models. However, the relationships of Q203 dose, dose schedule, duration, and host immune status to treatment outcomes remain unclear, as does the risk of emergence of drug resistance with Q203 monotherapy. Here, we used mouse footpad infection models in immunocompetent BALB/c and immunocompromised SCID-beige mice to compare different Q203 doses, different dosing schedules, and treatment durations ranging from 1 day to 2 weeks, on long-term outcomes. We also tested whether combining Q203 with a second drug can increase efficacy. Overall, efficacy depended on total dose more than on duration. Total doses of 5 to 20 mg/kg rendered nearly all BALB/c mice culture negative by 13 to 14 weeks posttreatment, without selection of Q203-resistant bacteria. Addition of a second drug did not significantly increase efficacy. Although less potent in SCID-beige mice, Q203 still rendered the majority of footpads culture negative at total doses of 10 to 20 mg/kg. Q203 resistance was identified in relapse isolates from some SCID-beige mice receiving monotherapy but not in isolates from those receiving Q203 combined with bedaquiline or clofazimine. Overall, these results support the potential of Q203 monotherapy for single-dose or other ultrashort therapy for BU, although highly immunocompromised hosts may require higher doses or durations and/or combination therapy.

Ultra-short-course and intermittent TB47-containing oral regimens produce stable cure against Buruli ulcer in a murine model and prevent the emergence of resistance for Mycobacterium ulcerans

Buruli ulcer (BU), caused by Mycobacterium ulcerans, is currently treated with rifampin-streptomycin or rifampin-clarithromycin daily for 8 weeks recommended by World Health Organization (WHO). These options are lengthy with severe side effects. A new anti-tuberculosis drug, TB47, targeting QcrB in cytochrome bc1:aa3 complex is being developed in China. TB47-containing regimens were evaluated in a well-established murine model using an autoluminescent M. ulcerans strain. High-level TB47-resistant spontaneous M. ulcerans mutants were selected and their qcrB genes were sequenced. The in vivo activities of TB47 against both low-level and high-level TB47-resistant mutants were tested in BU murine model. Here, we show that TB47-containing oral 3-drug regimens can completely cure BU in ≤2 weeks for daily use or in ≤3 weeks given twice per week (6 doses in total). All high-level TB47-resistant mutants could only be selected using the low-level mutants which were still sensitive to TB47 in mice. This is the first report of double mutations in QcrB in mycobacteria. In summary, TB47-containing regimens have promise to cure BU highly effectively and prevent the emergence of drug resistance. Novel QcrB mutations found here may guide the potential clinical molecular diagnosis of resistance and the discovery of new drugs against the high-level resistant mutants.

Six vs Eight Weeks of Antibiotics for Small Mycobacterium ulcerans Lesions in Australian Patients

BACKGROUND

Antibiotics are highly effective in curing Mycobacterium ulcerans lesions, but are associated with significant toxicity. In those not undergoing surgery, we compared 6 weeks with the currently recommended 8 weeks of combination antibiotic therapy for small M. ulcerans lesions.

METHODS

Mycobacterium ulcerans cases from an observational cohort at Barwon Health, Victoria, treated with antibiotics alone from 1 October 2010 to 31 March 2018 were included. The 6-week antibiotic group received ≥28 days and ≤42 days and the 8-week antibiotic group received ≥56 days of antibiotic therapy, respectively. Only World Health Organization category 1 lesions were included.

RESULTS

207 patients were included; 53 (25.6%) in the 6-week group and 154 (74.4%) in the 8-week group. The median age of patients was 53 years (interquartile range [IQR], 33-69 years) and 100 (48.3%) were female. Lesions were ≤900 mm2 in size in 79.7% of patients and 93.2% were ulcerative. Fifty-three patients (100%) achieved treatment cure in the 6-week group compared with 153 (99.4%) in the 8-week group (P = .56). No patients died or were lost to follow-up during the study. Median time to heal was 70 days (IQR, 60-96 days) in the 6-week group and 128 days (IQR, 95-173 days) in the 8-week group (P < .001). Two (3.8%) patients in the 6-week group experienced a paradoxical reaction compared with 39 (25.3%) patients in the 8-week group (P = .001).

CONCLUSIONS

For selected small M. ulcerans lesions, 6 weeks may be as effective as 8 weeks of combined antibiotic therapy in curing lesions without surgery.

