New and future drug therapies for rheumatoid arthritis

Vigeo attenuates cartilage and bone destruction in a collagen‑induced arthritis mouse model by reducing production of pro‑inflammatory cytokines

Rheumatoid arthritis (RA) is an autoimmune and chronic inflammatory disease characterized by articular cartilage destruction, bone destruction and synovial hyperplasia. It has been suggested that Vigeo, a mixture of Eleutherococcus senticosus, Achyranthes japonica and Atractylodes japonica fermented with Korean nuruk, has an anti-osteoporotic effect in a mouse model of inflammation-mediated bone loss. The present study evaluated the therapeutic effects of Vigeo in RA using a collagen-induced arthritis (CIA) mouse model. DBA/1J mice were immunized with bovine type II collagen on days 0 and 21 and Vigeo was administered daily for 20 days beginning the day after the second type II collagen injection. The mice were sacrificed on day 42 and the joint tissues were anatomically separated and subjected to micro computed tomography and histological analyses. In addition, the serum levels of TNF-α, IL-6 and IL-1β were determined by enzyme-linked immunosorbent assays. CIA in DBA/1J mice caused symptoms of RA, such as joint inflammation, cartilage destruction and bone erosion. Treatment of CIA mice with Vigeo markedly decreased the symptoms and cartilage pathology. In addition, radiological and histological analyses showed that Vigeo attenuated bone and cartilage destruction. The serum TNF-α, IL-6 and IL-1β levels following oral Vigeo administration were also reduced when compared with those in CIA mice. The present study revealed that Vigeo suppressed arthritis symptoms in a CIA-RA mouse model, including bone loss and serum levels of TNF-α, IL-6 and IL-1β.

Maintenance use of non-steroidal anti-inflammatory drugs and risk of gastrointestinal cancer in a nationwide population-based cohort study in Sweden

OBJECTIVES

Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) are potential candidates for chemoprevention of gastrointestinal cancer. We aimed to assess the association between contemporary NSAID use (≥180 days) and gastrointestinal cancer.

DESIGN

Nationwide Swedish population-based cohort study (2005-2012).

SETTING

Sweden PARTICIPANTS: All adults exposed to maintenance NSAIDs use (aspirin, n=783 870; unselective NSAIDs, n=566 209, selective cyclo-oxygenase (COX)-2 inhibitors, n=17 948) compared with the Swedish background population of the same age, sex and calendar period.

OUTCOME MEASURES

The risk of different gastrointestinal cancer types expressed as standardised incidence ratios (SIR) and 95% CIs, taking into account concurrent proton pump inhibitors (PPIs) and statins usage.

RESULTS

The SIR for gastrointestinal cancer for aspirin use was 1.02 (95% CI 1.00 to 1.04), with clearly reduced risk for long-term users (SIR=0.31, 95% CI 0.30 to 0.33 for 5.5-7.7 years), but an increased risk for short-term users (SIR=2.77, 95% CI 2.69 to 2.85), and stronger protective effect for low-dose aspirin (SIR=0.86, 95% CI 0.85 to 0.88). Users of non-selective NSAIDs showed an overall decreased risk of gastrointestinal cancer (SIR=0.79, 95% CI 0.77 to 0.82), in particular for cancer of the stomach, colorectum and oesophagus, and the SIRs were further decreased among long-term users. Users of selective COX-2 inhibitors showed a SIR=0.89 (95% CI 0.73 to 1.09) for gastrointestinal cancers. Both aspirin and unselective NSAIDs users who also were using PPIs, had higher risks for all gastrointestinal cancer types; and lower risk if using statins.

CONCLUSION

Long-term use of (low-dose) aspirin and non-selective NSAIDs was associated with a decreased risk of all gastrointestinal cancer types.

The correlations of socioeconomic status, disease activity, quality of life, and depression/anxiety in Chinese patients with rheumatoid arthritis

This study aimed (i) to investigate the relationships among socioeconomic status, disease activity, quality of life, and the psychological status in Chinese rheumatoid arthritis (RA) patients; (ii) to explore the possible risk factors of anxiety and depression. A total of 160 RA patients underwent standardized laboratory examinations and completed several questionnaires. Independent samples t-tests, χ² analyses, and logistic regression modeling were used to analyze the data. We found 30.6% RA patients were anxiety, and 27.5% had depression, which were significantly higher than the control group (7.8 and 11.7%, respectively). And there were significant correlations among education, pain, disease activity, medication adherence, functional capacity, quality of life, and anxiety/depression. Meanwhile, logistic regression analysis revealed that poor quality of life and low education level were significantly associated with anxiety/depression in RA patients. In conclusion, there were significant relationships among education, quality of life, and anxiety/depression in Chinese RA patients.

