An increase in urinary primaquine and a reduction in urinary primaquine-5,6-orthoquinone in the Thai population with CYP2D6 reduced enzyme function

Objectives

Primaquine is metabolized by the cytochrome P450-2D6 enzyme (CYP2D6) to an active primaquine-5,6-orthoquinone (POQ). No relationships of CYP2D6 polymorphisms with the pharmacokinetics of primaquine and POQ were reported in the Thai population.

Methods

We evaluated the genetic distribution of CYP2D6 in 345 Thai army populations together with the pharmacokinetic profiles of primaquine and POQ in plasma and urine (n = 44, descriptive data are presented in median (range)). All dose-related pharmacokinetic parameters were normalized by primaquine dose per body weight before statistical analysis.

Results

CYP2D6*10 was the allele observed with the highest frequency (56.62%) corresponding to CYP2D6*10/*10 (32.94%) and CYP2D6*1/*10 (27.94%) genotypes. CYP2D6 intermediate metabolizers (CYP2D6 IM) were found in 44.41% of the cohort and had an increase in the cumulative amount of primaquine excreted (CAE) in urine compared to normal metabolizers of CYP2D6 (CYP2D6 NM); (CYP2D6 IM vs. CYP2D6 NM: 2444 (1697-3564) vs. 1757 (1092-2185) μg/mg/kg, p = 0.039), a reduction in urine CAE of POQ (CYP2D6 IM vs CYP2D6 NM: 115 (46-297) vs. 318 (92-498) μg/mg/kg, p = 0.047) and a reduction in the POQ/primaquine CAE ratio in urine (CYP2D6 IM vs. CYP2D6 NM: 0.06 (0.01-0.11) vs. 0.16 (0.06-0.26), p = 0.009). No significant differences were found in the pharmacokinetic profiles of plasma primaquine and POQ.

Conclusions

The CYP2D6 polymorphisms influenced the changes in primaquine and POQ that were noticeable in the urine, supporting the role of the CYP2D6 gene testing before drug administration.

Tacrolimus dose adjustment is not necessary in dose to dose conversion from a twice daily to a prolonged release once daily dose form

Twice daily TAC (BID TAC) and prolonged released once daily dose tacrolimus (OD TAC) have different pharmacokinetic (PK) profiles in kidney transplant (KT) recipients. Precise dose adjustment recommendations when converting from BID TAC to OD TAC remain inconclusive. A single center, PK study was conducted in stable KT recipients taking constant doses of TAC, mycophenolic acid, and prednisolone. The area under the concentration-time curve (AUC) 0-24 and C_trough were measured before and 4 weeks after 1:1 conversion from BID TAC to OD TAC without subsequent dose adjustment. A 90% confidence interval (CI) of geometric mean ratio (GMR) of OD TAC/BID TAC within the range of 0.9-1.11 was utilized to indicate equivalence of the narrow therapeutic index drugs. The roles of CYP3A5 genotypic polymorphism on PK parameters were also assessed. There were 20 patients with median time since transplantation of 18 months. The mean of CKD-EPI eGFR was 60.7 ± 16.43 mL/min/1.73 m². The median total daily TAC dose of 0.058 mg/kg/day. The geometric means (%CV) of AUC_0-24 of OD and BID TAC were 205.16 (36.4%) and 210.3 (32.5%) ng/mL × h, respectively, with a GMR of 0.98 (90%CI 0.91-1.04). The geometric means (%CV) of C_trough of OD TAC and BID TAC were 5.43 (33.1%) and 6.09 (34.6%) ng/mL, respectively. The GMR of C_trough was 0.89 (90%CI 0.82-0.98), which was below 0.9. The newly calculated target C_trough level of OD TAC was 4.8-6.2 ng/mL. The best abbreviated AUC_0-24 was AUC = 0.97(C0) + 5.79(C6) + 18.97(C12) - 4.26. The GMR AUC_0-24 was within the range of 0.9-1.11 irrespective of CYP3A5 genotypic polymorphism while the GMR of C_trough was below 0.9 only in the CYP3A5 expressor patients. The 1:1 conversion from BID TAC to OD TAC without subsequent dose adjustment provided similar AUC_0-24 regardless of CYP3A5 genotypic polymorphism. However, the C_trough was lower in the CYP3A5 expressor group. Therefore, it is not necessary to routinely increase the OD TAC dose after conversion.Trial registration: Thai Clinical Trials Registry (TCTR20210715002).

