Abstract
Toxoplasmic encephalitis (TE) is caused by Toxoplasma gondii infection and can be a life-threatening disease in immunocompromised patients. This study evaluated the rate of relapse associated with pyrimethamine-based maintenance therapy (i.e. secondary prophylaxis) in patients with human immunodeficiency virus (HIV) or AIDs treated prior to and after the common use (i.e. 1996) of highly active antiretroviral therapy (HAART) (pre-HAART and post-HAART, respectively). PubMed, Google Scholar, and Cochrane databases were searched to 6 June 2016 using search terms: pyrimethamine, Daraprim, Fansidar, Metakelfin, Fansimef, 5-(4-chlorophenyl)-6-ethyl-2,4-pyrimidinediamine, encephalitis, cerebral, toxoplasmosis, toxoplasmic, and gondii. Single-arm cohort, retrospective, and randomized studies were included. Twenty-six studies with 1,596 patients were included in the analysis; twenty pre-HAART (n = 1,228) studies and six post-HAART (n = 368) were performed. Pooled proportions test for pyrimethamine-based therapy from pre-HAART studies indicated a relapse rate of 19.2% and 18.9% from the fixed-effects and random-effects models, respectively. The relapse rate in the post-HAART studies was 11.1% (fixed and random effects). Continuous therapy was suggestive of lower incidence of relapse compared with intermittent therapy in the pre-HAART era (range, 18.7 to 17.3% vs. 20.9 to 25.6%, respectively). These findings indicate that the likelihood of relapse associated with pyrimethamine-based therepy in patients with HIV and TE decreased after the introduction of HAART to approximately 11%. The findings have important implications as relapse may affect a patient’s disease severity and prognosis, increase utilization of health care resources, and result in additional health care expenditure.
Introduction
Toxoplasmic encephalitis (TE) results from infection by Toxoplasma gondii (T. gondii), a ubiquitous obligate intracellular parasite with a worldwide prevalence that infects humans and other warm-blooded animals [Citation1]. Approximately, one third of the population worldwide is chronically infected with T. gondii [Citation2], T. gondii seroprevalence varies world wide. In the United States, it is estimated that 22.5% of the population 12 years and older are infected with the parasite [Citation3]. It is estimated that 6.7% of people in Korea, 12.3% in China, 23.9% in Nigeria, 46% in Tanzania, and 47% in the rural areas of France are seropostive for T. gondii [Citation4−8]. In Brazil, up to 50% of elementary school children and 50 to 80% of women of child-bearing age have antibodies to T. gondii [Citation9]. T. gondii infection has two phases: active (acute) which is characterized by severe symptoms; and latent (dormant) which is typified by life-long persistence of cysts in tissues [Citation10]. TE typically results from reactivation of the dormant organism [Citation11].
TE is one of the most common opportunistic infections of the central nervous system (CNS) in patients with acquired immune deficiency syndrome (AIDS) worldwide, and in the United States between 10 and 40% of HIV-infected individuals have antibodies against T. gondii [Citation12−14]. TE is a life-threatening disease, especially for immunocompromised patients, such as those with AIDS [Citation13,15]. Encephalitis causes significant morbidity and mortality in patients with HIV, and toxoplasmosis was found to be the most common specified encephalitis-associated hospitalizations in patients with HIV [Citation16].
The National Institutes of Health (NIH) Guidelines recommend the use of pyrimethamine, sulfadiazine, and leucovorin for the initial treatment of TE in HIV-infected pateints [Citation17]. Pyrimethamine and sulfadiazine are thought to act synergistically to inhibit T. gondii proliferation and survival by blocking the folate metabolic pathway and consequently DNA synthesis [Citation11]. Leucovorin is added to reduce potential adverse reactions associated with folic acid metabolism [Citation11]. In case of allergy to sulfa drugs, the recommended alternative treatment is a combination of pyrimethamine, clindamycin, and leucovorin [Citation17]. Sulfa drug allergies are observed in about 5% of the population and up to 30% of HIV-infected patients [Citation18].
The incidence of TE in patients infected with HIV is closely related to the progression of immune deficiency and a reduction in CD4 T lymphocyte cell counts. TE is rare in patients with CD4 cell counts >200 cells/μL, while the risk of TE is greatest in patients with CD4 counts <50 cells/μL [Citation19]. It is recommended by the NIH/AIDS Guidelines to continue chronic maintenance treatment in patients who have responded to initial TE therapy until the person remains asymptomatic and their CD4 counts are >200 cells/μL after highly active anti-retroviral therapy (HAART) for for six months [Citation17].
