Debrisoquine

Debrisoquine is a derivative of guanidine.Wikipedia It is an antihypertensive drug similar to guanethidine. Debrisoquine is frequently used for phenotyping CYP2D6, a drug metabolizing enzyme.10.1038/sj.clpt.6100050

Most people are considered CYP2D6 extensive metabolizers (EM); while poor metabolizers (PM) show greater sensitivity to debrisoquine, and conversely, ultrarapid metabolizers (UM) may require significantly higher doses of debrisoquine to achieve therapeutic dosing. Inherited as a recessive condition, the PM phenotype is estimated to occur in about 5 - 10% of Caucasians, and may range up to 30% in some Asian populations.

The CYP2D6 page has a full table showing the reported higher or lower enzymatic activity levels of the various alleles; the alleles reported as having decreased activity correspond to poor metabolizers for debrisoquine, and the corresponding SNPs are shown for each allele in that table as well.