Cobimetinib (Oral)

Cobimetinib is a drug used in the treatment of advanced-stage melanoma, a type of skin cancer.


Cobimetinib is an MEK inhibitor, a drug that curbs the growth of MEK 1/MEK 2, which are also known as mitogen-activated protein kinase kinase enzymes. These enzymes are part of a signal cascade that are a factor in the formation of melanoma, a kind of skin cancer. It is used together with another medication, vemurafenib, to treat forms of melanoma that have certain unusual mutations.

Metastatic melanoma is the stage where cancer has spread to other parts of the body and when surgery is no longer possible. Cobimetinib works by inhibiting the growth and spread of these cancer cells. The doctor will test for the mentioned mutations before deciding whether the combination of cobimetinib and vemurafenib will be useful in combating the cancer.

Condition(s) treated

  • Advanced/metastasized melanoma

Type of medicine

  • Antineoplastic

Side effects

When taking cobimetinib, there is a chance of side effects, as medications combating cancer are usually very strong. Not all patients will encounter side effects, but if they do appear, it is best to contact the doctor immediately. Some side effects, however, are milder, and do not require medical attention. They will usually go away by themselves, and only require medical help if they show signs of persisting. These milder side effects are:

  • Acne or pimples
  • Nausea and/or vomiting
  • Diarrhea
  • Inflammation of the mouth and throat

If there is pain in the mouth and throat, the patient can try various methods to alleviate it, such as brushing gently and avoiding mouthwash that contains alcohol. A solution consisting of cool water mixed with salt or baking soda is recommended for rinsing the mouth often. While the inflammation continues, the patient may want to stick to moist and soft foods.

It is important to note that medication is typically prescribed despite the risk of side effects if it is thought that the positive outcomes of the medication outweigh the negative for the patient, and that it is essential to continue the course of treatment as prescribed by their doctor unless instructed otherwise. If the patient encounters any side effect, they should take note of the symptoms and contact their doctor with the details immediately.

Vigilant monitoring by both patient and doctor can reduce the risk of side effects. It is also advised that the patient check their blood pressure regularly to make sure it is not rising.

The following is an incomplete list of common side effects when taking cobimetinib:

  • Raising of blood pressure
  • Discomfort or pain in the chest
  • Changes to the skin (such as moles or warts appearing, skin sores, or unusual discoloration)
  • Skin rashes
  • Skin itching
  • Unusual bleeding, or bleeding easily (such as gums bleeding, nosebleeds, or cuts that do not stop bleeding)
  • Coughing up blood
  • Increase in menstrual flow or bleeding from the vagina
  • Black or red stools that are tarry in consistency
  • Brown or red urine
  • Clay colored stools
  • Stomach or abdominal pain or tenderness
  • Nausea and vomiting
  • Chills
  • Loss of or decrease in appetite
  • Difficulties with swallowing or breathing
  • Irregularities in heartbeat, such as slowing down, or a fast heartbeat
  • Fever
  • Headache
  • Dizziness
  • Feeling faint
  • Pounding in ears
  • Change in vision (such as blurred vision, seeing a curtain or veil appearing over vision, seeing flashes and sparks, or seeing floating spots)
  • Increased sensitivity in the skin to sunlight
  • Severe com/health/burns/">sunburns
  • Cramps and spasms in the muscles
  • Pain or stiffness in the muscles
  • Nervousness
  • Paralysis
  • Feeling unusually tired or weak
  • Yellow eyes or skin
  • Swelling in feet or lower legs

A rare but very serious side effect includes bleeding in the brain. If the patient encounters any of the following symptoms, they must get medical help right away:

  • Sudden vision changes
  • Slurred speech
  • Confusion
  • Severe headaches
  • Weakness on one side of the body
  • Seizures

Allergic reactions to the medication are uncommon but may happen. The patient should seek medical help immediately if they have signs of the following:

  • Itching and swelling, especially in the face, throat or tongue
  • Rashes
  • Severe dizziness
  • Trouble breathing


When taking cobimetinib, the patient should follow strictly the instructions of the doctor or instructions on the label, as dosages may vary from patient to patient. It is recommended that the patient read all available information from their doctor or pharmacist thoroughly, prior to starting treatment and, preferably, each time they get a refill.

