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Anti-PD-1 monoclonal antibody (immune checkpoint inhibitor) Pregnancy: Should not be used during pregnancy unless the clinical condition of the woman requires treatment with pembrolizumab. There are no data on use in pregnant women and animal reproduction studies have not been conducted; in murine models of pregnancy, blockade of PD-L1 signalling disrupted tolerance to the foetus and increased foetal loss, indicating a potential risk of foetal harm including increased rates of abortion or stillbirth. As an IgG4 antibody it has the potential to cross the placenta. Women of childbearing potential should use effective contraception during treatment and for at least 4 months after the last dose. Breast-feeding: it is unknown whether pembrolizumab is secreted in human milk and a risk to newborns/infants cannot be excluded — decide whether to discontinue breast-feeding or the medicine.

Pembrolizumab

Brand names: Keytruda

Pembrolizumab is an anti-PD-1 immune checkpoint inhibitor monoclonal antibody given by intravenous infusion, used in oncology across many tumour types; it is relevant to rheumatology mainly because it can trigger immune-related inflammatory conditions.

Adult dose

Dose: Adults — 'The recommended dose of KEYTRUDA in adults is either 200 mg every 3 weeks or 400 mg every 6 weeks administered as an intravenous infusion over 30 minutes.' This flat dose applies across the licensed oncology indications; therapy must be initiated and supervised by specialist physicians experienced in the treatment of cancer. Patients should be treated until disease progression or unacceptable toxicity (and up to a maximum duration of therapy where one is specified for an indication). INDICATION-SPECIFIC DURATIONS quoted in the same section: adjuvant melanoma, NSCLC or RCC — until disease recurrence, unacceptable toxicity, or for a duration of up to one year; first-line primary advanced or recurrent endometrial carcinoma — 200 mg every 3 weeks for 6 cycles with chemotherapy, then 400 mg every 6 weeks for up to 14 cycles as monotherapy; locally advanced cervical cancer — either schedule until disease progression, unacceptable toxicity or up to 24 months; neoadjuvant/adjuvant regimens for resectable NSCLC, cisplatin-ineligible MIBC, resectable locally advanced HNSCC and TNBC each specify a fixed number of doses at the same two strengths. For use in combination, see the Summary of Product Characteristics for the concomitant therapies.
Route: Intravenous infusion over 30 minutes. The concentrate for solution for infusion is for intravenous use only and 'is not intended for subcutaneous administration'; it 'must not be administered as an intravenous push or bolus injection' and 'should not be substituted for or with subcutaneous pembrolizumab because they have different recommended dosages and routes of administration'. Check the vial label to confirm the correct formulation. When given as part of a combination with intravenous chemotherapy, KEYTRUDA should be administered first; when given with enfortumab vedotin on the same day, KEYTRUDA should be administered after enfortumab vedotin. Dilute before administration per section 6.6.
Frequency: Every 3 weeks (200 mg) or every 6 weeks (400 mg)
Max: 400 mg per infusion on the 6-weekly schedule (200 mg per infusion on the 3-weekly schedule) — dosing is flat, not titrated. 'No dose reductions of KEYTRUDA are recommended': toxicity is managed by withholding or permanently discontinuing treatment according to the SPC's treatment-modification table.
SOURCE: UK SPC via the eMC, product 'KEYTRUDA 25 mg/mL concentrate for solution for infusion' (eMC product 2498), section 4.2 — quoted in full and NOT truncated. PATIENT SELECTION: where specified in the indication, PD-L1 tumour expression and MSI-H/dMMR tumour status must be confirmed by a validated test. SPECIAL POPULATIONS (quoted): elderly — no dose adjustment is necessary in patients 65 years and over; renal impairment — no dose adjustment for mild or moderate impairment, not studied in severe renal impairment; hepatic impairment — no dose adjustment for mild or moderate impairment, not studied in severe hepatic impairment. Patients must be given the patient card and informed about the risks of KEYTRUDA. DOSE DELAY/DISCONTINUATION: the SPC's Table 1 sets out withhold/permanently-discontinue rules for immune-mediated pneumonitis, colitis, nephritis, endocrinopathies, hepatitis, skin reactions, myocarditis, encephalitis, Guillain-Barre syndrome, myocarditis-myositis-myasthenia gravis overlap and infusion-related reactions; if treatment-related toxicity does not resolve to Grades 0-1 within 12 weeks of the last dose, or corticosteroid dosing cannot be reduced to 10 mg prednisone or equivalent per day or less within 12 weeks, KEYTRUDA should be permanently discontinued. TRUNCATION: sections 4.4 (warnings) and 4.8 (adverse reactions) in this bundle end at the source-fetch limit, so those lists are partial; the posology used for the dose above is complete.