Despite treatment efforts, a percentage of patients receiving maintenance therapy for TE will experience a relapse [Citation13]. Relapse of TE can have significant implications for patients who often develop new lesions in areas of the brain previously free of infection [Citation20], and for providers and the health care system as a relapse can result in rehospitalization and/or change in therapy.
Previous meta-analyses have assessed the efficacy and safety of pyrimethamine for acute TE [Citation21−23]; however, the incidence of relapse during maintenance therapy following resolution of acute TE has not been assessed [Citation21−24]. Therefore, to gain greater insight into the risk of TE relapse, we performed a systematic review and meta-analysis to evaluate the incidence of relapse associated with pyrimethamine-based maintenance therapy (i.e. secondary prophylaxis) in persons with HIV/AIDS. We also investigated whether the likelihood of relapse changed following the introduction of HAART therapy in the mid-1990s. This was of interest because HAART has greatly reduced AIDS-related morbidity and mortality and decreased the incidence of opportunistic infections in HIV-infected patients [Citation25]. The impact of HAART on the incidence of relapse of TE in patients with HIV is not clear. In order to incorporate the broadest scope of available evidence, the analysis protocol allowed for inclusion of studies of varying design, such as single-arm observational cohort, randomized, and retrospective studies.
Methods
Search strategy
The study was performed in accordance with PRISMA [Citation26], and the protocol can be found in Supplemental Material. PubMed, Google Scholar and Cochrane databases were searched up to 6 June 2016 using the following search terms: pyrimethamine, Daraprim, Fansidar, Metakelfin, Fansimef, 5-(4-chlorophenyl)-6-ethyl-2,4-pyrimidinediamine, encephalitis, cerebral, toxoplasmosis, toxoplasmic, gondii. Eligible studies included randomized controlled studies, observational prospective studies, and retrospective longitudinal studies. Studies had to report relapse of TE during maintenance therapy in patients with AIDS or HIV. All studies had to be published in peer-reviewed journals in English, Spanish, Portugueuse, or French. Studies that only provided relapse rates during acute treatment were rejected. Review articles, letters, comments, editorials, case reports, proceedings, personal communications, and preclinical studies were also excluded. Study eligibility for inclusion was determined by two independent reviewers, and in cases of uncertainty, a third reviewer was consulted.
Data extraction
Double data extraction was performed on all included studies to ensure data consistency. Discrepencies in extracted data between the two independent reviewers were resolved by a third reviewer. Non-English studies were reviewed by native speakers, and validated by a second reviewer for extracted data using Google Translator. The following data were extracted from the studies when reported: first author, publication year, study design, acute and maintence treatment regimens, number of patients, incidence of relapse, and duration of follow-up. For studies with insufficient reported data, we attempted to contact authors to obtain complete data. Studies were classified as being pre-HAART or post-HAART based on a cut-off date of 1996 for the conduct of the study (not publication date). The year 1996 is when the use of HAART therapy became widely available and dramatically decreased mortality of patients with AIDS (from 29.4/100 person years in 1995 to 8.8 per 100 person-years in the second quarter of 1997) [Citation25]. HAART status was verified by patient baseline characteristics and current treatments reported, although not all patients treated in the HAART period were receiving antiretroviral therapy. The abstracts were screened and data were extracted by the authors MPC and EG.
Quality assessment
The quality of the included studies was evaluated using Study Quality Assessment Tools of the National Heart, Lung, and Blood Institute of the NIH for quality assessment of observational cohort, cross-sectional, before–after (pre-post) studies with no control group, and case series studies [Citation27].
Statistical analysis
Pooled proportions meta-analysis
The primary outcome was rate of relapse during pyrimethamine-based maintenance therapy. The secondary outcome was rate of relapse with continuous (daily) or intermittent (two to three times per week) pyrimethamine-based therapy. For each outcome, rates in each study were transformed using the Freeman-Tukey double arcsine method. This transformation stabilizes the variance estimates, which is important for proportions close to 0 or 1 [Citation28]. Rates were then pooled using both fixed-effect and random-effects meta-analysis models. The fixed-effect model was performed using the inverse variance method and the random-effects model using the DerSimonian and Laird method, with the estimate of heterogeneity taken from the inverse variance model [Citation29]. Heterogeneity across studies was assessed by quantifying I2 inconsistency scores [Citation30]. I2 describes the percentage variation across studies attributed to heterogeneity rather than chance. Low I2 values (≤50%) suggest limited heterogeneity between studies, and I2 values >50 to 75% indicate moderate heterogeneity. Values >75% suggest high heterogeneity and the need to consider estimates from random-effects models [Citation30]. The analysis was performed using StatsDirect (Altrincham, UK) statistical program version 2.8.0 (27 October 2013). For ease of interpretating, the reported proportions were converted to percentages. Because the studies are non-comparative, we assessed active treatment arms independently; therefore, no comparative statistics were performed and only the combined relapse rate is reported.
