Balsalazide Disodium (Page 4 of 6)

8.6 Renal Impairment

Mesalamine is known to be substantially excreted by the kidney, and the risk of adverse reactions to balsalazide disodium capsules, which is converted to mesalamine, may be greater in patients with impaired renal function. Evaluate renal function in all patients prior to initiation and periodically while on balsalazide disodium capsule 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 [see Warnings and Precautions (5.1), Adverse Reactions (6.2), Drug Interactions (7.1)].

10 OVERDOSAGE

Balsalazide disodium 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) damage. There is no specific antidote for balsalazide overdose; however, conventional therapy for salicylate toxicity may be beneficial in the event of acute overdosage and may include gastrointestinal tract decontamination to prevent of further absorption. Proper medical care should be sought immediately with appropriate supportive care, including the possible use of emesis, cathartics, and activated charcoal to prevent further absorption. Correct fluid and electrolyte imbalance by the administration of appropriate intravenous therapy and maintain adequate renal function.

11 DESCRIPTION

Each Balsalazide Disodium Capsule, USP contains 750 mg of balsalazide disodium, a prodrug that is enzymatically cleaved in the colon to produce mesalamine (5-aminosalicylic acid or 5-ASA), an aminnosalicylate. Each capsule of balsalazide (750 mg) is equivalent to 267 mg of mesalamine. Balsalazide disodium has the chemical name (E)-5-[[4-[[(2-Carboxyethyl)amino]carbonyl] phenyl]azo]-2-hydroxybenzoic acid, disodium salt, dihydrate. Its structural formula is:

chem-structure-balsalazide-disodium.jpg
(click image for full-size original)

Molecular Weight: 437.31

Molecular Formula: C17 H13 N3 Na2 O6 •2H2 O

Balsalazide disodium is a yellow to orange crystalline powder. It is freely soluble in water and isotonic saline and DMSO, sparingly soluble in methanol and ethanol, and practically insoluble in all other organic solvents.

The inactive ingredients in Balsalazide Disodium Capsules, USP are colloidal silicon dioxide and magnesium stearate. Additionally, the capsule shell contains FD&C Blue #1, FD&C Red #40, FD&C Yellow #6, gelatin, and titanium dioxide. The black monogramming ink contains ammonium hydroxide, iron oxide black, isopropyl alcohol, n-butyl alcohol, propylene glycol, and shellac glaze. The sodium content of each capsule is approximately 79 mg.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Balsalazide disodium is delivered intact to the colon where it is cleaved by bacterial azoreduction to release equimolar quantities of mesalamine, which is the therapeutically active portion of the molecule, and the 4-aminobenzoyl-ß-alanine carrier moiety. The carrier moiety released when balsalazide disodium is cleaved is only minimally absorbed and is largely inert.

The mechanism of action of 5-ASA is not fully understood, but appears to be local 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 5-ASA diminishes inflammation by blocking production of arachidonic acid metabolites in the colon.

12.3 Pharmacokinetics

Balsalazide disodium capsules contain a powder of balsalazide disodium that is insoluble in acid and designed to be delivered to the colon as the intact prodrug. Upon reaching the colon, bacterial azoreductases cleave the compound to release 5-ASA, the therapeutically active portion of the molecule, and 4-aminobenzoyl-ß-alanine. The 5-ASA is further metabolized to yield N-acetyl-5-aminosalicylic acid (N-Ac-5-ASA), a second key metabolite.

Absorption:

In a study of adult patients with ulcerative colitis, who received balsalazide, 1.5 g twice daily, for over 1 year, systemic drug exposure, based on mean AUC values, was up to 60 times greater (0.008 mcg·hr/mL to 0.480 mcg·hr/mL) when compared to that obtained in healthy subjects who received the same dose.

Effect of Food:

The plasma pharmacokinetics of balsalazide and its key metabolites from a crossover study in healthy subjects are summarized in Table 3. In this study, a single oral dose of balsalazide 2.25 g was administered to healthy volunteers as intact capsules (3 x 750 mg) under fasting conditions, as intact capsules (3 x 750 mg) after a high-fat meal, and unencapuslated (3 x 750 mg) as sprinkles on applesauce.

Table 3: Plasma Pharmacokinetics for Balsalazide and Key Metabolites (5-ASA and N-Ac-5-ASA) with Administration of Balsalazide Following a Fast, a High-Fat Meal, and Drug Contents Sprinkled on Applesauce (Mean ± SD)

Fasting

N=17

High-fat Meal

N=17

Sprinkled

N=17

Cmax (mcg/mL)

Balsalazide

0.51 ± 0.32

0.45 ± 0.39

0.21 ± 0.12

5-ASA

0.22 ± 0.12

0.11 ± 0.136

0.29 ± 0.17

N-Ac-5-ASA

0.88 ± 0.39

0.64 ± 0.534

1.04 ± 0.57

AUClast (mcg·hr/mL)

Balsalazide

1.35 ± 0.73

1.52 ± 1.01

0.87 ± 0.48

5-ASA

2.59 ± 1.46

2.10 ± 2.58

2.99 ± 1.70

N-Ac-5-ASA

17.8 ± 8.14

17.7 ± 13.7

20.0 ± 11.4

Tmax (h)