Astragaloside IV suppresses inflammatory mediator production in synoviocytes and collagen‑induced arthritic rats

The aim of the current study was to investigate the effects of Astragaloside‑IV (AS‑IV) on inflammatory mediators in synoviocytes and collagen‑induced arthritic rats. Synoviocytes were stimulated with lipopolysaccharides (LPS) and Sprague‑Dawley rats were injected with type II collagen. AS‑IV was administered to the LPS‑stimulated synoviocytes and collagen‑induced arthritis (CIA) rats. The inflammation of LPS‑stimulated synoviocytes and CIA rats was assessed using enzyme‑linked immunosorbent assays and western blotting. Using Cell Counting Kit‑8 analysis, it was demonstrated that AS‑IV (5, 20 and 50 mg/ml) inhibited the LPS‑stimulated synoviocytes proliferation in a dose‑dependent manner. AS‑IV significantly inhibited the LPS‑stimulated inflammatory response, as indicated by the expression levels of TNF‑α, IL‑1β, IL‑6 and IL‑8. In addition, treatment with AS‑IV significantly reduced the LPS‑stimulated cyclooxygenase (COX)‑1, COX‑2, high mobility group box 1 protein (HMGB1) and intercellular adhesion molecule 1 overexpression, and intranuclear nuclear factor (NF)‑κBp65 subunit accumulation and activation of c‑Jun N‑terminal kinase (JNK)1/2 and p38. Similar to the protective effects of AS‑IV on LPS‑stimulated synoviocytes, AS‑IV treatment significantly reduced the expression levels of tumor necrosis factor α, interleukin (IL)‑1β, IL‑6 and IL‑8 expression levels, and attenuated intranuclear NF‑κBp65 subunit accumulation and overexpression of COX‑2 and inducible nitric oxide synthase in CIA rats. In conclusion, the results of the present study demonstrated for the first time, to the best of our knowledge, that AS‑IV protects synoviocytes against LPS‑ and collagen‑induced inflammatory responses through inhibition of the HMGB1‑dependent JNK1/2‑ and p38‑activated NF‑κB/COX‑2 pathway.

Tinospora cordifolia inhibits autoimmune arthritis by regulating key immune mediators of inflammation and bone damage

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation of the joints leading to tissue damage. Despite the availability of potent drugs including the biologics, many patients fail to respond to them, whereas others suffer adverse effects following long-term use of these drugs. Accordingly, the use of natural herbal products by RA patients has been increasing over the years. However, limited information about the mechanism of action of these natural products is a major shortcoming that prevents the widespread acceptance of herbal therapy by professionals and patients alike. In this study, we demonstrated the anti-arthritic activity of Tinospora cordifolia extract (TCE) using the rat adjuvant-induced arthritis model of human RA and elaborated the immune mechanisms underlying this effect. TCE treatment suppressed arthritic inflammation and bone and cartilage damage. The anti-inflammatory effect of TCE was mediated via reduction of the pro-inflammatory cytokines such as: IL-1β, TNF-α, IL-6, and IL-17; the frequency of IL-17-producing T cells; and the production of chemokines such as RANTES. Furthermore, TCE treatment limited bone damage by shifting the balance of mediators of bone remodeling (e.g., receptor activator of nuclear factor-kB ligand [RANKL] and MMP-9) in favor of anti-osteoclastic activity. Our results suggest that TCE and its bioactive components should be evaluated for their utility as therapeutic adjuncts to conventional drugs against RA.

Gene expression profiling of macrophages: implications for an immunosuppressive effect of dissolucytotic gold ions

Background

Gold salts has previously been used in the treatment of rheumatoid arthritis but have been replaced by biologicals such as TNF-α inhibitors. The mechanisms behind the anti-inflammatory effect of metallic gold ions are still unknown, however, recent data showed that charged gold atoms are released from pure metallic gold implants by macrophages via a dissolucytosis membrane, and that gold ions are taken up by local macrophages, mast cells and to some extent fibroblasts. These findings open the question of possible immunomodulatory effects of metallic gold and motivate efforts on a deeper understanding of the effect of metallic gold on key inflammatory cells as macrophages.

