5.1       Renal Impairment

Renal impairment, including minimal change disease, acute and chronic interstitial nephritis, and renal failure, has been reported in patients given products such as CANASA that contain mesalamine or are converted to mesalamine. In animal studies, the kidney was the principal organ of mesalamine toxicity [see Adverse Reactions (6.2), Nonclinical Toxicology (13.2)]. 

Evaluate renal function prior to initiation of CANASA and periodically while on therapy.

Evaluate the risks and benefits of using CANASA in patients with known renal impairment or a history of renal disease or taking concomitant nephrotoxic drugs. Discontinue CANASA if renal function deteriorates while on therapy [see Drug Interactions (7.1), Use in Specific Populations (8.6)].

5.2       Mesalamine-Induced Acute Intolerance Syndrome

Mesalamine has been associated with an acute intolerance syndrome that may be difficult to distinguish from an exacerbation of ulcerative colitis. Although the exact frequency of occurrence has not been determined, it has occurred in 3% of patients in controlled clinical trials of mesalamine or sulfasalazine. Symptoms include cramping, acute abdominal pain and bloody diarrhea, and sometimes fever, headache, malaise, pruritus, conjunctivitis, and rash. Monitor patients for worsening of these symptoms while on treatment. If acute intolerance syndrome is suspected, promptly discontinue treatment with CANASA.

5.3       Hypersensitivity Reactions

Hypersensitivity reactions have been reported in patients taking sulfasalazine. Some patients may have a similar reaction to CANASA or to other compounds that contain or are converted to mesalamine.

As with sulfasalazine, mesalamine-induced hypersensitivity reactions may present as internal organ involvement, including myocarditis, pericarditis, nephritis, hepatitis, pneumonitis and hematologic abnormalities. Evaluate patients immediately if signs or symptoms of a hypersensitivity reaction are present. Discontinue CANASA if an alternative etiology for the signs and symptoms cannot be established. 

5.4       Hepatic Failure

There have been reports of hepatic failure in patients with pre-existing liver disease who have been administered other products containing mesalamine. Evaluate the risks and benefits of using CANASA in patients with known liver impairment. 

5.5       Severe Cutaneous Adverse Reactions

Severe cutaneous adverse reactions, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP) have been reported in association with the use of mesalamine [see Adverse Reactions (6.2)]. Discontinue CANASA at the first signs or symptoms of severe cutaneous adverse reactions or other signs of hypersensitivity and consider further evaluation.

5.6       Photosensitivity

In patients treated with mesalamine or sulfasalazine who have pre-existing skin conditions such as atopic dermatitis and atopic eczema have reported more severe photosensitivity reactions. Advise patients to avoid sun exposure, wear protective clothing, and use a broad-spectrum sunscreen when outdoors.

5.7       Nephrolithiasis

Cases of nephrolithiasis have been reported with the use of mesalamine, including stones of 100% mesalamine content. Mesalamine-containing stones are radiotransparent and undetectable by standard radiography or computed tomography (CT). Ensure adequate hydration during treatment with CANASA.

5.8       Interaction with Laboratory Test for Urinary Normetanephrine

Use of mesalamine may lead to spuriously elevated test results when measuring urinary normetanephrine by liquid chromatography with electrochemical detection, because of the similarity in the chromatograms of normetanephrine and mesalamine's main metabolite, N-acetylaminosalicylic acid. Consider an alternative, selective assay for normetanephrine. 

6.1       Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The most common adverse reactions in adult patients with mildly to moderately active ulcerative proctitis in double-blind, placebo-controlled trials are summarized in the Table 1 below.

In a multicenter, open-label, randomized, parallel group study in 99 patients comparing the CANASA 1000 mg suppository administered nightly to that of the mesalamine 500 mg suppository twice daily. The most common adverse reactions in both groups were headache (14%), flatulence (5%), abdominal pain (5%), diarrhea (3%), and nausea (3%). Three (3) patients discontinued medication because of an adverse reaction; one of these adverse reactions (headache) was deemed possibly related to study medication. The recommended dosage of CANASA is 1000 mg administered rectally once daily at bedtime [see Dosage and Administration (2)].  

