Olsalazine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in inflammatory bowel disease

Current Pharmacologic Options and Emerging Therapeutic Approaches for the Management of Ulcerative Colitis: A Narrative Review

Introduction

Ulcerative colitis (UC) is a chronic inflammatory bowel disorder (IBD) with periods of relapse and remission. Current advancements in clinical research have led to the development of more refined and effective medical therapy for UC.

Summary of the Evidence

Traditional therapeutic agents such as 5-aminosalicylates (5-ASAs), sulfasalazine (SASP), corticosteroids, and immunomodulatory drugs have remained the gold standard for decades. However, their novel formulations and dosage regimens have changed their sequences in the medical management of UC. Several other novel drugs are in the final phases of clinical development or have recently received regulatory approval designed to target specific mechanisms involved in the inflammatory cascade for UC.

Conclusions

This narrative review sought to provide a comprehensive knowledge of the potential benefits of standard and emerging therapies, including novel formulations, new chemical entities, and novel therapeutic approaches in managing UC. Keywords: Ulcerative colitis, 5- Aminosalicylic acid, sulfasalazine, corticosteroids, biologics, immunomodulators, novel formulations.

Understanding the Impacts of Presystemic Metabolism on the Human Oral Bioavailability of Chemicals

Animal-free new approach methods promote chemical assessments based on the comparison between in vitro bioactivity and human internal concentrations, which necessitates a dependable knowledge of human oral bioavailability, i.e., the fraction of an orally ingested chemical that escapes from presystemic ("first-pass") metabolic processes and eventually enters systemic circulation. Using a physiologically based toxicokinetic model, we show how human oral bioavailability is impacted by presystemic metabolism within the gut lumen, gut wall, and liver and how this impact differs among chemicals with various permeability and stability properties. Our results highlight the gut lumen as a primary site of presystemic metabolism of certain chemicals, such as di-2-ethylhexyl phthalate (DEHP), for which the gut lumen may even exceed the liver in importance of presystemic metabolism due to these metabolic processes occurring in sequence. For chemicals with low transmembrane permeability and low stability, metabolism within the gut lumen is the most remarkable of the three presystemic metabolic processes. Notably, for chemicals that undergo substantial metabolism within the gut lumen, where the metabolites have high permeability, there is a notable discrepancy between the "theoretical bioavailability" (bioavailability of the unchanged parent compound) and the "apparent bioavailability" in measurement practices (bioavailability inferred from measured metabolites). Our work highlights the importance of considering presystemic metabolism, notably within the gut lumen, in human exposure and toxicokinetic modeling.

The aminosalicylate - folate connection

Two aminosalicylate isomers have been found to possess useful pharmacological behavior: p-aminosalicylate (PAS, 4AS) is an anti-tubercular agent that targets M. tuberculosis, and 5-aminosalicylate (5AS, mesalamine, mesalazine) is used in the treatment of ulcerative colitis (UC) and other inflammatory bowel diseases (IBD). PAS, a structural analog of pABA, is biosynthetically incorporated by bacterial dihydropteroate synthase (DHPS), ultimately yielding a dihydrofolate (DHF) analog containing an additional hydroxyl group in the pABA ring: 2'-hydroxy-7,8-dihydrofolate. It has been reported to perturb folate metabolism in M. tuberculosis, and to selectively target M. tuberculosis dihydrofolate reductase (mtDHFR). Studies of PAS metabolism are reviewed, and possible mechanisms for its mtDHFR inhibition are considered. Although 5AS is a more distant structural relative of pABA, multiple lines of evidence suggest a related role as a pABA antagonist that inhibits bacterial folate biosynthesis. Structural data support the likelihood that 5AS is recognized by the DHPS pABA binding site, and its effects probably range from blocking pABA binding to formation of a dead-end dihydropterin-5AS adduct. These studies suggest that mesalamine acts as a gut bacteria-directed antifolate, that selectively targets faster growing, more folate-dependent species.

Mechanisms and Clinical Implications of Human Gut Microbiota-Drug Interactions in the Precision Medicine Era

The human gut microbiota, comprising trillions of microorganisms residing in the gastrointestinal tract, has emerged as a pivotal player in modulating various aspects of human health and disease. Recent research has shed light on the intricate relationship between the gut microbiota and pharmaceuticals, uncovering profound implications for drug metabolism, efficacy, and safety. This review depicted the landscape of molecular mechanisms and clinical implications of dynamic human gut Microbiota-Drug Interactions (MDI), with an emphasis on the impact of MDI on drug responses and individual variations. This review also discussed the therapeutic potential of modulating the gut microbiota or harnessing its metabolic capabilities to optimize clinical treatments and advance personalized medicine, as well as the challenges and future directions in this emerging field.

Microbial metabolism marvels: a comprehensive review of microbial drug transformation capabilities

This comprehensive review elucidates the pivotal role of microbes in drug metabolism, synthesizing insights from an exhaustive analysis of over two hundred papers. Employing a structural classification system grounded in drug atom involvement, the review categorizes the microbiome-mediated drug-metabolizing capabilities of over 80 drugs. Additionally, it compiles pharmacodynamic and enzymatic details related to these reactions, striving to include information on encoding genes and specific involved microorganisms. Bridging biochemistry, pharmacology, genetics, and microbiology, this review not only serves to consolidate diverse research fields but also highlights the potential impact of microbial drug metabolism on future drug design and in silico studies. With a visionary outlook, it also lays the groundwork for personalized medicine interventions, emphasizing the importance of interdisciplinary collaboration for advancing drug development and enhancing therapeutic strategies.

The Interplay between Gut Microbiota and Oral Medications and Its Impact on Advancing Precision Medicine

Trillions of diverse microbes reside in the gut and are deeply interwoven with the human physiological process, from food digestion, immune system maturation, and fighting invading pathogens, to drug metabolism. Microbial drug metabolism has a profound impact on drug absorption, bioavailability, stability, efficacy, and toxicity. However, our knowledge of specific gut microbial strains, and their genes that encode enzymes involved in the metabolism, is limited. The microbiome encodes over 3 million unique genes contributing to a huge enzymatic capacity, vastly expanding the traditional drug metabolic reactions that occur in the liver, manipulating their pharmacological effect, and, ultimately, leading to variation in drug response. For example, the microbial deactivation of anticancer drugs such as gemcitabine can lead to resistance to chemotherapeutics or the crucial role of microbes in modulating the efficacy of the anticancer drug, cyclophosphamide. On the other hand, recent findings show that many drugs can shape the composition, function, and gene expression of the gut microbial community, making it harder to predict the outcome of drug-microbiota interactions. In this review, we discuss the recent understanding of the multidirectional interaction between the host, oral medications, and gut microbiota, using traditional and machine-learning approaches. We analyze gaps, challenges, and future promises of personalized medicine that consider gut microbes as a crucial player in drug metabolism. This consideration will enable the development of personalized therapeutic regimes with an improved outcome, ultimately leading to precision medicine.

