Poster Presentation Australian and New Zealand Stroke Organisation Conference 2026

Clopidogrel resistance in the Northland stroke cohort (#146)

Gabriel M Bickler 1 , Nicole M McGrath 1 , Alan J Davis 1
  1. Te Whatu Ora, Whangarei, NORTHLAND, New Zealand

Background: Cytochrome (CYP) 2C19 polymorphisms affect the efficacy of clopidogrel. This is a key drug in stroke secondary prevention but is known to lose its effect in carriers of CYP2C19 loss-of-function alleles.(1) Globally some 33% are thought to have these alleles.(2) Rates of clopidogrel resistance are thought to be high in the New Zealand Māori population.(3,4) In 2025, Ticagrelor was funded in NZ for use in acute TIA (Transient Ischaemic Attack) and minor stroke with clinical or genetic evidence of clopidogrel failure.

Aim: To identify the prevalence of loss of function clopidogrel alleles in stroke and TIA populations in Northland, thereby guiding preventive treatment strategies.

Method: In 2025, we introduced testing for CYP2C19 status in Northland in two important cohorts: Māori patients with ischaemic stroke/TIA, and those presenting with ischaemic stroke/TIA while already taking clopidogrel. We analysed results for 106 patients who had CYP2C19 genotyping tests performed between March 2025 and April 2026.

Results: Among Māori patients tested (n=73), 43.1% had loss-of-function alleles. Among those patients having an event while taking clopidogrel (n=44), 36.4% had loss-of-function alleles. Median ages were 65 years and 72 years, with 39.7% and 61.4% male respectively. Mean NIHSS scores were 4.7 and 2.8 respectively.

Conclusion: In this targeted but highly relevant population, resistance to clopidogrel is high. These patients are unlikely to experience benefit from clopidogrel following stroke/TIA. With the introduction of ticagrelor for treating clopidogrel-resistant patients, broader testing for CYP2C19 status is crucial to ensure the best preventive treatments.

  1. 1. Wang Y, Zhao X, Lin J, Li H, Johnston SC, Lin Y, et al. Association between CYP2C19 loss-of-function allele status and efficacy of clopidogrel for risk reduction among patients with minor stroke or transient ischemic attack. JAMA - J Am Med Assoc. 2016 Jul 5;316(1):70–8.
  2. 2. Koopmans AB, Braakman MH, Vinkers DJ, Hoek HW, van Harten PN. Meta-analysis of probability estimates of worldwide variation of CYP2D6 and CYP2C19. Vol. 11, Translational Psychiatry. Springer Nature; 2021.
  3. 3. Lea RA, Roberts RL, Green MR, Kennedy MA, Chambers GK. Allele frequency differences of cytochrome P450 polymorphisms in a sample of New Zealand Maori. N Z Med J. 2008;121(1272):33–7.
  4. 4. Larsen PD, Johnston LR, Holley A, La Flamme AC, Smyth L, Chua EW, et al. Prevalence and significance of CYP2C19*2 and CYP2C19*17 alleles in a New Zealand acute coronary syndrome population. Intern Med J. 2015 May 1;45(5):537–45.