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Chemotherapy: what to expect

Pemetrexed (Alimta, Pemgem, Pemnat) Side Effects and Why the Vitamins Cannot Stop

Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026

If your prescription includes folic acid tablets and a vitamin B12 injection alongside pemetrexed, that is not a suggestion. These supplements are a required part of the treatment. Stopping them — at any point — changes the safety of the chemotherapy.

Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026

Prescription-only medicine.

Pemetrexed is a prescription-only chemotherapy administered only in a hospital or licensed day-care setting under the direct supervision of a specialist oncologist. Nothing on this page is a substitute for the assessment, prescription, or clinical oversight of a qualified medical professional. It is not suitable for everyone — see who this is not for below.

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In short

Pemetrexed (sold in India as Alimta, Pemgem and Pemnat) is a chemotherapy used for certain lung cancers and mesothelioma. It requires daily folic acid tablets and a vitamin B12 injection before each cycle. These vitamins are not optional — they reduce serious side effects without reducing how the treatment works.

In detail

What is pemetrexed and which cancers is it used for?

Pemetrexed is a chemotherapy that works by blocking chemical pathways cancer cells rely on to copy their DNA. It belongs to a class called antifolates. In India it is dispensed under the brand names Alimta, Pemgem and Pemnat — these are the same medicine, not different treatments.

It is used for non-squamous non-small cell lung cancer and malignant pleural mesothelioma, which is a cancer of the lining around the lungs. Your oncologist will have established that your cancer type is one where pemetrexed is appropriate before prescribing it.

It is given as a short intravenous infusion in a hospital or day-care unit. You do not take it at home, and it is not available without a prescription.

In detail

Why does pemetrexed require folic acid and vitamin B12?

Pemetrexed disrupts folate pathways — the system cells use to build and repair DNA. This is effective against cancer cells, but it also affects healthy cells, particularly in the gut lining, mouth and bone marrow.

Folic acid tablets and a vitamin B12 injection are given to protect those healthy cells before each cycle. Guidance from NCCN and ESMO reflects consistent evidence that this supplementation substantially reduces serious side effects — particularly falls in blood counts and mouth inflammation — without reducing how the drug works against the cancer.

The vitamins are a required part of the treatment, not an optional add-on. Your team will give you precise timings: when to start folic acid before your first infusion and when each B12 injection is due. Follow those timings exactly — starting late or stopping early changes the safety of the chemotherapy.

Eligibility

Who should not receive pemetrexed?

Pemetrexed is not suitable for everyone. Eligibility is always decided by an oncologist on the individual case.

Significantly reduced kidney function: Pemetrexed is removed from the body primarily through the kidneys. When kidney function is substantially impaired, the drug can accumulate to toxic levels. Kidney function is tested before every cycle.
Squamous cell type lung cancer: Clinical evidence does not support pemetrexed for squamous-cell non-small cell lung cancer. It is indicated for non-squamous types only.
Pregnancy and breastfeeding: Pemetrexed can harm a developing baby. It is not given during pregnancy, and breastfeeding must be stopped before treatment begins.
Inability to take the required vitamin supplements: Folic acid and vitamin B12 are mandatory before every cycle. If these cannot be taken for any medical reason, pemetrexed cannot be given safely.
Severe liver impairment: Significant liver disease may alter how pemetrexed behaves in the body and may preclude its use.

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In detail

What side effects should you expect from pemetrexed?

The most commonly reported side effects are fatigue, nausea and a fall in blood cell counts. Low blood counts are why your team takes blood before every cycle — they check that counts have recovered before the next dose is given.

Mouth sores and skin rash occur in some patients. Your team may prescribe a short course of steroid tablets to be taken around each infusion to reduce the risk of skin reactions — ask them to confirm if this applies to you. Report any mouth pain or rash at your next contact rather than waiting for your scheduled appointment.

Appetite often decreases during treatment. Telling your dietitian early — before it affects your weight — gives you more options. Some patients notice mild hair thinning, which is generally less pronounced than with many other chemotherapy regimens.

Question by question

Questions patients commonly ask about pemetrexed

Can I stop taking folic acid between cycles, or when I feel well?

No. Folic acid must be taken continuously throughout your pemetrexed treatment — not just around the infusion day. The tablets maintain a protective level of folate in your blood over time. Stopping, even for a few days, reduces that protection. The side effects pemetrexed causes to healthy cells — particularly falls in blood count and mouth inflammation — become more likely and more severe when folic acid has been missed. If you have run out of tablets or received conflicting advice, contact your team before your next infusion rather than waiting for your scheduled appointment.

What if I forget to take a folic acid tablet?

Take it as soon as you remember, unless it is almost time for the next one — in that case, skip the missed tablet and continue your usual schedule. Do not take two tablets at once. The more important step is to tell your team how many doses you have missed and when your next infusion is. Do not assume a missed tablet does not matter. If several tablets have been missed and your infusion is approaching, call your team today rather than waiting for your next appointment.

