Pharmacokinetics and safety of stavudine in HIV-infected pregnant women and their infants: Pediatric AIDS Clinical Trials Group protocol 332

Pharmacokinetic considerations in the use of antivirals in neonates

INTRODUCTION

Neonatal patients, because of the inability of their immune system to properly respond to microbial challenge, are highly susceptible to viral infections. Immunoglobulins, monoclonal antibody and antiviral drugs are used for prophylaxis and treatment of viral diseases in neonates. Neonates and, especially, preterm infants differ in drug absorption, distribution, metabolism and excretion from adults and older children.

AREAS COVERED

This review will evaluate deficiencies of neonatal immune responses to microbial challenge that predispose newborns to viral infections, clinical manifestations and the treatment of viral diseases in neonates. We focus on published studies describing antiviral drug pharmacokinetics in neonates and make recommendations on the dosing of these drugs, allowing achievement of maximal clinical benefits in neonates.

EXPERT OPINION

While some efforts were undertaken to study pharmacokinetics and pharmacodynamics of antiviral drugs, much more needs to be done. Current data indicate that the pharmacokinetics of antiviral drugs may vary significantly depending on gestational age, maturation processes of drug-metabolizing enzymes and renal clearance. Specifics of pharmacokinetics of antiviral drugs need to be taken into consideration when they are prescribed to neonates and infants.

Protecting the fetus against HIV infection: a systematic review of placental transfer of antiretrovirals

BACKGROUND

Maternal-to-fetal transfer of antiretroviral drugs contributes to prevention of vertical transmission of HIV.

OBJECTIVE

This systematic review discusses published studies containing data pertaining to the pharmacokinetics of placental transfer of antiretrovirals in humans, including paired cord and maternal plasma samples collected at the time of delivery as well as ex vivo placental perfusion models.

METHODS

Articles pertaining to placental transfer of antiretrovirals were identified from PubMed, from references of included articles, and from US Department of Health and Human Services Panel on Treatment of HIV-infected Pregnant Women and Prevention of Perinatal Transmission guidelines. Articles from non-human animal models or that had no original maternal-to-fetal transfer data were excluded. PRISMA guidelines were followed.

RESULTS

A total of 103 published studies were identified. Data across studies appeared relatively consistent for the nucleoside reverse transcriptase inhibitors (NRTIs) and the non-nucleotide reverse transcriptase inhibitors (NNRTIs), with cord to maternal ratios approaching 1 for many of these agents. The protease inhibitors atazanavir and lopinavir exhibited consistent maternal-to-fetal transfer across studies, although the transfer may be influenced by variations in drug-binding proteins. The protease inhibitors indinavir, nelfinavir, and saquinavir exhibited unreliable placental transport, with cord blood concentrations that were frequently undetectable. Limited data, primarily from case reports, indicate that darunavir and raltegravir provide detectable placental transfer.

CONCLUSION

These findings appear consistent with current guidelines of using two NRTIs plus an NNRTI, atazanavir/ritonavir, or lopinavir/ritonavir to maximize placental transfer as well as to optimally suppress maternal viral load. Darunavir/ritonavir and raltegravir may reasonably serve as second-line agents.

Serious adverse events are uncommon with combination neonatal antiretroviral prophylaxis: a retrospective case review

