Abstract
No large study to date has ever evaluated the effectiveness, safety and tolerability of imipenem/clavulanate versus meropenem/clavulanate to treat multidrug- and extensively drug-resistant tuberculosis (MDR- and XDR-TB). The aim of this observational study was to compare the therapeutic contribution of imipenem/clavulanate versus meropenem/clavulanate added to background regimens to treat MDR- and XDR-TB cases.
84 patients treated with imipenem/clavulanate-containing regimens showed a similar median number of antibiotic resistances (8 versus 8) but more fluoroquinolone resistance (79.0% versus 48.9%, p<0.0001) and higher XDR-TB prevalence (67.9% versus 49.0%, p=0.01) in comparison with 96 patients exposed to meropenem/clavulanate-containing regimens. Patients were treated with imipenem/clavulanate- and meropenem/clavulanate-containing regimens for a median (interquartile range) of 187 (60–428) versus 85 (49–156) days, respectively.
Statistically significant differences were observed on sputum smear and culture conversion rates (79.7% versus 94.8%, p=0.02 and 71.9% versus 94.8%, p<0.0001, respectively) and on success rates (59.7% versus 77.5%, p=0.03). Adverse events to imipenem/clavulanate and meropenem/clavulanate were reported in 5.4% and 6.5% of cases only.
Our study suggests that meropenem/clavulanate is more effective than imipenem/clavulanate in treating MDR/XDR-TB patients.
Abstract
Meropenem/clavulanate is safe and more effective than imipenem/clavulanate in treating MDR and XDR-TB patients http://ow.ly/Z4S2o
Introduction
Over 480 000 new multidrug-resistant tuberculosis (MDR-TB) cases and 190 000 deaths were estimated to occur in 2014 by the World Health Organization (WHO), with only one MDR-TB case out of four being currently diagnosed and treated [1]. Half of the 123 000 cases of MDR-TB notified to the WHO in 2014 occurred in India, the Russian Federation and South Africa. Globally, 3.3% of new cases and 20% of previously treated cases of TB harbour MDR-TB strains of Mycobacterium tuberculosis. While overall 9.7% of the MDR-TB strains met the criteria defining extensively drug-resistant (XDR)-TB (e.g. resistance to at least one fluoroquinolone and a second-line injectable drug), this proportion was much higher in some of the former Soviet Union countries (Belarus 29%, Latvia 15% and Georgia 15%) [1, 2].
Recent evidence shows that treating MDR- and XDR-TB patients with the drugs available today is long, expensive, complicated and associated with frequent adverse events [3–8].
Presently a stepwise approach in the use of second-line anti-TB drugs (which are classified into five groups) is recommended by WHO [7, 9].
The main difficulty faced by clinicians treating MDR- and XDR-TB cases is to identify at least four active drugs which are necessary to design an effective multidrug regimen as per the WHO guidelines [3, 4, 7, 10, 11]. New drugs, such as delamanid, [12–14] and bedaquiline [15–20], and a few repurposed drugs (presently included in WHO Group 5, i.e. drugs with unknown/limited evidence on efficacy and/or tolerability) are presently attracting scientific interest [7, 21], among them linezolid [10, 22–28] and carbapenems [29–34]. The carbapenem group of drugs, which includes meropenem, imipenem and ertapenem, are currently used to treat MDR- and XDR-TB cases, although the evidence available on their efficacy, safety and tolerability is extremely limited [29–34].
The effectiveness of β-lactam antibiotics is unfortunately limited, as M. tuberculosis is protected through its potent β-lactamase, encoded by the blaC gene [35, 36]. Recent studies indicate that clavulanate (a β-lactamase inhibitor) can inhibit the activity of blaC-coded products in vitro [36]. Meropenem, offering a limited substrate to hydrolysis, has shown high bactericidal in vitro activity in association to clavulanate against M. tuberculosis (susceptible, MDR- and XDR-TB strains) as well as the in vivo ability to sterilise cultures within 2 weeks [37, 38]. Moreover, a study suggested synergy with amoxicillin and meropenem [39]. This has been confirmed in a murine model [40]. Its effectiveness, initially suggested in two case reports of 10 cases or less [30, 41], was then confirmed by two case–control studies. The first, with a limited sample size (37 patients at a single centre), suggested the drug was effective (offering up to 20–30% sterilising power) and well tolerated [29]. The second, more recent study, was conducted by the International Carbapenems Study Group (ICSG, formerly the European Carbapenems Study Group) in 17 centres and six countries in Europe and Latin America with over 90 cases. It confirmed that meropenem/clavulanate is safe and that the activity of the drug combination is promising, as nondifferent (noninferior) sputum smear conversion, culture conversion and treatment success rates between cases and controls have been identified despite controls having a much less severe resistance pattern than meropenem/clavulanate-treated cases [42].
