Maternal plasma samples at delivery and umbilical cord blood samples were available for 14 mother/infant pairs. Detectable atazanavir concentrations were present in all umbilical cord plasma samples, and the mean ratio of cord/maternal concentration was 0.13 and showed a low variability (95% CI 0.10–0.16; Fig. 2).
Clinical monitoring and tolerability
All women responded well to HAART. HIV-RNA levels were invariably below the detection limit (50 copies/ml) for all subjects at antepartum, delivery and postpartum evaluations. HAART was well tolerated during pregnancy and postpartum with no women stopping/changing the regimen or experiencing adverse events. At the antepartum evaluation, as an example, the total bilirubin mean level was 2.58 mg/dl (SD ± 1.64), whereas the same postpartum value was 2.02 mg/dl (SD ± 1.04).
All 17 infants (nine boys, eight girls) were live born. Their mean gestational age was 37.2 weeks (SD ± 0.56) and their mean birth weight was 2.912 kg (SD ± 0.195). None of the newborns presented with neonatal jaundice that required phototherapy for the treatment of hyperbilirubinemia. At birth all infants presented with an HIV-RNA level of less than 50 copies/ml and again tested negative 3 months after birth.
This is the first study describing the pharmacokinetics of atazanavir in pregnant women. The results show that overall atazanavir exposure is similar in the pregnant and non-pregnant states after a standard boosted dose.
The antepostpartum within-patient comparison demonstrated no difference in the atazanavir AUC0–24 and Ctrough values. During pregnancy, however, a slightly lower Cmax value was observed. Several physiological changes occurring during pregnancy, including increased gastric emptying time, intestinal transit time, increased gastric pH and increased blood volume, may explain this difference [3,5]. We showed that during the third trimester of pregnancy mean Tmax values were slightly higher and much more variable than those observed postpartum. This observation suggests that delayed drug absorption may be the reasonable explanation for the difference in Cmax values.
Even though peak concentrations were lower during pregnancy and were not equivalent to those observed postpartum, they were not significantly different from the latter. Furthermore, this slight blunting of Cmax during pregnancy was not accompanied by a decrease in the extent of oral absorption, as indicated by the equivalent AUC0–24 values, and it seems unlikely to be clinically relevant.
The major pharmacokinetic problem faced by PI during pregnancy is reduced overall exposure. When compared with postpartum results, lower AUC and Ctrough values have been reported for boosted lopinavir (lopinavir/ritonavir) , boosted saquinavir (saquinavir/ritonavir) , indinavir  and nelfinavir . Although the clinical implications of these altered concentrations in terms of the magnitude and durability of maternal virological response and the prevention of MTCT of HIV have been not completely addressed, the major risk is to expose pregnant women to subtherapeutic drug levels. Considerable data indicate that there is a significant association between antiretroviral drug concentrations and virological response, particularly for PI [13,14]. These relationships mean that antiretroviral drug exposure, especially the trough concentrations, should ideally be maintained above a defined threshold throughout the entire dosing interval in order to prevent viral replication and the development of resistant viral strains. Achieving adequate PI plasma levels would be particularly important in those patients who are first diagnosed with HIV infection during pregnancy and who may have on that occasion a very high viral load. Moreover, antiretroviral-experienced pregnant women may certainly benefit from higher drug plasma levels also in the third trimester to overcome some degree of viral resistance.
The mean atazanavir Ctrough of our women, in the third trimester of pregnancy, was 486 ng/ml, which was similar to the values reported in 16 pregnant women (373 ng/ml, range 71–1136 ng/ml) in the same time period . The latter study did not, however, measure the Ctrough in the postpartum, so we cannot compare the mean atazanavir Ctrough (514 ng/ml) measured in our subjects at the postpartum evaluation. This latter measure postpartum is lower than expected for individuals on boosted atazanavir. In a study with both boosted and unboosted atazanavir, the mean Ctrough of 94 patients was 663 and 125 ng/ml, respectively . Also another study reported a mean Ctrough of 862 ng/ml  for individuals on atazanavir boosted with ritonavir.
A number of reasons may provide an explanation for the lower than expected values found in our women. Seventeen subjects represent a relatively small sample size, and a large interpatient variability has been described for almost all PI, including atazanavir [17,18]. All that suggests the potential role of additional covariates in atazanavir pharmacokinetics. Genetic factors, such as polymorphisms at MDR1-3435, may significantly affect atazanavir plasma concentrations, even using ritonavir boosting . In addition, ethnicity may have played a role as nine out of the 17 women in our group were of African origin. Possible differences in drug clearance between men and women have been described for saquinavir (approximately 50% decrease in saquinavir clearance in women) , although both sex and age failed to show any effects in atazanavir pharmacokinetics in previous reports . In addition, although unlikely, we cannot rule out the potential bias caused by unreported co-medications, which may have negatively affected atazanavir plasma concentrations.
Finally, in our patients we did not measure ritonavir plasma levels, which are known to influence the pharmacokinetics of atazanavir greatly, as well as for almost all PI. One study  reported lower levels of ritonavir during gestation compared with the postpartum period in 13 women receiving boosted saquinavir (800/100 mg twice a day). Another study  in 11 pregnant women on lopinavir/ritonavir showed that ritonavir AUC and the 12-h postdose concentration were similar ante and postpartum, suggesting that the lower lopinavir concentration in late pregnancy is not secondary to reduced ritonavir exposure. Similarly, ritonavir Ctrough values were equivalent, during and off pregnancy, in seven women on lopinavir/ritonavir .
