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Antimicrobial Agents and Chemotherapy, October 2005, p. 4020-4025, Vol. 49, No. 10
0066-4804/05/$08.00+0 doi:10.1128/AAC.49.10.4020-4025.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Medical Department, Sappasithiprasong Hospital, Ubon Ratchathani,1 Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand,2 Menzies School of Health Research, Charles Darwin University and Northern Territory Clinical School, Flinders University, Darwin, Australia,3 Centre for Clinical Vaccinology and Tropical Medicine, Nuffield Department of Clinical Medicine, Churchill Hospital, University of Oxford, Oxford OX3 7LJ, United Kingdom4
Received 10 March 2005/ Returned for modification 28 June 2005/ Accepted 24 July 2005
| ABSTRACT |
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| INTRODUCTION |
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Our current oral regimen is a four-drug combination of trimethoprim-sulfamethoxazole (TMP-SMX), doxycycline, and chloramphenicol. This regimen is associated with high rates of adverse events, including gastrointestinal intolerance, anemia, and allergic reactions. In other centers, the use of a three-drug regimen or even TMP-SMX alone has been associated with low relapse rates (6, 7). Higher relapse rates have been found during clinical trials of amoxicillin-clavulanate with supplemental amoxicillin, doxycycline monotherapy, and a combination of azithromycin and ciprofloxacin (5, 6, 11). The aim of this study was to examine the efficacy and side effects associated with the four-drug (TMP-SMX, doxycycline, and chloramphenicol) regimen versus the three-drug (TMP-SMX and doxycycline) regimen.
| MATERIALS AND METHODS |
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Randomization was performed by a computer-generated sequence and was balanced after each block of 10 patients. Sealed envelopes were prepared by a member of the research unit who was not involved in enrollment. These were opened by a member of the study team following a decision to start oral treatment. Patients were randomly allocated to receive TMP-SMX (8 mg TMP and 40 mg SMX/kg of body weight daily; maximum dose, 160 mg TMP and 800 mg SMX twice daily), doxycycline (4 mg/kg daily; maximum dose, 100 mg twice daily), and chloramphenicol (40 mg/kg daily; maximum dose, 500 mg four times daily for the first 4 weeks of oral therapy) or TMP-SMX and doxycycline without chloramphenicol at the same doses. All study drugs were manufactured either by Thai pharmaceutical companies or the Government Pharmaceutical Organization and were provided free to study patients. Minimum duration of oral treatment was 12 weeks, but total duration was based on clinical history and the course of illness. Patients that had evidence of deep-seated infection (such as undrained visceral abscesses or infections involving bones or joints) or those with more severe disease on presentation tended to receive longer courses of antibiotics. Conversely, patients with mild disease, such as infections involving skin and soft tissue, or patients with parotid abscesses tended to receive shorter courses of antibiotics. Duration of antibiotic treatment was determined by a single clinician with extensive experience in the clinical management of melioidosis (W. Chaowagul), who undertook outpatient review within 4 weeks after discharge and periodically thereafter based on clinical progress.
Follow-up was continued until July 2004. Patients were primarily monitored through the outpatient department. Nonattendees were sent letters inquiring about their subsequent clinical course and visited at home by the study team if necessary.
Patients who failed to attend clinic appointments were deemed to have ceased their medications when last reviewed in the outpatient department. Recurrence of disease was treated as for the primary episode, with readmission for investigation and intensive intravenous therapy if required, followed by the four-drug conventional combination. Amoxicillin-clavulanate with supplemental amoxicillin was used for patients who developed suspected drug allergies.
The primary outcome measure was culture-confirmed relapse or time to death attributable to melioidosis. "Clinical relapse" was also determined; this was defined as possible relapse characterized by clinical features compatible with melioidosis that was treated with antibiotics active against B. pseudomallei but was culture negative. Mortality was categorized as attributable to primary infection or relapse or attributable to other causes.
Time to outcome was measured as the start of oral treatment to relapse or attributable death. Censoring events were death from causes other than culture-confirmed or clinical relapse and loss to follow-up. A comparison of adverse drug events was made between each group.