Methods

Human macrophage cells (cell line THP-1) were grown on gold foils and intracellular uptake was analysed by autometallography. The impact of phagocytised gold ions on viability of THP-1 cells was investigated by trypan blue staining and TUNEL assay. The global gene expression profile of THP-1 cells after incorporation of gold ions was studied using microarray analysis comprising approximately 20,000 genes. The gene expression data was confirmed by measurement of secreted proteins.

Results

Autometallography showed intracellular uptake of gold ions into THP-1 cells. No significant effect on viability of THP-1 cells was demonstrated. Our data revealed a unique gene expression signature of dissolucytotic THP-1 cells that had taken up gold ions. A large number of regulated genes were functionally related to immunomodulation. Gold ion uptake induced downregulation of genes involved in rheumatoid arthritis such as hepatocyte growth factor, tenascin-C, inhibitor of DNA binding 1 and 3 and matrix metalloproteinase 13.

Conclusion

The data obtained in this study offer new insights into the mode of action of gold ions and suggest for the investigation of effects on other key cells and a possible future role of metallic gold as implants in rheumatoid arthritis or other inflammatory conditions.

Immunomodulation of Autoimmune Arthritis by Herbal CAM

Rheumatoid arthritis (RA) is a debilitating autoimmune disease of global prevalence. The disease is characterized by synovial inflammation leading to cartilage and bone damage. Most of the conventional drugs used for the treatment of RA have severe adverse reactions and are quite expensive. Over the years, increasing proportion of patients with RA and other immune disorders are resorting to complementary and alternative medicine (CAM) for their health needs. Natural plant products comprise one of the most popular CAM for inflammatory and immune disorders. These herbal CAM belong to diverse traditional systems of medicine, including traditional Chinese medicine, Kampo, and Ayurvedic medicine. In this paper, we have outlined the major immunological pathways involved in the induction and regulation of autoimmune arthritis and described various herbal CAM that can effectively modulate these immune pathways. Most of the information about the mechanisms of action of herbal products in the experimental models of RA is relevant to arthritis patients as well. The study of immunological pathways coupled with the emerging application of genomics and proteomics in CAM research is likely to provide novel insights into the mechanisms of action of different CAM modalities.

Huo-Luo-Xiao-Ling Dan modulates antigen-directed immune response in adjuvant-induced inflammation

ETHNOPHARMACOLOGICAL RELEVANCE

HLXL is a traditional Chinese medicine that has long been used in folk medicine for the treatment of chronic inflammatory diseases. However, the precise immunological mechanisms by which HLXL mediates its anti-inflammatory activity are not fully defined.

AIM OF THE STUDY

To determine the effects of HLXL on antigen-specific immune parameters in adjuvant-induced inflammation model in the Lewis rat.

MATERIALS AND METHODS

Rats were fed daily with either HLXL (2.3g/kg) or vehicle (water) beginning 3 days before subcutaneous injection of heat-killed Mycobacterium tuberculosis H37Ra (Mtb), and then continued for another 6 days. After 9 days of Mtb injection, the draining lymph node cells were tested for T cell proliferative and cytokine responses against mycobacterial heat-shock protein 65 (Bhsp65). Moreover, sera were tested for anti-Bhsp65 antibodies and nitric oxide (NO).

RESULTS

HLXL-treated rats showed reduced T cell proliferative response to Bhsp65 compared to control rats. Furthermore, HLXL suppressed IL-17 response but enhanced IL-10 response without much effect on IFN-gamma. HLXL treatment also reduced the levels of anti-Bhsp65 antibodies but not that of NO.

CONCLUSIONS

HLXL feeding modulated both the cellular and the humoral immune response to Bhsp65 favoring an anti-inflammatory milieu for the suppression of adjuvant-induced inflammation.