An average dose of cobimetinib is 60 mg per day, split into three 20mg oral tablets, to be taken for 21 days and followed by a rest period of seven days. This totals up to a cycle of 28 days. However, it is important to keep in mind that the patient's dosage may differ, depending on their condition and the strength of the medication. The difference in dosage may include the length of time between doses and the amount of tablets required a day, among other factors.

The dosage for children is different and will be prescribed accordingly by the doctor.

If the patient vomits after a dose, they should not take another dose to replace it. Rather, they should contact their doctor or primary healthcare giver for further instructions. The same should be done if the patient misses a dose.

Cobimetinib should be taken regularly and on schedule so that the patient receives the maximum benefit from their medication. It is recommended that the patient take their medicine at a regular time each day to help them remember.

It may be taken with or without food.

The patient should not increase their dose or use it for longer or more often than has been prescribed by their doctor, as their condition will not improve if they do so and this may increase the risk of the patient experiencing side effects.


Drugs may interact with one another, which may lead to changes in the effectiveness of the medication or a higher chance of unwanted effects.

Prior to starting cobimetinib, the patient should keep a list of all drugs (prescription or non-prescription) and supplements they are consuming and inform the doctor of them. They should also notify their doctor while on cobimetinib if they decide to use other drugs or supplements.

There are several other drugs and supplements that can interact with this medication. If the patient is unsure about any products that they are consuming or wish to start on, they should seek medical advice. The following is an incomplete list of common interactions with cobimetinib:

  • Super B complex (multivitamin)
  • Vitamin D3 (Cholecalciferol)
  • Calcium 600+D Plus Minerals (multivitamin)
  • Lidocaine/Prilocaine (topical)
  • Prochlorperazine
  • Tbo-filgrastim
  • Ranitidine
  • Paclitaxel
  • Psyllium
  • Metronidazole (topical)
  • Saline nasal mist
  • Metoprolol

Certain medications may affect the removal of cobimetinib from the body and are listed below:

  • St. John's wort
  • Azole antifungals (such as itraconazole)
  • Efavirenz
  • Rifamycins (such as rifampin)
  • Drugs treating seizures (such as carbamazepine)

Patients should also avoid or be careful with grapefruit and its products, as it can affect the effectiveness of the medication, as well as the patient's blood levels. However, if the patient has already been consuming grapefruit on a regular basis, even after starting the medication, they should not stop their consumption abruptly. It is recommended that they consult their doctor for further medical advice.

Alcohol should not be consumed with the medication.


Prior to starting cobimetinib, the patient should inform their doctor of any allergies they have, as cobimetinib may contain inactive ingredients that can trigger an allergic reaction. They should also monitor themselves closely for any signs of an allergic reaction to the medication itself.

The doctor should also be made aware of the patient's medical history, especially if they have had eye problems, high blood pressure, heart problems, bleeding problems or liver disease.

If the patient is entering surgery, they should inform their doctors of any prior medical problems, as well as any drugs or supplements they are taking at the time.

It is important for the doctor to monitor the patient's progress during the course of the treatment, in order to determine the effectiveness of the medicine and to decide whether to continue or alter the current dosage. This may include blood tests to check for unwanted effects. The doctor should also check the patient's skin prior to taking cobimetinib, every two months while on the medicine, and for six months after finishing the course of treatment, as cobimetinib may increase risk of skin cancer.

While on cobimetinib, the patient may experience blurred vision, sensitivity of the skin to sunlight or other skin problems, and problems with unusual bleeding. As a precaution, the patient should avoid the sun as much as possible (including exposure to tanning booths and sunlamps), wear protective clothing and use sunscreen liberally.