Bias of the results was evaluated by the funnel plot and the Egger’s test [Citation31,32]. In the absence of bias, the graph is a symmetrical inverted funnel, and if there is bias, the funnel plot will appear asymmetrical [Citation31,32]. Reporting bias was assessed for the pre-HAART analysis, but not the post-HAART analysis as the minumum studies for this analysis should be >10; below this value, the test power is usually too low to distinguish chance from real asymmetry [Citation33].
Results
Search results
Of 1,307 studies initially identified, 1,121 were excluded following the ‘removal of duplicates and an initial abstract screen (Figure ). After full-text review, an additional 160 were removed for only describing methodology or a study protocol, being a pre-clinical study, being a case report, not reporting relapse rates, being an epidemiology or health care cost study, not evaluating TE, not administering pyrimethamine-based regimens, not investigating toxoplasmosis, describing finding for primary prophylaxis of TE, being a review article, not being published in English, French, Spanish, or Portugeuse, or evaluting an inappropriate patient population.
Figure 1. Search flow diagram.
Study characteristics
Twenty-six studies were included in the analysis with 1,596 patients (Tables and ). Twenty reported findings from studies that were performed up to 1996 (n = 1,228) (Table ) [Citation34−51], and six described results of studies performed after 1996 (n = 368) (Table ) [Citation52−57].
Table 1. Summary of study characteristics performed until 1996.
Table 2. Summary of study characteristics after 1996.
Study designs differed across both pre- and post-HAART studies. The pre-HAART studies included three randomized, six prospective, and 11 retrospective studies (Table ), and the post-HAART studies included two randomized, two prospective, and two retrospective studies (Table ). All studies included patients with AIDS or infected with HIV and who had received maintenance therapy for TE.
Among the studies, the pyrimethamine-based treatment regimens were heterogeneous, both for acute and maintenance therapy (Tables and ). In the pre- and post-HAART groups, the most common therapy both for acute and maintenance therapy was the combination of pyrimethamine and sulfadiazine. Other investigated pyrimethamine-based regimens included clindamycin, sulphamethopyrazine, sulfadoxine, clarithromycin, and atovaquone. Four studies in the pre-HAART group [Citation41,42,45,47] and two in the post-HAART group [Citation52,55] administered pyrimethamine alone for maintenance therapy. Most studies co-administered folinic acid (leucovorin) with pyrimethamine for acute therapy; only four did not report co-administering folinic acid with pyrimethamine – three in the pre-HAART group [Citation35,58,59] and one in the post-HAART group [Citation52]. Of the included studies, 11 did not report co-administering folinic acid with pyrimethamine during maintenance therapy [Citation34,35,38,41,45,47,49,51,52,54,60].
The follow-up for pre-HAART studies ranged from 3 months to 7 years and for the post-HAART studies from 4 to 22 months. For the pre-HAART studies, the rate of relapse ranged from 0 to 67% and for the post-HAART studies ranged from 0 to 12.9%.
Quality assessment
The majority of included studies obtained scores of medium–to-low quality due the varied trial designs. Despite the overall quality assessment, the relapse data reported were of sufficient quality for inclusion in the proportions analysis.
Meta-analysis
The pooled proportions test for pyrimethamine-based therapy in pre-HAART studies indicated a relapse rate of 19.2% and 18.9% from the fixed-effects and random-effects models, respectively (Table and Figure and Figure ). In the post-HAART period, the pooled proportions relapse rate was 11.1%, and was the same from both the fixed- and random-effect models due to limited heterogeneity in the data (I2 = 0%) (Table and Figure ).
Table 3. Pyrimethamine-based maintenance therapy: relapse rates in pre-HAART and post-HAART period.
Figure 2. Forest plot of fixed for analysis of pre-HAART studies.
Figure 3. Forest plot of random effect model for analysis of pre-HAART studies.
Figure 4. Forest plot of (A) fixed and (B) random effect model for analysis of post-HAART studies.
Six studies reported relapse rates of patients who received intermittent pyrimethamine-based therapy (two to three times per week); five pre-HAART [Citation40,43,45,49,61] and one post-HAART [Citation56]. We evaluated the rate of relapse in these studies compared with studies with continuous (daily) dosing. The relapse rate with intermittent pyrimethamine-based therapies in pre-HAART studies was 20.9% from the fixed-effect and 25.6% from the random-effect models, and for continous therapy was 18.7–17.3%, respectively (Table ). The rates for continuous therapy for post-HAART were 10.5%. Intermittent therapy was not analyzed in the post-HAART studies as only one study [Citation56] evaluated this type of treatment regimen.
