Discussion
The present study demonstrated significant differences in the BET pharmacokinetics in DC twin pregnancies. The AUC0-∞and CL/F were significantly lower and higher, respectively, in DC twin pregnancies compared to singleton and MC twin pregnancies while there were no differences in the other pharmacokinetic parameters. The understanding of the pharmacokinetics of drugs during pregnancy is crucial for the development of appropriate dosage regimens. The clinical BET pharmacokinetics have been investigated in healthy adults,20,21,23 as well as in pregnant women.19,22,11,15
Previous studies developed BET population pharmacokinetic models19,22 or classical pharmacokinetic approaches20,21 in both singleton and twin pregnancies. However, none of these studies evaluated the BET pharmacokinetics or BET placental transfer in twin pregnancies discriminated by chorionicity. This study is unprecedented regarding the BET pharmacokinetic studies in singleton, DC and MC twin pregnancies.
Many demographic and clinical variables such as body composition, blood volume, hormonal levels, hepatic and placenta metabolism could interfere with BET pharmacokinetics and explain the findings of the present study.28,29,11 Furthermore, the influence of the maternal physiological changes on the kinetics disposition of drugs is more remarkable in the third trimester of pregnancy and multiple pregnancies.28–30 It is worth mentioning that all pregnant women included in this clinical trial were in the last trimester of their pregnancies.
Few studies that investigated BET elimination in unchanged form in urine evidenced that the contribution of renal clearance in total clearance is not significant, supposing that BET is eliminated mainly by its metabolism.17,23,31 Although pathways that mediate the BET hepatic metabolism have not been fully established, some studies have proposed a primary and fundamental role for the cytochrome P450 enzymes, mainly CYP3A4.17,32 Even though some authors have suggested that BET placental metabolism seems to be low or negligible,33 others have highlighted the possibility of increased metabolism due to two or more fetoplacental units in twin pregnancies.11
Data on the impact of twin pregnancies on BET pharmacokinetics appear to be contradictory to date. Our data show BET AUC0-∞lower in DC twin pregnancies than in singleton and MC twin pregnancies. The presence of two fetoplacental units in DC twin pregnancies could result in a higher metabolism mediated by CYP3A enzymes. Besides, potentially higher hormone levels in DC pregnancy could induce CYP3A enzymes in both the placenta and maternal liver and explain these changes. Also, the increased hepatic flow during pregnancy could rise the BET clearance and reduce the AUC.
Although some studies have shown significant differences in CL/F or t1/2 between singleton and twin pregnancies,19,11 other research groups have not found similar results.22 Foissac and collaborators found a 28% increase in BET CL/F in twin pregnancies without chorionicity discrimination compared to singleton pregnancies.19 In the present study, the BET CL/F values did not differ between MC twin and singleton pregnancies, but DC twin pregnancies presented a 40% increase in this pharmacokinetics parameter compared other pregnancies. Enhanced hepatic metabolism can also explain the pregnancy-related increase in CL/F.
Our study showed a positive correlation between maternal body mass index and BET Vd/F. This finding is similar to the Della Torre et al. study, which showed that maternal lean body weight was a covariate for the Vd/F using a population pharmacokinetic model.22 Also, the magnitude of the values of the dose-independent parameters such as CL/F and Vd/F in the present study were similar to those of previous studies conducted with pregnant women (Table 2).19,22,11Betamethasone is a lipophilic drug and can bind significantly to tissue.34 The significant change in pregnant women’s body size with twin fetuses provides one more possible explanation for the lower AUC in these pregnancies than singleton ones.
Our study has some strengths. First, few studies have analyzed BET pharmacokinetics in twin pregnancies, and no study to date has analyzed BET pharmacokinetic parameters in twin pregnancies separated by chorionicity. Second, there was only one researcher conducting the clinical protocol. This ensured the correct interval between the BET administration and the first blood sample and the serial blood sampling intervals. Third, before BET pharmacokinetic analysis in the present study, a BET assay and analytical validation were performed, and the method showed suitable sensibility, linearity, accuracy and precision for pharmacokinetics and placental transfer studies in a twin pregnancy.
Our study was not without limitations. Preliminary data on BET placental transfer can be considered limited mainly due to the low number of patients in each group and different intervals between drug administration and delivery. On the other hand, a previous study showed that BET concentration in cord blood decreases within days.35 The analysis of umbilical vein/maternal vein and intervillous space/maternal vein ratios showed that BET concentration in intervillous space is higher than the fetal compartments. The inclusion of a more significant number of pregnant women and applying a protocol with greater precision in the intervals between the BET administration and the collection of maternal and fetal blood samples are being carried out to confirm this finding.
In conclusion, this study shows the influence of twin pregnancies on BET pharmacokinetics, suggesting that the presence of two fetoplacental units may increase the drug’s metabolism by CYP3A4 enzyme and increase its elimination. Pharmacokinetic-pharmacodynamic clinical studies are needed to investigate whether this BET pharmacokinetic changes have clinical repercussions for the newborns and require dose adjustment in DC twin pregnancies.
Data availability : The data that support the findings of this study are available on request from the corresponding author.
Funding statement: The authors thank the São Paulo Research Foundation (FAPESP) [grant 2017/19256-6] and in part by the Higher Education Improvement Coordination - Brazil (CAPES) [Finance Code 001].
Authorship statement: G.F.P.R. and A.C.M. designed the clinical study and wrote the manuscript; G.F.P.R., L.H.C.M. and S.F.F. performed blood sample collections; G.F.P.R., M.P.P. and V.L.L. performed the BET quantification in plasma. J.R.L.B and L.V.L. performed the pharmacokinetic ans statiscal analysis. G.F.P.R., R.C., E.C.D.M., G.D., A.C.M, J.R.L.B and L.V.L. performed manuscript review.
Conflict of interest disclosure : The authors have no conflicts of interest to declare.
Ethics approval statement: Protocol number 8676/2017, of University Hospital of the Ribeirão Preto Medical School (São Paulo, Brazil).
Clinical trial registration: The study protocol was registered on the Brazilian Registry of Clinical Trials (ReBEC, www.ensaiosclinicos.gov.br) under ID number RBR-2v2mwkz.