Design, Development, and Optimisation of Smart Linker Chemistry for Targeted Colonic Delivery-In Vitro Evaluation

Drug targeting is necessary to deliver drugs to a specific site of action at a rate dictated by therapeutic requirements. The pharmacological action of a drug can thereby be optimised while minimising adverse effects. Numerous colonic drug delivery systems have been developed to avoid such undesirable side effects; however, these systems lack site specificity, leaving room for further improvement. The objective of the present study was to explore the potential of amino-alkoxycarbonyloxymethyl (amino-AOCOM) ether prodrugs as a general approach for future colonic delivery. To circumvent inter- and intra-subject variabilities in enzyme activities, these prodrugs do not rely on enzymes but rather are activated via a pH-triggered intramolecular cyclisation−elimination reaction. As proof of concept, model compounds were synthesised and evaluated under various pH conditions, simulating various regions of the gastrointestinal tract (GIT). Probe 15 demonstrated excellent stability under simulated stomach- and duodenum-like conditions and protected 60% of the payload in a small intestine-like environment. Moreover, 15 displayed sustained release at colonic pH, delivering >90% of the payload over 38 h. Mesalamine (Msl) prodrugs 21 and 22 were also synthesised and showed better stability than probe 15 in the simulated upper GIT but relatively slower release at colonic pH (61−68% of Msl over 48 h). For both prodrugs, the extent of release was comparable to that of the commercial product Asacol. This study provides initial proof of concept regarding the use of a cyclisation-activated prodrug for colon delivery and suggests that release characteristics still vary on a case-by-case basis.

Colonic drug delivery: Formulating the next generation of colon-targeted therapeutics

Colonic drug delivery can facilitate access to unique therapeutic targets and has the potential to enhance drug bioavailability whilst reducing off-target effects. Delivering drugs to the colon requires considered formulation development, as both oral and rectal dosage forms can encounter challenges if the colon's distinct physiological environment is not appreciated. As the therapeutic opportunities surrounding colonic drug delivery multiply, the success of novel pharmaceuticals lies in their design. This review provides a modern insight into the key parameters determining the effective design and development of colon-targeted medicines. Influential physiological features governing the release, dissolution, stability, and absorption of drugs in the colon are first discussed, followed by an overview of the most reliable colon-targeted formulation strategies. Finally, the most appropriate in vitro, in vivo, and in silico preclinical investigations are presented, with the goal of inspiring strategic development of new colon-targeted therapeutics.

Pharmacokinetic and gut microbiota analyses revealed the effect of Lactobacillus acidophilus on the metabolism of Olsalazine in ulcerative colitis rats

Olsalazine is a typical 5-aminosalicylic acid (5-ASA) drug that depends on gut microbiota to liberate its anti-inflammatory moiety 5-ASA in the treatment of ulcerative colitis (UC). In recent decades, 5-ASA drugs combined with probiotics have achieved a better effective treatment for UC. Mechanisms of combination therapy have been widely discussed from a pharmacodynamic perspective. However, it is still unclear whether the better therapeutic efficacy of combination therapy was made by changing the metabolism of 5-ASA drugs in the colon under the regulation of probiotics. In the present study, combined with pharmacokinetic and gut microbiota analyses, we systematically evaluated the potential effect of Lactobacillus acidophilus (L. acidophilus) on the metabolism of Olsalazine at three levels (pharmacokinetic characteristics, metabolic microbiota, and metabolic enzymes) to offer some insights into this issue. As pharmacokinetic results showed, L. acidophilus barely had an influence on the pharmacokinetic parameters of Olsalazine, 5-ASA, and N-Ac-5-ASA. Notably, the colonic exposure of 5-ASA was not affected by L. acidophilus. Gut microbiota results also illustrated that L. acidophilus did not change the total abundance of azoreductase (azoR) and N-acetyltransferase (NAT) associated gut microbiota and enzymes, which are involved in the metabolism of Olsalazine. Both pharmacokinetic and gut microbiota results revealed that L. acidophilus did not increase the colonic exposure of 5-ASA to improve the efficacy of combination therapy. L. acidophilus played its role in UC treatment by regulating gut microbiota composition and amino acid, phenolic acid, oligosaccharide, and peptidoglycan metabolic pathways. There was no potential medication risk of combination therapy of Olsalazine and L. acidophilus. In summary, this research provided strong evidence of medication safety and a comprehensive understanding of therapeutic advantages for combination therapy of probiotics and 5-ASA drugs from the pharmacokinetic and gut microbiota perspectives.

Clinical translation of advanced colonic drug delivery technologies

Targeted drug delivery to the colon offers a myriad of benefits, including treatment of local diseases, direct access to unique therapeutic targets and the potential for increasing systemic drug bioavailability and efficacy. Although a range of traditional colonic delivery technologies are available, these systems exhibit inconsistent drug release due to physiological variability between and within individuals, which may be further exacerbated by underlying disease states. In recent years, significant translational and commercial advances have been made with the introduction of new technologies that incorporate independent multi-stimuli release mechanisms (pH and/or microbiota-dependent release). Harnessing these advanced technologies offers new possibilities for drug delivery via the colon, including the delivery of biopharmaceuticals, vaccines, nutrients, and microbiome therapeutics for the treatment of both local and systemic diseases. This review details the latest advances in colonic drug delivery, with an emphasis on emerging therapeutic opportunities and clinical technology translation.

Pectin based multi-particulate carriers for colon-specific delivery of therapeutic agents

In case of colon-specific delivery of therapeutic agents through oral route, microbial/enzyme-triggered release approach has several advantages over other approaches due to unique microbial ecosystem in the colon. Multiple-unit carriers have an edge over single-unit carriers for this purpose. Among different materials/polymers explored, pectin appears as a promising biopolymer to construct microbial-triggered colon-specific carriers. Pectin is specifically degraded by colonic enzymes but insusceptible to upper gastro-intestinal enzymes. In this article, utilization of pectin solely or in combination with other polymers and/or colonic-delivery approaches is critically discussed in detail in the context of multi-particulate systems. Several studies showed that pectin-based carriers can prevent the release of payload in the stomach but start to release in the intestine. Hence, pectin alone may construct delayed release formulation but may not be sufficient for effective colon-targeting. On the other hand, combination of pectin with other materials/polymers (e.g., chitosan and Eudragit® S-100) has demonstrated huge promise for colon-specific release of payload. Hence, smartly designed pectin-based multi-particulate carriers, especially in combination with other polymers and/or colon-targeting approaches (e.g., microbial-triggered + pH-triggered or microbial-triggered + pH-triggered + time-release or microbial-triggered + pH-triggered + pressure-based), can be successful colon-specific delivery systems. However, more clinical trials are necessary to bring this idea from bench to bedside.