6.2       Postmarketing Experience

The following adverse reactions have been identified during post-approval use of CANASA or other mesalamine-containing products. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

• Body as a Whole: drug fever, fatigue, lupus-like syndrome, medication residue
  
• Cardiac Disorders: myocarditis, pericarditis, pericardial effusion [see Warnings and Precautions (5.3)]
  
• Endocrine: Nephrogenic diabetes insipidus
  
• Eye disorders: eye swelling
  
• Gastrointestinal Disorders: abdominal cramps, abdominal distension, anal pruritus, anorectal discomfort, constipation, feces discolored, flatulence, frequent bowel movements, gastrointestinal bleeding, mucus stools, nausea, painful defecation, pancreatitis, proctalgia, rectal discharge, rectal tenesmus, stomach discomfort, vomiting  
  
• Hepatic Disorders: cholestatic jaundice, hepatitis, jaundice, Kawasaki-like syndrome including changes in liver enzymes, liver necrosis, liver failure
  
• Hematologic Disorders: agranulocytosis, aplastic anemia, thrombocytopenia
  
• Neurological/Psychiatric Disorders: Guillain-Barre syndrome, peripheral neuropathy, transverse myelitis, intracranial hypertension
  
• Renal Disorders: interstitial nephritis, renal failure, minimal change disease, nephrolithiasis [see Warnings and Precautions (5.1, 5.7)]
  ○ Urine discoloration occurring ex-vivo caused by contact of mesalamine, including inactive metabolite, with surfaces or water treated with hypochlorite containing bleach
  
• Respiratory, Thoracic and Mediastinal Disorders: hypersensitivity pneumonitis (including allergic alveolitis, eosinophilic pneumonitis, interstitial pneumonitis), pleuritis/pleurisy
  
• Skin and Subcutaneous Tissue Disorder: alopecia, erythema, erythema nodosum, pruritus, psoriasis, pyoderma gangrenosum, urticaria, SJS/TEN, DRESS and AGEP [see Warnings and Precautions (5.5)]
  
• Urogenital: reversible oligospermia

7.1       Nephrotoxic Agents, Including Non-Steroidal Anti-Inflammatory Drugs

The concurrent use of mesalamine with known nephrotoxic agents, including nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the risk of nephrotoxicity. Monitor patients taking nephrotoxic drugs for changes in renal function and mesalamine-related adverse reactions [see Warnings and Precautions (5.1)].

7.2       Azathioprine or 6-Mercaptopurine

The concurrent use of mesalamine with azathioprine or 6-mercaptopurine and/or other drugs known to cause myelotoxicity may increase the risk for blood disorders, bone marrow failure, and associated complications. If concomitant use of CANASA and azathioprine or 6-mercaptopurine cannot be avoided, monitor blood tests, including complete blood cell counts and platelet counts.

7.3       Interference With Urinary Normetanephrine Measurements

Use of mesalamine may lead to spuriously elevated test results when measuring urinary normetanephrine by liquid chromatography with electrochemical detection, because of the similarity in the chromatograms of normetanephrine and mesalamine's main metabolite, N-acetylaminosalicylic acid. Consider an alternative, selective assay for normetanephrine [see Warnings and Precautions (5.8)].

8.1       Pregnancy

Risk Summary

Limited published data on mesalamine use in pregnant women are insufficient to inform a drug-associated risk. No evidence of teratogenicity was observed in rats or rabbits when treated during gestation with orally administered mesalamine at doses greater than the recommended human intra-rectal dose (see Data).

The estimated background risk of major birth defects and miscarriage for the indicated populations is unknown. Adverse outcomes in pregnancy occur regardless of the health of the mother or the use of medications. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Data

Animal Data

Reproduction studies have been performed in rats at oral doses up to 320 mg/kg/day (about 1.7 times the recommended human intra-rectal dose of CANASA, based on body surface area) and in rabbits at oral doses up to 495 mg/kg/day (about 5.4 times the recommended human intra-rectal dose of CANASA, based on body surface area) following administration during the period of organogenesis, and have revealed no evidence of impaired fertility or harm to the fetus due to mesalamine.

