A pharmacogenetic basis for the safe and effective use of azathioprine and other thiopurine drugs in dermatologic patients

Purine Synthesis Inhibitors, 6-thioguanine and Azathioprine: Forgotten Treatment Options in Psoriasis and Psoriatic Arthritis

Background

The thiopurine drugs azathioprine and 6-thioguanine have been shown to induce significant clinical improvement in patients with moderate to severe psoriasis and/or psoriatic arthritis.

Objective

The aim of this paper is to present a comprehensive review of the available literature concerning the off-label role of thiopurine drugs in the treatment of psoriasis and psoriatic arthritis.

Methods

Studies published with English abstracts between 1960 and 2008 identified in MEDLINE and PubMed with the keywords purine synthesis inhibitors, thiopurine, 6-thioguanine, azathioprine, psoriasis and psoriatic arthritis were reviewed.

Results

Although 6-thioguanine and azathioprine have shown significant efficacy, their side effect profiles have discouraged their use for moderate to severe psoriasis.

Conclusion

For treatment of psoriasis and psoriatic arthritis, purine synthesis inhibitors should not be forgotten. They represent an entirely different option and provide an alternative therapy, especially for difficult cases.

An open, multicentre, randomized clinical study in patients with bullous pemphigoid comparing methylprednisolone and azathioprine with methylprednisolone and dapsone

BACKGROUND

Current treatment of bullous pemphigoid (BP) is based on the long-term use of topical and/or systemic corticosteroids, which are associated with a high rate of adverse events and increased mortality.

OBJECTIVES

To study the corticosteroid-sparing potential of azathioprine and dapsone.

METHODS

This was a prospective, multicentre, randomized, nonblinded clinical trial that compared the efficacy and safety of two parallel groups of patients with BP treated with oral methylprednisolone 0·5 mg kg^-1 per day in combination with either azathioprine 1·5-2·5 mg kg^-1 per day or dapsone 1·5 mg kg^-1 per day. Nine German and Austrian departments of dermatology included 54 patients based on clinical lesions, positive direct immunofluorescence (IF) microscopy and detection of serum autoantibodies by indirect IF microscopy, immunoblotting or enzyme-linked immunosorbent assay. The primary end point was the time until complete tapering of methylprednisolone, and the most important secondary end point was the cumulative corticosteroid dose.

RESULTS

In eight patients (five azathioprine, three dapsone), methylprednisolone could be discontinued after a median time of 251 days in the azathioprine group and 81 days in the dapsone group. The median cumulative corticosteroid dose was 2·65 g for azathioprine compared with 1·92 g for dapsone (P = 0·06). The median numbers of days when corticosteroids were applied were 148 and 51, respectively (P = 0·24). No significant difference in the number of adverse events was seen between the treatment arms. Four patients (8%) died within the observation period of 12 months.

CONCLUSIONS

Due to the lower than intended number of patients, the results of the primary and secondary end points were not or only barely significant. Dapsone appeared to have a moderately higher corticosteroid-sparing potential than azathioprine. The combination regimen of either drug with oral methylprednisolone is associated with a relatively low 1-year mortality in this vulnerable patient population.

Immunosuppressive and Cytotoxic Drugs in Dermatology: A Practical Overview and Personal Perspective

Background:

Cytotoxic/immunosuppressive drugs are regularly used to treat proliferative diseases of the skin and immunologically mediated inflammatory disorders.

Objective:

The rational use of cytotoxic/immunosuppressive drugs, which depends on the proper selection of both the patient and the drug, is discussed.

Conclusion:

Methotrexate, azathioprine, cyclophosphamide, chlorambucil, cyclosporine, and other related drugs have potential benefits in the treatment of severe recalcitrant cutaneous disease. Patients may survive otherwise fatal disorders, or may improve their life-style and become productive again. However, the beneficial effect of these agents is achieved when the blood level is at or near toxic level. Thus, the prescribing physician should have a familiarity with the potential toxicities and a knowledge of proper monitoring techniques.

Review article: recent advances in pharmacogenetics and pharmacokinetics for safe and effective thiopurine therapy in inflammatory bowel disease

BACKGROUND

Azathioprine and mercaptopurine have a pivotal role in the treatment of inflammatory bowel disease (IBD). However, because of their complex metabolism and potential toxicities, optimal use of biomarkers to predict adverse effects and therapeutic response is paramount.

AIM

To provide a comprehensive review focused on pharmacogenetics and pharmacokinetics for safe and effective thiopurine therapy in IBD.