Pharmacologic management of Mycobacterium ulcerans infection

INTRODUCTION

Pharmacological treatment of Buruli ulcer (Mycobacterium ulcerans infection; BU) is highly effective, as shown in two randomized trials in Africa.

AREAS COVERED

We review BU drug treatment - in vitro, in vivo and clinical trials (PubMed: '(Buruli OR (Mycobacterium AND ulcerans)) AND (treatment OR therapy).' We also highlight the pathogenesis of M. ulcerans infection that is dominated by mycolactone, a secreted exotoxin, that causes skin and soft tissue necrosis, and impaired immune response and tissue repair. Healing is slow, due to the delayed wash-out of mycolactone. An array of repurposed tuberculosis and leprosy drugs appears effective in vitro and in animal models. In clinical trials and observational studies, only rifamycins (notably, rifampicin), macrolides (notably, clarithromycin), aminoglycosides (notably, streptomycin) and fluoroquinolones (notably, moxifloxacin, and ciprofloxacin) have been tested.

EXPERT OPINION

A combination of rifampicin and clarithromycin is highly effective but lesions still take a long time to heal. Novel drugs like telacebec have the potential to reduce treatment duration but this drug may remain unaffordable in low-resourced settings. Research should address ulcer treatment in general; essays to measure mycolactone over time hold promise to use as a readout for studies to compare drug treatment schedules for larger lesions of Buruli ulcer.

Rifampicin and clarithromycin (extended release) versus rifampicin and streptomycin for limited Buruli ulcer lesions: a randomised, open-label, non-inferiority phase 3 trial

BACKGROUND

Buruli ulcer is a neglected tropical disease caused by Mycobacterium ulcerans infection that damages the skin and subcutis. It is most prevalent in western and central Africa and Australia. Standard antimicrobial treatment with oral rifampicin 10 mg/kg plus intramuscular streptomycin 15 mg/kg once daily for 8 weeks (RS8) is highly effective, but streptomycin injections are painful and potentially harmful. We aimed to compare the efficacy and tolerability of fully oral rifampicin 10 mg/kg plus clarithromycin 15 mg/kg extended release once daily for 8 weeks (RC8) with that of RS8 for treatment of early Buruli ulcer lesions.

METHODS

We did an open-label, non-inferiority, randomised (1:1 with blocks of six), multicentre, phase 3 clinical trial comparing fully oral RC8 with RS8 in patients with early, limited Buruli ulcer lesions. There were four trial sites in hospitals in Ghana (Agogo, Tepa, Nkawie, Dunkwa) and one in Benin (Pobè). Participants were included if they were aged 5 years or older and had typical Buruli ulcer with no more than one lesion (caterories I and II) no larger than 10 cm in diameter. The trial was open label, and neither the investigators who took measurements of the lesions nor the attending doctors were masked to treatment assignment. The primary clinical endpoint was lesion healing (ie, full epithelialisation or stable scar) without recurrence at 52 weeks after start of antimicrobial therapy. The primary endpoint and safety were assessed in the intention-to-treat population. A sample size of 332 participants was calculated to detect inferiority of RC8 by a margin of 12%. This study was registered with ClinicalTrials.gov, NCT01659437.

FINDINGS

Between Jan 1, 2013, and Dec 31, 2017, participants were recruited to the trial. We stopped recruitment after 310 participants. Median age of participants was 14 years (IQR 10-29) and 153 (52%) were female. 297 patients had PCR-confirmed Buruli ulcer; 151 (51%) were assigned to RS8 treatment, and 146 (49%) received oral RC8 treatment. In the RS8 group, lesions healed in 144 (95%, 95% CI 91 to 98) of 151 patients, whereas lesions healed in 140 (96%, 91 to 99) of 146 patients in the RC8 group. The difference in proportion, -0·5% (-5·2 to 4·2), was not significantly greater than zero (p=0·59), showing that RC8 treatment is non-inferior to RS8 treatment for lesion healing at 52 weeks. Treatment-related adverse events were recorded in 20 (13%) patients receiving RS8 and in nine (7%) patients receiving RC8. Most adverse events were grade 1-2, but one (1%) patient receiving RS8 developed serious ototoxicity and ended treatment after 6 weeks. No patients needed surgical resection. Four patients (two in each study group) had skin grafts.