Microbiota and Drug Response in Inflammatory Bowel Disease

A mutualistic relationship between the composition, function and activity of the gut microbiota (GM) and the host exists, and the alteration of GM, sometimes referred as dysbiosis, is involved in various immune-mediated diseases, including inflammatory bowel disease (IBD). Accumulating evidence suggests that the GM is able to influence the efficacy of the pharmacological therapy of IBD and to predict whether individuals will respond to treatment. Additionally, the drugs used to treat IBD can modualate the microbial composition. The review aims to investigate the impact of the GM on the pharmacological therapy of IBD and vice versa. The GM resulted in an increase or decrease in therapeutic responses to treatment, but also to biotransform drugs to toxic metabolites. In particular, the baseline GM composition can help to predict if patients will respond to the IBD treatment with biologic drugs. On the other hand, drugs can affect the GM by incrementing or reducing its diversity and richness. Therefore, the relationship between the GM and drugs used in the treatment of IBD can be either beneficial or disadvantageous.

Gut microbiota-driven drug metabolism in inflammatory bowel disease

BACKGROUND AND AIMS

The gut microbiota plays an important role in the metabolization and modulation of several types of drugs. With this study we aimed to review the literature about microbial drug metabolism of medication prescribed in inflammatory bowel disease practice.

METHODS

A systematic literature search was performed in Embase and PubMed from inception to October 2019. The search was conducted with predefined MeSH/Emtree and text terms. All studies about drug metabolism by microbiota of medication prescribed in inflammatory bowel disease practice were eligible. A total of 1018 records were encountered and 89 articles were selected for full text reading.

RESULTS

Intestinal bacterial metabolism or modulation is of influence in four specific drugs used in inflammatory bowel disease (mesalazines, methotrexate, glucocorticoids and thioguanine). The gut microbiota cleaves the azo-bond of sulfasalazine, balsalazide and olsalazine and releases the active moiety 5-aminosalicylic acid. It has an impact on the metabolization and potentially on the response of methotrexate therapy. Especially thioguanine can be converted by intestinal bacteria into the pharmacological active 6-thioguanine nucleotides without the requirement of host metabolism. Glucocorticoid compounds can be prone to bacterial degradation.

CONCLUSION

The human intestinal microbiota can have a major impact on drug metabolism and efficacy of medication prescribed in inflammatory bowel disease practice. A better understanding of these interactions between microbiota and drugs is needed and should be an integral part of the drug development pathway of new inflammatory bowel disease medication.

Mechanisms of gastrointestinal microflora on drug metabolism in clinical practice

Considered as an essential "metabolic organ", intestinal microbiota plays a key role in human health and the predisposition to diseases. It is an aggregate genome of trillions of microorganisms residing in the human gastrointestinal tract. Since the 20th century, researches have showed that intestinal microbiome possesses a variety of metabolic activities that are able to modulate the fate of more than 30 approved drugs and immune checkpoint inhibitors. These drugs are transformed to bioactive, inactive, or toxic metabolites by microbial direct action or host-microbial co-metabolism. These metabolites are responsible for therapeutic effects exerted by these drugs or side effects induced by these drugs, even for death. In view of the significant effect on the drugs metabolism by the gut microbiota, it is pivotal for personalized medicine to explore additional drugs affected by gut microbiota and their involved strains for further making mechanism clear through suitable animal models. This review mainly focus on specific mechanisms involved, with reference to the current literature about drugs metabolism by related bacteria or its enzymes available.

Effects of Gut Microbiota on Drug Metabolism and Guidance for Rational Drug Use Under Hypoxic Conditions at High Altitudes

BACKGROUND

Modern features of drug development such as low permeability, low solubility, and improved release affect the interplay of the gut microbiota and drug metabolism. In recent years, studies have established the impact of plateau hypoxia on gut microbiota, where drug use by plateau populations is affected by hypoxia- induced changes in intestinal microflora-mediated drug metabolism.

METHODS

In this review, we summarized the effects of gut microbiota on drug metabolism, and of plateau hypoxia on the intestinal flora, with the aim of providing guidance for the rational use of drugs in high-altitude populations.

RESULTS

The evidence clearly shows that alterations in gut microbiota can affect pro-drug activation, drug inactivation, and the biotransformation of xenobiotics. Additionally, plateau hypoxia alters drug metabolism by affecting intestinal flora.

CONCLUSION

This review provides an overview of the effects of gut microbiota on drug metabolism and provides guidance for rational drug use under hypoxic conditions at high altitudes.

The Role of the Human Microbiome in Chemical Toxicity

There is overwhelming evidence that the microbiome must be considered when evaluating the toxicity of chemicals. Disruption of the normal microbial flora is a known effect of toxic exposure, and these disruptions may lead to human health effects. In addition, the biotransformation of numerous compounds has been shown to be dependent on microbial enzymes, with the potential for different host health outcomes resulting from variations in the microbiome. Evidence suggests that such metabolism of environmental chemicals by enzymes from the host's microbiota can affect the toxicity of that chemical to the host. Chemical-microbial interactions can be categorized into two classes: Microbiome Modulation of Toxicity (MMT) and Toxicant Modulation of the Microbiome (TMM). MMT refers to transformation of a chemical by microbial enzymes or metabolites to modify the chemical in a way that makes it more or less toxic. TMM is a change in the microbiota that results from a chemical exposure. These changes span a large magnitude of effects and may vary from microbial gene regulation, to inhibition of a specific enzyme, to the death of the microbes. Certain microbiomes or microbiota may become associated with different health outcomes, such as resistance or susceptibility to exposure to certain toxic chemicals, the ability to recover following a chemical-induced injury, the presence of disease-associated phenotypes, and the effectiveness of immune responses. Future work in toxicology will require an understanding of how the microbiome interacts with toxicants to fully elucidate how a compound will affect a diverse, real-world population.

Effects of Drugs and Excipients on Hydration Status

Despite being the most essential nutrient, water is commonly forgotten in the fields of pharmacy and nutrition. Hydration status is determined by water balance (the difference between water input and output). Hypohydration or negative water balance is affected by numerous factors, either internal (i.e., a lack of thirst sensation) or external (e.g., polypharmacy or chronic consumption of certain drugs). However, to date, research on the interaction between hydration status and drugs/excipients has been scarce. Drugs may trigger the appearance of hypohydration by means of the increase of water elimination through either diarrhea, urine or sweat; a decrease in thirst sensation or appetite; or the alteration of central thermoregulation. On the other hand, pharmaceutical excipients induce alterations in hydration status by decreasing the gastrointestinal transit time or increasing the gastrointestinal tract rate or intestinal permeability. In the present review, we evaluate studies that focus on the effects of drugs/excipients on hydration status. These studies support the aim of monitoring the hydration status in patients, mainly in those population segments with a higher risk, to avoid complications and associated pathologies, which are key axes in both pharmaceutical care and the field of nutrition.

