Carboplatin, pemetrexed and pembrolizumab

Say it: KAR-bo-PLA-tin, PEM-eh-TREX-ed and PEM-bro-LIZ-yoo-mab

Carboplatin, pemetrexed and pembrolizumab

Carboplatin, pemetrexed and pembrolizumab combines two chemotherapy medicines with an immunotherapy, and it is one of the most common first treatments for advanced non-squamous lung cancer.

Also called: carbo pem pembro, carbo/pem/pembro, carboplatin pemetrexed pembrolizumab, carbo Alimta Keytruda, pemetrexed carboplatin Keytruda, KEYNOTE-189 regimen, cis pem pembro, cisplatin pemetrexed pembrolizumab, pem pembro maintenance, pemetrexed and pembrolizumab maintenance

What it is

Carboplatin and pemetrexed are chemotherapy medicines that damage cancer cells in different ways. Pembrolizumab is an immunotherapy that helps your own immune system find and attack the cancer. All 3 are given together at first, then carboplatin stops and pemetrexed and pembrolizumab continue as maintenance. The goal is to shrink the cancer, keep it controlled as long as possible and help you live longer and feel better.

Often used for

• Non-squamous non-small cell lung cancer (such as adenocarcinoma) that has spread or cannot be removed with surgery, as the first treatment
• Lung cancers without a gene change that can be treated with a targeted pill (such as EGFR or ALK)
• Pleural mesothelioma that cannot be removed with surgery

Induction (first 4 cycles)

All 3 medicines are given on day 1 every 21 days for 4 cycles, which is about 3 months.

Pemetrexed and pembrolizumab maintenance

After the first 4 cycles, carboplatin stops. Pemetrexed and pembrolizumab continue every 3 weeks as long as they are working and side effects are okay. Pembrolizumab is usually given for up to about 2 years in total. Pemetrexed may continue longer, or may be stopped earlier if side effects build up.

Cisplatin, pemetrexed and pembrolizumab

Cisplatin is used in place of carboplatin for some people who are younger and fit with healthy kidneys and hearing. It needs more IV fluids and a longer treatment day, and it causes more nausea. Cisplatin with pemetrexed is also used for some earlier stage lung cancers, before or after surgery.

For mesothelioma

The same medicines are used for pleural mesothelioma that cannot be removed with surgery. Your team will explain how long each part continues.

The medicines in this plan

Carboplatin

Platinum chemotherapy. Given through a vein over about 30 to 60 minutes on day 1, for the first 4 cycles only. Your dose is based on how well your kidneys work.

Pemetrexed

Chemotherapy that blocks cancer cells from using folate (a B vitamin) to grow. Given through a vein over about 10 minutes on day 1. It continues during maintenance.

Pembrolizumab

Immunotherapy that takes the brakes off your immune system. Given through a vein over about 30 minutes on day 1, every 3 weeks (or every 6 weeks during maintenance for some people).

Folic acid

A B vitamin pill taken once a day. It starts about 1 week before the first pemetrexed dose and continues until about 3 weeks after the last dose. It lowers the chance of serious side effects from pemetrexed.

Vitamin B12

A shot into the muscle given about 1 week before the first pemetrexed dose, then about every 9 weeks (every 3 cycles). It also protects you from pemetrexed side effects.

Dexamethasone

A steroid pill, usually taken twice a day the day before, the day of and the day after pemetrexed, to prevent a skin rash. It is also given by vein on day 1 to help with nausea.

Cisplatin

Only in the cisplatin version. Platinum chemotherapy given through a vein on day 1 in place of carboplatin, with extra IV fluids to protect the kidneys.

How you get it

This plan is given in an outpatient infusion clinic every 21 days, through an IV or a port (a small device placed under the skin of the chest). A treatment day usually takes about 3 to 4 hours. You start folic acid pills and get a vitamin B12 shot about 1 week before your first treatment. After 4 cycles, you continue pemetrexed and pembrolizumab alone, and those visits are shorter. Your schedule may be different.

A typical cycle

1 to 2 weeks before

Start daily folic acid pills and get your first vitamin B12 shot. Blood tests check your kidneys, liver and thyroid.