INTERPRETATION

Fully oral RC8 regimen was non-inferior to RS8 for treatment of early, limited Buruli ulcer and was associated with fewer adverse events. Therefore, we propose that fully oral RC8 should be the preferred therapy for early, limited lesions of Buruli ulcer.

FUNDING

WHO with additional support from MAP International, American Leprosy Missions, Fondation Raoul Follereau France, Buruli ulcer Groningen Foundation, Sanofi-Pasteur, and BuruliVac.

Shortening Buruli Ulcer Treatment with Combination Therapy Targeting the Respiratory Chain and Exploiting Mycobacterium ulcerans Gene Decay

Buruli ulcer is treatable with antibiotics. An 8-week course of rifampin (RIF) and either streptomycin (STR) or clarithromycin (CLR) cures over 90% of patients. However, STR requires injections and may be toxic, and CLR shares an adverse drug-drug interaction with RIF and may be poorly tolerated. Studies in a mouse footpad infection model showed that increasing the dose of RIF or using the long-acting rifamycin rifapentine (RPT), in combination with clofazimine (CFZ), a relatively well-tolerated antibiotic, can shorten treatment to 4 weeks. CFZ is reduced by a component of the electron transport chain (ETC) to produce reactive oxygen species toxic to bacteria. Synergistic activity of CFZ with other ETC-targeting drugs, the ATP synthase inhibitor bedaquiline (BDQ) and the bc ₁:aa ₃ oxidase inhibitor Q203 (now named telacebec), was recently described against Mycobacterium tuberculosis Recognizing that M. tuberculosis mutants lacking the alternative bd oxidase are hypersusceptible to Q203 and that Mycobacterium ulcerans is a natural bd oxidase-deficient mutant, we tested the in vitro susceptibility of M. ulcerans to Q203 and evaluated the treatment-shortening potential of novel 3- and 4-drug regimens combining RPT, CFZ, Q203, and/or BDQ in a mouse footpad model. The MIC of Q203 was extremely low (0.000075 to 0.00015 μg/ml). Footpad swelling decreased more rapidly in mice treated with Q203-containing regimens than in mice treated with RIF and STR (RIF+STR) and RPT and CFZ (RPT+CFZ). Nearly all footpads were culture negative after only 2 weeks of treatment with regimens containing RPT, CFZ, and Q203. No relapse was detected after only 2 weeks of treatment in mice treated with any of the Q203-containing regimens. In contrast, 15% of mice receiving RIF+STR for 4 weeks relapsed. We conclude that it may be possible to cure patients with Buruli ulcer in 14 days or less using Q203-containing regimens rather than currently recommended 56-day regimens.

Oxazolidinones Can Replace Clarithromycin in Combination with Rifampin in a Mouse Model of Buruli Ulcer

Rifampin (RIF) plus clarithromycin (CLR) for 8 weeks is now the standard of care for Buruli ulcer (BU) treatment, but CLR may not be an ideal companion for rifamycins due to bidirectional drug-drug interactions. The oxazolidinone linezolid (LZD) was previously shown to be active against Mycobacterium ulcerans infection in mice but has dose- and duration-dependent toxicity in humans. Sutezolid (SZD) and tedizolid (TZD) may be safer than LZD. Here, we evaluated the efficacy of these oxazolidinones in combination with rifampin in a murine BU model. Mice with M. ulcerans-infected footpads received control regimens of RIF plus either streptomycin (STR) or CLR or test regimens of RIF plus either LZD (1 of 2 doses), SZD, or TZD for up to 8 weeks. All combination regimens reduced the swelling and bacterial burden in footpads after two weeks of treatment compared with RIF alone. RIF+SZD was the most active test regimen, while RIF+LZD was also no less active than RIF+CLR. After 4 and 6 weeks of treatment, neither CLR nor the oxazolidinones added significant bactericidal activity to RIF alone. By the end of 8 weeks of treatment, all regimens rendered footpads culture negative. We conclude that SZD and LZD warrant consideration as alternative companion agents to CLR in combination with RIF to treat BU, especially when CLR is contraindicated, intolerable, or unavailable. Further evaluation could prove SZD superior to CLR in this combination.

