The absorption of low-dose methotrexate in patients with inflammatory bowel disease

Evidence-based efficacy of methotrexate in adult Crohn's disease in different intestinal and extraintestinal indications

INTRODUCTION

Methotrexate (MTX) is included in the therapeutic armamentarium of Crohn's disease (CD), although its positioning is currently uncertain in an era in which many effective biological drugs are available. No systematic reviews or meta-analysis have stratified the clinical outcomes of MTX according to the specific clinical scenarios of its use.

METHODS

Medline, PubMed and Scopus were used to extract eligible studies, from database inception to May 2021. A total of 163 studies were included. A systematic review was performed by stratifying the outcomes of MTX according to formulation, clinical indication and criteria of efficacy.

RESULTS

The use of MTX is supported by randomized clinical trials only in steroid-dependent CD, with similar outcomes to thiopurines. The use of MTX in patients with steroid-refractoriness, failure of thiopurines or in combination with biologics is not supported by high levels of evidence. Combination therapy with biologics can optimize the immunogenic profile of the biological drug, but the impact on long-term clinical outcomes is described only in small series with anti-TNFα. Other off-label uses, such as fistulizing disease, mucosal healing, postoperative prevention and extraintestinal manifestations, are described in small uncontrolled series. The best performance in most indications was shown by parenteral MTX, favouring higher doses (25 mg/week) in the induction phase.

DISCUSSION

Evidence from high-quality studies in favour of MTX is scarce and limited to the steroid-dependent disease, in which other drugs are the leading players today. Many limitations on study design have been found, such as the prevalence of retrospective underpowered studies and the lack of stratification of outcomes according to specific types of patients and formulations of MTX.

CONCLUSION

MTX is a valid option as steroid-sparing agent in steroid-dependent CD. Numerous other clinical scenarios require well-designed clinical studies in terms of patient profile, drug formulation and dosage, and criteria of efficacy.

Review article: The pharmacokinetics and pharmacodynamics of drugs used in inflammatory bowel disease treatment

BACKGROUND

The following review is a compilation of the recent advances and knowledge on the behaviour of the most frequently used compounds to treat inflammatory bowel disease in an organism.

RESULTS

It considers clinical aspects of each entity and the pharmacokinetic/pharmacodynamic relationship supported by the use of plasma monitoring, tissue concentrations, and certain aspects derived from pharmacogenetics.

Involvement of Multiple Transporters-mediated Transports in Mizoribine and Methotrexate Pharmacokinetics

Mizoribine is administered orally and excreted into urine without being metabolized. Many research groups have reported a linear relationship between the dose and peak serum concentration, between the dose and AUC, and between AUC and cumulative urinary excretion of mizoribine. In contrast, a significant interindividual variability, with a small intraindividual variability, in oral bioavailability of mizoribine is also reported. The interindividual variability is mostly considered to be due to the polymophisms of transporter genes. Methotrexate (MTX) is administered orally and/or by parenteral routes, depending on the dose. Metabolic enzymes and multiple transporters are involved in the pharmacokinetics of MTX. The oral bioavailability of MTX exhibits a marked interindividual variability and saturation with increase in the dose of MTX, with a small intraindividual variability, where the contribution of gene polymophisms of transporters and enzymes is suggested. Therapeutic drug monitoring of both mizoribine and MTX is expected to improve their clinical efficacy in the treatment of rheumatoid arthritis.

Patient-specific approach to combination versus monotherapy with the use of antitumor necrosis factor α agents for inflammatory bowel disease

It is likely that the debate surrounding combination versus monotherapy will continue for the foreseeable future, because there will always be a risk-benefit ratio that must be taken into account with IBD therapy. However, because more studies now include a thoughtful approach with respect to concomitant IS therapy with inclusion of objective end points such as mucosal healing and drug pharmacokinetics, it is anticipated that this issue will become clearer over time, which will benefit patients and practitioners. The BRIDGe approach described in this review is a useful tool but must be taken in the context of the subjectivity of much of the analyzed data and the individual perspectives that influenced the results. It cannot in any way be interpreted as a clinical practice guideline or standard of care, but rather a tool that seeks to interpret and incorporate the available literature and, it is hoped, aid clinicians in making sense of the conflicting data in this area. The decision regarding the risks and benefits of combination therapy must be carefully weighed in each individual patient.

