WHAT IS THIS MEDICINE AND WHAT IS IT USED FOR?
Pemetrex contains pemetrexed, a chemotherapy medicine that works by
blocking several enzymes involved in folate metabolism — processes that cancer
cells need to make DNA and divide. By disrupting these processes
simultaneously, pemetrexed stops cancer cells from growing and multiplying.
The 100mg vial is used for patients with lower body surface area or for
dose-adjusted protocols.
It is used in adults for: non-small cell lung cancer (NSCLC) — both
non-squamous NSCLC (in combination with platinum-based chemotherapy as
first-line treatment or as maintenance therapy) and in combination with
pembrolizumab for first-line treatment of metastatic NSCLC; and malignant
pleural mesothelioma (a type of cancer affecting the lining of the lungs, often
linked to asbestos exposure) — in combination with cisplatin.
3. HOW TO TAKE THIS MEDICINE
Pemetrexed is given as a slow drip into a vein (intravenous infusion)
over 10 minutes by trained healthcare staff in a hospital or cancer centre. It
is never self-administered. The dose is calculated based on body surface area.
A typical dose is 500mg per square metre of body surface area, given on day 1
of each 21-day cycle. Your oncologist will calculate your specific dose.
Folic acid (400 to 1000 micrograms daily) must be taken by mouth every
day, starting 5 to 7 days before the first pemetrexed infusion and continuing
throughout treatment and for 21 days after the last dose.
A vitamin B12 injection (1000 micrograms) must also be given
intramuscularly in the week before the first infusion and then every 3 cycles
(approximately every 9 weeks). These vitamins are not optional — they are
medically essential to reduce the risk of serious blood and gut side effects.
Your oncologist will prescribe them alongside pemetrexed.
⚠ PATIENT TIP: The vitamins — daily folic acid
tablets and the vitamin B12 injection every 9 weeks — are a critical and
non-negotiable part of your treatment. Never skip your folic acid. Missing
these supplements significantly increases the risk of serious side effects
including very low blood counts and mouth ulcers. Think of the vitamins as part
of the treatment itself.
4. POSSIBLE SIDE EFFECTS
|
How Common? |
Side Effects |
|
Very Common |
Low white blood cell
count (neutropenia — increasing infection risk), low red blood cell count
(anaemia — causing tiredness and breathlessness), low platelet count
(thrombocytopenia — causing bruising and bleeding), nausea, vomiting, mouth
sores (stomatitis), fatigue, loss of appetite, skin rash |
|
Common |
Diarrhoea or
constipation, raised liver enzymes on blood tests, kidney function changes,
hair thinning, nerve pain or tingling in hands/feet (peripheral neuropathy),
chest infection |
|
Serious — Seek Urgent
Medical Help |
Fever above 38°C with
low blood counts — go to hospital immediately (febrile neutropenia — a
medical emergency). Severe mouth ulcers preventing eating or drinking. Signs
of serious infection. Severe skin reactions (very rare: Stevens-Johnson
syndrome). Acute kidney injury. |
5. WHO SHOULD NOT TAKE THIS MEDICINE
Pemetrexed should not be given to patients who are receiving or are about
to receive the yellow fever vaccine. It must be used with caution in patients
with significant kidney impairment — the dose must be reduced or treatment
avoided. It is not safe during pregnancy.
Tell your oncologist about all medicines you take — particularly
ibuprofen and other anti-inflammatory drugs, which can reduce the kidney's
ability to clear pemetrexed.
⚠ FOLIC ACID AND VITAMIN B12 ARE MANDATORY:
These supplements significantly reduce the risk of serious toxicity and must be
started before the first infusion. Missing them is not safe. Your care team
will prescribe them — ensure you are collecting and taking them consistently.
⚠ KIDNEY FUNCTION: Pemetrexed is cleared by the
kidneys. Kidney function tests (creatinine, eGFR) are checked before each
cycle. NSAIDs (ibuprofen, naproxen, diclofenac) reduce kidney clearance of
pemetrexed and should be avoided in the days around each infusion.
⚠ NEUTROPENIC SEPSIS: A fever of 38°C or above
when blood counts are low is a medical emergency. Know the number for your
oncology helpline and go to hospital immediately if this happens.
