Maternal and umbilical cord serum zidovudine levels in human immunodeficiency virus infection

Pharmacokinetics, Placental and Breast Milk Transfer of Antiretroviral Drugs in Pregnant and Lactating Women Living with HIV

BACKGROUND

Remarkable progress has been achieved in the identification of HIV infection in pregnant women and in the prevention of vertical HIV transmission through maternal antiretroviral treatment (ART) and neonatal antiretroviral drug (ARV) prophylaxis in the last two decades. Millions of women globally are receiving combination ART throughout pregnancy and breastfeeding, periods associated with significant biological and physiological changes affecting the pharmacokinetics (PK) and pharmacodynamics (PD) of ARVs. The objective of this review was to summarize currently available knowledge on the PK of ARVs during pregnancy and transport of maternal ARVs through the placenta and into the breast milk. We also summarized main safety considerations for in utero and breast milk ARVs exposures in infants.

METHODS

We conducted a review of the pharmacological profiles of ARVs in pregnancy and during breastfeeding obtained from published clinical studies. Selected maternal PK studies used a relatively rich sampling approach at each ante- and postnatal sampling time point. For placental and breast milk transport of ARVs, we selected the studies that provided ratios of maternal to the cord (M:C) plasma and breast milk to maternal plasma (M:P) concentrations, respectively.

RESULTS

We provide an overview of the physiological changes during pregnancy and their effect on the PK parameters of ARVs by drug class in pregnancy, which were gathered from 45 published studies. The PK changes during pregnancy affect the dosing of several protease inhibitors during pregnancy and limit the use of several ARVs, including three single tablet regimens with integrase inhibitors or protease inhibitors co-formulated with cobicistat due to suboptimal exposures. We further analysed the currently available data on the mechanism of the transport of ARVs from maternal plasma across the placenta and into the breast milk and summarized the effect of pregnancy on placental and of breastfeeding on mammal gland drug transporters, as well as physicochemical properties, C:M and M:P ratios of individual ARVs by drug class. Finally, we discussed the major safety issues of fetal and infant exposure to maternal ARVs.

CONCLUSIONS

Available pharmacological data provide evidence that physiological changes during pregnancy affect maternal, and consequently, fetal ARV exposure. Limited available data suggest that the expression of drug transporters may vary throughout pregnancy and breastfeeding thereby possibly impacting the amount of ARV crossing the placenta and secreted into the breast milk. The drug transporter's role in the fetal/child exposure to maternal ARVs needs to be better understood. Our analysis underscores the need for more pharmacological studies with innovative study design, sparse PK sampling, improved study data reporting and PK modelling in pregnant and breastfeeding women living with HIV to optimize their treatment choices and maternal and child health outcomes.

Maternal and fetal zidovudine pharmacokinetics during pregnancy and labour: too high dose infused at labour?

AIMS

The main goal of the study was to describe the pharmacokinetics of maternal zidovudine (ZDV) administration during pregnancy and labour and to evaluate their impact on fetal concentrations and exposures.

METHODS

A total of 195 HIV-infected pregnant and non-pregnant women aged 16-59 years were included and 273 maternal and 79 cord blood ZDV concentrations were collected. A population pharmacokinetic model was developed to describe ZDV concentrations as a function of time in the mother and the fetus. Fetal exposures resulting from maternal oral administration and infusion were estimated and compared with therapeutic exposures (3-5 mg l(-1)  h) and to exposure providing higher risk of toxicity (>8.4 mg l(-1)  h). Different protocols for ZDV administration during labour were simulated.

RESULTS

The median fetal exposure and the percentage of children with values above 8.4 mg l(-1)  h were 3.20 mg l(-1)  h and 0% after maternal oral administration, respectively, and 9.71 mg l(-1)  h and 51% after maternal infusion during labour. Two options were considered to reduce fetal exposure during labour: (i) maternal infusion rates could be 1 mg kg(-1)  h(-1) during 1 h followed by 0.5 mg kg(-1)  h(-1) and (ii) the mother could only take oral ZDV every 5 h from start of labour until delivery with her neonate having their first ZDV dose as soon as possible after birth.

CONCLUSIONS

Zidovudine exposures are very important during labour and during the first days of a neonate's life. Maternal ZDV dose should be reduced in addition to the neonate doses reduction already proposed.

Zidovudine: a review of its use in the management of vertically-acquired pediatric HIV infection

