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Side Effects


Clinical Studies Experience

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

Adult Ulcerative Colitis

During clinical development, 259 adult patients with active ulcerative colitis were exposed to 6.75 g/day COLAZAL (balsalazide) in 4 controlled trials.

In the 4 controlled clinical trials patients receiving a COLAZAL (balsalazide) dose of 6.75 g/day most frequently reported the following adverse reactions: headache (8%), abdominal pain (6%), diarrhea (5%), nausea (5%), vomiting (4%), respiratory infection (4%), and arthralgia (4%). Withdrawal from therapy due to adverse reactions was comparable among patients on COLAZAL (balsalazide) and placebo.

Adverse reactions reported by 1% or more of patients who participated in the four controlled, Phase 3 trials are presented by treatment group in Table 1.

The number of placebo patients (35), however, is too small for valid comparisons. Some adverse reactions, such as abdominal pain, fatigue, and nausea were reported more frequently in women than in men. Abdominal pain, rectal bleeding, and anemia can be part of the clinical presentation of ulcerative colitis.

Table 1: Adverse Events occurring in ≥ 1% of Adult COLAZAL (balsalazide) Patients in Controlled Trials*

Adverse Reaction COLAZAL 6.75 g/day
Abdominal pain 16 (6%) 1 (3%)
Diarrhea 14 (5%) 1 (3%)
Arthralgia 9 (4%) 0%
Rhinitis 6 (2%) 0%
Insomnia 6 (2%) 0%
Fatigue 6 (2%) 0%
Flatulence 5 (2%) 0%
Fever 5 (2%) 0%
Dyspepsia 5 (2%) 0%
Pharyngitis 4 (2%) 0%
Coughing 4 (2%) 0%
Anorexia 4 (2%) 0%
Urinary tract infection 3 (1%) 0%
Myalgia 3 (1%) 0%
Flu-like disorder 3 (1%) 0%
Dry mouth 3 (1%) 0%
Cramps 3 (1%) 0%
Constipation 3 (1%) 0%
*Adverse events occurring in at least 1% of Colazal (balsalazide) patients which were less frequent than placebo for the same event were not included in the table.

Pediatric Ulcerative Colitis

In a clinical trial in 68 pediatric patients aged 5 to 17 years with mildly to moderately active ulcerative colitis who received 6.75 g/day or 2.25 g/day COLAZAL (balsalazide) for 8 weeks, the most frequently reported adverse reactions were headache (15%), abdominal pain upper (13%), abdominal pain (12%), vomiting (10%), diarrhea (9%), colitis ulcerative (6%), nasopharyngitis (6%), and pyrexia (6%). [see Table 2]

One patient who received COLAZAL (balsalazide) 6.75 g/day and 3 patients who received COLAZAL (balsalazide) 2.25 g/day discontinued treatment because of adverse reactions. In addition, 2 patients in each dose group discontinued because of a lack of efficacy.

Adverse reactions reported by 3% or more of pediatric patients within either treatment group in the Phase 3 trial are presented in Table 2.

Table 2: Treatment-Emergent Adverse Reactions Reported by ≥ 3% of Patients in Either Treatment Group in a Controlled Study of 68 Pediatric Patients

Adverse Reaction COLAZAL
6.75 g/day
2.25 g/day
Headache 5 (15%) 5 (14%) 10 (15%)
Abdominal pain upper 3 (9%) 6 (17%) 9 (13%)
Abdominal pain 4 (12%) 4 (11%) 8 (12%)
Vomiting 1 (3%) 6 (17%) 7 (10%)
Diarrhea 2 (6%) 4 (11%) 6 (9%)
Colitis ulcerative 2 (6%) 2 (6%) 4 (6%)
Nasopharyngitis 3 (9%) 1 (3%) 4 (6%)
Pyrexia 0 (0%) 4 (11%) 4 (6%)
Hematochezia 0 (0%) 3 (9%) 3 (4%)
Nausea 0 (0%) 3 (9%) 3 (4%)
Influenza 1 (3%) 2 (6%) 3 (4%)
Fatigue 2 (6%) 1 (3%) 3 (4%)
Stomatitis 0 (0%) 2 (6%) 2 (3%)
Cough 0 (0%) 2 (6%) 2 (3%)
Pharyngolaryngeal pain 2 (6%) 0 (0%) 2 (3%)
Dysmenorrhea 2 (6%) 0 (0%) 2 (3%)

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of balsalazide in clinical practice:

myocarditis, pericarditis, vasculitis, pruritus, pleural effusion, pneumonia (with and without eosinophilia), alveolitis, renal failure, interstitial nephritis, pancreatitis, and alopecia.

Because these reactions are reported voluntarily from a population of unknown size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. These adverse reactions have been chosen for inclusion due to a combination of seriousness, frequency of reporting, or potential causal connection to balsalazide.


Postmarketing adverse reactions of hepatotoxicity have been reported for products which contain (or are metabolized to) mesalamine, including elevated liver function tests (SGOT/AST, SGPT/ALT, GGT, LDH, alkaline phosphatase, bilirubin), jaundice, cholestatic jaundice, cirrhosis, hepatocellular damage including liver necrosis and liver failure. Some of these cases were fatal; however, no fatalities associated with these adverse reactions were reported in COLAZAL (balsalazide) clinical trials. One case of Kawasaki-like syndrome which included hepatic function changes was also reported, however, this adverse reaction was not reported in COLAZAL (balsalazide) clinical trials.

Read the Colazal (balsalazide) Side Effects Center for a complete guide to possible side effects


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-β-alanine (4-ABA) and N-acetyl-4-aminobenzoyl- β - 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 with are substrates of CYP1A2, CYP2C9, CYP2C19, CYP2D6, or CYP3A4/5.

Read the Colazal Drug Interactions Center for a complete guide to possible interactions

Last reviewed on RxList: 9/3/2008
This monograph has been modified to include the generic and brand name in many instances.

Side Effects

Colazal - User Reviews

Colazal User Reviews

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