METHODS

A literature search up to July 2015 was performed in PubMed using a combination of relevant MeSH terms.

RESULTS

Pre-treatment thiopurine S-methyltransferase typing plus measurement of 6-tioguanine nucleotides and 6-methylmercaptopurine ribonucleotides levels during treatment have emerged with key roles in facilitating safe and effective thiopurine therapy. Optimal use of these tools has been shown to reduce the risk of adverse effects by 3-7%, and to improve efficacy by 15-30%. For the introduction of aldehyde oxidase (AOX) into clinical practice, the association between AOX activity and AZA dose requirements should be positively confirmed. Inosine triphosphatase assessment associated with adverse effects also shows promise. Nucleoside diphosphate-linked moiety X-type motif 15 variants have been shown to predict myelotoxicity on thiopurines in East Asian patients. However, the impact of assessments of xanthine oxidase, glutathione S-transferase, hypoxanthine guanine phosphoribosyltransferase and inosine monophosphate dehydrogenase appears too low to favour incorporation into clinical practice.

CONCLUSIONS

Measurement of thiopurine-related enzymes and metabolites reduces the risk of adverse effects and improves efficacy, and should be considered part of standard management. However, this approach will not predict or avoid all adverse effects, and careful clinical and laboratory monitoring of patients receiving thiopurines remains essential.

Update 2014: advances to optimize 6-mercaptopurine and azathioprine to reduce toxicity and improve efficacy in the management of IBD

BACKGROUND

The thiopurine drugs, 6-mercaptopurine (6-MP) and azathioprine (AZA), remain as a mainstay therapy in inflammatory bowel disease (IBD). Differences in metabolism of these drugs lead to individual variation in thiopurine metabolite levels that can determine its therapeutic efficacy and development of adverse reactions. In this update, we will review thiopurine metabolic pathway along with the up-to-date approaches in administering thiopurine medications based on the current literature.

METHODS

A search of the PubMed database by 2 independent reviewers identifying 98 articles evaluating thiopurine metabolism and IBD management.

RESULTS

Monitoring thiopurine metabolites can assist physicians in optimizing 6-MP and AZA therapy in treating patients with IBD. Of the dosing strategies reviewed, we found evidence for monitoring thiopurine metabolite level, use of allopurinol with thiopurine, use of mesalamine with thiopurine, combination therapy with thiopurine and anti-tumor necrosis factor agents, and split dosing of AZA or 6-MP to optimize thiopurine therapy and minimize adverse effects in IBD.

CONCLUSIONS

Based on the currently available literature, various dosing strategies to improve therapeutic response and reduce adverse reactions can be considered, including use of allopurinol with thiopurine, use of mesalamine with thiopurine, combination therapy with thiopurine and anti-tumor necrosis factor agents, and split dosing of thiopurine.

Atopic dermatitis: a practice parameter update 2012

This parameter was developed by the Joint Task Force on Practice Parameters, representing the American Academy of Allergy, Asthma & Immunology (AAAAI); the American College of Allergy, Asthma & Immunology (ACAAI); and the Joint Council of Allergy, Asthma and Immunology. The AAAAI and the ACAAI have jointly accepted responsibility for establishing "Atopic dermatitis: a practice parameter update 2012." This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, and the Joint Council of Allergy, Asthma & Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion. Published practice parameters of the Joint Task Force on Practice Parameters for Allergy & Immunology are available online at http://www.jcaai.org.

Pros and cons of medical management of ulcerative colitis

Ulcerative colitis (UC) is a chronic inflammatory disease characterized by diffuse mucosal inflammation limited to the colon and rectum. Although a complete medical cure may not be possible, UC can be treated with medications that induce and maintain remission. The medical management of this disease continues to evolve with a goal to avoid colectomy and ultimately alter the natural history of UC. Emergence of antitumor necrosis factor-α (TNF-α) agents has expanded the medical armamentarium. 5-Aminosalicylates continue to be used in mild to moderate UC and corticosteroids are mainly used for induction of remission with immunomodulators (6-mercaptopurine/azathiopurine/methotrexate) being applied as steroid-sparing agents for maintenance therapy. Infliximab has been approved by the U.S. Food and Drug Administration and used in the treatment of moderate to severe UC; nevertheless, its use may be associated with significant adverse effects and have a negative impact on the postoperative course should the patients undergo restorative proctocolectomy. In addition, there is always a concern about patients' compliance to medical therapy, cost of medications, and risk for UC-associated dysplasia. The authors discuss the pros and cons of medications used in the treatment of UC.