Spontaneous healing of Mycobacterium ulcerans disease in Australian patients

Background

Mycobacterium ulcerans causes necrotising infections of skin and soft tissue mediated by the polyketide exotoxin mycolactone that causes cell apoptosis and immune suppression. It has been postulated that infection can be eradicated before the development of clinical lesions but spontaneous resolution of clinical lesions has been rarely described.

Methodology/Principal findings

We report a case series of five Australian patients who achieved healing of small M. ulcerans lesions without antibiotics or surgery. The median age of patients was 47 years (IQR 30–68 years) and all patients had small ulcerative lesions (median size 144mm², IQR 121-324mm²). The median duration of symptoms prior to diagnosis was 90 days (IQR 90–100 days) and the median time to heal from diagnosis without treatment was 68 days (IQR 63–105 days). No patients recurred after a median follow-up of 16.6 months (IQR 16.6–17.9 months) from the development of symptoms and no patients suffered long-term disability from the disease.

Conclusions

We have shown that healing without specific treatment can occur for small ulcerated M. ulcerans lesions suggesting that in selected cases a robust immune response alone can cure lesions. Further research is required to determine what lesion and host factors are associated with spontaneous healing, and whether observation alone is an effective and safe form of management for selected small M. ulcerans lesions.

Mycobacterium ulcerans causes a destructive infection of skin and soft tissue known as Buruli ulcer that when severe can lead to serious long-term deformity and disability. It is currently not well documented whether people with Mycobacterium ulcerans disease can cure themselves without treatment. In our study we describe five people with small ulcers who cured their disease without specific medical or surgical treatment. This suggests that a proportion of people can develop an immune response sufficient enough to eradicate the disease without the help of medical intervention. This is an important step, as recognition of this possibility provides important further insights into the human immune response against the disease. It also opens the possibility to further studies that may determine characteristics of the organism and hosts that favour spontaneous healing of lesions. This knowledge may in turn improve efforts to prevent and control the disease which are currently lacking.

Mycobacterium ulcerans disease management in Australian patients: the re-emergence of surgery as an important treatment modality

With the demonstration of the effectiveness of antibiotic treatment, the management of Mycobacterium ulcerans disease has changed from a predominantly surgically to a predominantly medically treated disease. However, research among Australian patients has revealed that antibiotic treatment alone is associated with prolonged wound healing times, high rates of treatment toxicity, and the potential for significant tissue destruction associated with severe paradoxical reactions. We present the current state of M. ulcerans management in Barwon Health, Australia, where a close working relationship exists between the Plastic Surgical and Infectious Diseases units. Here treatment has evolved based on nearly 20 years of experience gained from managing more around 600 patients from a M. ulcerans epidemic on the nearby Bellarine and Mornington Peninsulas. In our experience, surgery has re-emerged to play an important role in the treatment of M. ulcerans in improving the rate of wound healing, minimizing antibiotic associated toxicity and preventing further tissue loss associated with severe paradoxical reactions. For selected small lesions surgery without antibiotics may also be an effective treatment option, however aggressive surgical resection of lesions with wide margins through uninvolved tissue should no longer be performed. Furthermore, extensive excisional surgery that will require the use of split skin grafts and vascularized tissue flaps to repair skin defects should be avoided if possible.

Shorter-course treatment for Mycobacterium ulcerans disease with high-dose rifamycins and clofazimine in a mouse model of Buruli ulcer

Starting in 2004, the standard regimen for treatment of Buruli ulcer (BU) recommended by the World Health Organization has been daily treatment for eight weeks with rifampin (RIF) and streptomycin. Based on recent clinical trials, treatment with an all-oral regimen of RIF and clarithromycin (CLR) may be an effective alternative. With the achievement of an all-oral regimen, a new goal is to find a regimen that can shorten the duration of treatment without compromising efficacy. We recently observed that increasing the dose of RIF from the standard 10 mg/kg dose to 20 or 40 mg/kg, or replacing RIF with the more potent long-acting rifamycin, rifapentine (RPT) at 10 mg/kg or 20 mg/kg increased the bactericidal activity of the RIF+CLR regimen in a mouse model of BU. We also recently showed that replacing CLR with clofazimine(CFZ) at 25 mg/kg may have greater sterilizing activity than the RIF+CLR regimen. Here, we demonstrate that combining high-dose rifamycins with CFZ at a lower dose of 12.5 mg/kg results in similar reductions in swelling, bacterial burden and mycolactone concentrations in mouse footpads compared to the standard regimens and more rapid sterilization of footpads as determined by the proportions of footpads harboring viable bacteria three months after completion of treatment. The potential of these high-dose rifamycin and CFZ combinations to shorten BU treatment to four weeks warrants evaluation in a clinical trial.