Simplified and Rapid Determination of Primaquine and 5,6-Orthoquinone Primaquine by UHPLC-MS/MS: Its Application to a Pharmacokinetic Study

The method for the determination of primaquine (PQ) and 5,6-orthoquinone primaquine (5,6-PQ), the representative marker for PQ active metabolites, via CYP2D6 in human plasma and urine has been validated. All samples were extracted using acetonitrile for protein precipitation and analyzed using the ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) system. Chromatography separation was carried out using a Hypersil GOLD^TM aQ C₁₈ column (100 × 2.1 mm, particle size 1.9 μm) with a C₁₈ guard column (4 × 3 mm) flowed with an isocratic mode of methanol, water, and acetonitrile in an optimal ratio at 0.4 mL/min. The retention times of 5,6-PQ and PQ in plasma and urine were 0.8 and 1.6 min, respectively. The method was validated according to the guideline. The linearity of the analytes was in the range of 25–1500 ng/mL. The matrix effect of PQ and 5,6-PQ ranged from 100% to 116% and from 87% to 104% for plasma, and from 87% to 89% and from 86% to 87% for urine, respectively. The recovery of PQ and 5,6-PQ ranged from 78% to 95% and form 80% to 98% for plasma, and from 102% to from 112% to 97% to 109% for urine, respectively. The accuracy and precision of PQ and 5,6-PQ in plasma and urine were within the acceptance criteria. The samples should be kept in the freezer (−80 °C) and analyzed within 7 days due to the metabolite stability. This validated UHPLC-MS/MS method was beneficial for a pharmacokinetic study in subjects receiving PQ.

SLCO1B1 and ABCG2 Gene Polymorphisms in a Thai Population

Introduction

Genetic polymorphisms of drug transporters influence drug transporter activity and alter pharmacokinetic profiles of the drugs. Organic anion transporting polypeptide 1B1 (OATP1B1) and breast cancer resistance protein (BCRP) are important transporters encoded by solute carrier organic anion transporter family member 1B1 (SLCO1B1) gene and ATP-binding cassette subfamily G member 2 (ABCG2) gene, respectively. Polymorphisms in these genes are associated with increased plasma statins concentrations, statin-induced myopathy and poor response to allopurinol treatment.

Purpose

We explored allele and genotype frequencies of SLCO1B1 and ABCG2 genes including their predicted phenotypes in 53 Thai participants. Of these, 17 had chronic kidney disease and were on statins.

Materials and Methods

Genotyping analysis for SLCO1B1 c.521T>C (rs4149056), c.388A>G (rs2306283), g.-11187G>A (rs4149015), and ABCG2 c.421C>A (rs2231142) was done by using TaqMan^® Real time PCR. All were tested for Hardy–Weinberg Equilibrium.

Results

Most of the participants (80%) had normal function haplotypes SLCO1B1 (*1A and *1B) while decreased (*5, *15, and *17) and unknown (*21) function haplotypes were less observed. Four phenotypes of SLCO1B1 were observed: 69.81% had normal function (*1A/*1A,*1A/*1B, and *1B/*1B), 13.21% had intermediate function (*1A/*17, *1B/*15 and *1B/*17), 9.43% had indeterminate function (*1A/*21 and *1B/*21) and 7.55% had low function (*5/*15, *15/*15, and *15/*17). ABCG2 c.421A allele frequency was 25%. The frequency of ABCG2 c.421CA and AA phenotypes were 37.7% and 5.7%, respectively. The allele and genotype frequencies observed are consistent with reports in Asians. However, there were differences in major allele distributions between Asians and Caucasians for SLCO1B1 c.388A>G; SLCO1B1 c.388G were highly found in Asians, but c.388A were more observed in Caucasians.

Conclusion

This study showed that in the Thai population, there were 4 SNPs of SLCO1B1 and ABCG2 genes. This finding may be clinically applied to minimize inter-individual variability of drugs such as statins and allopurinol. Further study with a larger sample size is needed to assess the drug profiles and responses to treatment.

Glutathione and its antiaging and antimelanogenic effects

Background

Previous studies showed that supplementation of reduced form of glutathione (GSH, 500 mg/d) has a skin-lightening efficacy in humans. This study was designed to evaluate the influences of both GSH and oxidized form (GSSG), at doses lower than 500 mg/d, on improving skin properties.

Patients and methods

A randomized, double-blind, placebo-controlled, parallel, three-arm study was conducted. Healthy female subjects were equally randomized into three groups and took GSH (250 mg/d), GSSG (250 mg/d), or placebo orally for 12 weeks. At each visit at baseline and for 12 weeks, skin features including melanin index, wrinkles, and other relevant biophysical properties were measured. Blood samples were collected for safety monitoring.

Results

In generalized estimating equation analyses, melanin index and ultraviolet spots of all sites including face and arm when given GSH and GSSG tended to be lower than placebo. At some sites evaluated, subjects who received GSH showed a significant reduction in wrinkles compared with those taking placebo. A tendency toward increased skin elasticity was observed in GSH and GSSG compared with placebo. There were no serious adverse effects throughout the study.

Conclusion

We showed that oral glutathione, 250 mg/d, in both reduced and oxidized forms effectively influences skin properties. Overall, glutathione in both forms are well tolerated.