Six weeks of zidovudine (ZDV) is recommended for postnatal prophylaxis of HIV-exposed infants, but combination antiretrovirals are indicated if HIV transmission risk is increased. We investigated the frequency and severity of adverse events (AE) in infants receiving multiple drug prophylaxis compared to ZDV alone. In this retrospective review of 148 HIV-exposed uninfected infants born between 1997–2009, we determined clinical and laboratory AE that occurred between days of life 8–42. Thirty-six infants received combination prophylaxis; among those, a three-drug regimen containing ZDV, lamivudine, and nevirapine was most common (53%). Rates of laboratory AE grade ≥1 were as follows for the combination prophylaxis and ZDV alone groups, respectively: neutropenia 55% and 39%; anemia 50% and 39%; thrombocytopenia 0 and 3%; elevated aspartate aminotransferase 3% and 3%; elevated alanine aminotransferase 0 and 1%; hyperbilirubinemia 19% and 42%. Anemia occurred more frequently in infants who received three-drug prophylaxis compared to infants who received ZDV alone (63% vs. 39%, p = 0.04); all anemia AE were grade 1 or 2 in the three-drug prophylaxis group. Overall, 75% of infants on combination prophylaxis and 66% of infants on ZDV alone developed grade ≥1 AE (p = 0.32), and 17% of infants in either group developed grade ≥3 AE. Stavudine was substituted for ZDV in 23 infants due to anemia or neutropenia. After this antiretroviral change, 50% of evaluable infants demonstrated improvement in AE grade, and 25% had no change. In conclusion, low grade anemia, neutropenia, and hyperbilirubinemia occurred frequently regardless of the prophylactic regimen, but serious AE were uncommon. Although most AE were typical of ZDV toxicity, the combination of ZDV with lamivudine and nevirapine resulted in an increased frequency of low-grade anemia. Further studies are needed to identify prophylactic regimens with less toxicity for infants born to HIV-infected mothers.

Potential effect of pharmacogenetics on maternal, fetal and infant antiretroviral drug exposure during pregnancy and breastfeeding

Mother-to-child-transmission rates of HIV in the absence of any intervention range between 20 and 45%. However, the provision of antiretroviral drugs (ARVs) during pregnancy, delivery and breastfeeding can reduce HIV transmission to less than 2%. Physiological changes during pregnancy can influence ARV disposition. Associations between SNPs in genes coding for metabolizing enzymes, and/or transporters, and ARVs disposition are well described; however, relatively little is known about the influence of these SNPs on ARV pharmacokinetics during pregnancy and lactation as well as their effect on distribution into the fetal compartment and breast milk excretion. Differences in maternal, fetal and infant ARV exposure due to SNPs may affect the efficacy and safety of ARVs used to prevent mother-to-child-transmission. The aim of this review is to provide an update on the effect of pregnancy-induced changes on the pharmacokinetics of ARVs and highlight the potential role of pharmacogenetics.

Pharmacokinetic optimization of antiretroviral therapy in pregnancy

Antiretroviral therapy suppresses replication of HIV allowing restoration and/or preservation of the immune system. Providing combination antiretroviral therapy during pregnancy can treat maternal HIV infection and/or reduce perinatal HIV transmission. However, providing treatment to pregnant women is challenging due to physiological changes that can alter antiretroviral pharmacokinetics. Suboptimal drug exposure can result in HIV RNA rebound, the selection of resistant virus or an increased risk of HIV-1 transmission to the infant. Increased drug exposure can produce unwarranted maternal adverse effects and/or fetal toxicity. Subsequently, dose adjustments may be necessary during pregnancy to achieve comparable antiretroviral exposure to non-pregnant adults. For several antiretrovirals, systemic exposure is decreased during the last trimester of pregnancy. By 6-12 weeks postpartum, concentrations return to those prior to pregnancy. Also, the extent of antiretroviral placental transfer to the fetus and degree of antiretroviral excretion into breast milk varies within, and between, antiretroviral drug classes. It is necessary to consider the pharmacological characteristics of each antiretroviral when optimizing combination therapy during pregnancy to treat maternal HIV infection and prevent perinatal HIV transmission.