Methotrexate in ulcerative colitis: a Spanish multicentric study on clinical use and efficacy

BACKGROUND

Few data are available on the efficacy of methotrexate (MTX) in ulcerative colitis (UC).

AIM

To evaluate the efficacy and safety of MTX in UC patients.

PATIENTS AND METHODS

UC patients who had been treated with MTX were identified from the databases of 8 Spanish IBD referral hospitals. Patients were included in the study if they received MTX for steroid dependency or steroid refractoriness. Therapeutic success was defined as the absence of UC-related symptoms, complete steroid withdrawal and no requirement of rescue therapies within the first 6 months after starting MTX.

RESULTS

Forty patients were included, 70% treated for steroid dependency and 27% for steroid refractoriness. Thiopurines had been previously attempted in 87.5% of patients. The median dose of MTX used for induction was 25mg (IIQ 17.5-25) weekly given parenterally in 82.5% of cases. Eighty-five percent of patients were on steroids when MTX was started. Forty-five percent of patients met criteria for therapeutic success. Initial treatment failures were mainly due to inefficacy (50%) or intolerance (36%). After a median follow-up of 28 months (IQR 22-47), 38% of patients with initial therapeutic success required new steroid courses, 22% started biological therapy, and only 1 patient required colectomy. The cumulative probability of maintaining steroid-free clinical remission was 60%, 48%, and 35% at 6, 12, and 24 months after starting MTX, respectively. Eleven patients (27.5%) experienced adverse events, leading to MTX discontinuation in only 8 of them.

CONCLUSIONS

MTX appears to be effective to maintain clinical remission in UC, at least in the short-term, with an acceptable safety profile.

Efficacy of methotrexate in ulcerative colitis: failure or promise

BACKGROUND

Low-dose methotrexate is a widely used and efficacious therapy in chronic inflammatory disorders such as psoriasis and rheumatoid arthritis. Prospective randomized controlled trials have demonstrated the efficacy of parenteral methotrexate in Crohn's disease (CD). We performed a systematic review of the efficacy of methotrexate in ulcerative colitis (UC) and discuss the results in the context of the known pharmacokinetics and adverse events of methotrexate therapy in inflammatory bowel diseases and other inflammatory conditions.

MATERIALS AND METHODS

We performed a systematic review of the literature in Medline, Embase, and Web of Science. All publications describing patients with UC treated with methotrexate were included.

RESULTS

We identified 12 studies or retrospective case series and 5 meeting abstracts that met the inclusion criteria. Only 1 study reported a prospective randomized placebo-controlled trial using methotrexate at a dose of 12.5 mg orally with no significant clinical benefit. However, the majority of uncontrolled retrospective analyses suggest a clinical response to methotrexate therapy in a range of 30%-80% when the drug is applied by parenteral route in doses between 20-25 mg.

CONCLUSIONS

The only randomized controlled trial of methotrexate in UC employed oral dosing and doses lower than those shown to be effective in CD and did not demonstrate efficacy, whereas uncontrolled, retrospective studies using doses and routes of administration similar to those employed in CD suggest benefit. Well-designed, prospective, placebo-controlled trials of methotrexate in UC are needed.

Low-dose oral methotrexate for maintaining Crohn's disease remission: where we stand

Methotrexate has been considered a second-line immunomodulating therapy, behind azathioprine (AZA) or its metabolite 6-mercaptopurine (6-MP), for the treatment of Crohn's disease (CD). Approximately 27% to 50% of patients with refractory CD are intolerant or resistant to AZA or 6-MP. Two well-designed randomized double-blind placebo-controlled trials have demonstrated that low-dose methotrexate (<25 mg/wk), given intramuscularly (IM), is effective in inducing and maintaining remission in CD. In clinical practice, IM injection involves an inconvenience for patients and higher costs. Furthermore, frequent IM injections increase the risk of complications such as peripheral nerve injury, local irritation, pain, bleeding, fibrosis, abscess formation, gangrene, and contractures. Alternatively, subcutaneous (SQ) injection has been advocated because it has been shown to have similar pharmacokinetics to IM injection. However, because of a recent and ongoing national shortage of parenteral methotrexate, patients who were receiving IM methotrexate had to switch to the oral form until the parenteral formulation becomes available. Oral methotrexate has been used with great success in treatment of rheumatoid arthritis and psoriasis for the past 50 years. However, the data on the usage of low-dose oral methotrexate in maintaining CD remission are scanty and controversial. The purpose of this article is to review the mechanism of action, absorption, and the objective evidence in supporting the use of oral methotrexate in maintaining CD remission.

