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Table 2 PharmGKb clinical annotation levels. Descriptions are adapted from the PharmGKb website available at:

From: Using a pilot-centric, qualitative drug risk assessment model to identify opportunities for implementing pharmacogenetics

PharmGKb Level of Evidence Description
1A Strongest level of evidence. At least one publication and clinical guidelines or a drug label with variant-specific prescribing guidance
1B High level of evidence supporting the drug-variant combination, but no variant-specific prescribing recommendations. Supported by at least two independent publications
2A Moderate level of evidence. Variants are on the PharmGKb pharmacogene list with implied causality of drug phenotypes. Supported by at least two independent publications
2B Moderate level of evidence, possibly conflicting results. Variants are not in known pharmacogenes, but drug-variant associations have been reported in at least two independent publications
3 Low level of evidence. Variant-drug association may have been reported in only a single study, several studies may contradict an observed association, or the association is based upon preliminary evidence such as a case report or in vitro molecular studies
4 Available evidence score is negative, indicating that the evidence does not support an association between the variant and observed phenotype