Stavudine concentrations in women receiving postpartum antiretroviral treatment and their breastfeeding infants

First-line antiretroviral treatment regimens in resource-limited settings used in breastfeeding mothers often include stavudine (d4T). Limited data describing d4T concentrations in breast milk are available. We analyzed d4T concentrations in 52 mother-infant pairs using ultra-performance liquid chromatography-tandem mass spectrometry (lower limit of quantification: 5 ng/mL in plasma, 20 ng/mL in breast milk). Median (interquartile range) d4T concentrations were 86 (36-191) ng/mL in maternal plasma, 151 (48-259) ng/mL in whole milk, 190 (58-296) ng/mL in skim milk, and <5 (<5 to <5) ng/mL in infant plasma. Although d4T is concentrated in breast milk relative to maternal plasma, the infant d4T dose received from breast milk is very small and not clinically significant.

Effect of pregnancy on emtricitabine pharmacokinetics

OBJECTIVES

The aim of the study was to describe emtricitabine pharmacokinetics during pregnancy and postpartum.

METHODS

The International Maternal Pediatric and Adolescent AIDS Clinical Trials (IMPAACT), formerly Pediatric AIDS Clinical Trials Group (PACTG), study P1026s is a prospective pharmacokinetic study of HIV-infected pregnant women taking antiretrovirals for clinical indications, including a cohort taking emtricitabine 200 mg once daily. Intensive steady-state 24-hour emtricitabine pharmacokinetic profiles were performed during the third trimester and 6-12 weeks postpartum, and on maternal and umbilical cord blood samples collected at delivery. Emtricitabine was measured by liquid chromatography-mass spectrometry with a quantification limit of 0.0118 mg/L. The target emtricitabine area under the concentration versus time curve, from time 0 to 24 hours post dose (AUC(0-24) ), was ≥7 mg h/L (≤30% reduction from the typical AUC of 10 mg h/L in nonpregnant historical controls). Third-trimester and postpartum pharmacokinetics were compared within subjects.

RESULTS

Twenty-six women had pharmacokinetics assessed during the third trimester (median 35 weeks of gestation) and 22 postpartum (median 8 weeks postpartum). Mean [90% confidence interval (CI)] emtricitabine pharmacokinetic parameters during the third trimester vs. postpartum were, respectively: AUC: 8.0 (7.1-8.9) vs. 9.7 (8.6-10.9) mg h/L (P = 0.072); apparent clearance (CL/F): 25.0 (22.6-28.3) vs. 20.6 (18.4-23.2) L/h (P = 0.025); 24 hour post dose concentration (C(24) ): 0.058 (0.037-0.063) vs. 0.085 (0.070-0.010) mg/L (P = 0.006). The mean cord:maternal ratio was 1.2 (90% CI 1.0-1.5). The viral load was <400 HIV-1 RNA copies/mL in 24 of 26 women in the third trimester, in 24 of 26 at delivery, and in 15 of 19 postpartum. Within-subject comparisons demonstrated significantly higher CL/F and significantly lower C(24) during pregnancy; however, the C(24) was well above the inhibitory concentration 50%, or drug concentration that suppresses viral replication by half (IC(50) ) in all subjects.

CONCLUSIONS

While we found higher emtricitabine CL/F and lower C(24) and AUC during pregnancy compared with postpartum, these changes were not sufficiently large to warrant dose adjustment during pregnancy. Umbilical cord blood concentrations were similar to maternal concentrations.

Antiretroviral pharmacology: special issues regarding pregnant women and neonates

Antiretrovirals may be used in pregnant women infected with the HIV and their newborns both for treatment of maternal HIV disease and for prevention of mother-to-child transmission of HIV. More than 25 antiretroviral agents in 5 classes have been approved, with new drugs and classes in development. This article reviews current knowledge of the pharmacology of these drugs during pregnancy and in the newborn period, highlighting those pharmacologic issues critical to the safe and effective use of antiretrovirals in these populations.

