A 32-year-old woman with systemic lupus erythematosus (SLE) on mycophenolate mofetil (MMF) 2 g/day presents with a 3-day history of severe diarrhoea, abdominal cramping, and fever (38.5°C). She has no recent antibiotic use. Stool culture and C. difficile toxin are negative. What is the most appropriate next step in management?

Explanation

## Clinical Context Mycophenolate mofetil (MMF) is a selective inosine monophosphate dehydrogenase (IMPDH) inhibitor used in lupus nephritis and other autoimmune conditions. Gastrointestinal toxicity—particularly diarrhoea—is a well-recognized dose-related adverse effect occurring in 20–30% of patients. ## Management of MMF-Induced Diarrhoea **Key Point:** MMF-associated diarrhoea is dose-dependent and reversible; the first-line approach is dose reduction with clinical monitoring, NOT immediate discontinuation. ### Diagnostic Workup Already Complete The clinical presentation (acute diarrhoea + fever + no recent antibiotics) has been appropriately investigated: - Stool culture: negative (excludes bacterial pathogens) - C. difficile toxin: negative (excludes CDI) - No recent antibiotic exposure (makes CDI unlikely) This pattern is consistent with **MMF-related gastrointestinal intolerance**. ### Stepwise Management Algorithm ```mermaid flowchart TD A[MMF-induced diarrhoea diagnosed]:::outcome --> B{Severity?}:::decision B -->|Mild-moderate| C[Reduce MMF dose by 25-50%]:::action B -->|Severe/refractory| D[Temporarily hold MMF]:::action C --> E[Add probiotics or dietary modification]:::action D --> E E --> F[Monitor for 1-2 weeks]:::action F --> G{Resolution?}:::decision G -->|Yes| H[Gradually re-escalate MMF as tolerated]:::action G -->|No| I[Switch to alternative agent<br/>e.g. azathioprine]:::action ``` ### Why Dose Reduction Is Preferred 1. **Reversibility**: MMF-related GI toxicity resolves in 80–90% of patients with dose reduction. 2. **Preserves efficacy**: Maintaining some degree of immunosuppression is critical in active SLE; abrupt discontinuation risks disease flare. 3. **Evidence-based**: Major rheumatology guidelines (ACR, EULAR) recommend dose reduction as first-line for MMF intolerance. 4. **Adjunctive measures**: Probiotics, dietary fibre restriction, and timing of doses (with food) improve tolerance. **High-Yield:** Mycophenolate diarrhoea is **not an allergic reaction** and does not require immediate cessation; it is a pharmacodynamic effect that responds to dose titration. ### When to Switch Agents Switch to azathioprine or other agents only if: - Diarrhoea persists despite 50% dose reduction - Patient is unable to tolerate even low-dose MMF - Severe colitis or perforation is suspected (rare) **Clinical Pearl:** In SLE patients, maintaining continuous immunosuppression is essential to prevent lupus flares; abrupt drug withdrawal carries higher risk than dose adjustment. ## Why Other Options Are Suboptimal | Option | Rationale for Rejection | |--------|------------------------| | Continue full dose + loperamide | Antimotility agents can worsen inflammatory diarrhoea and mask underlying toxicity; does not address the root cause | | Immediate discontinuation + switch to azathioprine | Premature escalation; colonoscopy is unnecessary (infectious causes excluded); risks disease flare | | Continue full dose + mesalamine + ciprofloxacin | Mesalamine is for IBD, not drug-induced diarrhoea; ciprofloxacin is empiric and unjustified (cultures negative); full MMF dose perpetuates toxicity | [cite:KD Tripathi 8e Ch 12]