Sulindac

SULINDAC- sulindac tablet
Major Pharmaceuticals

DESCRIPTION

Sulindac is a non-steroidal, anti-inflammatory indene derivative designated chemically as (Z)-5-fluoro-2-methyl-1-[[ρ-(methylsulfinyl)phenyl]methylene]-1H -indene-3-acetic acid. It is not a salicylate, pyrazolone or propionic acid derivative. Its empirical formula is C₂₀ H₁₇ FO₃ S, with a molecular weight of 356.42. Sulindac, a yellow crystalline compound, is a weak organic acid practically insoluble in water below pH 4.5, but very soluble as the sodium salt or in buffers of pH 6 or higher.

Sulindac is available in 150 and 200 mg tablets for oral administration. Each tablet contains the following inactive ingredients: magnesium stearate, microcrystalline cellulose, plasdone and sodium starch glycolate.

Following absorption, sulindac undergoes two major biotransformations — reversible reduction to the sulfide metabolite, and irreversible oxidation to the sulfone metabolite. Available evidence indicates that the biological activity resides with the sulfide metabolite.

The structural formulas of sulindac and its metabolites are:

structure-formula

CLINICAL PHARMACOLOGY

Pharmacodynamics

Sulindac is a non-steroidal anti-inflammatory drug (NSAID) that exhibits anti-inflammatory, analgesic and antipyretic activities in animal models. The mechanism of action, like that of other NSAIDs, is not completely understood but may be related to prostaglandin synthetase inhibition.

Pharmacokinetics

Absorption

The extent of sulindac absorption from Sulindac Tablets USP is similar as compared to sulindac solution.

There is no information regarding food effect on sulindac absorption. Antacids containing magnesium hydroxide 200 mg and aluminum hydroxide 225 mg per 5 mL have been shown not to significantly decrease the extent of sulindac absorption.

TABLE 1

PHARMACOKINETIC PARAMETERS	NORMAL	ELDERLY
Tmax	Age 19-41 (n=24) (200 mg tablet) 3.38 ± 2.30 S 4.88 ± 2.57 SP 4.96 ± 2.36 SF	Age 65-87 (n=12) (400 mg qd) 2.54± 1.52 S 5.75 ± 2.81 SF 6.83 ± 4.19 S
	(150 mg tablet) 3.90± 2.30 S 5.85± 4.49 SP 6.15± 3.07 SF
Renal Clearance	(200 mg tablet) 68.12± 27.56 mL/min S 36.58 ± 12.61mL/min SP (150 mg tablet) 74.39± 34.15 mL/min S 41.75± 13.72 mL/min SP
Mean effective Half life (h)	7.8 S 16.4 SF
	S = Sulindac SP = Sulindac Sulfide SP = Sulindac Sulfone

Distribution

Sulindac, and its sulfone and sulfide metabolites, are 93.1, 95.4, and 97.9% bound to plasma proteins, predominantly to albumin. Plasma protein binding measured over a concentration range (0.5-2.0 µg/mL) was constant. Following an oral, radiolabeled dose of sulindac in rats, concentrations of radiolabel in red blood cells were about 10% of those in plasma. Sulindac penetrates the blood-brain and placental barriers. Concentrations in brain did not exceed 4% of those in plasma. Plasma concentrations in the placenta and in the fetus were less than 25% and 5% respectively, of systemic plasma concentrations. Sulindac is excreted in rat milk; concentrations in milk were 10 to 20% of those levels in plasma. It is not known if sulindac is excreted in human milk.

Metabolism

Sulindac undergoes two major biotransformations of its sulfoxide moiety: oxidation to the inactive sulfone and reduction to the pharmacologically active sulfide. The latter is readily reversible in animals and in man. These metabolites are present as unchanged compounds in plasma and principally as glucuronide conjugates in human urine and bile. A dihydroxydihydro analog has also been identified as a minor metabolite in human urine.

With the twice-a-day dosage regimen, plasma concentrations of sulindac and its two metabolites accumulate: mean concentration over a dosage interval at steady state relative to the first dose averages 1.5 and 2.5 times higher, respectively, for sulindac and its active sulfide metabolite.

Sulindac and its sulfone metabolite undergo extensive enterohepatic circulation relative to the sulfide metabolite in animals. Studies in man have also demonstrated that recirculation of the parent drug sulindac and its sulfone metabolite is more extensive than that of the active sulfide metabolite. The active sulfide metabolite accounts for less than six percent of the total intestinal exposure to sulindac and its metabolites.

Biochemical as well as pharmacological evidence indicates that the activity of sulindac resides in its sulfide metabolite. An in-vitro assay for inhibition of cyclooxygenase activity exhibited an EC₅₀ of 0.02µM for sulindac sulfide. In-vivo models of inflammation indicate that activity is more highly correlated with concentrations of the metabolite than with parent drug concentrations.

Elimination

Approximately 50% of the administered dose of sulindac is excreted in the urine with the conjugated sulfone metabolite accounting for the major portion. Less than 1% of the administered dose of sulindac appears in the urine as the sulfide metabolite. Approximately 25% is found in the feces, primarily as the sulfone and sulfide metabolites.

The mean effective half life (T_1/2 ) is 7.8 and 16.4 hours, respectively, for sulindac and its active sulfide metabolite.

Because sulindac is excreted in the urine primarily as biologically inactive forms, it may possibly affect renal function to a lesser extent than other non-steroidal anti-inflammatory drugs; however, renal adverse experiences have been reported with sulindac (see ADVERSE REACTIONS).

In a study of patients with chronic glomerular disease treated with therapeutic doses of sulindac, no effect was demonstrated on renal blood flow, glomerular filtration rate, or urinary excretion of prostaglandin E₂ and the primary metabolite of prostacyclin, 6-keto-PGF_1α . However, in other studies in healthy volunteers and patients with liver disease, sulindac was found to blunt the renal responses to intravenous furosemide, i.e., the diuresis, natriuresis, increments in plasma renin activity and urinary excretion of prostaglandins. These observations may represent a differentiation of the effects of sulindac on renal functions based on differences in pathogenesis of the renal prostaglandin dependence associated with differing dose-response relationships of different NSAIDs to the various renal functions influenced by prostaglandins (see PRECAUTIONS).

In healthy men, the average fecal blood loss, measured over a two-week period during administration of 400 mg per day of sulindac, was similar to that for placebo, and was statistically significantly less than that resulting from 4800 mg per day of aspirin.