Introduction: Genetic factors affecting warfarin maintenance dose have been well established, but patient acceptance is a necessary consideration for the successful clinical implementation of warfarin pharmacogenetic testing (WPGT). In this study, we aimed to determine the attitudes toward WPGT among Singaporean Chinese.

Methods: A total of 194 warfarin patients and 187 members of the public completed a structured survey on paper and the Internet, respectively. Attitudes were expressed as willingness to undergo WPGT (single item with 5-point response) and expectations and concerns about WPGT (two multi-item scales). Relationships between attitudes and socio-demographic and clinical variables were explored using Fisher's exact test, Student's t-test, one-way analysis of variance or Pearson's correlation.

Results: Majority of respondents were willing to or neutral about undergoing WPGT. Both patients and public had relatively high expectations (mean [SD]: 3.77 [0.63], and 3.97 [0.55], respectively) and moderately high concerns (mean [SD]: 3.30 [0.69] and 3.33 [0.68], respectively) about WPGT. Willingness to undergo WPGT was associated with gender, educational status, length of warfarin treatment, and number of chronic diseases among warfarin patients, and with history of adverse drug reactions and number of chronic diseases among the public. Higher expectation of WPGT was associated with higher willingness (p < .001 in both populations), while higher concern was associated with lower willingness to undergo WPGT among the public (p = .004) but not among patients (p = .072).

Conclusion: Patient acceptance is not a major barrier to clinical implementation of WPGT but patient education is necessary and the ethical, social, and legal issues should be addressed.

Objectives: The study aims at evaluating the economic evidence related to testing for genetic variants of the drug-metabolizing enzyme, TPMT. Detecting TPMT genetic variants before the administration of azathioprine (AZA) has the potential to prevent serious and costly adverse drug reactions (ADRs), such as neutropenia. In particular, our analysis concentrated on assessing the reliability of data on costs of neutropenia and performing the tests, the two main cost categories that could inform an economic evaluation of TPMT pharmacogenetic testing.

Methods: A systematic literature review was performed to gather evidence on the costs of testing and neutropenia. Articles were critically appraised for their comprehensiveness and quality. To better estimate costs of TPMT tests, a small-scale survey of European diagnostic laboratories was conducted.

Results: Only seven articles were retrieved specifying the costs associated with the management and treatment of AZA-induced neutropenia. Most of these studies are based on theoretical modeling reconstructed with key-informants or on very few cases of ADRs, and either the methodology for cost calculation is not specified or costs are based on national cost databases and tariffs. After critical appraisal of these studies, we considered €2,116 as the most reliable estimate for the cost of a case of neutropenia. Literature review accompanied by the survey of several diagnostic laboratories also provided an estimate (€68) for TPMT testing. Based on these values, the net cost per prevented case of neutropenia equals to €5,300.

Conclusions: Solid economic considerations related to TPMT pharmacogenetic testing are still limited by underreporting of ADRs and high level of approximation related to cost data. Ad hoc observational studies and the ADR recording process embedded in pharmacovigilance systems, established across Europe, should represent more reliable sources of cost data in the future.