Gut microbiota modulates drug pharmacokinetics

Gut microbiota, one of the determinants of pharmacokinetics, has long been underestimated. It is now generally accepted that the gut microbiota plays an important role in drug metabolism during enterohepatic circulation either before drug absorption or through various microbial enzymatic reactions in the gut. In addition, some drugs are metabolized by the intestinal microbiota to specific metabolites that cannot be formed in the liver. More importantly, metabolizing drugs through the gut microbiota prior to absorption can alter the systemic bioavailability of certain drugs. Therefore, understanding intestinal flora-mediated drug metabolism is critical to interpreting changes in drug pharmacokinetics. Here, we summarize the effects of gut microbiota on drug pharmacokinetics, and propose that the influence of intestinal flora on pharmacokinetics should be organically related to the therapeutic effects and side effects of drugs. More importantly, we could rationally perform the strategy of intestinal microflora-mediated metabolism to design drugs.

Human gut microbiota plays a role in the metabolism of drugs

BACKGROUND AND AIMS

The gut microbiome, an aggregate genome of trillions of microorganisms residing in the human gastrointestinal tract, is now known to play a critical role in human health and predisposition to disease. It is also involved in the biotransformation of xenobiotics and several recent studies have shown that the gut microbiota can affect the pharmacokinetics of orally taken drugs with implications for their oral bioavailability.

METHODS

Review of Pubmed, Web of Science and Science Direct databases for the years 1957-2016.

RESULTS AND CONCLUSIONS

Recent studies make it clear that the human gut microbiota can play a major role in the metabolism of xenobiotics and, the stability and oral bioavailability of drugs. Over the past 50 years, more than 30 drugs have been identified as a substrate for intestinal bacteria. Questions concerning the impact of the gut microbiota on drug metabolism, remain unanswered or only partially answered, namely (i) what are the molecular mechanisms and which bacterial species are involved? (ii) What is the impact of host genotype and environmental factors on the composition and function of the gut microbiota, (iii) To what extent is the composition of the intestinal microbiome stable, transmissible, and resilient to perturbation? (iv) Has past exposure to a given drug any impact on future microbial response, and, if so, for how long? Answering such questions should be an integral part of pharmaceutical research and personalised health care.

Aminosalicylates for induction of remission or response in Crohn's disease

BACKGROUND

Randomized trials investigating the efficacy of aminosalicylates for the treatment of mildly to moderately active Crohn's disease have yielded conflicting results. A systematic review was conducted to critically examine current available data on the efficacy of sulfasalazine and mesalamine for inducing remission or clinical response in these patients.

OBJECTIVES

To evaluate the efficacy of aminosalicylates compared to placebo, corticosteroids, and other aminosalicylates (alone or in combination with corticosteroids) for the treatment of mildly to moderately active Crohn's disease.

SEARCH METHODS

We searched PubMed, EMBASE, MEDLINE and the Cochrane Central Library from inception to June 2015 to identify relevant studies. There were no language restrictions. We also searched reference lists from potentially relevant papers and review articles, as well as proceedings from annual meetings (1991-2015) of the American Gastroenterological Association and American College of Gastroenterology.

SELECTION CRITERIA

Randomized controlled trials that evaluated the efficacy of sulfasalazine or mesalamine in the treatment of mildly to moderately active Crohn's disease compared to placebo, corticosteroids, and other aminosalicylates (alone or in combination with corticosteroids) were included.

DATA COLLECTION AND ANALYSIS

Data extraction and assessment of methodological quality was independently performed by the investigators and any disagreement was resolved by discussion and consensus. We assessed methodological quality using the Cochrane risk of bias tool. The overall quality of the evidence supporting the outcomes was evaluated using the GRADE criteria. The primary outcome measure was a well defined clinical endpoint of induction of remission or response to treatment. Secondary outcomes included mean Crohn's disease activity index (CDAI) scores, adverse events, serious adverse events and withdrawal due to adverse events. For dichotomous outcomes we calculated the pooled risk ratio (RR) and corresponding 95% confidence interval (CI) using a random-effects model. For continuous outcomes we calculated the mean difference (MD) and 95% CI using a random-effects model. Sensitivity analyses based on a fixed-effect model and duration of therapy were conducted where appropriate.

MAIN RESULTS

Twenty studies (2367 patients) were included. Two studies were judged to be at high risk of bias due to lack of blinding. Eight studies were judged to be at high risk of bias due to incomplete outcomes data (high drop-out rates) and potential selective reporting. The other 10 studies were judged to be at low risk of bias. A non-significant trend in favour of sulfasalazine over placebo for inducing remission was observed, with benefit confined mainly to patients with Crohn's colitis. Forty-five per cent (63/141) of sulfasalazine patients entered remission at 17-18 weeks compared to 29% (43/148) of placebo patients (RR 1.38, 95% CI 1.00 to 1.89, 2 studies). A GRADE analysis rated the overall quality of the evidence supporting this outcome as moderate due to sparse data (106 events). There was no difference between sulfasalazine and placebo in adverse event outcomes. Sulfasalazine was significantly less effective than corticosteroids and inferior to combination therapy with corticosteroids (RR 0.64, 95% CI 0.47 to 0.86, 1 study, 110 patients). Forty-three per cent (55/128) of sulfasalazine patients entered remission at 17 to 18 weeks compared to 60% (79/132) of corticosteroid patients (RR 0.68, 95% CI 0.51 to 0.91; 2 studies, 260 patients). A GRADE analysis rated the overall quality of the evidence supporting this outcome as moderate due to sparse data (134 events). Sulfasalazine patients experienced significantly fewer adverse events than corticosteroid patients (RR 0.43, 95% CI 0.22 to 0.82; 1 study, 159 patients). There was no difference between sulfasalazine and corticosteroids in serious adverse events or withdrawal due to adverse events. Olsalazine was less effective than placebo in a single trial (RR 0.36, 95% CI 0.18 to 0.71; 91 patients). Low dose mesalamine (1 to 2 g/day) was not superior to placebo for induction of remission. Twenty-three per cent (43/185) of low dose mesalamine patients entered remission at week 6 compared to 15% (18/117) of placebo patients (RR = 1.46, 95% CI 0.89 to 2.40; n = 302). A GRADE analysis indicated that the overall quality of the evidence supporting this outcome was low due to risk of bias (incomplete outcome data) and sparse data (61 events). There was no difference between low dose mesalamine and placebo in the proportion of patients who had adverse events (RR 1.33, 95% CI 0.91 to 1.96; 3 studies, 342 patients) or withdrew due to adverse events (RR 1.21, 95% CI 0.75 to 1.95; 3 studies, 342 patients). High dose controlled-release mesalamine (4 g/day) was not superior to placebo, inducing a clinically non significant reduction in CDAI (MD -19.8 points, 95% CI -46.2 to 6.7; 3 studies, 615 patients), and was also inferior to budesonide (RR 0.56, 95% CI 0.40 to 0.78; 1 study, 182 patients, GRADE = low). While high dose delayed-release mesalamine (3 to 4.5 g/day) was not superior to placebo for induction of remission (RR 2.02, 95% CI 0.75 to 5.45; 1 study, 38 patients, GRADE = very low), no significant difference in efficacy was found when compared to conventional corticosteroids (RR 1.04, 95% CI 0.79 to 1.36; 3 studies, 178 patients, GRADE = moderate) or budesonide (RR 0.89, 95% CI 0.76 to 1.05; 1 study, 307 patients, GRADE = moderate). However, these trials were limited by risk of bias (incomplete outcome data) and sparse data (small numbers of events). There was a lack of good quality clinical trials comparing sulfasalazine with other mesalamine formulations. Adverse events that were commonly reported included headache, nausea, vomiting, abdominal pain and diarrhea.

