Cobimetinib is used in adults to treat a certain type of metastatic melanoma (skin cancer) that has spread to other parts of the body and cannot be removed with surgery. Cobimetinib is usually given together with another medicine called vemurafenib.

Cobimetinib is used only if your tumor has a specific genetic marker, for which your doctor will test.

Cobimetinib is also used alone to treat adults with blood cancers called histiocytic neoplasms.

Cobimetinib may also be used for purposes not listed in this medication guide.

Melanoma:

Indicated for unresectable or metastatic melanoma in patients with a BRAF V600E or V600K mutation, in combination with vemurafenib.

Histiocytic Neoplasms:

Indicated as a single agent for adults with histiocytic neoplasms.

Reversible inhibitor of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 1 (MEK1) and MEK2.

MEK proteins are upstream regulators of the extracellular signal-related kinase (ERK) pathway, which promotes cellular proliferation.

BRAF V600E and K mutations result in constitutive activation of the BRAF pathway, which includes MEK1 and MEK2.

Cobimetinib and vemurafenib target 2 different kinases in the RAS/RAF/MEK/ERK pathway; compared with either drug alone, coadministration resulted in increased apoptosis in vitro and reduced tumor growth in mouse implantation models of tumor cell lines harboring BRAF V600E mutations.

Cobimetinib also prevented vemurafenib-mediated growth enhancement of a wild-type BRAF tumor cell line in an in vivo mouse implantation model.

Usual Adult Dose for Melanoma—Metastatic:

• 60 mg orally once a day for the first 21 days of each 28-day cycle until disease progression or unacceptable toxicity.

Usual Adult Dose for Histiocytic Neoplasm:

• 60 mg orally once a day for the first 21 days of each 28-day cycle until disease progression or unacceptable toxicity.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Your doctor will perform tests to make sure cobimetinib is the right treatment for you.

Cobimetinib is given in a 28-day treatment cycle. You may need to use the medicine only during the first 21 days of each cycle. Your doctor will determine how long to treat you with cobimetinib.

Do not change your doses or medication schedule without your doctor's advice.

You may take cobimetinib with or without food.

If you vomit shortly after taking cobimetinib, do not take another dose. Take your next dose as scheduled.

Check your skin on a regular basis while you are using cobimetinib. Tell your doctor if you notice any new skin changes, such as redness, sores that will not heal, a new wart, or a mole that has changed in size or color.

You will need frequent medical tests.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Cobimetinib may cause serious side effects. Call your doctor at once if you have:

Vision changes, partial vision loss, seeing halos around lights;

Unexplained muscle pain, tenderness, or weakness (especially if you also have fever and dark-colored urine);

Easy bruising or bleeding (nosebleeds, bleeding gums);

Signs of bleeding inside the body—weakness, dizziness, headache, red or pink urine, bloody or tarry stools, coughing up blood, or vomit that looks like coffee grounds;

Signs of a heart problem—cough, wheezing, shortness of breath (even with mild exertion), chest pain, fast heartbeats, swelling in your feet or ankles;

Low levels of sodium in the body—headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;

Liver problems—nausea, upper stomach pain, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); or

Severe skin reaction—skin pain, itching, redness, bumps or pimples, thickened or wrinkled skin, and skin rash that spreads and causes blistering and peeling.

Your cancer treatments may be delayed or permanently discontinued if you have certain side effects.

Sometimes it is not safe to use certain medicines at the same time. Some drugs can affect your blood levels of other drugs you use, which may increase side effects or make the medicines less effective.

Other drugs may affect cobimetinib, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all other medicines you use.

Cobimetinib could make you sunburn more easily. Avoid sunlight or tanning beds. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.

Store at room temperature away from moisture and heat.

You should not use cobimetinib if you are allergic to it.

Tell your doctor if you have ever had:

Heart disease, heart rhythm disorder;

A history of eye problems (especially a problem with your retina);

Liver or kidney disease;

Skin problems not related to melanoma;

A muscle disorder;

A bleeding or blood clotting disorder such as hemophilia; or

A condition for which you take a blood thinner such as warfarin (Coumadin, Jantoven).

May harm an unborn baby. Do not use if you are pregnant. Use effective birth control while using cobimetinib and for at least 2 weeks after your last dose. Tell your doctor if you become pregnant.

Do not breastfeed while using cobimetinib and for at least 2 weeks after your last dose.

Cobimetinib may affect fertility in men or women. Pregnancy could be harder to achieve while either parent is using this medicine.