Buruli ulcer, a neglected tropical skin disease caused by Mycobacterium ulcerans, is treatable since 2004 with antibiotics instead of surgery. Treatment with either rifampin plus streptomycin or, more recently, rifampin plus clarithromycin requires taking the drugs daily for 8 weeks. Streptomycin is administered by injection and may result in hearing loss. Clarithromycin often causes gastrointestinal discomfort. Our goal is to identify a regimen that is both shorter and associated with fewer side effects. Rifampin, previously an expensive drug, is well tolerated not only at the standard dose of 10 mg/kg but at doses of 20 and 40 mg/kg. The related rifamycin, rifapentine, has a longer half-life and is also well tolerated. We tested in a mouse model of Buruli ulcer whether higher doses of these rifamycins together with clofazimine, a drug that has transient skin pigmentation side effects but no toxicities, could effectively reduce lesion size, the number of bacteria, and production of the mycolactone toxin, in a shorter time than that for the existing drug regimens. We found that treatment for 4 weeks with a high dose rifamycin plus clofazimine is as effective as 8 weeks of the current standard regimens of rifampin plus streptomycin or rifampin plus clarithromycin.

Wound healing: Natural history and risk factors for delay in Australian patients treated with antibiotics for Mycobacterium ulcerans disease

BACKGROUND

Healing times following treatment with antibiotics, and factors that influence healing, have not been reported in Australian patients with Mycobacterium ulcerans.

METHODOLOGY/PRINCIPAL FINDINGS

Healing times were determined for all M. ulcerans cases treated by a single physician with antibiotics at Barwon Health, Victoria, from 1/1/13-31/12/16. Lesions were categorised by induration size: category A ≤ 400mm2, Category B 401-1600mm2 and Category C ≥1601mm2. A logistic regression analysis was performed to determine risk factors for prolonged wound healing (>150 days from antibiotic commencement). 163 patients were included; 92 (56.4%) were male and median age was 58 years (IQR 39-73 years). Baseline lesion size [available in 145 (89.0%) patients] was categorised as A in 46 (31.7%), B in 67 (46.2%) and C in 32 (22.1%) patients. Fifty (30.7%) patients had surgery. In those treated with antibiotics alone, 83.0% experienced a reduction in induration size after 2 weeks, then 70.9% experienced an increase in induration size from the lowest point, and 71.7% experienced an increase in ulceration size. A linear relationship existed between the time induration resolved and wound healing began. Median time to heal was 91 days (IQR 70-148 days) for category A lesions; significantly shorter than for category B lesions (128 days, IQR 91-181 days, p = 0.05) and category C lesions (169 days, IQR 159-214 days, p<0.001). Fifty-seven (35.0%) patients experienced a paradoxical reaction. Of those treated with antibiotics alone, lesions experiencing a paradoxical reaction had longer healing times [median time to heal 177 days (IQR 154-224 days) compared to 107 days (IQR 79-153 days), p<0.001]. On multivariable logistic regression, lesion size at baseline (p<0.001) and paradoxical reactions (p<0.001) were independently associated with prolonged healing times. For category A and B lesions, healing time was significantly shorter with antibiotics plus excision and direct closure compared with antibiotics alone [Category A lesions median 55 days (IQR 21-63 days) compared with 91 days (IQR 70-148 days), p<0.001; Category B lesions median 74 days (IQR 21-121 days) compared to 128 days (IQR 97-181 days), p<0.001].

CONCLUSIONS

In Australian patients treated with antibiotics M. ulcerans lesions usually initially improve, then clinically deteriorate with increased induration and ulceration, before healing after the inflammation associated with lesions resolves. The time to complete healing of lesions is generally long, and is further prolonged in those with larger initial lesion size or who develop paradoxical reactions. For small lesions (<4cm2), excisional surgery may reduce healing times.