Evidence on imipenem/clavulanate is even more limited, consisting of a series of 10 patients and one case report [33, 34].
Recently, the TB reference centres belonging to the ICSG [31, 42] conducted a large observational study evaluating the therapeutic contribution of imipenem/clavulanate added to a background regimen (as per the WHO guidelines) when treating MDR- and XDR-TB cases.
The aim of the present study was to compare the effectiveness, safety and tolerability profile of meropenem/clavulanate and imipenem/clavulanate in a large observational cohort of MDR-TB patients.
Material and methods
The methodological characteristics were previously described [42]. MDR-TB reference centres located in European and Southern American countries recruited culture-confirmed MDR-TB patients aged ≥15 years. An MDR-TB case was defined as an individual with TB caused by M. tuberculosis strains phenotypically resistant to at least isoniazid and rifampicin. Patients were consecutively selected on the basis of their exposure to meropenem/clavulanate and imipenem/clavulanate during their intensive and/or continuation phase.
An individualised TB regimen was administered following the results of the drug-susceptibility test (DST) carried out by externally quality-assured laboratories [11]. The attending physician prescribed anti-TB drugs without any compelling criteria of experimental protocols and, consequently, blinding or randomised methods were not followed. Meropenem/clavulanate was administered at a daily dosage of meropenem 1 g three times daily intravenously plus amoxicillin/clavulanic acid 1.2 g three times daily. The only exception was represented by the Belgium centre where meropenem was prescribed at a daily dosage of 2 g three times daily (17/180, 9.4%). Imipenem/clavulanate was administered at a dose of 500 mg imipenem four times daily plus amoxicillin/clavulanic acid as above.
Standardised ad hoc E-forms were prepared to collect epidemiological (i.e. duration of hospital stay, age, place of birth, sex, residence, immigration from a TB high-burden country), clinical (i.e. HIV status, administration of HIV drugs, previous TB diagnosis and treatment, previous treatment outcomes, radiological findings, TB therapy and related adverse events, duration of exposure to meropenem/clavulanate and imipenem/clavulanate, surgery, sputum smear and culture positivity at the treatment baseline, at 30, 60 and 90 days, time to sputum smear and culture conversion, WHO treatment outcomes) and microbiological (i.e. DST results) information from official medical files.
Qualitative and quantitative variables were summarised with percentages and mean±sd or median (interquartile range (IQR)) depending on their normality. The Chi-squared or Fisher's exact and the Mann–Whitney test were adopted to compare qualitative and quantitative variables, respectively. Differences in terms of sputum smear and culture conversions between imipenem/clavulanate and meropenem/clavulanate groups were assessed with a survival analysis and a log-rank test. A p-value <0.05 (two-tailed) was considered statistically significant. Statistical computations were performed with Stata 13.0 (StataCorp, College Station, TX, USA).
Ethical approval for the collection and analysis of anonymous and retrospective data and for the compassionate use of the drugs was obtained by the institutional review boards of the participating institutions as per legislation in force in the different ICSG countries and at the coordinating centre.
Results
180 MDR-TB patients were selected for the analysis: 96 (53.3%) exposed to meropenem/clavulanate and 84 (46.7%) exposed to imipenem/clavulanate (table 1).
Demographic, epidemiological and clinical characteristics of multidrug- and extensively drug-resistant tuberculosis (MDR- and XDR-TB) patients treated with meropenem/clavulanate (MC)- versus imipenem/clavulanate (IC)-containing regimens
The prevalent sex of the cohort was male (105, 58.3%) and the median (IQR) age was 35 (26–45) years (table 1).
Migrants coming from high TB prevalence countries accounted for 100 (55.6%) patients, whereas only a low proportion (5.8%) were HIV-infected. A higher proportion of migrants (76.0% versus 32.1%, p<0.0001) and of patients born in Europe (75.0% versus 45.2%, p<0.0001) was observed in the meropenem/clavulanate-treated group (table 1).