A review of nucleoside reverse transcriptase inhibitor use to prevent perinatal transmission of HIV

Worldwide, women comprise > 50% of all people living with HIV and the vast majority of these women are of childbearing age. In fact, a significant proportion of these women are identified as HIV-infected during pregnancy. Preventing perinatal transmission has been one of the greatest prevention successes of the HIV epidemic with < 2% of live births resulting in an HIV-infected infant. The strategic use of combination antiretroviral therapy has been a critical component of this reduction. With more antiretroviral agents available for HIV, the appropriate selection of therapy is often based on provider familiarity with the various agents. Although benefits of antiretroviral use in pregnancy tremendously outweigh the risks, concerns regarding short- and long-term toxicity in mothers and their children, in addition to the risk of the development of HIV resistance, remain subjects of discussion. The choice of antiretroviral 'backbone' is supported by extensive data showing efficacy in the prevention of HIV vertical transmission. Co-formulated zidovudine/lamivudine is the most commonly used combination in pregnancy. Long-term consequences of in utero exposure to antiretroviral agents are not fully understood. In this article, we review the data regarding nucleoside reverse transcriptase inhibitors with a focus on tenofovir.

Implications of gender and pregnancy for antiretroviral drug dosing

PURPOSE OF REVIEW

This review briefly outlines the influences of gender and pregnancy on drug disposition, and describes the available antiretroviral pharmacokinetic data and dosing recommendations in these groups.

RECENT FINDINGS

Recent studies in pregnant women continue to document altered exposure of different classes of drugs during pregnancy. While new information shows that tenofovir exposure is significantly decreased during pregnancy, the magnitude of the decrease will not likely necessitate dose changes, similar to other nucleoside reverse transcriptase inhibitors. In contrast, standard doses of lopinavir/ritonavir in the third trimester showed markedly decreased exposure, and higher doses of this co-formulated agent should be given to women during the third trimester. Likewise, nelfinavir exposure using the new 625-mg tablets is also decreased during pregnancy, and higher doses should be considered in the third trimester.

SUMMARY

The majority of antiretrovirals studied have altered pharmacokinetics during pregnancy. Understanding the extent of these changes is necessary to recommend dose changes during pregnancy when appropriate. The correct dose is critical to maintain efficacy and safety of these agents for both the mother and the fetus. Innovative study designs are needed to facilitate the study of antiretrovirals during pregnancy.

Safety and efficacy of initiating highly active antiretroviral therapy in an integrated antenatal and HIV clinic in Johannesburg, South Africa

OBJECTIVE

To describe the safety and efficacy of highly active antiretroviral therapy (HAART) in pregnant women treated in an integrated antiretroviral antenatal clinic (ANC ARV).

METHODS

A retrospective analysis was performed on patients attending the ANC ARV from August 2004 through February 2007.

RESULTS

Data were collected on 689 treatment-naive pregnant women initiated on HAART. The mean age was 29.2 years. The mean baseline CD4 count was 154 cells per microliter, and mean baseline HIV viral load was 101,561 copies per milliliter. Tuberculosis was the most prevalent presenting opportunistic infection (7.7%). Stavudine, lamivudine, and nevirapine were initiated in 82% of women with the most frequent adverse drug reaction being nevirapine-associated skin rash (3.5%). Mean gestational age at HAART initiation was 27 weeks. Among women with follow-up data, 80% gained 50 or more CD4 cells per microliter and 80.5% achieved viral suppression to <1,000 copies per milliliter. Of 302 mother-infant pairs who completed postnatal follow-up, the HIV transmission rate was 5%. In women who received more than 7 weeks of HAART during pregnancy, transmission was 0.3%.

CONCLUSIONS

Within the ANC ARV program, initiating pregnant women on HAART was feasible, safe, and effective. Advanced gestational age at treatment initiation and loss to follow-up emerge as important challenges in this population.

Pharmacokinetics and safety of nelfinavir when used in combination with zidovudine and lamivudine in HIV-infected pregnant women: Pediatric AIDS Clinical Trials Group (PACTG) Protocol 353

BACKGROUND

Combination antiretroviral regimens including nelfinavir (NFV) are commonly used in pregnancy. We studied the safety, antiviral effect, and pharmacokinetics of NFV and its M8 metabolite with two dosing regimens in combination with zidovudine (ZDV) and lamivudine (3TC) in HIV-infected pregnant women.