Day before

Start dexamethasone pills, usually twice a day for 3 days (the day before, the day of and the day after treatment).

Day 1

Blood tests and a check in with your team. Then anti-nausea medicines, then IV pembrolizumab, pemetrexed and carboplatin.

Days 2 to 7

Tiredness and nausea are most common now. Keep taking folic acid every day.

Days 8 to 14

Blood counts are lowest. Watch closely for fever and mouth sores.

Days 15 to 21

Recovery before the next cycle. Scans are usually done every 2 to 3 cycles.

Common side effects and what helps

• Tiredness, which can build up over time. Short walks and rest breaks both help.
• Nausea and poor appetite. Take your anti-nausea medicines as prescribed and eat small meals often.
• Low blood counts, which raise the risk of infection, bleeding and tiredness. Wash hands often and stay away from people who are sick.
• Skin rash. Taking every dexamethasone dose helps prevent it. Use gentle soap and moisturizer.
• Mouth sores. Rinse often with a mild salt and baking soda rinse and use a soft toothbrush.
• Constipation or diarrhea. Drink plenty of fluids and ask about medicines that help.
• Swelling of the legs or around the eyes, which can happen after many cycles of pemetrexed.
• Immune side effects from pembrolizumab, such as rash, itching, diarrhea, cough or thyroid changes (feeling very tired, cold or hot). Report them early so they can be treated.
• Hair thinning is possible, but full hair loss is uncommon with this plan.

Call your care team right away if you have

• A fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or chills
• Trouble breathing, chest tightness, flushing, rash or swelling of the face or throat during or soon after the infusion
• New or worse cough, shortness of breath or chest pain
• Diarrhea 4 or more times a day above your normal, belly pain, or blood or mucus in your stool
• Yellow skin or eyes, dark urine, or pain on the right side of your belly
• A severe rash, blisters, peeling skin or sores in your mouth or eyes
• A very bad headache, confusion, vision changes or extreme weakness
• Peeing much less than usual, or feeling very thirsty and peeing a lot
• Not able to keep fluids down, or feeling dizzy when you stand
• Bleeding that will not stop, or new bruises you cannot explain

Good to know

• This plan is for non-squamous lung cancer. Pemetrexed does not work well for squamous lung cancer, which is treated with a different plan.
• Before starting, your tumor is tested for gene changes (such as EGFR, ALK, ROS1, KRAS and others) and PD-L1. If a gene change is found, a targeted pill may be a better first choice.
• Taking folic acid every day and getting your vitamin B12 shots is very important. Skipping them raises the risk of serious low blood counts and mouth sores.
• Pemetrexed leaves the body through the kidneys. Your kidney function is checked before each dose. Ask before taking ibuprofen, naproxen or other NSAID pain relievers, especially in the days around treatment.
• Immune side effects can affect any organ, including the lungs, bowels, liver, thyroid, kidneys and skin, even months after the last dose. Most are treated with steroids if caught early.
• Tell your team if you have an autoimmune disease (such as lupus, rheumatoid arthritis or Crohn disease) or an organ transplant before starting immunotherapy.
• Do not get pregnant or father a child during treatment; use birth control your team approves.

At home

• Take folic acid every day, even on days you feel fine. Set a daily phone alarm.
• Take your dexamethasone pills on the right days, with food.
• Carry a card or list saying you get immunotherapy, and show it at any urgent care or ER.
• Keep a thermometer at home and check your temperature if you feel unwell.
• Drink about 8 to 10 cups of fluid a day unless your team told you otherwise.
• Use acetaminophen (Tylenol) for minor aches unless your team told you otherwise, and ask before using ibuprofen or naproxen.

Questions to ask

• Is my lung cancer the non-squamous type, and what did gene and PD-L1 testing show?
• Will I get carboplatin or cisplatin, and why?
• How long will I stay on pemetrexed and pembrolizumab maintenance?
• When should I start folic acid, and when is my next vitamin B12 shot?
• Which immune side effects should make me call right away?
• Which pain relievers are safe for me to take?

Lung cancer

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.