AUTHORS' CONCLUSIONS

Sulfasalazine is only modestly effective with a trend towards benefit over placebo and is inferior to corticosteroids for the treatment of mildly to moderately active Crohn's disease. Olsalazine and low dose mesalamine (1 to 2 g/day) are not superior to placebo. High dose mesalamine (3.2 to 4 g/day) is not more effective than placebo for inducing response or remission. However, trials assessing the efficacy of high dose mesalamine (4 to 4.5 g/day) compared to budesonide yielded conflicting results and firm conclusions cannot be made. Future large randomized controlled trials are needed to provide definitive evidence on the efficacy of aminosalicylates in active Crohn's disease.

Determination of mesalazine, a low bioavailability olsalazine metabolite in human plasma by UHPLC-MS/MS: Application to a pharmacokinetic study

Olsalazine sodium, salicylate derivative (prodrug) is effectively bioconverted to mesalazine (5-aminosalicylic acid; 5-ASA), which has an anti-inflammatory activity in ulcerative colitis. In this article, a novel highly sensitive and selective method was developed and validated to determine mesalazine in human plasma using a derivatization technique to enhance the signal intensity by using ultra- high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) with an electrospray ionization interface. The sample preparation consisted of a derivatization with propionyl anhydride followed by liquid liquid extraction (LLE) to remove the interference and minimize the matrix effect of human plasma. The multiple reaction monitoring (MRM) mode of the negative ion was performed and the transitions of m/z 208.1→107.0 and m/z 211.1→110.1 were used to measure the derivative of mesalazine and mesalazine-d3. The chromatographic separation was achieved using kinetex XB-C18 (100×4.6mm 2.6μ) analytical column with 0.1% formic acid in water and acetonitrile as mobile phase with a gradient elution. Nominal retention times of mesalazine and IS were 3.08 and 3.07min, respectively. Absolute recovery was found to be between 82-95% for analyte and about 78% for IS. The standard curves was linear (r(2)>0.995) in the concentration range 0.10 to 12.0ng/mL with lower limit of quantification (LLOQ) in human plasma was 0.10ng/mL. The average intra-day/inter-day precision values (%CV) were in the range from 0.6-2.9 % and 1.3-3.8 %, respectively, while the average accuracy value was 103.8-107.2%. This method has been successfully applied to the human pharmacokinetics of olsalazine sodium 250mg capsules following single oral administration.

The influence of gut microbiota on drug metabolism and toxicity

INTRODUCTION

Gut microbiota plays critical roles in drug metabolism. The variation of gut microbiota contributes to the interindividual differences toward drug therapy including drug-induced toxicity and efficacy. Accordingly, the investigation and elucidation of gut microbial impacts on drug metabolism and toxicity will not only facilitate the way of personalized medicine, but also improve rational drug design.

AREAS COVERED

This review provides an overview of the microbiota-host co-metabolism on drug metabolism and summarizes 30 clinical drugs that are co-metabolized by host and gut microbiota. Moreover, this review is specifically focused on elucidating the gut microbial modulation of some clinical drugs, in which the gut microbial influences on drug metabolism, drug-induced toxicity and efficacy are discussed.

EXPERT OPINION

The gut microbial contribution to drug metabolism and toxicity is increasingly recognized, but remains largely unexplored due to the extremely complex relationship between gut microbiota and host. The mechanistic elucidation of gut microbiota in drug metabolism is critical before any practical progress in drug design or personalized medicine could be made by modulating human gut microbiota. Analytical technique innovation is urgently required to strengthen our capability in recognizing microbial functions, including metagenomics, metabolomics and the integration of multidisciplinary knowledge.

Investigation of Host-Gut Microbiota Modulation of Therapeutic Outcome

A broader understanding of factors underlying interindividual variation in pharmacotherapy is important for our pursuit of "personalized medicine." Based on knowledge gleaned from the investigation of human genetics, drug-metabolizing enzymes, and transporters, clinicians and pharmacists are able to tailor pharmacotherapies according to the genotype of patients. However, human host factors only form part of the equation that accounts for heterogeneity in therapeutic outcome. Notably, the gut microbiota possesses wide-ranging metabolic activities that expand the metabolic functions of the human host beyond that encoded by the human genome. In this review, we first illustrate the mechanisms in which gut microbes modulate pharmacokinetics and therapeutic outcome. Second, we discuss the application of metabonomics in deciphering the complex host-gut microbiota interaction in pharmacotherapy. Third, we highlight an integrative approach with particular mention of the investigation of gut microbiota using culture-based and culture-independent techniques to complement the investigation of the host-gut microbiota axes in pharmaceutical research.

Insights on the human microbiome and its xenobiotic metabolism: what is known about its effects on human physiology?

INTRODUCTION

Our microbiome harbours a metabolic capacity far beyond our own. Moreover, its gene pool is highly adaptable and subject to selective pressure, including host exposure to xenobiotics. Yet, the resulting adaptations do not necessarily follow host well-being and can therefore contribute to disease or unfavourable metabolite production.

AREAS COVERED

This review provides an overview of our host-microbiome relationship in light of bacterial (xenobiotic) metabolism, community dynamics, entero-endocrine crosstalk, dysbiosis and potential therapeutic targets. In addition, it will highlight the need for a systematic analysis of the microbiome's potential for substance toxification.

EXPERT OPINION

The influence of our microbiota reaches from primary metabolites to secondary effects such as substrate competition or the activation of eukaryotic Phase I and Phase II enzymes. Further on it plays a hitherto underestimated role in drug metabolism, toxicity and pathogenesis. These effects are partly caused by entero-endocrine crosstalk and interference with eukaryotic regulatory networks. On first sight, the resulting concept of a metabolically competent microbiome adds enormous complexity to human physiology. Yet, the potential specificity of microbial targets harbours therapeutic promise for diseases such as diabetes, cancer and psychiatric disorders. A better physiological and biochemical understanding of the microbiome is thus of high priority for academia and biomedical research.

