Mesalazine (Mezavant XL)
Is It Right for You?
A complete guide to Mesalazine (Mezavant XL) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Mesalazine (Mezavant XL)?
Mesalazine (5-aminosalicylic acid, 5-ASA), marketed in the extended-release formulation as Mezavant XL 1200 mg modified-release tablets, is a locally acting anti-inflammatory aminosalicylate used for the induction and maintenance of remission in mild-to-moderately active ulcerative colitis (UC). It is the first-line pharmacological treatment for UC in the UK, as recommended by NICE and BSG guidelines.
Mezavant XL uses a multi-matrix (MMX) tablet technology that delivers mesalazine consistently throughout the colon — including the proximal colon, which is poorly reached by other mesalazine formulations, enemas, or suppositories. This pan-colonic delivery in a single once-daily tablet provides significant adherence advantages over formulations requiring multiple daily doses.
Mesalazine is a prescription-only medication in the UK. A clinician must confirm the diagnosis of ulcerative colitis and exclude other causes of colitis before initiating treatment.
What Conditions Is Mesalazine Used For?
Mesalazine is indicated for:
treatment of mild-to-moderately active UC to achieve clinical and endoscopic remission; Mezavant XL 2.4–4.8 g once daily is used for this purpose
long-term daily mesalazine therapy to prevent relapse after remission has been achieved; continuous maintenance therapy substantially reduces the risk of relapse and the long-term risk of colorectal cancer in UC
long-term mesalazine use is associated with a significant reduction in the relative risk of colorectal cancer in patients with longstanding UC
Mesalazine is an effective anti-inflammatory agent for UC but does not modify the underlying immune dysregulation that drives the condition. Long-term maintenance therapy is required in most patients. Patients who relapse frequently or develop moderate-to-severe disease may require escalation to immunomodulators (azathioprine, mercaptopurine) or biological therapies under gastroenterological supervision.
How Does Mesalazine Work?
Mesalazine (5-ASA) is the active anti-inflammatory moiety of sulfasalazine, separated from the sulphapyridine carrier that was responsible for many of sulfasalazine's systemic side effects. Once released in the colonic lumen, mesalazine exerts a range of locally acting anti-inflammatory effects:
NF-κB pathway inhibition: Mesalazine inhibits nuclear factor kappa-B (NF-κB) — the principal transcription factor driving the production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8) in colonic epithelial cells and immune cells. This reduces the inflammatory cascade that drives mucosal ulceration and haemorrhage in UC.
Inhibition of arachidonic acid metabolites: Mesalazine inhibits both the cyclooxygenase (COX) and lipoxygenase (LOX) pathways in the colonic mucosa, reducing the production of prostaglandins, leukotrienes, and thromboxanes that mediate mucosal inflammation and promote colonic permeability.
Reactive oxygen species (ROS) scavenging: Mesalazine acts as a free radical scavenger, neutralising the reactive oxygen species generated by activated neutrophils and macrophages at sites of colonic inflammation — protecting epithelial cells from oxidative injury.
Induction of epithelial apoptosis regulation: Mesalazine promotes normal programmed cell death pathways in colonic epithelial cells, which may contribute to its protective effect against dysplasia and colorectal cancer in long-standing UC.
The key pharmacological principle of Mezavant XL is topical delivery: mesalazine acts locally on the colonic mucosa, with relatively low systemic absorption, which accounts for its favourable systemic safety profile compared to systemic immunosuppressants.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Take Mezavant XL tablets once daily with a meal. The MMX coating requires food to activate correctly; taking on an empty stomach may compromise the controlled-release mechanism and reduce colonic delivery.
Swallow tablets whole. Do not crush, chew, or break Mezavant XL tablets — this destroys the MMX matrix technology and releases the full dose immediately rather than throughout the colon.
Take at the same time each day. Consistent once-daily dosing supports sustained colonic drug levels and maximises the maintenance effect.
Do not stop maintenance therapy when feeling well. This is one of the most common and consequential mistakes in UC management. Mesalazine works continuously to suppress mucosal inflammation; stopping it when asymptomatic leads to relapse, often within weeks to months.
Report any change in symptoms promptly. Bloody diarrhoea, increased stool frequency, urgency, or abdominal pain during maintenance treatment may indicate a relapse requiring clinical assessment and dose escalation.
Side Effects of Mesalazine
Most side effects are mild and resolve on their own. Serious side effects are rare but require immediate medical attention.