Balsalazide

0.8 ± 0.85

1.2 ± 1.11

1.6 ± 0.44

5-ASA

8.2 ± 1.98

22.0 ± 8.23

8.7 ± 1.99

N-Ac-5-ASA

9.9 ± 2.49

20.2 ± 8.94

10.8 ± 5.39

A relatively low systemic exposure was observed under all three administered conditions (fasting, fed with high-fat meal, sprinkled on applesauce), which reflects the variable, but minimal absorption of balsalazide disodium and its metabolites. The data indicate that both Cmax and AUClast were lower, while Tmax was markedly prolonged, under fed (high-fat meal) compared to fasted conditions. Moreover, the data suggest that dosing balsalazide disodium as a sprinkle or as a capsule provides highly variable, but relatively similar mean pharmacokinetic parameter values. No inference can be made as to how the systemic exposure differences of balsalazide and its metabolites in this study might predict the clinical efficacy under different dosing conditions (i.e., fasted, fed with high-fat meal, or sprinkled on applesauce) since clinical efficacy after balsalazide disodium administration is presumed to be primarily due to the local effects of 5-ASA on the colonic mucosa [see Dosage and Administration (2.1)].

Distribution:

The binding of balsalazide to human plasma proteins was ≥ 99%.

Elimination:

Metabolism:

The products of the azoreduction of this compound, 5-ASA and 4-aminobenzoyl-ß-alanine, and their N-acetylated metabolites have been identified in plasma, urine and feces.

Excretion:

Following single-dose administration of 2.25 g balsalazide (three 750 mg capsules) under fasting conditions in healthy subjects, mean urinary recovery of balsalazide, 5-ASA, and N-Ac-5-ASA was 0.20%, 0.22% and 10.2%, respectively.

In a multiple-dose study in healthy subjects receiving a balsalazide dose of two 750 mg capsules twice daily (3 g/day) for 10 days, mean urinary recovery of balsalazide, 5-ASA, and N-Ac-5-ASA was 0.1%, 0%, and 11.3%, respectively. During this study, subjects received their morning dose 0.5 hours after being fed a standard meal, and subjects received their evening dose 2 hours after being fed a standard meal.

In a study with 10 healthy subjects, 65% of a single 2.25 g dose of balsalazide was recovered as 5-ASA, 4-aminobenzoyl-ß-alanine, and the N-acetylated metabolites in feces, while <1% of the dose was recovered as parent compound.

In a study that examined the disposition of balsalazide in patients who were taking 3 to 6 g of balsalazide daily for more than 1 year and who were in remission from ulcerative colitis, less than 1% of an oral dose was recovered as intact balsalazide in the urine. Less than 4% of the dose was recovered as 5-ASA, while virtually no 4-aminobenzoyl-ß-alanine was detected in urine. The mean urinary recovery of N-Ac-5-ASA and N-acetyl-4-aminobenzoyl-ß-alanine comprised <16% and <12% of the balsalazide dose, respectively. No fecal recovery studies were performed in this population.

Use in Specific Populations:

Pediatric Patients:

In studies of pediatric patients with mild-to-moderate active ulcerative colitis receiving three 750 mg balsalazide capsules 3 times daily (6.75 g/day) for 8 weeks, steady state was reached within 2 weeks, as observed in adult patients. Likewise, the pharmacokinetics of balsalazide, 5-ASA, and N-Ac-5-ASA were characterized by very large inter-patient variability, which is also similar to that seen in adult patients.

The pro-drug moiety, balsalazide, appeared to exhibit dose-independent (i.e., dose-linear) kinetics in children, and the systemic exposure parameters (Cmax and AUC0-8 ) increased in an almost dose-proportional fashion after the 6.75 g/day versus the 2.25 g/day doses. However, the absolute magnitude of these exposure parameters was greater relative to adults. The Cmax and AUC0-8 observed in pediatric patients were 26% and 102% greater than those observed in adult patients at the 6.75 g/day dosage level. In contrast, the systemic exposure parameters for the active metabolites, 5-ASA and N-Ac-5‑ASA, in pediatric patients increased in a less than dose-proportional manner after the 6.75 g/day dose versus the 2.25 g/day dose. Additionally, the magnitude of these exposure parameters was decreased for both metabolites relative to adults. For the metabolite of key safety concern from a systemic exposure perspective, 5-ASA, the Cmax and AUC0-8 observed in pediatric patients were 67% and 64% lower than those observed in adult patients at the 6.75 g/day dosage level. Likewise, for N-Ac-5-ASA, the Cmax and AUC0-8 observed in pediatric patients were 68% and 55% lower than those observed in adult patients at the 6.75 g/day dosage level.

All pharmacokinetic studies with balsalazide are characterized by large variability in the plasma concentration versus time profiles for balsalazide and its metabolites, thus half-life estimates of these analytes are indeterminate.

Drug Interaction Studies:

In Vitro Data:

In an in vitro study using human liver microsomes, balsalazide and its metabolites [5- aminosalicylic acid (5-ASA), N‑acetyl-5-aminosalicylic acid (N-Ac-5-ASA), 4-aminobenzoyl-ß-alanine (4-ABA) and N-acetyl-4-aminobenzoyl-ß-alanine (N-Ac-4-ABA)] were not shown to inhibit the major CYP enzymes evaluated (CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4/5). Therefore, balsalazide and its metabolites are not expected to inhibit the metabolism of other drugs which are substrates of CYP1A2, CYP2C9, CYP2C19, CYP2D6, or CYP3A4/5.

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