Zidovudine is a thymidine analog that, after intracellular phosphorylation to zidovudine triphosphate metabolite, inhibits HIV-specific reverse transcriptase and terminates proviral DNA. Zidovudine administered to mildly symptomatic women with HIV infection in the antepartum (100mg orally 5 times/day), intrapartum (2 mg/kg intravenously over 1 hour then 1 mg/kg/h) and then to the neonate for 6 weeks (2 mg/kg), significantly reduced the rate of vertical HIV transmission by about two thirds, in the absence of breast-feeding (The Pediatric AIDS Clinical Trials Group 076 trial, standard protocol). Shorter zidovudine regimens, reduced the risk of transmission of HIV by 50% in a non-breast-feeding population and by about 37% in breast-feeding populations. Zidovudine (standard protocol) in combination with lamivudine was superior to zidovudine alone. A short oral zidovudine regimen was not as effective as a two-dose oral nevirapine regime, although the combination of short-course zidovudine plus lamivudine was as effective. Suppression of viral replication in neonates, infants and children has been achieved with zidovudine when used in triple-therapy regimens that include other antiviral drugs. Results from a trial of treatment-naive children indicate that the antiviral efficacy of combinations of zidovudine and lamivudine or abacavir, given with the protease inhibitor nelfinavir, is superior to treatment with this combination minus nelfinavir. When zidovudine was used in other highly active antiretroviral therapy regimens significant improvements in surrogate markers were consistently seen. Changing to ritonavir-containing regimens was superior to changing to treatment with two new nucleoside reverse transcriptase inhibitors. Short- and long-term (up to 5.6 years) outcomes from clinical trials showed that prenatal and neonatal exposure to zidovudine was generally well tolerated with the exception of mild anemia that resolved spontaneously after treatment cessation. Zidovudine was generally well tolerated as monotherapy in clinical trials of pediatric patients with HIV infection, and adverse events were similar to those reported in adults, with anemia and neutropenia being the most common.

CONCLUSION

Zidovudine, as monotherapy or in combination with other antiretroviral agents, remains a first-choice therapy for the prophylaxis of mother-to-child HIV transmission as shown by substantial reductions in transmission rates. Where feasible, the optimal strategy to prevent vertical transmission is to combine drug therapy with Cesarean section delivery and no breast-feeding. In addition, zidovudine in combination with another nucleoside analogue and a protease inhibitor is a first- or second-choice therapy for the treatment of pediatric HIV infection as significant and sustained reductions in viral load have been shown in both plasma and cerebrospinal fluid.

Effect of immediate neonatal zidovudine on prevention of vertical transmission of human immunodeficiency virus type 1

OBJECTIVE

To describe the effects of various short zidovudine (ZDV) prophylactic regimens on vertical transmission of human immunodeficiency virus type 1 (HIV-I) infection, especially the effect of immediate neonatal ZDV prophylaxis.

MATERIALS AND METHODS

The study included children of HIV-1-infected mothers who were born at a teaching hospital in Bangkok. The ZDV prophylaxis regimens varied by time periods that included: (1) no ZDV (1991-1996); (2) antenatal oral ZDV, 250 mg given twice a day starting at 34 to 36 weeks gestation and continued until labor (1995-1998); (3) antenatal oral ZDV plus immediate neonatal oral ZDV, 6 mg/0.6 mL/dose started within the first 2 hours after birth and continued at 6-hour intervals for 4 to 6 weeks (1997-1998); and (4) intrapartum intravenous ZDV given in addition to regimen 3 (1998-1999). Neonatal ZDV was administered within 2 hours after birth in 95% of the neonates.

RESULTS

In a cohort of 136 children born at least 9 months before the analysis date, the HIV-1 vertical infection rates were: (1) no ZDV, 11 of 48 (22.9%, 95% confidence interval [CI] = 12.0-37.3); (2) late antenatal ZDV, 10 of 47 (21.3%, 95% CI = 10.7-35.7); (3) late antenatal ZDV plus immediate neonatal ZDV, 0 of 28 (0%, 95% CI = 0-12.3); (4) late antenatal, intrapartum intravenous ZDV, plus immediate neonatal ZDV, 0 of 13 (0%, 95% CI = 0-24.7). An estimated 0% (95% CI = 0-8.6) of the infants who received immediate neonatal ZDV with or without intrapartum ZDV were infected, as compared with 22.1% (95% CI = 14.2-31.8 ) of those who received no ZDV or only late antenatal ZDV (P < 0.001).

CONCLUSIONS

The results of this study suggests high protective effect of immediate administration of neonatal ZDV. Perinatal components of antiretroviral prophylaxis provided the best results for protecting against vertical HIV-1 transmission.

Timing and mechanism of perinatal human immunodeficiency virus-1 infection

There is sufficient evidence indicating a higher vertical HIV-1 transmission rate in the last trimester and during labour compared with the first trimester. Antiretroviral therapy either single or in combination given to the mother during the last trimester and delivery can reduce the viral load in the maternal circulation. Vertical HIV-1 transmission during delivery can be minimized by appropriate timing and route of delivery. Elective Caesarean section before the onset of labour with an intact bag of forewaters provides the least mother-to-fetus microtransfusion compared to other modes of delivery. Since an effective combination of HIV-1 immunoglobulin and HIV-1 vaccine given to the HIV-1 exposed newborns to prevent HIV-1 transmission similar to the viral hepatitis B model is not firmly established at present, postexposure antiretroviral prophylaxis and nonbreast-feeding are advocated for infants born from the HIV-1 infected mothers. In cases of advanced stage of maternal HIV-1 infection, and in developing areas where malnutrition prevails, an adequate supply of essential micronutrients is proposed as an adjunctive measure to reduce HIV-1 perinatal transmission.