- Headache
- Nausea and abdominal pain
- Diarrhoea --- can be difficult to distinguish from UC disease activity; persist beyond the first week warrants review
- Flatulence
- Elevated liver enzymes (usually mild and transient)
- Acute mesalazine-induced colitis --- rare; worsening of colitis symptoms shortly after starting mesalazine may represent a hypersensitivity reaction to the drug rather than disease activity; clinically challenging to distinguish; report any worsening to your clinician
- Nephrotoxicity --- mesalazine can cause tubulo-interstitial nephritis, which may be clinically silent until significant renal impairment has developed; regular renal function monitoring is mandatory
- Severe hypersensitivity reactions --- including pericarditis, pleuritis, hepatitis, pulmonary infiltrates, and peripheral neuropathy; rare but well-documented mesalazine-associated reactions
- Blood dyscrasias --- rare; leucopenia, agranulocytosis, aplastic anaemia; report any unusual bruising, infections, or pallor
- Myocarditis / pericarditis --- rare but serious; new chest pain or breathlessness requires urgent assessment
Mesalazine-induced renal damage (interstitial nephritis) can develop silently without symptoms, progressing to significant renal impairment before detection. Renal function (eGFR and urinalysis for proteinuria) must be measured before starting treatment and then at 3 months, 6 months, and annually thereafter for the duration of treatment. Any significant decline in eGFR requires immediate clinical review and probable mesalazine dose reduction or cessation.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting Mesalazine
mesalazine inhibits thiopurine methyltransferase (TPMT), the principal enzyme metabolising azathioprine and mercaptopurine; concurrent use increases the risk of azathioprine/mercaptopurine toxicity (myelosuppression); TPMT status should be known before combining, and full blood count monitored closely.
increased risk of nephrotoxicity with concurrent NSAID use; avoid regular NSAID use in patients on mesalazine.
mesalazine may potentiate the anticoagulant effect of warfarin; monitor INR at initiation and following dose changes.
no clinically significant interaction with Mezavant XL's MMX technology.
Important Warnings
Mesalazine can cause tubulo-interstitial nephritis that may be clinically silent until advanced. Renal function (eGFR, creatinine, urinalysis) must be monitored before treatment initiation and at regular intervals throughout — at minimum annually. Any decline in renal function requires urgent clinical review.
Mezavant XL contains sodium metabisulphite as an excipient; patients with known sulphite allergy or sensitivity should inform their clinician before starting this preparation, as allergic reactions including bronchoconstriction may occur.
Mesalazine is a salicylate. Patients with known hypersensitivity to salicylates (including aspirin) should not take mesalazine without specialist assessment, as cross-reactivity is possible.
Patients with longstanding UC (>8–10 years) have an elevated risk of colorectal cancer that is substantially mitigated by continuous mesalazine use. Compliance with recommended colonoscopic surveillance intervals (as advised by the gastroenterology team) is an essential component of long-term UC management.
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The treatment you need, when you need it.
Mesalazine FAQs
Mesalazine's maintenance benefit is dependent on continuous daily use. Even when you are in remission and have no symptoms, subclinical mucosal inflammation persists in many patients, and stopping mesalazine — even briefly — substantially increases the risk of relapse. Long-term continuous use also reduces the risk of colorectal cancer in UC, which is a key long-term benefit beyond symptom control.
Mezavant XL uses MMX (multi-matrix) technology that delivers mesalazine throughout the entire colon — including the proximal colon — in a single once-daily tablet. Many other mesalazine preparations require two or three daily doses to achieve comparable colonic exposure. Once-daily dosing significantly improves adherence, which is strongly associated with better long-term outcomes in UC.
Mesalazine can silently damage the kidneys (interstitial nephritis) without causing symptoms until significant impairment has occurred. Regular monitoring of kidney function (eGFR, creatinine, and urine for protein) allows early detection and intervention before irreversible damage occurs. This is a mandatory safety requirement for all patients on long-term mesalazine.
Sulfasalazine (the original 5-ASA drug) consists of mesalazine linked to sulphapyridine by a diazo bond. Colonic bacteria cleave this bond, releasing the active mesalazine moiety. The sulphapyridine component is responsible for most of sulfasalazine's side effects (nausea, headache, male infertility, haematological effects). Mesalazine preparations deliver the active component without sulphapyridine, resulting in a much more favourable side-effect profile.
Yes. Mesalazine substantially reduces but does not eliminate the risk of relapse. Triggers for UC flare include concurrent infections (particularly GI infections), NSAIDs, antibiotic use, stress, and stopping or missing doses. Any new or worsening symptoms — increased bloody diarrhoea, urgency, or abdominal cramping — should be reported to your gastroenterologist promptly for assessment and management.