The original study design called for 226 patients to achieve an 80% power to detect a difference in relapse rates of 25% and 10% at the 0.05 significance level. All analyses were done on an intention-to-treat basis and then repeated per protocol. In the per-protocol analyses, patients who switched treatment to the other study arm were reallocated according to the final treatment they received. In this analysis, patients who changed treatment regimens to antibiotics that did not include a study regimen were not reallocated.
Statistical tests were performed using the statistical program STATA/SE, version 8.0 (StataCorp LP, College Station, Tex.). Comparisons of continuous data were performed using a Student's t test or the Mann Whitney U test where appropriate. Proportions were compared using Fisher's exact test. Time-to-event endpoints were compared using the log-rank test or Wilcoxon test as appropriate and were depicted graphically using a Kaplan-Meier graph. A Cox proportional hazards model was used to adjust the treatment effect for potential confounding factors; the following variables were considered in the forward-variable selection procedure: age, distribution of infection, initial use of ceftazidime, history of chronic renal failure, diabetes mellitus, and failure to complete at least 12 weeks of therapy for analysis of relapse after cessation of oral treatment. The final Cox proportional hazards models were reanalyzed with TMP-SMX resistance as a variable to explore its effect.
Susceptibility to ceftazidime, imipenem, chloramphenicol, doxycycline, and amoxicillin-clavulanate was performed by the Kirby-Bauer disk diffusion test. As TMP-SMX susceptibility testing by this method is not reliable and testing for MICs was not in routine use at this time (10), test results were not reported to clinicians during this trial. Susceptibility testing using the Etest (AB Biodisk) was retrospectively performed on isolates stored at 70°C in trypticase soy broth with 15% glycerol using NCCLS methodology and breakpoints for B. pseudomallei (susceptible,
2/38 µg trimethoprim-sulfamethoxazole; resistant, >4/76 µg) (9, 12).
| RESULTS |
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The culture-confirmed relapse rate for 124 patients who received a total of at least 12 weeks of oral therapy was 11.8% in the four-drug group and 5.4% in the three-drug group (P = 0.296, log-rank test). In a multiple-variable Cox proportional hazards model, failure to complete at least 12 weeks of therapy was associated with a shorter time to relapse or death (HR = 5.70; 95% CI, 2.61 and 12.45; P < 0.001). Adjusting for these predictors, the allocated treatment arm was not associated with outcome (HR = 1.28; 95% CI, 0.58 and 2.85; P = 0.54).
There were nine protocol violations, as follows. Amoxicillin-clavulanate with supplemental amoxicillin was substituted for the allocated treatment in seven patients (two patients allocated to four drugs and five patients to three drugs). Two patients allocated to receive four-drug therapy received the three-drug regimen; these were included in the analysis. In a per-protocol analysis, culture-confirmed relapse was not significantly different between the two groups (8.1% in the four-drug group versus 9.8% in the three-drug group; P = 0.47, log-rank test).
A total of 169 B. pseudomallei isolates were available for susceptibility testing. Of these, 9 out of 82 (11%) in the four-drug group and 7 out of 87 (8.1%) in the three-drug group were resistant to TMP-SMX by Etest (P = 0.52). In a multiple-variable Cox proportional hazards model adjusting for allocated regimen, age, and failure to complete 12 weeks of therapy, TMP-SMX resistance was not statistically associated with shorter relapse-free duration from the commencement of oral therapy (HR = 2.05; 95% CI, 0.44 and 9.62; P = 0.36) or the cessation of oral therapy (HR = 1.62; 95% CI, 0.20 and 13.02; P = 0.65).