Drug delivery strategies in the therapy of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a frequently occurring disease in young people, which is characterized by a chronic inflammation of the gastrointestinal tract. The therapy of IBD is dominated by the administration of anti-inflammatory and immunosuppressive drugs, which suppress the intestinal inflammatory burden and improve the disease-related symptoms. Established treatment strategies are characterized by a limited therapeutical efficacy and the occurrence of adverse drug reactions. Thus, the development of novel disease-targeted drug delivery strategies is intended for a more effective therapy and demonstrates the potential to address unmet medical needs. This review gives an overview about the established as well as future-oriented drug targeting strategies, including intestine targeting by conventional drug delivery systems (DDS), disease targeted drug delivery by synthetic DDS and disease targeted drug delivery by biological DDS. Furthermore, this review analyses the targeting mechanisms of the respective DDS and discusses the possible field of utilization in IBD.

Synthesis and evaluation of mutual azo prodrug of 5-aminosalicylic acid linked to 2-phenylbenzoxazole-2-yl-5-acetic acid in ulcerative colitis

In this study, the syntheses of 4-aminophenylbenzoxazol-2-yl-5-acetic acid, (an analogue of a known nonsteroidal anti-inflammatory drug [NSAID]) and 5-[4-(benzoxazol-2-yl-5-acetic acid)phenylazo]-2-hydroxybenzoic acid (a novel mutual azo prodrug of 5-aminosalicylic acid [5-ASA]) are reported. The structures of the synthesized compounds were confirmed using infrared (IR), hydrogen-1 nuclear magnetic resonance (1H NMR), and mass spectrometry (MS) spectroscopy. Incubation of the azo compound with rat cecal contents demonstrated the susceptibility of the prepared azo prodrug to bacterial azoreductase enzyme. The azo compound and the 4-aminophenylbenzoxazol-2-yl-5-acetic acid were evaluated for inflammatory bowel diseases, in trinitrobenzenesulfonic acid (TNB)-induced colitis in rats. The synthesized diazo compound and the 4-aminophenylbenzoxazol-2-yl-5-acetic acid were found to be as effective as 5-aminosalicylic acid for ulcerative colitis. The results of this work suggest that the 4-aminophenylbenzoxazol-2-yl-5-acetic acid may represent a new lead for treatment of ulcerative colitis.

Developing a metagenomic view of xenobiotic metabolism

The microbes residing in and on the human body influence human physiology in many ways, particularly through their impact on the metabolism of xenobiotic compounds, including therapeutic drugs, antibiotics, and diet-derived bioactive compounds. Despite the importance of these interactions and the many possibilities for intervention, microbial xenobiotic metabolism remains a largely underexplored component of pharmacology. Here, we discuss the emerging evidence for both direct and indirect effects of the human gut microbiota on xenobiotic metabolism, and the initial links that have been made between specific compounds, diverse members of this complex community, and the microbial genes responsible. Furthermore, we highlight the many parallels to the now well-established field of environmental bioremediation, and the vast potential to leverage emerging metagenomic tools to shed new light on these important microbial biotransformations.

Aminosalicylates for induction of remission or response in Crohn's disease

BACKGROUND

Controlled clinical trials investigating the efficacy of aminosalicylates for the treatment of mildly to moderately active Crohn's disease have yielded conflicting results. A systematic review was conducted to critically examine current available data on the efficacy of sulfasalazine and mesalamine for inducing remission or clinical response in patients with mildly to moderately active Crohn's disease.

OBJECTIVES

To evaluate the efficacy of aminosalicylates compared to placebo, corticosteroids, and other aminosalicylates (alone or in combination with corticosteroids) for the treatment of mildly to moderately active Crohn's disease.

SEARCH STRATEGY

Separate MEDLINE (1966-July 2010), Cochrane Central Register of Controlled Trials (CENTRAL; Issue 3, 2010) and EMBASE database searches (1985-July 2010) of all relevant English and non-English language articles were performed, followed by manual searches of the reference list from potentially relevant papers and review articles, as well as proceedings from annual meetings (1991-2010) of the American Gastroenterological Association (AGA) and American College of Gastroenterology (ACG).

SELECTION CRITERIA

Randomized controlled trials that evaluated the efficacy of sulfasalazine or mesalamine in the treatment of mildly to moderately active Crohn's disease compared to placebo, corticosteroids, and other aminosalicylates (alone or in combination with corticosteroids) were included.

DATA COLLECTION AND ANALYSIS

Data extraction and assessment of methodological quality of each selected study was independently performed by the investigators and any disagreement was resolved by discussion and consensus. The primary outcome measure was a well defined clinical endpoint of induction of remission or response to treatment. Nineteen studies met the inclusion criteria and were analyzed. Pooled relative risks (RR) for inducing remission or clinical response and their 95% confidence intervals were calculated (random effects model) where appropriate.

MAIN RESULTS

Sulfasalazine was more likely to induce remission (RR 1.38; 95% CI 1.02 to 1.87; n = 263) compared to placebo with benefit confined mainly to patients with colitis. Sulfasalazine was less effective than corticosteroids (RR 0.66; 95% CI 0.53 to 0.81; n = 260). Olsalazine was less effective than placebo in a single trial. Low dose mesalamine (1 to 2 g/day) was not superior to placebo (RR = 1.46, 95% CI 0.89-2.40; n = 302) and was less effective than corticosteroids. High dose mesalamine (3 to 4.5 g/day) was not superior to placebo for induction of remission (RR 2.02; 95% CI 0.75 to 5.45) or response (Weighted Mean Difference -19.8 points; 95% CI -46.2 to 6.7; n = 615). In a single randomized controlled trial, 5-ASA was inferior to budesonide (RR 0.56; 95% CI 0.40 to 0.78). No statistically significant difference was found between high dose mesalamine and conventional corticosteroids (RR 1.04; 95% CI 0.79 to 1.36; n = 178). However, relatively few patients were available for analysis. There was a lack of good quality clinical trials comparing sulfasalazine with other mesalamine formulations.

AUTHORS' CONCLUSIONS

Sulfasalazine has modest efficacy compared to placebo and is inferior to corticosteroids for the treatment of mild to moderately active Crohn's disease. Olsalazine and low dose mesalamine (1 to 2 g/day) are not superior to placebo. High dose mesalamine (3 to 4.5 g/day) is not more effective than placebo for inducing response or remission. High dose mesalamine was inferior to budesonide for inducing remission in a single trial. In conclusion, sulfasalazine shows modest efficacy for the treatment of active Crohn's disease. However, the existing data show little benefit for 5-aminosalicylates.

Colonic treatments and targets: issues and opportunities

The colon provides a plethora of therapeutic opportunities. There are multiple disease targets, drug molecules, and colon-specific delivery systems to be explored. Clinical studies highlight the potential for systemic delivery via the colon, and the emerging data on the levels of cell membrane transporters and metabolic enzymes along the gut could prove advantageous for this. Often efflux transporters and metabolic enzyme levels are lower in the colon, suggesting a potential for improved bioavailability of drug substrates at this site. The locoregional distribution of multiple metabolic enzymes (including cytochromes), efflux transporters (including P-glycoprotein and breast cancer resistance proteins), and influx transporters (including the solute carrier family) along the intestine is summarized. Local delivery to the colonic mucosa remains a valuable therapeutic option. New therapies that target inflammatory mediators could improve the treatment of inflammatory bowel disease, and old and new anticancer molecules could, when delivered topically, prove to be beneficial adjuncts to the current systemic or surgical treatments. New issues such as pharmacogenomics, chronotherapeutics, and the delivery of prebiotics and probiotics are also discussed in this review. Targeting drugs to the colon utilizes various strategies, each with their advantages and flaws. The most promising systems are considered in the light of the physiological data which influence their in vivo behavior.

