What Are DAYBUE Side Effects & How to Manage Diarrhea

DAYBUE (trofinetide) is a breakthrough treatment for adults and pediatric patients 2 years of age and older with Rett syndrome ^[1][2]. While it offers significant potential benefits, it comes with a very common and challenging side effect: severe diarrhea. In the pivotal phase 3 LAVENDER trial, over 80% of participants experienced diarrhea ^[3].

Fortunately, clinical practice has shown that this side effect can often be managed through a proactive, multi-step approach that involves stopping prior laxatives, starting anti-diarrheal medications and dietary fiber early, maintaining strict hydration via safe methods (such as G-tube flushes), and temporarily adjusting the dose under medical supervision ^[3][4].

How DAYBUE Works and Its Efficacy

DAYBUE is the first FDA-approved medication specifically for Rett syndrome ^[1]. It is given as an oral liquid solution twice daily, and it can be taken with or without food ^[5].

Trofinetide is a synthetic version of glycine-proline-glutamate (GPE), a naturally occurring molecule in the brain derived from Insulin-like Growth Factor-1 (IGF-1) ^[3][1]. While the exact mechanism is still being studied, trofinetide is thought to work by reducing neuroinflammation (calming overactive immune cells in the brain) and supporting the formation and function of synapses, which are the vital connections between brain cells ^[6][7].

In the phase 3 LAVENDER trial, patients taking DAYBUE showed statistically significant improvements compared to those taking a placebo ^[3]. After 12 weeks, improvements were seen in two main areas:

• RSBQ (Rett Syndrome Behaviour Questionnaire): A caregiver-rated scale measuring core Rett symptoms like breathing issues, hand behaviors, and mood ^[3].
• CGI-I (Clinical Global Impression-Improvement): A physician-rated scale measuring the patient’s overall clinical status and improvement ^[3].

Long-term follow-up studies (such as LILAC and LILAC-2) have shown that these behavioral and communication improvements are maintained with continued use of the medication ^[8][9].

The Most Common Side Effect: Diarrhea

Because many people with Rett syndrome struggle with chronic constipation, the onset of severe, loose stools from DAYBUE can be a drastic and challenging shift.

Diarrhea is the most common side effect of DAYBUE, occurring in 80.6% of patients in the LAVENDER trial, compared to 19.1% of patients on a placebo ^[3]. It was also the most frequent reason families chose to stop the medication ^[8][10].

The diarrhea caused by DAYBUE is typically osmotic—meaning the medication draws excess water into the bowel ^[4][11]. It is usually mild to moderate in severity and is most likely to start during the first month of treatment ^[3][12]. Because of the rapid fluid loss, proactive management during the first few weeks is essential to prevent dehydration ^[12].

Concrete Strategies for Managing Diarrhea

Managing DAYBUE-induced diarrhea requires a proactive plan established with your doctor before starting the medication. Caregivers and nurses in clinical trials developed a practical approach that significantly helped patients stay on the medication ^[3][4]. This strategy involves five primary considerations:

1. Stop Laxatives

Many patients with Rett syndrome are on a daily bowel regimen for constipation. Because DAYBUE causes a strong laxative effect, your care team will likely recommend stopping all laxatives and stool softeners exactly when starting DAYBUE ^[4]. Do not stop them too early before you have the medication in hand, as this could risk dangerous bowel impaction.

2. Start Anti-Diarrheals and Fiber

Do not wait for the diarrhea to become severe. At the first sign of loose or watery stools, doctors typically recommend starting an over-the-counter anti-diarrheal medication, primarily loperamide (Imodium) ^[3][4]. Additionally, incorporating a daily dietary fiber supplement can help add bulk to the stool and absorb excess water in the gut ^[4].

3. Hydrate Safely (Addressing Dysphagia)

Because the diarrhea draws water out of the body, severe dehydration is a major risk ^[11]. However, since many individuals with Rett syndrome have severe dysphagia (swallowing difficulties), simply “drinking more fluids” is often not safe or possible, and forcing oral fluids can lead to aspiration. Work with your care team to establish a safe hydration protocol. For those with a G-tube, this often means calculating and adjusting daily G-tube water flushes to compensate for fluid lost in the stool.

4. Dose Titration and Adjustments

DAYBUE is dosed based on the patient’s weight ^[13][14]. If diarrhea remains unmanageable despite stopping laxatives and using loperamide, your doctor may recommend a dose adjustment. This could involve temporarily reducing the dose or briefly interrupting the medication until the bowel stabilizes, then slowly reintroducing it ^[3][4].

Important Warning: Caregivers should never independently change the dose or stop the medication without direct guidance from a healthcare provider. Doing so can dangerously affect treatment safety and efficacy.

5. Skin Care for Incontinence

Transitioning from constipation to severe, frequent diarrhea can be incredibly harsh on the skin, especially for incontinent patients in diapers. Stock up on high-quality, thick barrier creams (such as those containing zinc oxide) and apply them generously with every diaper change to proactively prevent severe skin breakdown.

Other Potential Side Effects

While diarrhea is the overwhelming primary concern, other side effects can occur:

• Vomiting and Aspiration Risk: Along with diarrhea, vomiting was one of the most common side effects reported ^[8][9]. For a non-ambulatory patient with breathing irregularities and poor motor control, vomiting carries a severe, life-threatening risk of aspiration pneumonia (inhaling vomit into the lungs). Discuss safe positioning techniques with your doctor and seek emergency medical care immediately if you suspect aspiration or if the patient is struggling to breathe.
• Weight Loss: Due to rapid fluid loss and potential vomiting, some patients experience weight loss ^[3][9]. Monitoring weight closely during the first few months is crucial. For patients who cannot stand on a standard scale, watch for changes in how clothing fits or schedule regular weight checks at a clinic equipped with a wheelchair scale.
• FPIES (Rare but Serious): While the typical diarrhea is a predictable osmotic issue, there have been rare reports of an immune-mediated reaction called Food Protein-Induced Enterocolitis Syndrome (FPIES) ^[11]. This can present with profound vomiting, extreme pallor (paleness), and lethargy. If you observe these severe signs, seek immediate emergency medical care.