Review article: practical management of inflammatory bowel disease patients taking immunomodulators

Azathioprine, mercaptopurine, methotrexate, ciclosporin and tacrolimus all have their respective niches in the treatment of inflammatory bowel disease. These immunomodulators are potent and effective medications; however, they potentially have serious toxicity. To maximize benefit and minimize risk, clinicians must understand the mechanism of action, appropriate indications, range of toxicity and proper dosing of these medications. Furthermore, once initiating therapy, patients need to be monitored appropriately for evidence of efficacy and toxicity. This review includes the rationale behind recommendations for the management and monitoring of patients using immunomodulators. For the purine antagonists--azathioprine and mercaptopurine--the evidence for utility of thiopurine methyltransferase testing and mercaptopurine metabolite monitoring is addressed. The roles of liver biopsy and screening for methylenetetrahydrofolate reductase mutations in patients taking methotrexate are reviewed. With appropriate monitoring, the calcineurin inhibitors--ciclosporin and tacrolimus--can be used safely and effectively. Immunomodulators are important agents for the treatment of Crohn's disease and ulcerative colitis, and prescribing clinicians should be comfortable recognizing both their value and their limitations.

Membrane permeability and antipyrine absorption in a rat model of ischemic colitis

The aim of this study was to determine whether the duration of ischemia affects antipyrine absorption in the large intestine. This was carried out in a rat model of ischemic colitis in which ischemia and associated inflammation was induced by marginal vessel ligation. Blood flow was disrupted by positioning an o-ring around the distal rectum and ligating the marginal vessel at two locations in the hind-gut ligament artery region. Ligation was performed for 1, 2, 3, and 5h. We assessed large intestine damage by measuring key indicators of inflammation, myeloperoxidase (MPO) activity and thiobarbituric acid reactant substrates (TBARS) in the mucosa and by histological staining with hematoxylin-eosin stain. Antipyrine membrane permeability was assessed in Ussing-type diffusion chambers, and related pharmacokinetics were calculated from antipyrine plasma concentration measurements following colon administration of the drug. Vessel ligation caused some sloughing of epithelial cells and elevated the MPO and TBARS levels. Prolonged ligation failed to affect the apparent permeability coefficient (P(app)) of antipyrine. Prolonged ligation, however, gradually increased plasma antipyrine concentrations to near control levels. This increase was paralleled by increases in the absorption rate constant AUC and antipyrine bioavailability. Taken together, these results suggest that the absorption kinetics of antipyrine may depend on blood flow changes in the large intestine that occur with inflammation.

Review article: monitoring of immunomodulators in inflammatory bowel disease

The armamentarium of medications for the treatment of inflammatory bowel disease is growing and becoming more complicated to use. Immunomodulators are a class of medications that have found a niche for the treatment of Crohn's disease and ulcerative colitis. Because of the mounting supporting evidence for efficacy, the most commonly-used immunomodulators are azathioprine, mercaptopurine, methotrexate and ciclosporin. These medications are being used more often due to their steroid-sparing and potentially surgery-sparing effects. Immunomodulators are also known for a significant side-effect profile and require careful monitoring. This review provides the latest information for clinicians on efficacy, side-effects, dosing and monitoring of these medications for treatment of inflammatory bowel disease.

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.

Comparison between methotrexate and azathioprine in the treatment of chronic active Crohn's disease: a randomised, investigator-blind study

BACKGROUND AND AIMS

The efficacy of azathioprine in the treatment of chronic active Crohn's disease is well established. However, this drug has a long onset of action. Methotrexate has also been shown to be effective in chronic active Crohn's disease. The aim of this study was to evaluate the efficacy and safety of methotrexate in comparison with azathioprine, and to establish whether methotrexate has a shorter onset of action in this setting.