Optimizing 6-mercaptopurine and azathioprine therapy in the management of inflammatory bowel disease

The thiopurine drugs, 6-mercaptopurine (6-MP) and azathioprine, are efficacious in the arsenal of inflammatory bowel disease (IBD) therapy. Previous reports indicate that 6-thioguanine nucleotide (6-TGN) levels correlate with therapeutic efficacy, whereas high 6-methylmercaptopurine (6-MMP) levels are associated with hepatotoxicity and myelotoxicity. Due to their complex metabolism, there is wide individual variation in patient response therein, both in achieving therapeutic drug levels as well as in developing adverse reactions. Several strategies to optimize 6-TGN while minimizing 6-MMP levels have been adopted to administer the thiopurine class of drugs to patients who otherwise would not tolerate these drugs due to side-effects. In this report, we will review different approaches to administer the thiopurine medications, including the administration of 6-mercaptopurine in those unsuccessfully treated with azathioprine; co-administration of thiopurine with allopurinol; co-administration of thiopurine with anti-tumor necrosis factor α; 6-TGN administration; desensitization trials; and split dosing of 6-MP.

Primer on the human genome

The study of the expression patterns of many genes, or even the entire genome, is now routinely possible. Such powerful tools have enabled hypothesis-generating research at a scale never before possible. Moreover, spatially or temporally linked gene and protein expression, implying co-regulation and functional relatedness, has led to the identification of particular clusters of genes important for fundamental biologic processes, such as development and cancer. Not only is this expected to yield further mechanistic insights into disease processes, but perhaps most exciting, it will likely establish the foundation of predictive medicine, in which understanding of individual genomic signatures leads to the use of appropriately targeted therapy.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to understand the fundamental tenets of molecular biology as they relate to the field of genomics.

Introducing a fast and simple PCR-RFLP analysis for the detection of mutant thiopurine S-methyltransferase alleles TPMT*3A and TPMT*3C

BACKGROUND

Azathioprine, in combination with corticosteroids, is the first-line therapy of severe forms of pemphigus vulgaris. Patients with an impaired thiopurine S-methyltransferase (TPMT) activity are at risk of developing severe myelo-suppression upon treatment with thiopurines such as azathioprine. Analysis of the TPMT status prior to drug administration is therefore highly recommended. However, because of the limited availability of TPMT testing outside of specialized centres, pre-emptive TPMT testing is not widespread. To avoid laborious biochemical and sequencing assays, we evaluated a new restriction fragment length polymorphism (RFLP) analysis.

METHODS

We designed a rapid genetic polymerase chain reaction (PCR)-RFLP screen for the most prevalent mutant TPMT*3A and TPMT*3C alleles that are known to result in reduced TPMT enzyme activity.

RESULTS

Validating our fast system on 871 Caucasian DNA samples, we observed that 8.61% of our probands carried the TPMT*3A allele and 0.23% were heterozygous for the TPMT*3C allele, which is in concordance with previously reported allele frequencies.

CONCLUSION

This simple and low-cost PCR-RFLP TPMT polymorphism testing approach can be performed in a standard laboratory. It should be applied to all patients prior to receiving thiopurine drug therapy to avoid the severe, but predictable, haematopoietic side-effects of thiopurine drug administration.

Pharmacokinetics of azathioprine following single-dose intravenous and oral administration and effects of azathioprine following chronic oral administration in horses

OBJECTIVE

To determine pharmacokinetics of azathioprine (AZA) and clinical, hematologic, and serologic effects of i.v. and oral administration of AZA in horses.

ANIMALS

6 horses.

PROCEDURE

In study phase 1, a single dose of AZA was administered i.v. (1.5 mg/kg) or orally (3.0 mg/kg) to 6 horses, with at least 1 week between treatments. Blood samples were collected for AZA and 6-mercaptopurine (6-MP) analysis 1 hour before and at predetermined time points up to 4 hours after AZA administration. In study phase 2, AZA was administered orally (3 mg/kg) every 24 hours for 30 days and then every 48 hours for 30 days. Throughout study phase 2, blood samples were collected for CBC determination and serum biochemical analysis.