Analysis of reporting bias
Funnel plot analysis was performed for the pre-HAART studies (Figure ). The analysis indicated the presence of reporting bias as indicated by significant funnel plot asymmetry (Eggar bias: 3.12386 (95% CI = 1.196098 to 5.051621); P = 0.0031).
Figure 5. Funnel plot analysis of reporting bias.
Discussion
This systematic review and meta-analysis assessed the incidence of TE relapse following pyrimethamine-based therapy in patients with HIV or AIDS. The anlysis found that the incidence of relapse was higher in pre-HAART (19.2% for fixed effect model and 18.9% for random effect model) compared with post-HAART (11.1% for both fixed- and random-effect models). The drop in the incidence of relapse with the use of HAART therapy is consistent with the impact of HAART on the immune status of patients with HIV or AIDs. To our knowledge, this is the first meta-analysis to evaluate the rate of relapse of TE in HIV-infected or AIDS patients, and specifically illustrates the benefits of HAART therapy for preventing relapse.
Relapse during maintenance therapy may result from a number of causes including treatment efficacy, dosing regimen, patient characteristics, and treatment adherence. The importance of the dosing regimen is indicated by our results that sugggest intermittent therapy administered two to three times per week was associated with a higher relapse rate compared with continuous therapy, and supports the NIH Guidelines of daily dosing of pyrimethamine plus sulfadiazine for maintenance treatment [Citation17].
The analysis described here focused on pyrimethamine-based therapy for the prevention of relapse due to the extensive history of the use of pyrimethamine in the clinic and the significant number of observational and retrospective clinical studies that have evaluated the effect of pyrimethamine-based therapy in treating TE. Much less-published information is available regarding the use of other off-label treatments for TE, such as the trimethoprim–sulfamethoxazole (TMP-SMX) combination. A similar search identified only five studies that evaluated TMP-SMX for maintenance therapy and reported relapse of HIV-infected patients with TE [Citation48,62−65], four of which were performed post-1996 [Citation62−65]. Across the five studies, the rate of TE relapse ranged from 3 to 39%.
Evidence from randomized controlled trials serve as the gold-standard for studies to be included in meta-analyses to reduce bias in the results. However, challenges exist in applying randomized control trial results to the real-world clinical setting due to differences between subjects recruited and the types of patients encountered in clinical practice [Citation66]. We included both prospective observational and retrospective studies due to the shortage of available randomized studies with pyrimethamine relative to the number of other study designs in TE. The inclusion of these studies in our analysis broadens the range of evidence and may improve the generalizability of the findings. This approach is consistent with other health service researchers who have included observational study designs in meta-analyses, and has been applied in other disease areas [Citation67,68].
The analysis described here has several limitations that are worth considering. Significant heterogeneity across studies was present with respect to study design, dosing regimen, and defintion of relapse, and the majority of studies were of mediumto-low quality. Also, the size of the patient population for the post-HAART analysis was small. Furthermore, not all patients were receiving HAART therapy for various reasons, and the results were not presented by HAART precluding an assessment of how this would influence results. Although, based on the analysis described here it is likely to have diminished effectiveness and increased likelihood of relapse. Reporting bias was also present which may have confounded the results. In addition, duration of follow-up varied between studies which could influence the rate of relapse. It is also important to emphasize that the proportions reported here are independently evaluated; therefore, it was not feasible to infer whether differences in relapse rates reported here are significantly different.
This study comprehensively evaluated the relapse rate of TE in patients with HIV or AIDS who received pyrimethamine-based maintenance therapy. The findings indicate that the incidence of relapse decreased after the introduction of HAART. The reduction in relapse following the introduction of HAART is consistent with the ability of HAART to control HIV infection. In addition, this study suggests that daily pyrimethamine-based maintenance therapy is likely more efficacious in preventing TE relapse compared with intermittent therapy. These findings have important medical and cost implications as relapse may affect a patient’s prognosis and healthcare resource utilization, and result in additional healthcare expenditure.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by Turing Pharmaceuticals.
Supplementary data
Supplemental data for this article can be accessed here.
YPGH_1273597_Supplemental_Material.zip
Download Zip (14.5 KB)Acknowledgment
The authors would like to thank Melissa Giraldo for assisting with the literature search, and Julio Casoy, MD and Rubben Ben-Harari, PhD for critically reading and reviewing the manuscript.
Related Research Data
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