Paediatric dose

Dose: 2 mg/kg
Route: Intravenous infusion over 30 minutes (concentrate must be diluted before administration; not for subcutaneous use, IV push or bolus)
Frequency: Every 3 weeks
Max: Maximum 200 mg per dose
Concentration: 25 mg/ml
MONOTHERAPY ONLY, and only in the two paediatric populations named in the label: 'The recommended dose of KEYTRUDA as monotherapy in paediatric patients aged 3 years and older with cHL [classical Hodgkin lymphoma] or patients aged 12 years and older with melanoma is 2 mg/kg bodyweight (bw) (up to a maximum of 200 mg), every 3 weeks administered as an intravenous infusion over 30 minutes.' This is the label's own paediatric figure, not a scaled adult dose. It is a per-DOSE figure given every 3 weeks, not a daily dose. 'The safety and efficacy of KEYTRUDA in children below 18 years of age have not been established except in paediatric patients with melanoma or cHL' — do not extrapolate to any other paediatric indication. The concentration of 25 mg/mL is the strength of the concentrate as supplied, so any calculated volume is the volume of CONCENTRATE to withdraw for dilution, not the volume infused. Verify against a children's formulary and specialist paediatric oncology protocols before use.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

MONOTHERAPY ONLY, and only in the two paediatric populations named in the label: 'The recommended dose of KEYTRUDA as monotherapy in paediatric patients aged 3 years and older with cHL [classical Hodgkin lymphoma] or patients aged 12 years and older with melanoma is 2 mg/kg bodyweight (bw) (up to a maximum of 200 mg), every 3 weeks administered as an intravenous infusion over 30 minutes.' This is the label's own paediatric figure, not a scaled adult dose. It is a per-DOSE figure given every 3 weeks, not a daily dose. 'The safety and efficacy of KEYTRUDA in children below 18 years of age have not been established except in paediatric patients with melanoma or cHL' — do not extrapolate to any other paediatric indication. The concentration of 25 mg/mL is the strength of the concentrate as supplied, so any calculated volume is the volume of CONCENTRATE to withdraw for dilution, not the volume infused. Verify against a children's formulary and specialist paediatric oncology protocols before use.

Verify in a children's formulary

Contraindications

  • Hypersensitivity to the active substance (pembrolizumab) or to any of the excipients listed in section 6.1

Side effects

  • Immune-mediated adverse reactions are the reactions most commonly associated with pembrolizumab, including severe and fatal cases; most resolved after appropriate medical therapy or withdrawal. Incidence with monotherapy was 37% all Grades and 9% Grades 3-5 in the adjuvant setting, and 25% all Grades and 6% Grades 3-5 in the metastatic setting
  • Monotherapy (7,631 patients across tumour types) — most frequent reactions: fatigue (31%), diarrhoea (22%), nausea (20%); the majority were Grade 1 or 2
  • In combination with chemotherapy, radiotherapy or chemoradiotherapy (7,015 patients) — most frequent reactions: anaemia (51%), nausea (50%), fatigue (36%), diarrhoea (35%), constipation (32%), vomiting (27%), decreased appetite (26%)
  • Severe infusion-related reactions (the most serious reactions alongside immune-mediated reactions)
  • Organ-specific immune-mediated reactions addressed in the dose-modification table: pneumonitis, colitis, nephritis, hepatitis, skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis, endocrinopathies (adrenal insufficiency, hypophysitis, type 1 diabetes with hyperglycaemia, hyperthyroidism, hypothyroidism), myocarditis, encephalitis, Guillain-Barre syndrome and myocarditis-myositis-myasthenia gravis overlap syndrome
  • NOTE: section 4.8 in this bundle ends at the source-fetch limit — this list is partial and does not include the full tabulated frequency list

Monitoring

  • Record the product name and batch number of every administered dose (biological traceability requirement)
  • Monitor for immune-mediated adverse reactions throughout and after treatment — they can occur after the last dose and can affect more than one body system simultaneously; evaluate suspected cases to confirm aetiology or exclude other causes
  • Liver function (AST, ALT, total bilirubin) — withhold at Grade 2 (AST/ALT more than 3 to 5 times ULN or bilirubin more than 1.5 to 3 times ULN) and permanently discontinue at Grade 3 or above (AST/ALT more than 5 times ULN or bilirubin more than 3 times ULN)
  • Renal function (creatinine) — withhold at Grade 2 with creatinine more than 1.5 to 3 times ULN; permanently discontinue at Grade 3 or above with creatinine more than 3 times ULN
  • Blood glucose and thyroid function — type 1 diabetes with Grade 3 or higher hyperglycaemia (glucose above 250 mg/dL or 13.9 mmol/L) or ketoacidosis, and Grade 3 or higher hyperthyroidism, require treatment to be withheld; hypothyroidism may be managed with replacement therapy without interruption
  • Where the indication specifies it, confirm PD-L1 expression and/or MSI-H/dMMR status by a validated test before starting
  • This list may be incomplete — check the full SPC.

Clinical monograph

How it works

It blocks the PD-1 receptor on T cells, preventing engagement by PD-L1/PD-L2 and thereby releasing the brakes on T-cell-mediated anti-tumour immune responses.

Prescribing in practice

  • Immune-related adverse events can affect almost any organ — including colitis, pneumonitis, hepatitis, endocrinopathies, nephritis and inflammatory arthritis — and may be severe or fatal, so recognise early and manage promptly, usually with corticosteroids and treatment interruption per the SPC.
  • Endocrinopathies such as thyroid dysfunction, hypophysitis and adrenal insufficiency are common and may be permanent, requiring hormone replacement.
  • Severe infusion reactions can occur and warrant interruption or discontinuation.

Monitoring

Monitor thyroid, liver, renal and glucose parameters and review for new symptoms in any organ system at each cycle so that immune-related toxicities are caught and treated early.

Counselling the patient

  • Report any new diarrhoea, breathlessness, rash or severe fatigue promptly.
  • Tell any clinician you are on immunotherapy, even after stopping.
  • Joint pain or swelling can occur and should be reviewed.

Evidence & guidelines

Its broad oncology indications are supported by numerous randomised trials demonstrating improved survival across multiple cancers.

Reference: multiple NICE TAs; ESMO Immuno-oncology toxicity guidelines; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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