Mesalamine (Page 3 of 5)

10 OVERDOSAGE

Mesalamine absorption from the colon is limited; however, mesalamine is an aminosalicylate, and symptoms of salicylate toxicity include nausea, vomiting and abdominal pain, tachypnea, hyperpnea, tinnitus, and neurologic symptoms (headache, dizziness, confusion, seizures). Severe salicylate intoxication may lead to electrolyte and blood pH imbalance and potentially to other organ (e.g., renal and liver) involvement. There is no specific antidote for mesalamine overdose. Correct fluid and electrolyte imbalance by the administration of appropriate intravenous therapy and maintain adequate renal function.

11 DESCRIPTION

The active ingredient in mesalamine 1000 mg suppositories for rectal use is mesalamine, also known as mesalazine or 5-aminosalicylic acid (5-ASA). Chemically, mesalamine is 5-amino-2-hydroxybenzoic acid, and is classified as an aminosalicylate. Each mesalamine rectal suppository contains 1000 mg of mesalamine (USP) in a base of Hard Fat, NF.

The empirical formula is C7H7NO3, representing a molecular weight of 153.14. The structural formula is:

The structural formula for mesalamine 1000 mg suppositories for rectal use is mesalamine, also known as mesalazine or 5-aminosalicylic acid (5-ASA). Chemically, mesalamine is 5-amino-2-hydroxybenzoic acid, and is classified as an anti-inflammatory drug. Each mesalamine rectal suppository contains 1000 mg of mesalamine (USP) in a base of Hard Fat, NF.
The structural formula for mesalamine 1000 mg suppositories for rectal use is mesalamine, also known as mesalazine or 5-aminosalicylic acid (5-ASA). Chemically, mesalamine is 5-amino-2-hydroxybenzoic acid, and is classified as an anti-inflammatory drug. Each mesalamine rectal suppository contains 1000 mg of mesalamine (USP) in a base of Hard Fat, NF.

12 CLINICAL PHARMACOLOGY

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 NONCLINICAL TOXICOLOGY

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 mesalamine, 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 mesalamine, 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 mesalamine, based on body surface area) and at intravenous doses of >214 mg/kg (about 1.2 times the recommended human intra-rectal dose of mesalamine, 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 mesalamine, 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 mesalamine, 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 mesalamine, 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 mesalamine, 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 mesalamine, 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 mesalamine, 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 mesalamine, based on body surface area) and above.

14 CLINICAL STUDIES

Two double-blind, placebo-controlled, multicenter trials of mesalamine suppositories were conducted in North America in adult patients with mildly to moderately active ulcerative proctitis. The regimen in Study 1 was a 500 mg mesalamine suppository administered rectally three times daily and in Study 2 was a 500 mg mesalamine suppository administered rectally twice daily. In both trials, patients had an average extent of proctitis (upper disease boundary) of approximately 10 cm and approximately 80% of patients had multiple prior episodes of proctitis. A total of 173 patients were evaluated (Study 1, N=79; Study 2, N=94), of which 89 patients received mesalamine, and 84 patients received placebo. The mean age of patients was 39 years (range 17 to 73 years), 60% were female, and 97% were white.

The primary measures of efficacy were clinical disease activity index (DAI) and histologic evaluations in both trials. The DAI is a composite index reflecting rectal bleeding, stool frequency, mucosal appearance at endoscopy, and a physician’s global assessment of disease. Patients were evaluated clinically and sigmoidoscopically after 3 and 6 weeks of treatment.

Compared to placebo, mesalamine suppositories were statistically (p<0.01) superior to placebo in both trials with respect to improvement in stool frequency, rectal bleeding, mucosal appearance, disease severity, and overall disease activity after 3 and 6 weeks of treatment. The effectiveness of mesalamine suppositories was statistically significant irrespective of sex, extent of proctitis, duration of current episode, or duration of disease.

An additional multicenter, open-label, randomized, parallel group study in 99 patients diagnosed with mildly to moderately ulcerative proctitis compared 1000 mg mesalamine administered rectally once daily at bedtime (N=35) to 500 mg mesalamine suppository administered rectally twice daily, in the morning and at bedtime (N=46), for 6 weeks.

The primary measures of efficacy included the clinical disease activity index (DAI) and histologic evaluations. Patients were evaluated clinically and sigmoidoscopically at 3 and 6 weeks of treatment.

The efficacy at 6 weeks was not different between the treatment groups. Both were effective in the treatment of ulcerative proctitis and resulted in a significant decrease at 6 weeks in DAI: in the mesalamine 500 mg twice daily group, the mean DAI value decreased from 6.6 to 1.6, and in the 1000 mg at bedtime group, the mean DAI value decreased from 6.2 to 1.3, which represents a decrease of greater than 75% in both groups. After 6 weeks of treatment, a DAI score of less than 3 was achieved in 78% of patients in the mesalamine 500 mg twice daily group and 86% of patients in the mesalamine 1000 mg once daily group. The recommended dosage of mesalamine is 1000 mg administered rectally once daily at bedtime [see Dosage and Administration ( 2)].

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