An experimental study on ulcerative colitis as a potential target for probiotic therapy by Lactobacillus acidophilus with or without "olsalazine"

Traditional medical treatments for ulcerative colitis (UC) are still compromised by its adverse effects and not potent enough to keep in remission for long-term periods. So, new therapies that are targeted at specific disease mechanisms have the potential to provide more effective and safe treatments for ulcerative colitis. Probiotics is recently introduced as a therapy for ulcerative colitis. In the present study, Lactobacillus acidophilus was selected as a probiotic therapy to investigate its effects in oxazolone-induced colitis model in rats that mimics the picture in human. The rats were grouped (8 rats each) as normal control group (Group I), Group II served as untreated oxazolone-induced colitis, Group III oxazolone-induced colitis treated with probiotic L. acidophilus (1×10(7) colony-forming units (CFU)/mL/day oral for 14 days), Group IV oxazolone-induced colitis treated with olsalazine (60 mg/kg/day oral for 14 days), Group V oxazolone-induced colitis treated with probiotic L. acidophilus and olsalazine in the same doses and duration. Disease activity index (DAI) was recorded, serum levels of C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and intrleukin-6 (IL-6) was assessed as inflammatory markers and the histopathological picture of the colon of each rat was studied. Disease activity index (DAI) showed significant positive correlation with the elevated serum levels of CRP (r=0.741, p<0.05), TNF-α (r=0.802, p<0.05) and IL-6 (r=0.801, p<0.05). Treatment with either L. acidophilus (group III) or olsalazine (group IV) resulted in significant reduction in serum levels of CRP, TNF-α and IL-6, as well as disease activity index (DAI). Treatment with combination of L. acidophilus and olsalazine (group V) offered more significant reduction in serum levels of CRP, TNF-α, IL-6 and disease activity index (DAI) when compared to either group II (untreated group), group III (treated with L. acidophilus) or group IV (treated with olsalazine). So, it was concluded that L. acidophilus probiotic could be recommended as adjuvant therapy in combination with olsalazine to achieve more effective treatment for ulcerative colitis. For application in human, this needs to be verified in further clinical studies.

Colonic targeting of aminosalicylates for the treatment of ulcerative colitis

Aminosalicylates (5-aminosalicylic acid) represent drugs of first choice in the treatment of ulcerative colitis. Two different therapeutic approaches have been employed to target the active 5-aminosalicylic acid to its site of action. Either inactive azo-prodrugs (e.g. sulfasalazine, olsalazine, balsalazide) or special galenic formulations have been developed for topical delivery of 5-aminosalicylic acid to the colon. However, as intestinal physiology, the extent of ulcerative colitis as well as drug disposition demonstrate large interindividual differences, acute healing rates (40-80%) and the maintenance of remission are quite variable. Apparently, therapeutic effects depend on local concentrations of 5-aminosalicylic acid in the colonic mucosa whereas systemic drug exposure might be one determinant of side effects. In general, 5-aminosalicylic acid is well tolerated and withdrawal from therapy is rare. Following administration of azo-prodrugs (e.g. olsalazine), lower plasma concentrations and higher delivery into the colon of 5-aminosalicylic acid can be observed in comparison to special galenic formulations of 5-aminosalicylic acid. Whether such changes in drug disposition will affect therapeutic efficacy remains to be proved by clinical data. Consequently, selection of a particular agent should be based primarily on clinical efficacy, profile of adverse effects, patients' acceptance and economic considerations.

Mesalamine delivery systems: do they really make much difference?

Sulfasalazine's role as the first-line of therapy in patients with inflammatory bowel disease has led to the development of other "designer" aminosalicylates, which eliminate the sulfa-moiety, and attempt to target the topically active mesalamine to the inflamed bowel. Olsalazine sodium and balsalazide disodium utilize the same azo-bond structure as sulfasalazine, requiring release of active mesalamine by colonic bacteria, and thus targeting these agents to the colon. Other mesalamine delivery systems use pH-dependant- or moisture-release to liberate the active mesalamine in both the large and small bowel. Direct application of mesalamine via enema or suppository is also effective in patients with distal colitis. The pharmacology and thus the undesirable drug absorption rates differ between drugs, although the clinical importance of these characteristics is debatable. Differences in release-systems, the impact of the fed and fasting state, and unique patient intolerances to individual agents demand an understanding of each of these products, and their application to patient therapy.

Topical delivery of therapeutic agents in the treatment of inflammatory bowel disease

For targeting local and systemic inflammatory processes in inflammatory bowel disease (IBD) therapeutic agents of first choice (e.g. aminosalicylates, corticosteroids) have been developed in special galenic forms to accomplish the topical delivery of the active compounds to the terminal ileum (Crohn's disease) and/or the colon (Crohn's disease and ulcerative colitis). However, it has to be realized that intestinal physiology (e.g. motility, intraluminal pH profiles), extent and pattern of IBD as well as drug disposition demonstrate large interindividual differences resulting in variable clinical response rates between about 35% and 75%. 5-Aminosalicylate (5-AS) can be delivered to the colon either by azo-prodrugs (e.g. sulfasalazine, olsalazine or balsalazide) or by direct rectal administration of 5-AS in form of enemas, foam or suppositories. Such formulations will be only effective in patients with ulcerative colitis (UC). Various slow/controlled release preparations of 5-AS have been developed for oral use. Some of them (e.g. Pentasa, Salofalk) release sufficient 5-AS already in the small bowel which could provide some additional benefit in Crohn's disease (CD). As urinary and faecal recoveries of total 5-AS are similar for all oral formulations, no major clinical differences can be expected. Extent of the disease, profile of adverse effects and patient's acceptance provide some guidance for selection of the particular agent. Rectal installation of several glucocorticosteroids has been employed for many years. More recently scientific and clinical interest has been focused on budesonide which is extensively presystemically metabolized in the intestinal wall and the liver. Therefore, its systemic availability is low (10-15%) independent whether budesonide is administered orally as controlled release formulation in patients with CD or rectally as enema in patients with UC. Numerous pharmacokinetic and clinical studies have documented the anticipated topical delivery and clinical efficacy of this corticosteroid without serious side effects such as cushingoid features. It can be assumed that for any novel therapeutic principle in IBD the approach of topical delivery will be also tried.