Effects of disease-modifying anti-rheumatic drugs (DMARDs) on the activities of rheumatoid arthritis-associated cathepsins K and S

Rheumatoid arthritis is an inflammatory and disabling joint disease affecting 0.5-1.5% of the population. Although various anti-inflammatory (NSAIDs) and disease-modifying (DMARDs) drugs are in clinical use, their precise mechanisms of action are not always defined. In this report, we discuss the effects of widely used DMARDs such as gold derivatives and chloroquine on cathepsins K and S, which have been implicated as critical mediators of inflammation and joint erosion in rheumatoid arthritis. We demonstrate that clinically potent gold derivatives inhibit cathepsins K and S in in vitro and cell-based assays. An X-ray analysis of the gold thiomalate/cathepsin K complex reveals that the inhibitor is bound to the active-site cysteine residue of the protease. Chloroquine, a lysosomotropic agent of lower clinical potency than gold derivatives, inhibits neutral pH-labile cathepsins intracellularly, but does not affect the neutral pH-stable cathepsin S. The potent inhibition of cathepsins implicated in the pathogenesis of rheumatoid arthritis by gold derivatives may explain the therapeutic efficacy of these drugs.

Alternative Decision Analysis Modeling in the Economic Evaluation of Tumor Necrosis Factor Inhibitors for Rheumatoid Arthritis

OBJECTIVES

To provide a review of the studies that use decision models in the economic evaluation of tumor necrosis factor (TNF) inhibitors in rheumatoid arthritis (RA) and to address some important issues surrounding the choice of such modeling techniques in these economic evaluations.

METHODS

A systematic literature search was conducted by 1 author from the literature published from January 1996 to March 2005 through Medline, Embase, and Cochrane library databases.

RESULTS

The review yielded 29 studies that used decision models. Only 10 studies used a decision model in the economic analysis of the TNF inhibitors and were included in the final review. Decision model types included the following in the review articles: decision tree (2), Markov model (7), and discrete event simulation (1). These models vary in complexity and their choice depends on the course of disease, the impact of treatment, and the available data.

CONCLUSIONS

Based on the results derived from alternative modeling techniques, it is safe to say that all methods can provide useful information with regard to economic evaluations of TNF inhibitors. Even though different modeling techniques provide an appropriate representation of available data, their results should be interpreted contingent on the input data, assumptions, sensitivity analyses, and other alternative scenario analyses.

RELEVANCE

The transparency in the models will encourage end users such as policymakers and prescribers to make informed judgments regarding the appropriateness of the methods and the validity of the results.

Health services research in rheumatology: a great deal accomplished, a great deal left to do

Although rheumatology has been on the cutting edge of health services research for decades, there are many unresolved issues for patients, clinicians, insurers, and policy makers. This article explore three areas in which methodologic controversies present tradeoffs to a health care system that is grappling with larger issues around cost and access to care. Specifically, we examine issues around the use of large databases, the appropriate instruments for measuring patient-centered outcomes, and the questions that are raised from cost effectiveness studies of new treatments for rheumatoid arthritis. The issues are presented in the context of a need to provide better information to those who are providing care and those who are paying for it.

Pursuit of optimal outcomes in rheumatoid arthritis

The aim of this review is to describe methods of quantifying disease activity and symptomatology and discuss treatment goals for rheumatoid arthritis (RA). The benefits and limitations of existing therapeutic approaches, the importance of early therapy in preventing disease progression and the place of biologicals in early therapy will be discussed. Disease activity and symptomatology in RA are often measured using a set of core endpoints that incorporate pain, patient global assessment, physical disability, swollen joints, tender joints, acute phase reactants, physician global assessment and radiographic imaging of joints. Imaging of joints is the only means by which to measure the effects of disease-modifying antirheumatic drugs (DMARDs) on the irreversible joint damage that occurs during RA. There is increasing evidence that this damage and its functional consequences occur early in the onset of disease. The consensus is that patients with RA should be treated with DMARDs earlier rather than later in the disease process. Remission, or a state of sustained response or low disease activity that is not damaging or disabling, is the ideal goal of therapy for RA, but formal criteria defining a state of remission need to be revised and, ideally, updated to include a radiographic component. Currently available DMARDs are limited in their ability to achieve early, sustained response or remission, by delayed onset of action, cumulative toxicity and lack of long-term therapeutic response. It is hoped that the emergence of novel DMARDs--targeted biological agents, such as anti-tumour necrosis factor-alpha (anti-TNF-alpha)--will help to counteract such limitations and will allow early DMARD use to be adopted as standard practice in place of their use as a last resort therapy after failure of other treatment. One such biological agent, etanercept, has been shown to reduce radiographic disease progression and induce overall clinical response during the early stages of RA. It is significantly more effective and fast-acting than methotrexate, one of the most effective, commonly used DMARDs.