RESULTS

Plasma concentrations of AZA and its metabolite, 6-MP decreased rapidly from plasma following i.v. administration of AZA, consistent with the short mean elimination half-life of 1.8 minutes. Oral bioavailability of AZA was low, ranging from 1% to 7%. No horses had abnormalities on CBC determination or serum biochemical analysis, other than 1 horse that was lymphopenic on day 5 and 26 of daily treatment. This horse developed facial alopecia from which 1 colony of a Trichophyton sp was cultured; alopecia resolved within 1 month after the study ended.

CONCLUSIONS AND CLINICAL RELEVANCE

Overall, no adverse effects were observed with long-term oral administration of AZA to horses, although 1 horse did have possible evidence of immunosuppression with chronic treatment. Further investigation of the clinical efficacy of AZA in the treatment of autoimmune diseases in horses is warranted.

The Use of Systemic Immune Moderators in Dermatology: An Update

In addition to corticosteroids, dermatologists have access to an array of immunomodulatory therapies. Azathioprine, cyclophosphamide, methotrexate, cyclosporine, and mycophenolate mofetil are the systemic immunosuppressive agents most commonly used by dermatologists. In addition, new developments in biotechnology have spurred the development of immunobiologic agents that are able to target the immunologic process of many inflammatory disorders at specific points along the inflammatory cascade. Alefacept, efalizumab, etanercept, and infliximab are the immunobiologic agents that are currently the most well known and most commonly used by dermatologists. This article reviews the pharmacology, mechanism of action, side effects, and clinical applications of these therapies.

Identification and functional analysis of two rare allelic variants of the thiopurine S-methyltransferase gene, TPMT*16 and TPMT*19

Human thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. TPMT is genetically polymorphic and is associated with large interindividual variations in thiopurine drug toxicity and therapeutic efficacy. During routine genotyping of patients with Crohn's disease, one novel missense mutation, 365A>C (TPMT*19, Lys(122)Thr), and a recently described missense mutation, 488G>A (TPMT*16, Arg(163)His), were identified in a Caucasian and a Moroccan patient, respectively. Using a heterologous yeast expression system, kinetic parameters (K(m) and V(max)) of the two variants with respect to 6-thioguanine S-methylation were determined and compared with those obtained with the wild-type enzyme. The Lys(122)Thr exchange did not significantly decrease the intrinsic clearance value (V(max)/K(m)) of the variant enzyme. In contrast, the Arg(163)His substitution significantly decreased the intrinsic clearance value by three-fold. The Arg(163) is located in a highly conserved region of the human TPMT protein and, as such, the Arg(163)His substitution is expected to result in a marked reduction of enzyme activity, as confirmed by the in vitro data. Phenotyping by measurement of red blood cell TPMT activity indicated that the patient heterozygous for the Lys(122)Thr mutation had normal TPMT activity, whereas the patient heterozygous for the Arg(163)His mutation was an intermediate methylator, which demonstrated a positive correlation between TPMT phenotyping and the in vitro data. The identification of a novel non-functional allele of the TPMT gene improves our knowledge of the genetic basis of interindividual variability in TPMT activity. These data further enhance the efficiency of genotyping methods to predict patients at risk of an inadequate response to thiopurine therapy.

Clinical utility of thiopurine S-methyltransferase genotyping

Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme that plays a major role in the metabolism of thiopurine drugs such as mercaptopurine and azathioprine. The interindividual differences in response to thiopurine administration is in part due to the presence of genetic polymorphisms in the gene that regulates TPMT activity. TPMT genotype correlates well with the in vivo enzyme activity within erythrocytes. Patients with genetically determined decreased TPMT activity develop severe myelosuppression when treated with standard doses of thiopurine drugs because an excess of thioguanine nucleotides accumulates in hematopoietic tissues. TPMT genotyping provides clinicians with a reliable method for identifying TPMT-deficient patients who can benefit from low doses of thiopurine drugs in order to reduce the risk of developing adverse effects. Moreover, the administration of higher doses of the drug could improve therapeutic response in patients in whom the TPMT genotyping demonstrates the absence of mutated alleles.

Medical treatment of ulcerative colitis

Ulcerative colitis is a chronic inflammatory disease of the colon with an increasing incidence worldwide. The medical management of this disease continues to expand as drugs to induce and maintain remission are sought to avoid the need for colectomy. This article will review the standard of care for the treatment of mild, moderate, and severe ulcerative colitis. The efficacy, optimal usage, and adverse events profile of agents such as 5-aminosalicylates, corticosteroids, azathioprine, and cyclosporine will be discussed and an algorithm for their use will be developed. Alternative and experimental therapies such as monoclonal antibodies, probiotics, and heparin will also be addressed.