Advances in Colonic Drug Delivery

Targeting drugs and delivery systems to the colonic region of the gastrointestinal tract has received considerable interest in recent years. Scientific endeavour in this area has been driven by the need to better treat local disorders of the colon such as inflammatory bowel disease (ulcerative colitis and Crohn's disease), irritable bowel syndrome and carcinoma. The colon is also receiving significant attention as a portal for the entry of drugs into the systemic circulation. A variety of delivery strategies and systems have been proposed for colonic targeting. These generally rely on the exploitation of one or more of the following gastrointestinal features for their functionality: pH, transit time, pressure or microflora. Coated systems that utilise the pH differential in the gastrointestinal tract and prodrugs that rely on colonic bacteria for release have been commercialised. Both approaches have their own inherent limitations. Many systems in development have progressed no further than the bench, while others are expensive or complex to manufacture, or lack the desired site-specificity. The universal polysaccharide systems appear to be the most promising because of their practicality and exploitation of the most distinctive property of the colon, abundant microflora.

Systematic review: the pharmacokinetic profiles of oral mesalazine formulations and mesalazine pro-drugs used in the management of ulcerative colitis

AIM

: To quantify through systematic review the pharmacokinetic profiles of the oral delayed release and sustained release mesalazine (5-aminosalicylate, 5ASA) formulations (Asacol, Salofalk, Mesasal, Claversal, Pentasa) and pro-drugs (sulfasalazine, olsalazine, balsalazide) used in the management of ulcerative colitis.

METHODS

: Selected articles had: (1) adult healthy volunteers or patients with ulcerative colitis and (2) quantification of pharmacokinetic data to include, at a minimum, urinary excretion of total 5ASA [5ASA plus N-Acetyl-5ASA (N-Ac-5ASA)].

DATA COLLECTION AND ANALYSIS

: Pharmacokinetic data (Tmax, Cmax, AUC, urinary excretion, faecal excretion) of 5ASA, its major metabolite N-Acetyl-5ASA, total 5ASA, and the parent pro-drug compounds was extracted.

MAIN RESULTS

: The summary results for urinary excretion of total 5ASA over 24-96 h in all subjects (either mean or median) were: sulfasalazine mean 11-33% or median 22%; olsalazine mean 14-31% or median 16-27%; balsalazide mean 12-35% or median 20%; Asacol mean 10-35% or median 18-40%; Pentasa mean 15-53% or median 23-34%; Salofalk, Mesasal and Claversal mean 27-56% or median 31-44%. The summary results for faecal excretion of total 5ASA over 24-96 h in all subjects (either mean or median) were: sulfasalazine mean 23-75% or median 38%; olsalazine mean 47-50% or median 17-36%; balsalazide mean 46% or median 22%; Asacol mean 40-64% or median 20-56%; Pentasa mean 12-51% or median 39-59%; Salofalk, Mesasal and Claversal mean 37-44% or median 23-35%.

CONCLUSIONS

: The systemic exposure to 5ASA, as measured by urinary excretion of total 5ASA, and the faecal excretion of total 5ASA is comparable for all oral mesalazine formulations and pro-drugs. Thus, selection of a mesalazine therapy for the treatment of ulcerative colitis should be based on other factors such as efficacy, dose-response, toxicity of the parent compound and its metabolites, compliance issues related to dose forms and dosing schedules, and costs.

Pharmacokinetic considerations in the treatment of inflammatory bowel disease

This review describes the pharmacokinetics of the major drugs used for the treatment of inflammatory bowel disease. This information can be helpful for the selection of a particular agent and offers guidance for effective and well tolerated regimens. The corticosteroids have a short elimination half-life (t1/2beta) of 1.5 to 4 hours, but their biological half-lives are much longer (12 to 36 hours). Most are moderate or high clearance drugs that are hepatically eliminated, primarily by cytochrome P450 (CYP) 3A4-mediated metabolism. Prednisone and budesonide undergo presystemic elimination. Any disease state or comedication affecting CYP3A4 activity should be taken into account when prescribing corticosteroids. Depending on the preparation used, 10 to 50% of an oral or rectal dose of mesalazine is absorbed. Rapid acetylation in the intestinal wall and liver (t1/2beta 0.5 to 2 hours) and transport probably by P-glycoprotein affect mucosal concentrations of mesalazine, which apparently determine clinical response. Any clinical condition influencing the release and topical availability of mesalazine might modify its therapeutic potential. Metronidazole has high (approximately 90%) oral bioavailability, with hepatic elimination characterised by a t1/2beta of 6 to 10 hours and a total clearance of about 4 L/h/kg. Ciprofloxacin is largely excreted unchanged both renally (about 45% of dose) and extrarenally (25%), with a relatively short t1/2beta (3.5 to 7 hours). Thus, renal function affects the systemic availability of ciprofloxacin. Both mercaptopurine and its prodrug azathioprine are metabolised to active compounds (6-thioguanine nucleotides; 6-TGN) by hypoxanthine-guanine phosphoribosyltransferase and to inactive metabolites by the polymorphically expressed thiopurine S-methyltransferase (TPMT) and xanthine oxidase. Patients with low TPMT activity have a higher risk of developing haemopoietic toxicity. Both mercaptopurine and azathioprine have a short t1/2beta (1 to 2 hours), but the t1/2beta of 6-TGN ranges from 3 to 13 days. Therapeutic response seems to be related to 6-TGN concentration. Almost complete bioavailability has been observed after intramuscular and subcutaneous administration of methotrexate, which is predominantly (85%) excreted as unchanged drug with a t1/2beta of up to 50 hours. Thus, renal function is the major determinant for disposition of methotrexate. Cyclosporin is slowly and incompletely absorbed. It is extensively metabolised by CYP3A4/5 in the liver and intestine (median t1/2beta and clearance 7.9 hours and 0.46 L/h/kg, respectively), and inhibitors and inducers of CYP3A4 can modify response and toxicity. Infliximab is predominantly distributed to the vascular compartment and eliminated with a t1/2beta between 10 and 14 days. No accumulation was observed when it was administered at intervals of 4 or 8 weeks. Methotrexate may reduce the clearance of infliximab from serum.

Review article: balsalazide therapy in ulcerative colitis

Balsalazide is a 5-aminosalicylic acid (mesalazine) pro-drug which has an inert carrier molecule instead of the sulfapyridine moiety of sulfasalazine. It is designed to deliver 5-aminosalicylic acid to the colonic mucosa without the sulfapyridine-associated side-effects encountered with sulfasalazine. Several studies have confirmed the efficacy and patient tolerance of balsalazide. When compared to mesalazine at equivalent doses, it induced symptomatic and complete remission of acute ulcerative colitis in a greater proportion of patients. In particular, patients with resistant left-sided disease were shown to have a higher probability of achieving remission. Balsalazide was beneficial in patients with troublesome nocturnal symptoms. It has a similar efficacy in maintaining remission when compared to sulfasalazine and mesalazine. The advantage of balsalazide over other 5-aminosalicylic acid compounds is its superior patient tolerability with minimal side-effects.