METHODS

Patients with chronic active Crohn's disease were admitted to this investigator-blind study. Chronicity was defined as the need for steroid therapy of > or = 10 mg/day for at least 4 months during the preceding 12 months, with at least one attempt to discontinue treatment. The disease had to be clinically active at entry, with a Crohn's Disease Activity Index of > or = 200. Six patients treated with azathioprine and methotrexate, respectively, were found to have enterocutaneous and perianal fistulas. At entry, all patients received prednisolone (40 mg once a day) which was tapered over a period of 12 weeks unless their clinical condition deteriorated. All patients were randomised to receive i.v. methotrexate 25 mg/week, or oral azathioprine 2 mg/kg per day, for a 6-month follow-up period. After the first 3 months, methotrexate was switched to oral administration maintaining the same dose. The primary efficacy outcome considered was the proportion of patients entering first remission after 3 and 6 months of therapy. Clinical remission was defined as the lack of need for steroid treatment and a Crohn's Disease Activity Index score of < or = 150 points at each scheduled visit.

RESULTS

In the 54 patients (26 F, 28 M, mean age 34 years, range 18-60) randomly assigned to methotrexate (n=27) or azathioprine (n=27), no statistically significant difference was found between the two treatment regimens with respect to remission rate after 3 (methotrexate 44%, azathioprine 33%, p=0.28, (95% CI, 0.369-0.147), and 6 months (methotrexate 56%, azathioprine 63%, p=0.39, 95% CI, 0.187-0.335), respectively. Six patients withdrew from therapy due to adverse events: 3/27 (11%) in methotrexate and 3/27 (11%) in azathioprine. Drug-related adverse events (asthenia, nausea and vomiting) that did not require withdrawal from therapy were more frequent in the methotrexate group (azathioprine: 2/27 (7%); methotrexate: 12/27 (44%), p=0.00009). The frequency of these adverse events was comparable during the intravenous or oral administration of the drug.

CONCLUSIONS

This study confirms that methotrexate is effective in inducing remission in patients with chronic active Crohn's disease, therapeutic efficacy being comparable, but not faster, than that of azathioprine.

Bioavailability of oral vs. subcutaneous low-dose methotrexate in patients with Crohn's disease

BACKGROUND

Oral methotrexate and folic acid are partly absorbed by a common intestinal transporter.

AIM

: To determine the relative bioavailability of oral low-dose methotrexate administered with and without concomitant folic acid vs. subcutaneous administration in patients with stable Crohn's disease.

METHODS

Ten patients were randomized to receive their regular maintenance dose of methotrexate (15-25 mg) for three consecutive weeks: orally, orally with 5 mg folic acid or subcutaneously. Blood samples were drawn at specified intervals during 24 h, and methotrexate levels were determined by fluorescence immunoassay. Areas under the curve extrapolated to infinity (AUC infinity ) were compared between the three routes.

RESULTS

The geometric mean AUC infinity values (95% confidence intervals) were 360 nmol x h/L (301-430 nmol x h/L), 261 nmol x h/L (214-318 nmol x h/L) and 281 nmol x h/L (209-377 nmol x h/L) per milligram of methotrexate administered for subcutaneous, oral and oral with folic acid administration, respectively (P < 0.05 and P < 0.01 for oral with folic acid and oral vs. subcutaneous administration, respectively). The geometric mean relative bioavailabilities (95% confidence intervals) were 0.73 (0.62-0.86) and 0.77 (0.60-0.99) for oral and oral with folic acid administration, respectively (difference not significant).

CONCLUSIONS

In patients with stable Crohn's disease, the oral bioavailability of methotrexate is highly variable and averages 73% of that of subcutaneous administration. Concomitant folic acid has no significant effect on the bioavailability. Dose adjustments based on individual pharmacokinetic assessment should be considered when switching patients from parenteral to oral therapy.

Low-dosage methotrexate for treatment and maintenance of remission in patients with inflammatory bowel disease

A literature search was conducted to examine the safety and effectiveness of low-dosage methotrexate for treatment and maintenance of remission in patients with inflammatory bowel disease. Nine published articles indicated that for patients with Crohn's disease, oral or intramuscular methotrexate 20-25 mg/week is safe and effective to induce remission, followed by a lower dosage to maintain remission. In addition, methotrexate allows for corticosteroid dosage reduction. Therapy may be continued until the disease flares or adverse events occur. Evidence is insufficient to support methotrexate as treatment for ulcerative colitis.

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.

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.