Drug interactions of clinical significance for the dermatologist: recognition and avoidance

While it would be impossible for any dermatologist to remember all potential drug interactions, knowledge of the mechanisms of drug interactions can help reduce the risk of serious adverse outcomes. Most drugs are associated with interactions but the majority do not produce significant outcomes. Dealing with drug interactions is a challenge in all clinical practice, including dermatology. New information continues to appear, and dermatologists need to know about the drugs they use.This article focuses on the mechanisms of drug interactions. In particular, the life of a drug in terms of absorption, distribution, metabolism and excretion are reviewed with the focus on points of importance and relevance to drug interactions. The most clinically important drug interactions in dermatological practice are caused by alterations in drug metabolism. The contributions of P-glycoprotein, pharmacogenetic variation and genetic polymorphisms to drug interactions are highlighted, and the best evidence for drug interactions involving drug classes relevant to the dermatologist is presented. Since the initial evidence for clinically relevant drug interactions comes from case reports, prescribing physicians can have a major role in collating information on interactions. By understanding the mechanisms behind drug interactions and staying alert for toxicities, we can help make drug therapy safer and reduce the fear of drug interactions.

Recent Advances in Treatment Strategies for Atopic Dermatitis

A wide range of different therapeutic regimens are used for atopic dermatitis. Although many treatment modalities are well established worldwide among clinicians, only the minority of these therapy recommendations are based on results of randomised controlled trials (RCTs). To close the gap between such 'generally' recommended therapies and therapies that are based on data from controlled trials, this review focuses not only on the pharmacological and clinical aspects of the currently proven agents, but also on the advantages and disadvantages of therapies that have not yet been completely tested.A review of the available literature concerning the pharmacological profile and also the level of evidence of therapeutic efficacy of all currently known topical and systemic agents for the treatment of atopic dermatitis reveals a large gap between the knowledge concerning the pharmacological action in vitro and the evidence of clinical efficacy in many cases. We agree with the conclusion of previous reviews that numerous therapies for atopic dermatitis urgently require more independent RCTs and especially comparative trials (e.g. corticosteroids vs calcineurin inhibitors). These are required in order to facilitate the choice of therapeutic strategy for the individual treatment of atopic dermatitis, with its broad spectrum of clinical manifestations and potential complications in adult patients and, particularly, in children.Finally, we also review preclinical trials with several new drugs. Immunomodulators appear to promise a new dimension for the future of therapy for atopic dermatitis, especially for severe and otherwise refractory forms or as alternatives to corticosteroids, that is, to treat facial atopic eczema without the risk of adverse effects.

Maintenance of Remission in Crohn???s Disease

Crohn's disease is a chronic inflammatory bowel disorder with a relapsing and remitting course. Once remission is achieved, the main aim of the management of Crohn's disease is maintenance of that remission. Significant advances have been made into understanding the aetiology and pathogenesis of inflammatory bowel disease. With these advances in understanding come increasing numbers of new agents and therapies, aimed both at active disease and the subsequent maintenance of remission in Crohn's disease. Current therapeutic strategies in maintaining remission in Crohn's disease include 5-aminosalicylates (e.g. sulfasalazine, mesalazine), thiopurines (e.g. azathioprine, 6-mercaptopurine [mercaptopurine]), methotrexate and infliximab. The 5-aminosalicylates appear to have efficacy limited to either surgically induced remission and/or limited small bowel Crohn's disease. The immunomodulators now have an established role in Crohn's maintenance. Azathioprine and 6-mercaptopurine are effective in chronic active disease and corticosteroid-dependent Crohn's disease. Methotrexate has similar indications, although it appears to be an alternative in patients who are intolerant of, or resistant to, the thiopurines. The most recent breakthrough has been in the field of biological therapy for maintenance of remission in Crohn's disease. Treatment of patients with the anti-tumour necrosis factor (TNF)-alpha antibody infliximab has been shown already to be effective in inducing remission. Recent studies have now confirmed a role for infliximab in delaying relapse and maintaining remission in patients responsive to infliximab induction therapy. However, results with soluble TNF alpha receptors have been disappointing. A number of other biological and nonbiological agents have shown potential, though trials of the 'newer' biological agents have thus far been disappointing, in the maintenance of remission in Crohn's disease. The evidence for theses agents is currently limited, in many cases to treating active disease; however, these data are discussed in this article in order to provide an overview of future potential therapies. The aim of this review is to provide clinicians with an insight into current and emerging therapeutic agents for the maintenance of remission of Crohn's disease.