A rat model for testing pharmacologic treatments of pressure-related bone loss

Fluid pressure, instability, or particles have been suggested to initiate the process leading to loosening of prosthetic implants. In a rat model where bone resorption is caused by oscillating fluid pressure, the resorptive response seems much stronger than the response that can be induced by particles or instability. Bone resorption is caused by osteoclasts. It has been suggested that the formation of osteoclasts is influenced by tumor necrosis factor-alpha, which can be blocked by etanercept. Osteoclasts can be inactivated with bisphosphonates, which bind to bone and inactivate osteoclasts when the bisphosphonate-containing bone is resorbed. Bone formation can be increased dramatically by intermittent parathyroid hormone treatment, especially at sites with high bone turnover. This might compensate for increased osteoclastic activity. Forty-two rats received a plate implant, by which fluid pressure was applied to a bone surface by compressing a soft tissue membrane. Eight rats were treated with etanercept 0.75 mg/kg/day, six rats were treated with alendronate 205 microg/kg/day, six rats received saline, and six rats were nonpressurized controls. Nine rats received intermittent parathyroid hormone treatment with nine separate controls. The area of bone resorption under the implant was evaluated by histomorphometry. Alendronate-treated rats showed less bone resorption, but etanercept, intermittent parathyroid hormone treatment, or saline did not reduce the fluid pressure-induced bone resorption. This model is a comparatively simple way of testing pharmacologic reduction of local bone resorption in vivo.

Leflunomide for treating rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease. Leflunomide, as an inhibitor of pyrimidine synthesis, has a different mechanism of action than other existing disease modifying anti-rheumatic drugs (DMARD).

OBJECTIVES

To determine the efficacy and toxicity of leflunomide compared to placebo or other DMARDs in the treatment of RA.

SEARCH STRATEGY

We conducted a search in MEDLINE, EMBASE, Current Contents and the Cochrane Controlled Trial Register for trials up to December 2001. We also hand-searched reference lists and consulted content experts.

SELECTION CRITERIA

Two independent reviewers selected the trials that met predetermined inclusion criteria.

DATA COLLECTION AND ANALYSIS

Two independent reviewers extracted data and assessed methodologic quality using standardized forms.

MAIN RESULTS

Six trials were included in this review. Using the ACR20 improvement criteria, there was an absolute difference in improvement of 28% (95% confidence interval: 21 - 35%) favouring leflunomide (232 out of 413 leflunomide treated patients compared to 89 out of 311 placebo patients met the criteria). There was no difference in ACR20 response rate between the patients treated with leflunomide and SSZ or MTX at 6 and 12 months. Other clinical outcomes were improved significantly in the leflunomide group compared to placebo but not different from SSZ or MTX. Withdrawals due to adverse events with leflunomide were 10% greater than placebo (70 out of 416 compared to 18 out of 311 respectively). Important adverse events included gastrointestinal symptoms, elevated liver function tests, alopecia, and infections. Overall adverse events and withdrawals in the leflunomide group were not significantly different from SSZ or MTX.

REVIEWER'S CONCLUSIONS

Leflunomide appears to improve all clinical outcomes and delay radiologic progression at both 6 and 12 months of treatment compared to placebo. Its efficacy and adverse events at 2 years of treatment are comparable to SSZ and MTX. Long-term efficacy and toxicity remains to be established.

Serum interleukin 2 levels in patients with rheumatoid arthritis and correlation with insulin sensitivity

Interleukin 2 (IL-2), a Th1 lymphocyte-derived cytokine, is thought to play an important role in the pathogenesis of type 2 diabetes and rheumatoid arthritis (RA). The aim of our study was to evaluate changes in serum IL-2 levels and their correlation with glucose metabolism abnormalities, such as insulin resistance, in patients with RA. Thirty-six subjects with varying degrees of disease activity and 20 healthy age-, sex- and body mass index-matched control individuals were evaluated. Patients with any causes of peripheral insulin resistance were excluded. After a 12-h overnight fast, fasting insulin levels, homeostatic model assessment-insulin resistance (HOMA-IR) estimated insulin sensitivity, and serum IL-2 levels were significantly higher in all patients with RA than in the control individuals. Fasting insulin, HOMA-IR scores and IL-2 levels were correlated in the RA group. This study showed that patients with RA have altered IL-2 regulation, and that there was a significant correlation between serum IL-2 levels and insulin sensitivity.