8.2       Lactation

Risk Summary

Mesalamine and its N-acetyl metabolite are present in human milk in undetectable to small amounts (see Data). There are limited reports of diarrhea in breastfed infants. There is no information on the effects of the drug on milk production. The lack of clinical data during lactation precludes a clear determination of the risk of CANASA to an infant during lactation; therefore, the developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for CANASA and any potential adverse effects on the breastfed child from CANASA or from the underlying maternal conditions.  

Clinical Considerations

Monitor breastfed infants for diarrhea.

Data

In published lactation studies, maternal mesalamine doses from various oral and rectal formulations and products ranged from 500 mg to 3 g daily. The concentration of mesalamine in milk ranged from non-detectable to 0.11 mg/L. The concentration of the N-acetyl-5-aminosalicylic acid metabolite ranged from 5 to 18.1 mg/L. Based on these concentrations, estimated infant daily dosages for an exclusively breastfed infant are 0 to 0.017 mg/kg/day of mesalamine and 0.75 to 2.72 mg/kg/day of N-acetyl-5-aminosalicylic acid.

8.4       Pediatric Use

The safety and effectiveness of CANASA in pediatric patients for the treatment of mildly to moderately active ulcerative proctitis have not been established. CANASA was evaluated for the treatment of ulcerative proctitis in a 6-week, open-label, single-arm study in 49 patients 5 to 17 years of age, which only included 14 patients with histologically-confirmed cases of ulcerative proctitis. However, efficacy was not demonstrated. Adverse reactions seen in pediatric patients in this trial (abdominal pain, headache, pyrexia, pharyngolaryngeal pain, diarrhea and vomiting) were similar to those seen in adult patients.

8.5       Geriatric Use

Clinical trials of CANASA did not include sufficient numbers of patients aged 65 years and over to determine whether they respond differently from younger patients. Reports from uncontrolled clinical studies and postmarketing reporting systems suggested a higher incidence of blood dyscrasias (i.e., agranulocytosis, neutropenia and pancytopenia) in patients receiving mesalamine-containing products such as CANASA who were 65 years or older compared to younger patients. Monitor complete blood cell counts and platelet counts in elderly patients during treatment with CANASA. In general, consider the greater frequency of decreased hepatic, renal, or cardiac function, and of concurrent disease or other drug therapy in elderly patients when prescribing CANASA [see Use in Specific Populations (8.6)].

8.6       Renal Impairment

Mesalamine is known to be substantially excreted by the kidney, and the risk of adverse reactions may be greater in patients with impaired renal function. Evaluate renal function in all patients prior to initiation and periodically while on CANASA therapy. Monitor patients with known renal impairment or history of renal disease or taking nephrotoxic drugs for decreased renal function and mesalamine-related adverse reactions. Discontinue CANASA if renal function deteriorates while on therapy [see Warnings and Precautions (5.1), Adverse Reactions (6.2), Drug Interactions (7.1)].

12.1       Mechanism of Action

The mechanism of action of mesalamine is not fully understood, but appears to be a topical anti-inflammatory effect on colonic epithelial cells. Mucosal production of arachidonic acid metabolites, both through the cyclooxygenase pathways, i.e., prostanoids, and through the lipoxygenase pathways, i.e., leukotrienes and hydroxyeicosatetraenoic acids, is increased in patients with ulcerative colitis, and it is possible that mesalamine diminishes inflammation by blocking cyclooxygenase and inhibiting prostaglandin production in the colon.

12.3       Pharmacokinetics

Absorption 

Mesalamine (5-ASA) administered as a rectal suppository is variably absorbed. In patients with ulcerative colitis treated with mesalamine 500 mg rectal suppositories, administered once every eight hours for six days, the mean mesalamine peak plasma concentration (Cmax) was 353 ng/mL (CV=55%) following the initial dose and 361 ng/mL (CV=67%) at steady state. The mean minimum steady state plasma concentration (Cmin) was 89 ng/mL (CV=89%). Absorbed mesalamine does not accumulate in the plasma.

Distribution

Mesalamine administered as a rectal suppository distributes in rectal tissue to some extent.