In vitro characterization of four novel non-functional variants of the thiopurine S-methyltransferase

Human thiopurine S-methyltransferase (TPMT) is an enzyme responsible for the detoxification of widely used thiopurine drugs such as azathioprine (Aza). Its activity is inversely related to the risk of developing severe hematopoietic toxicity in certain patients treated with standard doses of thiopurines. DNA samples from four leucopenic patients treated with Aza were screened by PCR-SSCP analysis for mutations in the 10 exons of the TPMT gene. Four missense mutations comprising two novel mutations, A83T (TPMT*13, Glu(28)Val) and C374T (TPMT*12, Ser(125)Leu), and two previously described mutations, G430C (TPMT*10, Gly(144)Arg) and T681G (TPMT*7, His(227)Gln) were identified. Using a recombinant yeast expression system, kinetic parameters (K(m) and V(max)) of 6-thioguanine S-methylation of the four TPMT variants were determined and compared to those obtained with wild-type TPMT. This functional analysis suggests that these rare allelic variants are defective TPMT alleles. The His(227)Gln variant retained only 10% of the intrinsic clearance value (V(max)/K(m) ratio) of the wild-type enzyme. The Ser(125)Leu and Gly(144)Arg variants were associated with a significant decrease in intrinsic clearance values, retaining about 30% of the wild-type enzyme, whereas the Glu(28)Val variant produced a more modest decrease (57% of the wild-type enzyme). The data suggest that the sporadic contribution of the rare Glu(28)Val, Ser(125)Leu, Gly(144)Arg, and His(227)Gln variants may account for the occurrence of altered metabolism of TPMT substrates. These findings improve our knowledge of the genetic basis of interindividual variability in TPMT activity and would enhance the efficiency of genotyping methods to predict patients at risk of inadequate responses to thiopurine therapy.

Drug interactions: Proteins, pumps, and P-450s

The two major concerns in drug safety are adverse drug reactions and drug interactions. When multiple drug therapies are prescribed, drug interactions become an important consideration for patients and physicians. The life of a drug is reviewed with emphasis on absorption, distribution, metabolism, and excretion. Pharmacokinetic and pharmacodynamic mechanisms for drug interactions are reviewed. The contributions of P-glycoprotein, pharmacogenetic variation, and genetic polymorphisms to drug interactions are highlighted. Prediction of drug interactions is possible with knowledge of which agents are likely to cause alterations in drug metabolism. (J Am Acad Dermatol 2002;47:467-84.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should have an understanding of the life of a drug. This knowledge should help predict important potential drug interactions.

Immunosuppressive and cytotoxic drugs in the treatment of rheumatic skin disorders

Cytotoxic and immunosuppressive drugs are regularly used to treat proliferative, immunologically mediated inflammatory disorders and some neoplastic diseases of the skin. Methotrexate, azathioprine, mycophenolate mofetil, cyclosporin cyclophosphamide, chlorambucil, and other related drugs have potential benefits in the treatment of severe and/or recalcitrant rheumatic skin diseases. The therapeutic window for these agents is narrow. The major uses of these drugs are for life-threatening cutaneous disorders or as steroid-sparing agents.

Thioguanine for refractory psoriasis: a 4-year experience

BACKGROUND

A variety of systemically administered drugs are used to treat psoriasis, including methotrexate, cyclosporine, acitretin, and hydroxyurea. Unfortunately, some patients are unresponsive to these agents. For others, side effects and cumulative toxicity prevent continued use.

OBJECTIVE

Our purpose is to report the results of thioguanine (6-thioguanine) treatment of 21 patients with refractory psoriasis.

METHODS

We conducted a retrospective review of the treatment courses of 21 patients with psoriasis who were treated with thioguanine. Daily dosing and pulse dosing were both used, from 20 mg two times a week to 120 mg daily. All patients had been treated with other systemic therapies, and the majority (86%) had been treated with methotrexate.

RESULTS

Patient outcome (response to treatment relative to baseline) was classified into 3 groups: those with more than 90% improvement, those with between 50% and 90% improvement, and those with less than 50% improvement. Outcome data were based on the patient's subjective rating of disease severity before the start of thioguanine therapy and during the entire treatment course. Of the 18 patients able to be evaluated, 14 of 18 (78%) had dramatic improvement (>90%); 3 of 18 (17%) had lesser improvement (50%-90%); and only 1 of 18 had less than 50% improvement. The mean duration of treatment was 15.5 months. The primary side effect was myelosuppression, mild in 9 of 18 (white blood cell counts ranging from 1600-3700/microL; platelet counts ranging from 90,000-122,000/microL, and hematocrit values ranging from 24%-31%), and severe in 1 of 18 (white blood cell count of 1300/microL, platelet count of 17,000/microL, and hematocrit of 20%).