Pulmonary TB was diagnosed in 176 out of 179 (98.3%) cases. The proportion of sputum smear- and culture-positive cases was 89.4% and 97.8%, respectively (table 2).
Treatment outcomes of multidrug- and extensively drug-resistant tuberculosis (MDR- and XDR-TB) patients treated with meropenem/clavulanate (MC)-versus imipenem/clavulanate (IC)-containing regimens
More than half were affected by XDR-TB (57.8%; 67.9% and 49.0% in the imipenem/clavulanate and meropenem/clavulanate group, respectively, p=0.01), but the median number of drug resistances was similar (8 versus 8 in the meropenem/clavulanate and imipenem/clavulanate group, respectively, p=0.34) (table 2).
Over three-quarters of cases were previously treated for drug-susceptible or -resistant TB; however, patients exposed to imipenem/clavulanate-containing regimens had been treated more frequently for a previous TB diagnosis (91.7% versus 69.5%, p<0.0001). However, the median (IQR) number of previous anti-TB treatments was similar in the meropenem/clavulanate- and imipenem/clavulanate-treated groups (2 (1–4) versus 2 (1–3)) (table 1).
The prevalence of resistance to any fluoroquinolone was significantly higher among the imipenem/clavulanate-treated cases (79.0% versus 48.9%, p<0.0001); moreover, a higher prevalence of resistance to capreomycin (63.9% versus 46.9%, p=0.04) and kanamycin (75.8% versus 49.3%, p<0.002) was observed in comparison with the meropenem/clavulanate-treated group. The prevalence of resistance to amikacin was similar in both groups (50.0% versus 48.8%, respectively) (table 1).
Patients were treated with meropenem/clavulanate- and imipenem/clavulanate-containing regimens for a median (IQR) of 85 (49–156) and 187 (60–428) days (table 3). Adjuvant surgical therapy was performed in 18.2% of the cases.
Safety of meropenem/clavulanate (MC)-versus imipenem/clavulanate (IC)-containing regimens
Sputum smear and culture conversion rates were significantly higher in those exposed to meropenem/clavulanate (94.8% and 94.8%, respectively) than in those exposed to imipenem/clavulanate (79.7% and 71.9%, p=0.02 and p<0.0001, respectively). Similar proportional differences for the culture conversion were achieved when subgroup analyses were performed according to MDR/XDR-TB status and the median number of drug resistances (i.e. ≥8 drug resistances) (table 2).
The time to culture conversion was shorter in the meropenem/clavulanate- than in the imipenem/clavulanate-treated group (44 (28–75) versus 60 (30–90) days, p=0.05) (table 2 and figure 1).
a) Sputum smear and b) culture conversion in multidrug- and extensively drug-resistant tuberculosis patients treated with meropenem/clavulanate (MC)-versus imipenem/clavulanate (IC)-containing regimens.
Overall, cases treated with meropenem/clavulanate achieved higher statistically significant success rates than those treated with imipenem/clavulanate (77.5% versus 59.7%, p=0.03) (table 2).
Adverse events were reported only in six (6.5%) meropenem/clavulanate- and three (5.4%) imipenem/clavulanate-treated patients (p=1.0) (table 3).
Discussion
The aim of the present study was to retrospectively compare the effectiveness, safety and tolerability profile of meropenem/clavulanate and imipenem/clavulanate in a large cohort of XDR- and MDR-TB patients.
The results of our study demonstrated that, overall, the meropenem/clavulanate-containing regimens achieved better results than imipenem/clavulanate-containing regimens. In particular, 1) culture conversion rates were statistically higher (both in the whole cohort and in the XDR/MDR-TB subgroups), 2) the time to culture conversion was shorter and 3) the treatment success rates were significantly higher (both in the overall cohort and in the patients with ≥8 resistances) in the meropenem/clavulanate- than in the imipenem/clavulanate-containing group.
Furthermore, the study demonstrated that both drugs were well tolerated and adverse events were rare (only 6.5% in the meropenem/clavulanate- and 5.4% in the imipenem/clavulanate-containing regimens).