Elimination 

In patients with ulcerative proctitis treated with mesalamine 500 mg as a rectal suppository every 8 hours for 6 days, the mean elimination half-life was 5 hours (CV=73%) for 5-ASA and 5 hours (CV=63%) for N-acetyl-5-ASA, the active metabolite, following the initial  dose. At steady state, the mean elimination half-life was 7 hours for both 5-ASA and N-acetyl-5-ASA (CV=102% for 5-ASA and 82% for N-acetyl-5-ASA).

Metabolism

The absorbed mesalamine is extensively metabolized, mainly to N-acetyl-5-ASA in the liver and in the gut mucosal wall. In patients with ulcerative colitis treated with one mesalamine 500 mg rectal suppository every eight hours for six days, the peak concentration (Cmax) of N-acetyl-5-ASA ranged from 467 ng/mL to 1399 ng/mL following the initial dose and from 193 ng/mL to 1304 ng/mL at steady state.

Excretion      

Mesalamine is eliminated from plasma mainly by urinary excretion, predominantly as N-acetyl-5-ASA. In patients with ulcerative proctitis treated with mesalamine 500 mg as a rectal suppository every 8 hours for 6 days, 12% or less of the dose was eliminated in urine as unchanged 5-ASA and 8% to 77% was eliminated as N-acetyl-5-ASA following the initial dose. At steady state, 11% or less of the dose was eliminated in the urine as unchanged 5-ASA and 3% to 35% was eliminated as N-acetyl-5-ASA.

13.1       Carcinogenesis, Mutagenesis, Impairment of Fertility

Mesalamine caused no increase in the incidence of neoplastic lesions over controls in a two-year study of Wistar rats fed up to 320 mg/kg/day of mesalamine admixed with diet (about 1.7 times the recommended human intra-rectal dose of CANASA, based on body surface area).

Mesalamine was not mutagenic in the Ames test, the mouse lymphoma cell (TK+/-) forward mutation test, or the mouse micronucleus test.

No effects on fertility or reproductive performance of the male and female rats were observed at oral mesalamine doses up to 320 mg/kg/day (about 1.7 times the recommended human intra-rectal dose of CANASA, based on body surface area).

13.2       Animal Toxicology and/or Pharmacology

Toxicology studies of mesalamine were conducted in rats, mice, rabbits and dogs, and the kidney was the main target organ of toxicity. In rats, adverse renal effects were observed at a single oral dose of 600 mg/kg (about 3.2 times the recommended human intra-rectal dose of CANASA, based on body surface area) and at intravenous doses of >214 mg/kg (about 1.2 times the recommended human intra-rectal dose of CANASA, based on body surface area). In a 13-week oral gavage toxicity study in rats, papillary necrosis and/or multifocal tubular injury were observed in males receiving 160 mg/kg (about 0.86 times the recommended human intra-rectal dose of CANASA, based on body surface area) and in both males and females at 640 mg/kg (about 3.5 times the recommended human intra-rectal dose of CANASA, based on body surface area). In a combined 52-week toxicity and 127-week carcinogenicity study in rats, degeneration of the kidneys and hyalinization of basement membranes and Bowman’s capsule were observed at oral doses of 100 mg/kg/day (about 0.54 times the recommended human intra-rectal dose of CANASA, based on body surface area) and above. In a 14-day rectal toxicity study of mesalamine suppositories in rabbits, intra-rectal doses up to 800 mg/kg (about 8.6 times the recommended human intra-rectal dose of CANASA, based on body surface area) was not associated with any adverse effects. In a six-month oral toxicity study in dogs, doses of 80 mg/kg (about 1.4 times the recommended human intra-rectal dose of CANASA, based on body surface area) and higher caused renal pathology similar to that described for the rat. In a rectal toxicity study of mesalamine suppositories in dogs, a dose of 166.6 mg/kg (about 3 times the recommended human intra-rectal dose of CANASA, based on body surface area) produced chronic nephritis and pyelitis. In the 12-month eye toxicity study in dogs, keratoconjunctivitis sicca (KCS) occurred at oral doses of 40 mg/kg (about 0.72 times the recommended human intra-rectal dose of CANASA, based on body surface area) and above.