CONCLUSION

Thioguanine appears to be an effective treatment for patients with severe recalcitrant psoriasis. Myelosuppression is a significant, but easily monitored side effect that can now be more accurately predicted by determining thiopurine methyltransferase levels before starting thioguanine. Further prospective studies are needed to establish criteria, which will maximize efficacy of this drug in the treatment of psoriasis and minimize toxicity.

Clinical pharmacology of inflammatory bowel disease therapies

Knowledge about the clinical pharmacology of medical therapy of inflammatory bowel disease has incrementally advanced. Small studies with mesalamine have suggested that intestinal mucosal concentrations of mesalamine may predict clinical response to mesalamine therapy. Increased expression of glucocorticoid receptor beta and increased expression of the multidrug resistance drug pump P-glycoprotein 170 have been proposed as markers of drug resistance to glucocorticoids. A baseline determination of thiopurine methyltransferase phenotype or genotype may predict early leukopenia in patients treated with azathioprine or 6- mercaptopurine. Serial measurement of erythrocyte 6-thioguanine nucleotides may be useful in tailoring the dose of these medications. A loading dose of intravenous azathioprine does not accelerate the time to response in patients with steroid-treated Crohn's disease; however, standard azathioprine may work more quickly than previously reported. Methotrexate, 15 to 25 mg/wk, is effective for the treatment of Crohn's disease (active or in remission), and there is no significant difference in the erythrocyte concentrations of methotrexate polyglutamate in patients with inflammatory bowel disease receiving 15 mg, compared with 25 mg, subcutaneously on a weekly basis.

Systemic therapy of atopic dermatitis

Atopic dermatitis is a chronic, relapsing, inflammatory skin disease. Topical therapy is the mainstay, but patients with widespread moderate to severe atopic dermatitis may require systemic therapy. Immunosuppressants, immune response modifiers, antihistamines and antibiotics are among the classes of systemic medications frequently used to treat extensive atopic dermatitis; the indications and scientific support for the use of these and other less commonly used medications will be reviewed in this article.

Severe 6-thioguanine-induced marrow aplasia in a child with acute lymphoblastic leukemia and inherited thiopurine methyltransferase deficiency

6-thioguanine (6TG) is undergoing investigation for use in the maintenance phase of acute lymphoblastic leukemia (ALL). Just as with 6-mercaptopurine (6MP), it is be expected that 6TG would cause pancytopenia in individuals with inherited thiopurine methyltransferase (TPMT) deficiency. We report the first case of severe and prolonged pancytopenia caused by 6-thioguanine in an 8-year-old boy with ALL and inherited TPMT deficiency. Neutropenia lasted 67 days, whereas anemia and thrombocytopenia did not recover for 96 days. To obviate this life-threatening complication, clinicians should consider assaying TPMT activity before initiating therapy with 6MP and, particularly, 6TG in children with ALL.

Allelic variants of the thiopurine S-methyltransferase deficiency in patients with ulcerative colitis and in healthy controls

OBJECTIVE

Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme that catalyzes the inactivation of mercaptopurine, azathioprine, and thioguanine. The genetic polymorphisms in the TPMT gene that regulate TPMT activity are inherited as an autosomal recessive trait and patients with genetically determined low levels of TPMT activity develop severe myelosuppression when treated with standard doses of the above-mentioned drugs. We have analyzed the frequencies of the allelic variants of the TPMT gene in a white European population of healthy blood donors from Spain and The Netherlands, and in a group of patients suffering from ulcerative colitis (UC) with a similar genetic background.

METHODS

Two hundred and thirteen unrelated healthy individuals (HC) and 146 UC patients were typed for the polymorphic sites at positions 460 (G-->A) and 719 (A-->G) of the TPMT gene using specific polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) methods.

RESULTS

There were no significant differences between the allele frequencies observed in the group of UC patients and those of the control group (10% of cases were heterozygous carriers of a TPMT mutant allele). The most frequent mutant allele in both UC and HC groups was TPMT3A (A460-->G719) (60% of carriers). TPMT3B (A460-->A719) and TPMT3C (G460-->G719) alleles were more often found in our study than in previously reported studies, reflecting the different genetic backgrounds of the European populations analyzed.