This is, to the best of our knowledge, the first study in the scientific literature describing the efficacy, safety and tolerability of imipenem/clavulanate-containing regimens, and comparing the clinical performances of two of the core carbapenems (i.e. imipenem/clavulanate and meropenem/clavulanate) in a large cohort of XDR- and MDR-TB patients.
In a previous study by the same group [42] the performance of the meropenem/clavulanate-containing regimens was compared with a control group. The study results suggested that meropenem/clavulanate is active, as meropenem/clavulanate-containing regimens achieved nondifferent results than the controls in spite of a much more severe resistance profile.
Although it is always difficult to attribute the causality of the results observed to meropenem/clavulanate and imipenem/clavulanate, we can underline that imipenem/clavulanate-containing regimens achieved bacteriological and treatment success rates comparable to those of other cohorts of MDR-TB cases [3, 4], while meropenem/clavulanate-containing-regimens had promising results (94.8% sputum smear and culture conversion, and 77.5% treatment success). In order to remove the “background noise” caused by the observational design, the study findings need to be confirmed by randomised controlled clinical trials.
Based on the molecular mechanism of action, imipenem is more active than meropenem [43]. However, this does not necessarily translate into better clinical results. The pharmacokinetic/pharmacodynamic index, as well as the free drug concentration exceeding the minimal inhibitory concentration, could have favoured the group with the meropenem/clavulanate-containing regimens. In addition, synergy with the other anti-TB drugs could have been different for the carbapenems prescribed in this study.
As meropenem/clavulanate appears to be more active against M. tuberculosis than imipenem/clavulanate, the former should be favoured in the treatment of MDR-TB. Should meropenem/clavulanate be unavailable, higher doses of imipenem/clavulanate as per Pseudomonas infection could probably be administered (i.e. 1 g four times daily) given that the drug is well tolerated.
Among the strengths of the study we mention the large size of the imipenem/clavulanate and meropenem/clavulanate cohorts, and the detailed information collected from the participating centres in Europe and Latin America. The drug resistance patterns, number of previous anti-treatment cycles as well as most of the demographic, epidemiological and clinical variables did not differ significantly in the meropenem/clavulanate and imipenem/clavulanate cohorts.
However, the observational and retrospective design of the study determines several interpretational limitations. In particular, we mention the missing pre-study definition of a sample size and the possibility to randomise and ensure blindness, which could increase the probability of a selection bias. Furthermore, the latter methodological issue is clearly highlighted by the higher prevalence of resistance to any fluoroquinolone in the imipenem/clavulanate cohort, as well as a higher prevalence of resistance to two out of three second-line anti-TB injectables (kanamycin and capreomycin). Furthermore, exposure to previous anti-TB treatment and the proportion of previous treatment failures was higher in the imipenem/clavulanate cohort.
As meropenem/clavulanate seems to perform better, but imipenem/clavulanate is cheaper and more widely available, economic analyses will be important to finally assess the future role of these compounds. However, the new information provided by this observational study allows clinicians managing difficult-to-treat TB cases to know how to use carbapenems and other repurposed drugs in case the minimum number of active drugs necessary to design an effective regimen is lacking [3, 4, 9, 44–47].
In this context, other second-line drugs such as fluoroquinolones or clofazimine might contribute to cardiologic or other adverse events [48]. Unlike all of the above, the repurposed carbapenems are frequently well tolerated and offer few drug–drug interactions, and should the need arise can replace other TB drugs based on their advantageous safety and tolerability profile. The authors believe that the benefits of β-lactam use for the treatment of TB outweighs the risks of further antimicrobial resistance.
Although new compounds will hopefully appear soon to support the move towards TB elimination [49], the carbapenems are confirmed to have a particular role. The authors would recommend the use of meropenem/clavulanate in the intensive phase of treatment, particularly to manage the most severe cases until bacteriological conversion has been achieved. If active drugs are lacking to design an effective regimen in the continuation phase, ertapenem/clavulanate or faropenem/clavulanate could potentially be considered in the continuation phase. Given the widespread use of amoxicillin/clavulanic acid in the community, DST for meropenem/clavulanate is recommended before using the drug in a regimen.
Footnotes
Conflict of interest: None declared.
Copyright ©ERS 2016
- Received January 28, 2016.
- Accepted February 26, 2016.
- Copyright ©ERS 2016
References