In our study Ctrough atazanavir levels, although presenting a quite high interpatient variability, were comparable in the pregnant and non-pregnant period and, most important, invariably allowed the calculation of an inhibitory quotient several fold greater than the atazanavir 90% IC for wild-type HIV, minimizing the risk of residual viral replication and the selection for resistant viral strains. All treated women achieved and maintained an undetectable viral load throughout the whole study period. Although limited in number, we obtained evidence that atazanavir was also effective in preventing MTCT.
From a pharmacokinetic point of view, this result may partly be explained by the transplacental passage of atazanavir. Several data have confirmed an overall low level of placental passage for PI. In line with the considerable intersubject variability seen for maternal levels [17,18,21], umbilical cord/maternal blood ratios vary substantially in different studies, mostly limited by the small sample size, and with possible differences in threshold limits or the methodological approach. In one study  involving 13 maternal cord blood sample pairs, the reported ratios were extremely low for all PI (nine patients on nelfinavir, two on ritonavir, one on saquinavir and one on lopinavir), most of them being below the limit of detection. Data from the PACTG 1026 study team  on lopinavir/ritonavir in pregnancy reported a ratio equal to 0.2 for the umbilical cord to maternal blood lopinavir concentration in 10 paired detectable samples. For three additional women, however, maternal delivery lopinavir concentrations were below the limit of detection. No measurable PI concentrations in cord blood have been reported in six mother/infant pairs receiving nelfinavir and in six receiving lopinavir/ritonavir . In another study  cord blood concentrations were below the detectable threshold in 10 of 40 samples (25%), 25 of 40 (62%), nine of 11 (81%), four of six (66%) and five of six (83%) for nelfinavir, M8 metabolite, ritonavir, indinavir and saquinavir, respectively. Other authors  reported cord blood concentrations of lopinavir between 5 and 25% of the maternal plasma levels, averaging 16.7%. Only one single case  has been published on human placental transfer of atazanavir/ritonavir in a pregnant woman. At delivery, the cord blood atazanavir level was 362 ng/ml, whereas the maternal atazanavir level was 1515 ng/ml (ratio 0.23). As PI do not cross the placenta to an appreciable degree, the extent to which they can provide direct protection for the newborn is uncertain and probably modest. Reasons for the limited placental transfer are probably the high protein binding capacity of PI and their large molecular size .
We obtained a maternal blood/umbilical cord ratio of 0.10 that showed a clear positive linear correlation with maternal plasma levels. Consequently, even considering maternal Ctrough levels, the fetal exposure to atazanavir would fall into a therapeutic range approximately fourfold higher than wild-type HIV IC90. Whether significant plasma levels of antiretroviral drugs in the fetus could effectively decrease the risk of vertical transmission deserves further investigation. On the other hand, a limited, but still therapeutic, placental transfer of atazanavir may protect the fetus against the potential toxic effects of the drug. In this respect, we point out that none of the newborns presented with a clinically significant neonatal jaundice requiring phototherapy. These findings are consistent with recent data  in 33 women exposed to atazanavir/ritonavir during pregnancy, supporting its safety in this setting.
In summary, atazanavir overall exposure at steady state during the third trimester of pregnancy is similar to that observed in the non-pregnant state. Over the whole dosing interval, therapeutic drug concentrations are maintained well above the wild-type HIV IC90. Atazanavir crosses the placenta and this may potentially contribute to reduce the risk of vertical transmission further.
As pregnancy does not appear to alter plasma exposure to atazanavir, no dose adjustment is required in pregnant women. Pharmacokinetic results suggest that a standard boosted atazanavir dose is a reasonable component of HAART during pregnancy.
We are in debt with Dr G Remuzzi, from the Mario Negri Institute for Pharmacological Research, Bergamo (Italy), for his invaluable support and cooperation which made this research possible.
Conflicts of interest and financial disclosure: F.M. has served as a consultant on advisory boards for Bristol-Myers Squibb, Gilead, GlaxoSmithKline, Roche, Tibotec; he has received lecture fees from Abbott, Bayer, Bristol-Myers Squibb, Gilead, GlaxoSmithKline, Merck Sharpe and Dohme, Roche and has received research and educational grants from Bristol-Myers Squibb, Boehringer Ingelheim, GlaxoSmithKline, Jansen-Cilag and Roche. D.C. has received a travel award from Wyeth Italia, and lecture fees from Sanofi-Aventis and AstraZeneca. F.S. has served as a consultant on advisory boards for Bristol-Myers Squibb and Roche; he has also served as speaker for GlaxoSmithKline and Boehringer Ingelheim, and has received research and educational grants from Bristol-Myers Squibb, Gilead, Boehringer Ingelheim, GlaxoSmithKline, Jansen-Cilag and Roche. The others authors have no conflicts.
The study was spontaneous and was not supported by private or public research grants.
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Keywords:© 2007 Lippincott Williams & Wilkins, Inc.
Atazanavir; HIV-1 infection; pharmacokinetics; placental transfer; pregnancy