6. MEDICINES THAT INTERACT WITH THIS TREATMENT
NSAIDs (ibuprofen, naproxen, aspirin at anti-inflammatory doses,
diclofenac) reduce kidney clearance of pemetrexed and increase toxicity risk —
these should be avoided for 2 days before and at least 2 days after each
infusion (or for 5 days if using longer-acting NSAIDs like naproxen). Use
paracetamol for pain instead.
Nephrotoxic medicines (drugs that can damage the kidneys) increase the
risk of pemetrexed accumulation. Cisplatin and carboplatin are commonly given
alongside pemetrexed in combination protocols — this is planned and expected.
7. HOW TO STORE THIS MEDICINE
Store below 25°C. Prepare and dilute as directed by hospital pharmacy.
Prepared infusion solutions are stable for a defined time period — use within
the timeframe specified. Single-use vials — discard unused portion.
8. PRESCRIPTION REQUIREMENT
|
Field |
Details |
|
Status |
Prescription Only
Medicine (POM) — Specialist (oncology) prescription required; hospital
pharmacy preparation and administration only |
9. GUIDANCE FOR PATIENTS & CAREGIVERS
This treatment is given to you as a drip in a cancer centre. Before your
first infusion, start taking your daily folic acid tablets and receive your
vitamin B12 injection — these are essential, not optional. Continue folic acid
tablets every day throughout your treatment and for 21 days after your last
infusion. Avoid ibuprofen and other anti-inflammatory painkillers around the
time of each infusion — use paracetamol instead.
Attend all blood test appointments. If you develop a temperature of 38°C
or above, go to hospital immediately. Report severe mouth ulcers, unusual
bruising or bleeding, or any signs of infection to your care team without
delay.
10. PHARMACIST & PRESCRIBER NOTES
|
Field |
Details |
|
Clinical Dispensing
Notes |
Mandatory vitamin
supplementation protocol: folic acid 400–1000 mcg daily PO from 5–7 days
pre-first infusion through to 21 days post-last infusion; vitamin B12 1000
mcg IM in week prior to first infusion then every 3 cycles (every ~9 weeks).
Verify these are co-prescribed before dispensing pemetrexed. Dexamethasone
(4mg BD for 3 days, starting day before infusion) is standard prophylaxis for
skin rash — confirm it is prescribed. Dose based on BSA — verify calculation
against current height and weight. Renal function (eGFR) assessment mandatory
before each cycle — dose reduction required for eGFR <45 mL/min; do not
administer if eGFR <45. NSAID avoidance: 2 days (short-acting) to 5 days
(long-acting) around each infusion — counsel patient and flag to oncologist
if NSAIDs are part of concurrent medication. FBC before each cycle. Febrile
neutropenia emergency protocol counselling. Embryo-fetal toxicity:
contraception required during and for 6 months after treatment. |
11. FREQUENTLY ASKED QUESTIONS
Q: Why do I have to take folic acid and vitamin B12 with chemotherapy?
Pemetrexed works by blocking enzymes that process folate, but it can
block these enzymes in healthy cells as well as cancer cells, causing serious
side effects like very low blood counts and severe mouth ulcers. Folic acid and
vitamin B12 supplements 'top up' the levels of these vitamins in healthy cells,
protecting them from being harmed, without reducing pemetrexed's effectiveness
against the cancer.
Q: Can I take ibuprofen for a headache or joint pain?
Not around the time of your infusion. Ibuprofen and other
anti-inflammatory painkillers (NSAIDs) reduce the kidneys' ability to clear
pemetrexed from the body, which can lead to toxic build-up. Use paracetamol for
pain relief instead, and always check with your pharmacist or oncology team
before taking any new medicine.
Q: How long does each infusion take?
Each pemetrexed infusion takes just 10 minutes — it is a relatively short
infusion. The appointment itself will be longer to allow for blood tests,
assessments, and any concurrent medicines (like cisplatin).
Q: How often do I have treatment?
Pemetrexed is typically given on day 1 of a 21-day cycle — so once every
3 weeks. The number of cycles depends on your cancer type, how well the
treatment is working, and how well you are tolerating it.