They should also make sure not to operate machinery or engage in any activity that requires clear vision until they are absolutely sure they can perform such activities safely. If they experience any of the above symptoms, they should contact their doctor right away.

It is not recommended for patients who are pregnant, intending to get pregnant or breastfeeding to use cobimetinib. The drug can be absorbed through both the skin and lungs, and may harm fetuses or infants. Pregnant or breastfeeding people should not handle the medication or breathe in its dust. Patients of childbearing age are strongly recommended to use reliable birth control methods to avoid getting pregnant, up to two weeks after the last dose of their medication. If the patient should become pregnant, they must notify their doctor immediately.

The medication may also cause problems with fertility. The patient should talk to their doctor if they plan to have children in the future.

Usage of cobimetinib may increase risks of other diseases and problems, listed as follows:

  • Cardiomyopathy, or heart disease. Symptoms for this include persistent coughing and wheezing, shortness of breath, pain in the chest, an irregular heartbeat that may be too fast, or slowed, or pounding. There may also be swelling in the feet or lower legs, and the patient may feel unusually tired or weak.
  • Rhadomyolysis, a severe muscle problem. The patient may experience fevers, unusual tiredness or weakness and dark-colored urine. Muscle cramps, spasms and pain may also occur.
  • Hepatotoxicity or liver disease. It may show in signs like yellow eyes or skin, pale stools, dark-colored urine, loss in appetite, nausea, and pain or tenderness in the abdominal area. The patient may also feel unusually tired or weak.
  • Ocular toxicities or problems with the eyes and vision. If the patient experiences changes in vision which include blurred vision or loss of vision, the doctor may recommend an additional check up by an ophthalmologist, a specialist eye doctor.
  • Risk of unusual bleeding. The patient may have gums that bleed easily, dizziness, headaches and abdominal pain. They should especially keep an eye out for blood in the stools or urine, which will result in black or red tarry stools, and red or dark brown urine. Unusual vaginal bleeding may also occur.
  • Skin problems. As cobimetinib may increase the skin's sensitivity to sunlight, the patient may get sun rashes, skin irritation, bumps and tiny papules. Their skin may feel hot to the touch, or itchy and painful, and the texture may become thickened, dry and wrinkly. It is especially important that the patient notify their doctor if they notice any discoloration of their skin, or notice a new or changed wart or mole. They may also notice a reddish bump which bleeds or refuses to heal.

It is extremely important that the patient monitors themselves closely and seeks medical advice immediately if they encounter any of the above effects at all.


Cobimetinib should be stored in a closed container, in a cool and dry place that is out of reach from children and animals. It should also be kept from direct sunlight. Avoid freezing the medication.

If the medication is expired or no longer needed, it should be disposed of properly. The patient should ask their doctor or local waste management for help with disposal if they are unsure of how to dispose of their medication safely.


Cobimetinib is a MEK inhibitor drug usually prescribed together with vemurafenib to treat melanoma that has either metastasized or is untreatable with surgery. However, it is only prescribed for melanoma that has specific mutations, which the doctor will test for prior to starting treatment. Cobimetinib works by curbing the spread and growth of cancer cells.

As is the case with most drugs that treat cancer, cobimetinib is very strong and can cause several serious side effects. It is not recommended for pregnant or breastfeeding people.

Some problems or diseases that can develop with the use of cobimetinib include heart problems, vision problems, liver disease and rhadomyolysis, which involves problems with muscular function. Usage of cotimetinib may also increase the risk of skin cancer, as there is a possibility of increased sensitivity to sunlight, whether it is natural or artificial.

Cobimetinib is prescribed in order to combat metastasized melanoma, which can be a life-threatening disease. Despite the long list of side effects, it is used if the doctor believes that the benefits of this treatment far outweigh the negatives and will help the patient live a longer, healthier life.