Determination of Cytochrome P450 Isoenzyme 2D6 (CYP2D6) Genotypes and Pharmacogenomic Impact on Primaquine Metabolism in an Active-Duty US Military Population

Abstract

Background: Plasmodium vivax malaria requires a 2-week course of primaquine (PQ) for radical cure. Evidence suggests that the hepatic isoenzyme cytochrome P450 2D6 (CYP2D6) is the key enzyme required to convert PQ into its active metabolite.

Methods: CYP2D6 genotypes and phenotypes of 550 service personnel were determined, and the pharmacokinetics (PK) of a 30-mg oral dose of PQ was measured in 45 volunteers. Blood and urine samples were collected, with PQ and metabolites were measured using ultraperformance liquid chromatography with mass spectrometry.

Results: Seventy-six CYP2D6 genotypes were characterized for 530 service personnel. Of the 515 personnel for whom a single phenotype was predicted, 58% had a normal metabolizer (NM) phenotype, 35% had an intermediate metabolizer (IM) phenotype, 5% had a poor metabolizer (PM) phenotype, and 2% had an ultrametabolizer phenotype. The median PQ area under the concentration time curve from 0 to ∞ was lower for the NM phenotype as compared to the IM or PM phenotypes. The novel 5,6-ortho-quinone was detected in urine but not plasma from all personnel with the NM phenotype.

Conclusion: The plasma PK profile suggests PQ metabolism is decreased in personnel with the IM or PM phenotypes as compared to those with the NM phenotype. The finding of 5,6-ortho-quinone, the stable surrogate for the unstable 5-hydroxyprimaquine metabolite, almost exclusively in personnel with the NM phenotype, compared with sporadic or no production in those with the IM or PM phenotypes, provides further evidence for the role of CYP2D6 in radical cure.

Clinical trials registration: NCT02960568.

Keywords: 5,6-ortho-quinone; CYP2D6; Primaquine; genotype; metabolism; military; pharmacokinetics; phenotype.

Figure 1.

Predicted CYP2D6 metabolizer phenotypes according to race/ethnicity. Percentages of each phenotype are listed next to pie sections. The PM phenotype was not detected in Asian or Native American/Alaska Native volunteers.

Figure 2.

Pharmacokinetic profiles in plasma (A and C) and urine (B and D, dotted lines) specimens from volunteers with the normal metabolizer (NM) phenotype (circles; n = 8), the intermediate metabolizer (IM) phenotype (triangles; n = 20), and the poor metabolizer (PM) phenotype (squares; n = 16) for primaquine (PQ; A and B) and carboxyprimaquine (cPQ; C and D) at scheduled time points after administration of 30 mg of PQ orally. Data are median values.

Figure 3.

Pharmacokinetic profile of primaquine (PQ) in plasma specimens according to activity score (AS-A). Data are median plasma PQ concentrations after administration of 30 mg of PQ orally. Measurements were made at 0, 1, 2, 4, 6 8, 10 and 24 hours. Data are for 6 volunteers with an AS-A of 2 (solid circles), 2 with an AS-A of 1.5 (open circles), 2 with an AS-A of 1.0 (solid black triangles), 12 with an AS-A of 0.5 (triangles with a gray border), 5 with an AS-A of 0.25 (upside-down triangles), and 16 with an AS-A of 0 (squares). Two volunteers with duplications were not included.

Figure 4.

Concentrations of 5,6-ortho-quinone in urine specimens collected 4, 10, and 24 hours after primaquine (PQ) dosing from volunteers with a normal metabolizer (NM) phenotype and an activity score (AS-A) of 2 (dark circles) or 1.5 (open circles); from those with an intermediate metabolizer (IM) phenotype and an AS-A score of 1.0 (black triangles), 0.5 (light triangle with gray outline), or 0.25 (upside down triangles); and from those with a poor metabolizer (PM) phenotype (squares).

Figure 5.

Pharmacokinetic profile of urinary 5,6-ortho-quinone 0, 4, 10, and 24 hours after primaquine (PQ) dosing, by CYP2D6 metabolizer phenotype. A, 5,6-ortho-quinone levels in all volunteers with a normal metabolizer (NM) phenotype (n = 8). Those with an activity score (AS-A) of 2 are indicated by dotted lines and filled circles, and those with an AS-A of 1.5 are indicated by solid lines and open circles. B, 5,6-ortho-quinone levels in volunteers from the intermediate metabolizer (IM) group in whom 5,6-ortho-quinone was detected at ≥2 time points (n = 9). Two volunteers from the IM group with an AS-A of 1.0 are indicated by dotted black lines and stars. The 5 volunteers with an AS-A of 0.5 are indicated by gray triangles (for those with a maximum concentration [C_max] at 4 hours) or open triangles (for those with a C_max at 24 hours). Two volunteers from the IM group had an AS-A of 0.25, of whom one had a C_max at 4 hours (open square) and the other had a C_max at 10 hours (open diamond). Not shown are data for 1 volunteer with an IM phenotype who had 5,6-ortho-quinone detected only at 4 hours, data for 2 who had 5,6-ortho-quinone detected only at 10 hours, and data for 2 who had 5,6-ortho-quinone detected only at 24 hours. 5,6-ortho-quinone was not detected in 5 volunteers from the IM group.