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# PARP inhibitors

Oral drugs that block a DNA-repair enzyme, PARP, and kill cancer cells that already lack homologous recombination repair, such as BRCA-mutated tumours.

Updated Nov 1, 2026

## What they are

Olaparib, niraparib, rucaparib and talazoparib (suffix «-parib») are used in ovarian, breast, prostate and pancreatic cancers with BRCA1/2 mutations or other homologous recombination defects, often as maintenance after a response to platinum chemotherapy.

## Mechanism of action

PARP1 and PARP2 detect single-strand DNA breaks and use NAD+ to build poly(ADP-ribose) chains that recruit repair proteins. PARP inhibitors compete with NAD+ at the catalytic site and also trap PARP on the DNA. Unrepaired breaks turn into double-strand breaks during replication. Normal cells fix them by homologous recombination, but cells with faulty BRCA1 or BRCA2 cannot, and they die: two defects together are lethal although each alone is not (synthetic lethality).

Target: Poly(ADP-ribose) polymerases PARP1 and PARP2

## Key points

- Synthetic lethality: PARP blocked plus BRCA-deficient homologous recombination kills the tumour cell.
- A BRCA or homologous recombination test is done before treatment.
- Class warning: myelodysplastic syndrome and acute myeloid leukaemia; blood counts are followed.
- Niraparib raises blood pressure; rucaparib raises warfarin effect and causes photosensitivity; talazoparib is the strongest PARP trapper.

## Drugs in this class

- [**Olaparib** The first PARP inhibitor: an oral drug for BRCA-mutated ovarian, breast, pancreatic and prostate cancers. Watch blood… Poly(ADP-ribose) polymerases PARP1 and PARP2](https://durgical.com/en/pharmacology/olaparib/)
- [**Niraparib** A once-daily PARP inhibitor used as maintenance in ovarian cancer after a platinum response. Watch platelets and blood… Poly(ADP-ribose) polymerases PARP1 and PARP2](https://durgical.com/en/pharmacology/niraparib/)
- [**Rucaparib** A PARP inhibitor for BRCA-mutated ovarian and prostate cancer. It causes photosensitivity and can raise the effect of… Poly(ADP-ribose) polymerases PARP1 and PARP2](https://durgical.com/en/pharmacology/rucaparib/)
- [**Talazoparib** The strongest PARP trapper: for BRCA-mutated HER2-negative breast cancer and, with enzalutamide, prostate cancer… Poly(ADP-ribose) polymerases PARP1 and PARP2](https://durgical.com/en/pharmacology/talazoparib/)

## Test yourself

Think of the answer, then tap the question to see it.

## What is synthetic lethality in the context of PARP inhibitors?

Cell death when two repair defects coincide: PARP blocked by the drug and homologous recombination lost through BRCA mutation.

## Which cofactor do PARP inhibitors compete with?

NAD+, the donor of ADP-ribose units.

## Which haematological malignancies are a class warning for PARP inhibitors?

Myelodysplastic syndrome and acute myeloid leukaemia.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L01XK) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [Olaparib - NCI](https://www.cancer.gov/about-cancer/treatment/drugs/olaparib) (National Cancer Institute, 2025).

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