Frequencies of ABCB1 and CYP Gene Polymorphisms
The ABCB1-3435-T allelic frequency was 0.35 in the whole cohort; however, the frequencies were less common in black, non-Hispanic (P = 0.006). Similarly, there were significant differences in the frequencies of ABCB1-G2677T (P < 0.001) and ABCB1-C1236T genotypes (P < 0.001) in black, non-Hispanic, compared with others. The CYP2C19-681-A allelic frequency was 0.19 in whole cohort, and the frequencies were similar among race/ethnicity (P = 0.35) (). All patients had the CYP2C19-636-G/G genotype.
The ABCB1-3435C> T Genotype is Associated With NFV CL/F
NFV CL/F differed significantly among the ABCB1-3435C>T genotype (P < 0.001); children with the ABCB1-3435-C/C genotypes had higher median NFV CL/F [47.2 L/h/m2, interquartile range (IQR): 32.7–68.7 L·h−1·m−2 ] compared with those with the C/T (36.1 L/h/m2, IQR: 28.1– 56.7 L·h−1·m−2) and the T/T genotype (35.4 L/h/m2, IQR: 17.8-61.3 L·h−1·m−2). NFV CL/F did not differ among subjects with the other ABCB1 genotype (P > 0.17). There was no difference in the association when examined by each race/ethnic group (P > 0.11).
The CYP2C19-681G>A Polymorphism is Associated With NFV CL/F
NFV CL/F differed significantly among the CYP2C19-681G>A genotypes (P < 0.001). When the data were analyzed in each race/ethnicity (), a significant difference in NFV CL/F was observed in black, non-Hispanics (P < 0.001). The same trends were also observed for Hispanics (P = 0.12) and white, non-Hispanics (P = 0.25), but the differences did not achieve the level of significance.
Figure 1 Oral clearance rate (CL/F, L/h/m2) for nelfinavir in children with the CYP2C19-681G>A genotypes in each race/ethnicity. Each circle represents nelfinavir CL/F in each subject with the CYP2C19-681-G/G (left), -G/A (heterozygous, middle), and -A/A (more ...)
Association Between the CYP2C19-681G>A Genotype and the M8 to NFV Ratio
Overall, the median M8 to NFV ratio was associated with the CYP2C19-681G>A genotype (P < 0.001); the ratio was 0.45 (IQR: 0.22–0.96) in those with the -G/G genotype compared with 0.26 (IQR: 0.13–0.47) in -G/A or 0.02 (IQR: 0.01–0.08) for the -A/A genotype. The association between the CYP2C9-681G>A genotype was particularly strong for the black, non-Hispanic group (P < 0.001), but not for the Hispanic (P = 0.56), and white, non-Hispanic (P = 0.30) groups. No other genotypes were associated with the M8 to NFV ratio (P = 0.29–0.87).
Virologic and Immunologic Responses During HAART in Children With ABCB1 and CYP Genotypes
The percentages in children who reached plasma HIV RNA <400 copies per milliliter at week 12 did not differ by the CYP2C19-681G>A genotypes (P = 0.14–1.00). However, at week 24, the percentage of subjects among the CYP2C19-681G>A genotype who reached plasma HIV RNA <400 copies per milliliter differed significantly (P = 0.01): 46% of subjects with the CYP2C19-681-G/G genotype achieved virologic suppression compared with 69% of those with the -G/A genotype, and 63% of those with the -A/A genotype. When examined by race/ethnicity, these differences were observed for the black, non-Hispanic group (P = 0.02) and the white, non-Hispanic group (P = 0.03), but not for Hispanics (P = 0.84). No differences were observed when the data were analyzed with the ABCB1-3435C>T genotype (P = 0.06) or the CYP3A4-392A>G genotype at week 24 (P = 0.26). Regarding immunologic recovery, changes in CD4+ T-cell percentage from baseline to weeks 12 and 24 were not different among the 3 genotypes in CYP2C19-681G>A (P = 0.50, P = 0.44, respectively) or ABCB1-3435C>T (P = 0.08, P = 0.21, respectively).
Other Factors Contributing to NFV CL/F Concomitant Antiretrovirals
Because nevirapine induces hepatic CYP3A and decreases the levels of PIs12
and ritonavir acts as a potent PK enhancer for CYP substrates,13
we evaluated the association between NFV CL/F and concomitant use of nevirapine or ritonavir. NFV CL/F was not different between subjects who received nevirapine and those who did not receive nevirapine (P
= 0.70). In contrast, ritonavir use decreased NFV CL/F significantly (P
= 0.002); the median NFV CL/F in patients who received ritonavir (35.8 L/h/m2
, IQR: 24.7– 47.5 L·h−1
) was lower compared with those who did not receive ritonavir (47.4 L/h/m2
, IQR: 32.5–70.6 L·h−1
Association of Race/Ethnicity on NFV CL/F and Clinical Outcomes
Because race/ethnicity is an important determinant of these SNPs, we also analyzed the data based on their race/ethnicity. Black, non-Hispanics (43.4 L·h−1·m−2, IQR: 33.1–66.6 L·h−1·m−2) and Hispanics (45.2 L·h−1·m−2, IQR: 26.2–65.2 L·h−1·m−2) had higher median NFV CL/F compared with white, non-Hispanics (31.7 L·h−1·m−2, IQR: 27.3–53.3 L·h−1·m−2), but it did not reach a statistical significance (P = 0.09). M8 to NFV ratio was not associated with race/ethnicity (P = 0.67). Furthermore, clinical outcomes including percentages in children who reached plasma HIV RNA <400 copies per milliliter at week 12 (P = 0.54) or changes in CD4+ T-cell percentage from baseline to weeks 12 (P = 0.89) was not associated with race/ethnicity.
A Multivariate Analysis for Predicting NFV CL/F
A multivariate analysis showed that the CYP2C19-681G>A variants (P < 0.001), concomitant use of ritonavir (P < 0.001), and age (P = 0.03) were independently associated with NFV CL/F. However, the ABCB1-3435 variants (P = 0.61), CYP3A4-392 homozygous variants (P = 0.42), and race/ethnicity (black, non-Hispanics) (P = 0.07) were no longer statistically significant. Thus, the CYP2C19-681G>A genotype remains an important pharmacogenetic determinant of NFV CL/F even after controlling for other factors.