Psychological interventions for rheumatoid arthritis: a meta-analysis of randomized controlled trials

OBJECTIVE

To carry out a systematic review of the literature examining the efficacy of psychological interventions (e.g., relaxation, biofeedback, cognitive-behavioral therapy) in the treatment of rheumatoid arthritis (RA).

METHODS

Studies that met the following criteria were included: random assignment, wait-list or usual care control condition; publication in peer-reviewed journals; treatment that included some psychological component beyond simply providing education information; and separate data provided for patients with RA if subjects with conditions other than RA were included. Two investigators independently extracted data on study design, sample size and characteristics, type of intervention, type of control, direction and nature of the outcome(s).

RESULTS

Twenty-five trials met the inclusion criteria. Methodologic quality was assessed, and effect sizes were calculated for 6 outcomes. Significant pooled effect sizes were found postintervention for pain (0.22), functional disability (0.27), psychological status (0.15), coping (0.46), and self efficacy (0.35). At followup (averaging 8.5 months), significant pooled effect sizes were observed for tender joints (0.33), psychological status (0.30), and coping (0.52). No clear or consistent patterns emerged when effect sizes for different types of treatment and control conditions were compared, or when higher quality trials were compared to lower quality ones. Findings do, however, suggest that these psychological interventions may be more effective for patients who have had the illness for shorter duration.

CONCLUSIONS

Despite some methodologic flaws in the literature, psychological interventions may be important adjunctive therapies in the medical management of RA.

Neuroimmune alterations in the complex regional pain syndrome

This review focuses on some clinical aspects of the complex regional pain syndrome, such as oedema, local temperature changes and chronic pain, as a result of supposed neurogenic inflammation. Involvement of the immune system could imply the subsequent release of neuropeptides, pro-inflammatory cytokines and eicosanoids, which in turn leads to a complex cross-talk of primary and secondary generated mediators of inflammation. The development and application of drugs that act through selective receptor antagonism or enzymatic synthesis inhibition to prevent further stimulation of this cascade that could inevitably lead to chronicity of this disease are extensively discussed.

Pituitary adenylate cyclase-activating polypeptide inhibits collagen-induced arthritis: an experimental immunomodulatory therapy

Rheumatoid arthritis is a chronic, systemic, autoimmune, and inflammatory disorder that affects the synovial lining of the joints. We describe the beneficial effects of the pituitary adenylate cyclase-activating polypeptide (PACAP) in the collagen-induced arthritis experimental murine model being proposed as a novel therapeutic approach in the treatment of rheumatoid arthritis. PACAP greatly decreases arthritis frequency and severity in the studied mice by improving clinical symptoms, ameliorating joint damage, and blocking both the inflammatory and autoimmune mediators which are the main keys of the pathogenesis of this disease. With this study, PACAP emerges as a promising candidate for the treatment of a pathology with a high world incidence but currently no effective treatment.

Combination therapy in rheumatoid arthritis

It has become clear that early suppression of rheumatoid arthritis disease activity is important in preventing progressive joint destruction and functional decline. To achieve this goal, many rheumatologists today advocate a more aggressive approach, using combinations of classic disease-modifying antirheumatic drugs-often including methotrexate-or new drugs. During the last 2 years, the combination of methotrexate, sulfasalazine, hydroxychloroquine, and prednisolone has been demonstrated to be more beneficial than monotherapy in patients with early rheumatoid arthritis. In addition, the superior efficacy of the combination of new tumor necrosis factor-alpha blocking agents plus methotrexate to methotrexate alone in patients with chronic disease is very promising. Most studies of combination therapy focus on the efficacy of a combination compared with monotherapy, rather than on the efficacy of a treatment strategy. Although these studies of combination therapy provide useful information about the possible synergistic action of combinations of drugs, many questions remain unanswered, and studies evaluating different treatment strategies are needed before a new approach can be suggested.