In total, 63 patients required a change in treatment, of which 48 (53%) were in the four-drug group and 22 (25%) in the three-drug group (P < 0.001) (Table 2). Patients randomized to receive four drugs switched treatment to amoxicillin-clavulanate (n = 23) or three-drug therapy (n = 25). Patients randomized to the three-drug therapy switched treatment to amoxicillin-clavulanate (n = 17), TMP-SMX (n = 4), or doxycycline (n = 1). A higher proportion of patients reported adverse drug events in the four-drug group (Table 3) and switched therapy within the first four weeks: 42 out of 48 (87.5% in the four-drug group) versus 13 out of 22 (59.1% in the three-drug group; P = 0.007). Gastrointestinal intolerance and anemia were reported at lower rates in the three-drug group. Allergic phenomena were similar in both groups. In the four-drug group, chloramphenicol was ceased prior to 4 weeks in 41 patients (45%).
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| DISCUSSION |
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Other alternatives to the four-drug regimen have been explored previously. A ciprofloxacin-azithromycin regimen and doxycycline monotherapy have both been associated with relapse rates exceeding 20% in clinical trials in Thailand (5, 6). In one of these trials the comparator arm was the three-drug regimen in which only one relapse was recorded in 33 patients that received this regimen (relapse rate, 3%; 95% CI, 0 and 16%) (6). Quinolone monotherapy was associated with a relapse rate of 29% in an uncontrolled study (4). Amoxicillin-clavulanate with supplemental amoxicillin was associated with a higher relapse rate than the four-drug conventional therapy in 101 patients, although poor adherence to the 20-week course of therapy appeared to be a more important factor than antibiotic regimen (11). Factors previously demonstrated to be associated with relapse include eradication regimens of less than 12 weeks, severity of disease, and the use of amoxicillin-clavulanate in place of the intensive intravenous phase (3).
Higher rates of culture-positive relapse were seen by the end of this trial compared with previous studies. This may be explained in part by the longer follow-up (up to 5.5 years) and larger sample size (two to three times) in this study compared to those reported previously, our active surveillance for follow-up, and the poor tolerance to the regimens generally. When the analysis time was limited to 52 weeks, the overall relapse rate was similar to that of previous trials (6% compared to 2 to 4%) (5, 6, 11). These findings reinforce the need for ongoing follow-up as relapse may occur many years after initial infection (8).
A high rate of TMP-SMX resistance in clinical isolates was demonstrated in this study. Testing for TMP-SMX has been problematic; testing by the Kirby Bauer disk diffusion technique has tended to overestimate the rates of resistance (10). We have recently reported the results of TMP-SMX susceptibility testing by Etest for a large number of isolates stored at our center, including those from patients in this study (12). The high rate of resistance to TMP-SMX has clear implications for a potential future trial of TMP-SMX alone in this region. No major differences were seen in patients infected with TMP-SMX-resistant isolates, but this study was underpowered to examine the effect of resistance on relapse rates reflected in the wide confidence intervals in the estimate.
There are several limitations to this open-label trial. Awareness of the treatment received may have influenced reporting of adverse events, although it is unlikely to have influenced the more objective endpoint of culture-confirmed relapse. A significant proportion of patients were lost to follow-up, highlighting the difficulty in monitoring long-term outcome in this primarily rural population. The high rate of switching of drug regimens reflects the poor tolerance of both regimens. Adherence to therapy was not formally assessed by pill counts or drug levels.
This study suggests that the three-drug regimen is better tolerated and is as effective as the four-drug regimen for oral eradication therapy of melioidosis in adults. However, both regimens in this study were associated with significant rates of intolerance. As tolerance is a key factor in promoting adherence to prolonged antibiotic therapy, it is likely that the use of simpler therapies are likely to improve outcomes. TMP-SMX alone is used for eradication therapy in Australia (7); a prospective, multicenter randomized trial is now planned to compare the efficacy and side effect profile of the three-drug regimen versus TMP-SMX alone.
| ACKNOWLEDGMENTS |
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S.J.P. is supported by a Wellcome Trust Career Development Award in Clinical Tropical Medicine, and A.C. was supported by an Australian National Health and Medical Research Council Training Scholarship. This study was part of the Wellcome Trust-Mahidol University-Oxford Tropical Medicine Research Programme funded by the Wellcome Trust of Great Britain.
| FOOTNOTES |
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| REFERENCES |
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