Is pemetrexed given alone or with other medicines?

Pemetrexed is often given alongside a platinum chemotherapy — most commonly carboplatin or cisplatin — particularly at the start of treatment. In some situations it is given alone, for instance as a maintenance treatment after an initial course is completed. Whether you receive it in combination or alone, and for how many cycles, depends on your diagnosis, stage and how your cancer has responded. Your oncologist will have explained your specific plan. If it is not clear to you, ask at your next appointment and request it in writing.

Are there medicines I should avoid while taking pemetrexed?

Anti-inflammatory painkillers — the group that includes ibuprofen, naproxen and diclofenac, sold under many Indian brand names — can affect how pemetrexed is cleared through the kidneys, which may alter its level in the blood. Tell your oncology team about every medicine you are taking: tablets bought without a prescription, Ayurvedic or homeopathic preparations, and supplements. Your team will tell you which are safe and which to avoid in the days around each infusion. Do not stop or change any medicine without asking your team first.

What blood tests will I need, and how often?

Before every cycle, your team will check your full blood count to confirm that red cells, white cells and platelets have recovered from the previous infusion. Kidney function is tested because pemetrexed is removed from the body through the kidneys, and impaired clearance changes the safety of the next dose. Liver function may also be checked. If a result falls outside the range your oncologist considers acceptable, your next cycle will be delayed until it recovers. A delay is not a sign that treatment has failed — it is the protocol working as it should.

Will I need to stay in hospital after the infusion?

Pemetrexed is given as a short infusion and most patients go home the same day. Day care rather than an overnight stay is the standard setting. You will usually be observed for a period after the infusion before being discharged. If you live far from the treatment centre, or if your team has a specific concern after a particular cycle, they may ask you to stay longer. Ask your team what to expect on your first infusion day — including who to contact if you feel unwell after you get home.

Worth knowing

Did you know?

Folic acid and vitamin B12 supplementation before pemetrexed is one of the most rigorously studied supportive care protocols in modern oncology.

The evidence that led to its routine inclusion showed that patients who received the supplementation correctly experienced substantially fewer serious side effects than those who did not — and the drug's action against the cancer was unchanged.

Source: NCCN Guidelines for Non-Small Cell Lung Cancer; ESMO Clinical Practice Guidelines for Malignant Pleural Mesothelioma

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Common questions

Frequently asked questions

What is the difference between Alimta, Pemgem and Pemnat?

Alimta is the originator brand of pemetrexed. Pemgem and Pemnat are Indian generic versions containing the same active molecule. All three require the same folic acid and vitamin B12 supplementation protocol. If you are switched from one brand to another during your treatment, confirm with your team that your supplementation schedule remains unchanged — it should, but it is worth asking. The name on the packaging does not change what the medicine is or how to take the vitamins alongside it.

How long before my first infusion do I need to start folic acid?

Your team will give you a specific start date for the folic acid tablets before your first infusion. This is not approximate — the timing is built into the treatment protocol and matters for your safety. If you have been given a folic acid prescription but have not been told exactly when to begin, or if you are unsure whether you are on the right schedule, call your oncology team today rather than waiting for your next appointment. Starting late reduces the protection the supplement is meant to provide.

Can I eat normally during pemetrexed treatment?

Yes, though nausea and a reduced appetite are common in the days after each infusion. There are no specific foods you must avoid because of pemetrexed itself, but your team may give guidance based on your wider treatment. If eating becomes difficult, tell your dietitian early — before weight loss has become a problem. Managing nutrition throughout chemotherapy is easier when problems are flagged early rather than after they have already affected your strength and ability to tolerate treatment.

What should I do if I get mouth sores or a rash?

Report it at your next contact with the team rather than waiting for your scheduled appointment. Mouth sores and skin rash on pemetrexed can be managed effectively when they are caught early. When you call, tell your team when it started, how severe it is, and whether it is improving or getting worse. Do not use over-the-counter treatments without checking first — some products can mask worsening that your team needs to assess. If the sores are making it hard to eat or drink, that is a same-day call.

How many cycles of pemetrexed will I need?

The number of cycles depends on your diagnosis, your cancer type, and how your disease is responding to treatment. There is no single answer that applies to all patients, and this page cannot and does not provide survival or response figures. Your oncologist will review scans and blood results at defined intervals and use those findings to decide whether to continue, pause or change your treatment. Ask what they will be looking for at each assessment and at what point they expect to review the plan.

Is pemetrexed given as a day-care infusion?

Yes. Pemetrexed is administered as a short intravenous infusion and most patients are treated in a day-care setting, going home the same day rather than staying overnight. Response-assessment scans such as PET-CT, used to evaluate how your cancer is responding between cycles, are arranged separately with imaging partners and timed so that results are available at the right point in your treatment. Your team will coordinate this so you know when and where to go for each part of your care.

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