The differential cytotoxicity of methotrexate in rat hepatocyte monolayer and spheroid cultures

It is important to assess the usefulness of long-term in vitro liver models for studying chronic toxicity, since acute assays may not reflect the in vivo situation. A potential long-term hepatocyte culture (i.e. liver spheroids) was investigated and compared to primary rat hepatocyte monolayer cultures following exposure to methotrexate (MTX), a well-documented chronic hepatotoxin. Following up to 7 days' treatment with MTX, cultures were morphologically assessed and assayed for enzyme leakage, intracellular reduced glutathione (GSH) and adenosine triphosphate (ATP). Spheroids maintained higher concentrations of GSH over the 14-day culture and ATP was maintained, but at a concentration not significantly different from monolayer cultures. Treatment of monolayer cultures resulted in concentration-related decreases in GSH and ATP, accompanied by enzyme leakage. In contrast, only ATP was affected following treatment of spheroids for 7 days. Spheroids appeared to be less sensitive to exposure to MTX, when compared with monolayer cultures. This may result from the maintenance of cellular functions, or from the lack of compound penetration into the three-dimensional spheroid structure. Therefore, the usefulness of spheroids to chronic in vitro toxicity testing may be limited.

Therapy for Crohn disease

Medical therapy for Crohn disease has advanced incrementally: Small, non-definitive controlled trials of mesalamine continue to be reported, but the results are not sufficient to change the conclusion of a large meta-analysis that shows only marginal benefit of mesalamine in Crohn disease. Low-dose, controlled ileal-release budesonide is not effective for preventing postoperative recurrence of Crohn disease. A loading dose of intravenous azathioprine does not accelerate the time to response in patients with steroid-treated Crohn disease; however, standard azathioprine may work more quickly than previously reported. Mycophenolate mofetil may be therapeutically equivalent to azathioprine for active Crohn disease. There is a trend toward benefit of oral methotrexate (15 mg/wk) for active Crohn disease, and there is no significant difference in the blood concentrations of methotrexate in patients with inflammatory bowel disease who receive methotrexate (15 or 25 mg weekly) administered subcutaneously. Results in a pilot study suggest that tacrolimus may close perianal fistulas in patients with Crohn disease. The anti-tumor necrosis factor antibody infliximab is effective in closing perianal and enterocutaneous fistulas and in maintaining remission in patients with Crohn disease. Infliximab also leads to endoscopic and histologic remission. There is a trend toward benefit of subcutaneous recombinant interleukin-11 for active Crohn disease. Two pilot studies have shown that thalidomide may be of benefit in patients with refractory Crohn disease.

Systemic and intestinal pharmacokinetics of methotrexate in patients with inflammatory bowel disease

BACKGROUND

The pharmacokinetics of low-dose subcutaneous methotrexate have not been determined throughout the standard weekly dosing interval. It is not known whether methotrexate concentrations in the gastrointestinal tract are sufficient for pharmacologic activity in inflammatory bowel disease.

METHODS

Ten patients with inflammatory bowel disease participated in the study. After the patients started taking 15 or 25 mg subcutaneous methotrexate once a week, erythrocyte methotrexate concentration was measured every 2 weeks. The absorption, rectal distribution, metabolism, and elimination of methotrexate were measured. The effect of methotrexate on proliferation of an intestinal epithelial cell line was determined.

RESULTS

After weekly subcutaneous administration of methotrexate was begun, trough erythrocyte concentration rose to reach a plateau after 6 to 8 weeks, ranging from 150 to 300 nmol/L. More than 90% of subcutaneously administered methotrexate was rapidly excreted in the urine. The methotrexate plasma time course after subcutaneous administration fit a 2-compartment first-order model with biphasic elimination and trough concentration of about 1 nmol/L. Trough and peak methotrexate concentrations (mean value +/- SD) were 64 +/- 33 and 206 +/- 64 fmol/mg in the rectal mucosa and 4 +/- 3 and 51 +/- 26 nmol/L in the rectal lumen. These methotrexate concentrations were in the range found to be pharmacologically active against Caco-2 cell growth, that is, a 50% inhibitory concentration from 10 to 46 nmol/L.

CONCLUSION

Subcutaneous methotrexate was well absorbed and distributed to the site of the lesions in patients with inflammatory bowel disease. Methotrexate was concentrated intracellularly in blood and in the rectum. The methotrexate concentration in the rectal mucosa remained within a pharmacologically active range throughout the dosing interval. The findings represent a pharmacologic explanation for the sustained efficacy of weekly methotrexate therapy.