A retrospective analysis of adverse drug reaction case reports for PARP inhibitors: a comparative study of olaparib and niraparib

Background Olaparib and niraparib are the most widely used poly (ADP-ribose) polymerase inhibitors (PARPis) in clinical practice. However, clinical trial data inadequately capture rare and delayed adverse drug reactions (ADRs) in real-world settings, and a systematic comparison of their ADR profiles is lacking, hindering individualized therapy and risk management. This study systematically analyzes published case reports of ADRs associated with these two drugs to summarize their characteristics. Methods This retrospective study systematically retrieved case reports on olaparib- and niraparib-related ADRs from seven databases (CNKI, Wanfang, VIP, PubMed, Web of Science, ScienceDirect, and Embase) up to June 2026. Following screening, we extracted baseline data, ADR manifestations, interventions, and outcomes. Adverse events were classified by System Organ Class using the Medical Dictionary for Regulatory Activities (MedDRA), and comparative analyses were conducted on ADR spectra, time-to-onset, and prognosis between the two drugs. Results A total of 45 case reports involving 55 patients (68 ADR events) were included, of which 33 cases (40 events) were olaparib-related and 22 cases (28 events) niraparib-related. Seven patients were male (all olaparib users) and 48 females (male-to-female ratio 1:6.8). Most patients were aged >50 years (47 cases, 85.45%), with a mean age of 61.02 ± 10.76 years. Ovarian cancer (OC) was the predominant primary disease (40 cases, 72.73%). Both drugs exhibited a predilection for middle-aged and elderly patients, with the first 30 days of treatment representing the peak period for ADR occurrence; with toxicities affecting the haematological, cutaneous, and respiratory systems in both groups. Distinct toxicity profiles were also observed: olaparib-associated ADRs were multisystemic, involving skin and subcutaneous tissue disorders (13 events, 32.50%), respiratory and mediastinal disorders (11 events, 27.50%), haematological and lymphatic disorders (9 events, 22.50%), and hepatobiliary disorders (4 events, 10.00%), with delayed organ toxicities such as drug-induced liver injury and myelodysplastic syndrome. Temporally, olaparib exhibited a bimodal onset pattern: early cutaneous toxicity followed by mid-to-late pulmonary and hepatobiliary injury. Niraparib-associated ADRs were highly concentrated in the haematological system (20 events, 71.43%), with thrombocytopenia as the core feature, accompanied by neuromuscular toxicities including dysgeusia and elevated creatine kinase; temporally, an early unimodal distribution was observed, with new ADRs significantly reduced after day 91. Twenty-four patients in the olaparib group improved after drug discontinuation, dose adjustment, or symptomatic treatment, seven died due to ADRs or disease progression, and 2 had unreported outcomes; in the niraparib group, 21 improved, 1 showed no improvement, and no drug-related deaths occurred. Upon rechallenge, ADRs recurred mostly within 1 week, and dose reduction effectively lowered recurrence risk. Causality assessment using the Naranjo scale identified 8 cases as “definite”, 42 as “probable”, and 5 as “possible”. Conclusions Olaparib and niraparib presented markedly different ADR profiles. Drug selection and monitoring should be individualized based on patient characteristics in clinical practice. Olaparib requires sustained vigilance for cutaneous, pulmonary, and hepatobiliary toxicities, with attention to delayed organ injury; niraparib warrants prioritized prevention of early thrombocytopenia. These findings complement real-world safety evidence for PARP inhibitors and provide a reference for individualized drug selection and stratified safety monitoring in clinical practice.