CONCLUSIONS

Genotyping methods provide a simple and reliable screening to identify patients with a high risk of developing severe bone marrow toxicity if treated with thiopurine drugs. In UC patients, TPMT genotype should be determined before the initiation of azathioprine therapy.

Old, new, and emerging therapies for atopic dermatitis

Atopic dermatitis is the most common skin condition in children under the age of 11 years. The chronic, cyclical, pruritic course of AD exacts a huge financial and emotional toll on its sufferers. Confusion about appropriate skin care and the role of allergic factors further complicates management. Although diligent moisturization and judicious use of topical steroids remain the therapeutic standard, new, effective local and systemic agents are now available, and several promising nonsteroidal products may be available soon.

Tilapia (Oreochromis niloticus) dosed with azathioprine display immune effects similar to those seen in mammals, including apoptosis

Azathioprine, an anti-neoplastic drug and therapeutic immunosuppressant, was administered intraperitoneally at 10.0 and 50.0 mg/kg to 3-6-month-old tilapia (Oreochromis niloticus). Consistent alterations in immune cellular parameters of the blood, pronephros (hematopoietic kidney) and spleen were observed. Peripheral blood total cellularity decreased as the azathioprine dose increased, to approximately half that of the control. Differential analysis of white blood cells indicated a decline in lymphocyte number, in particular, with increased dosage of azathioprine. Pronephric total cellularity was depressed in fish receiving the 10.0 or 50.0 mg/kg dose. In contrast, both splenic weight and splenic total cellularity increased proportionately with the increase in the drug dosage. Histopathologic examination of the spleens showed normal patterns for both control and 10.0 mg/kg dose groups. At 50.0 mg/kg, spleens were characterized by marked expansion of the white pulp, although lymphocytes were rare. Melanomacrophage centers at the higher dose were also larger and more numerous than in the control group. Evaluation of splenic and pronephric leukocytes with apoptotic markers showed an increase in apoptotic cells in the pronephros with increasing drug dose. These changes in fish are consistent with those seen in humans and laboratory rodents dosed with azathioprine, suggesting that fish may be potentially useful as preliminary models for detecting immunosuppressive compounds.

Immunosuppressive agents in dermatology. An update

Azathioprine, cyclophosphamide, methotrexate, and cyclosporine are the immunosuppressive agents most commonly used by dermatologists. Azathioprine has a relatively good safety profile and is therefore often preferred for the treatment of chronic eczematous dermatitides and bullous disorders. Awareness of the role of genetic polymorphisms in its metabolism can increase the efficacy and safety of this drug. Cyclophosphamide is an antimetabolite that has a more rapid onset of immunosuppressive effect than azathioprine, but has significant short-term and long-term toxicity. It is of use in fulminant, life-threatening cutaneous disease. Methotrexate is an antimetabolite that has significant anti-inflammatory activity. Despite its hepatotoxicity, its role in inflammatory dermatoses is broadening. Likewise, the role of cyclosporine is being expanded. This drug has potent T-cell inhibitory effects secondary to interference with intracellular signal transduction. Given the evidence for cumulative renal toxicity, it currently has a role in the short-term treatment of refractory psoriasis and atopic dermatitis, as well as in select inflammatory dermatoses. Familiarity with disease-specific clinical efficacy, side-effect profile, and dosage allows the successful and judicious use of these drugs in dermatologic disorders.

Mechanisms of drug reactions: the metabolic track

Hypersensitivity syndrome (HSR) describes a drug-induced symptom complex consisting of fever, rash, and internal organ involvement. Although these reactions are rare, they are very important because of their severity and unpredictability. The metabolic conversion of drugs to chemically-reactive products is now established as a prerequisite for many idiosyncratic drug reactions. In the setting of HSR, an imbalance in the rates of formation of reactive metabolites and of enzymatic detoxification can lead to accumulation of these byproducts. Reactive metabolites could act as haptens eliciting an immune response, covalently bind target proteins causing cell death, or interact with nucleic acids leading to mutations. The lymphocyte toxicity assay (LTA) provides an in vitro assessment of host susceptibility to reactive metabolites of a given drug. It has validated the clinical finding of increased risk of HSR in first degree relatives of patients. It is hoped that the LTA will be used to predict host susceptibility before drug exposure. Ultimately it is hoped that the genetic defects that lead to drug reactions will be identified. This would improve drug development safety and allow primary prevention of serious reactions.