Gomekli Side Effects: What to Expect and When to Call Your Doctor

Like all effective cancer treatments, Gomekli (mirdametinib) can cause side effects. Understanding what to expect — and knowing which symptoms require immediate medical attention — is essential for anyone taking this medication. This guide covers the most common and the most serious side effects of Gomekli, along with practical tips for managing them.

Common Side Effects of Gomekli

In the pivotal ReNeu clinical trial, the most common adverse events — occurring in more than 25% of adult patients — were:

Rash — The most common side effect. Can range from mild acne-like or eczema-like rash to more serious blistering. Start gentle moisturizer at the first sign of skin irritation.

Diarrhea — Common with MEK inhibitors. Stay hydrated and ask your care team about anti-diarrheal medications if it is interfering with daily activities.

Nausea — Eating small, frequent meals and staying hydrated can help. Anti-nausea medications may be prescribed if needed.

Musculoskeletal pain — Muscle and joint aches are common. Discuss pain management options with your care team.

Vomiting — If you vomit after taking a dose, do not take an additional dose. Take your next scheduled dose at the regular time.

Fatigue — Rest as needed. The 7-day off-week in Gomekli's 28-day cycle may help fatigue improve.

In pediatric patients, additional common side effects (also >25%) included abdominal pain, headache, paronychia (nail fold inflammation), and left ventricular dysfunction.

Serious Side Effects: When to Call Your Doctor or Go to the ER

Gomekli carries several important warnings for potentially serious side effects that require prompt medical attention:

Eye Problems (Ocular Toxicity)

Gomekli can cause serious eye problems that may lead to vision loss. In clinical trials, ocular toxicity occurred in 28% of adult patients and 19% of pediatric patients. Types of eye problems include:

Retinal vein occlusion (RVO) — blocked blood vessels in the eye (2.7% of adults)

Retinal pigment epithelial detachment (RPED) — a separation of retinal layers (1.3% of adults)

Blurred vision (9% of adults)

Call your doctor right away if you notice: sudden vision changes, blurry vision, dark spots, flashes of light, new floaters, or eye pain.

Heart Problems (Left Ventricular Dysfunction)

Gomekli may cause your heart to have trouble pumping blood effectively (left ventricular dysfunction). The risk may be higher in children. Your doctor will check your heart with an echocardiogram before you start Gomekli, every 3 months during the first year, and periodically after that.

Call your doctor if you notice: shortness of breath, cough, chest discomfort, swelling in legs or ankles, sudden weight gain, unusual tiredness, or faster-than-normal heart rate.

Severe Skin Reactions

While most rash from Gomekli is manageable, severe skin reactions can occur. These may require dose reduction or discontinuation.

Get medical attention immediately if you develop: blistering, peeling, or painful sores in the skin. These can be signs of a severe reaction known as Stevens-Johnson syndrome or toxic epidermal necrolysis, which require emergency care.

Embryo-Fetal Toxicity

Gomekli can cause harm to an unborn baby. If you can become pregnant, you must use effective contraception during treatment and for 6 weeks after the last dose. Males with female partners of reproductive potential should use contraception during treatment and for 3 months after the last dose. A pregnancy test is required before starting Gomekli.

Tips for Managing Common Side Effects

Rash: Use gentle, fragrance-free moisturizer. Avoid harsh skin products and sun exposure. Report any new rash to your care team early — it is easier to treat when caught at the mild stage.

GI symptoms: Eat small, frequent meals. Stay well-hydrated. Ask your care team about anti-nausea or anti-diarrheal medications.

Missed doses: If you miss a dose, skip it. Take your next dose at the regularly scheduled time. Never double up.

For information about medications and substances that may interact with Gomekli, see our guide on Gomekli drug interactions.