METHOD

HIV-infected pregnant women between 14 and 34 weeks gestation received NFV (Cohort 1: 750 mg tid, n = 10; Cohort 2: 1250 mg bid, n = 23) with ZDV and 3TC. Serial blood sampling for NFV concentrations was performed antepartum (AP) and 6 weeks postpartum (PP). Maternal and cord blood samples were also obtained at delivery. NFV and M8 levels were determined by high-performance liquid chromatography. The pharmacokinetic (PK) target was an extrapolated NFV AUC0-24 > 30 mug . h/mL. Mothers were followed frequently for potential clinical and laboratory toxicity.

RESULTS

Overall, NFV in combination with ZDV and 3TC was well tolerated. The PK target was met in 3/8 AP and 5/7 PP in Cohort 1 and 17/21 AP and 16/17 PP in Cohort 2. When Cohort 2 NFV PK parameters AP and PP were compared, median Cmax (3.90 microg/mL vs. 5.01 microg/mL, p < .05) and AUC0-24 (56.6 vs. 86.8 microg . h/mL, p < .05) were increased PP and oral clearance (Cl/F; 44.2 vs. 28.8 L/h, p < .05) was decreased PP. The average M8/NFV ratio was increased PP compared to AP (0.085 vs. 0.29, p < .001). Placental transfer of NFV was low with a median cord blood:maternal plasma ratio at delivery of 0.05. Maternal mean CD4+ T cell counts increased significantly and plasma HIV-1 RNA levels decreased from entry to delivery and 6 to 12 weeks postpartum.

CONCLUSION

NFV used in combination with ZDV and 3TC was well tolerated in pregnant HIV-infected women and produced a significant improvement in HIV disease parameters. NFV drug exposure is inadequate in most pregnant women receiving 750 mg tid but is much improved with 1250 mg bid. NFV crosses the placenta poorly. The AP increase in NFV oral clearance and decrease in M8/NFV ratio suggest that CYP3A activity increases relative to CYP2C19 activity during pregnancy.

Mitochondrial disease in the offspring as a result of antiretroviral therapy

Nucleoside analogue reverse transcriptase inhibitors (NRTIs) have substantially lowered the risk of the mother-to-child transmission of HIV. Evidence of mitochondrial toxicity in vitro, in animal models and in adult HIV-infected patients, has raised concern about the perinatal safety of these antiretrovirals. In zidovudine-exposed, but HIV-uninfected infants, transient anaemia and additional long-term blood abnormalities (neutropenia, thrombopenia and lymphopenia) and hyperlactatemia have been documented. The overall risk of mortality and congenital abnormalities does not appear to be increased, but rare mitochondrial events cannot be excluded for lack of statistical power. French data suggest an above background incidence of mitochondrial symptomatology. Preclinical data demonstrate zidovudine also to be a carcinogen. Long-term systematic follow-up of exposed babies in large cohorts is needed, as are randomised trials with NRTIs carrying a lower risk of mitochondrial toxicity.

Age-related differences in the pharmacokinetics of stavudine in 272 children from birth to 16 years: a population analysis

AIMS

To develop a population pharmacokinetic model for stavudine in children and to investigate the consistency of the currently recommended dose based on adult target concentrations.

METHODS

The pharmacokinetics of stavudine were investigated using a population approach. Individual estimates of CL/F were used to calculate the stavudine dose required to achieve the area under the concentration-time curve reported in adults given recommended doses.

RESULTS

Stavudine pharmacokinetics were well described by a one-compartment model with zero-order absorption. Typical population estimates (% interindividual variability) of the apparent distribution volume (V/F) and plasma clearance (CL/F) were 40.9 l (32%) and 16.5 l h(-1) (38%), respectively. Stavudine V/F and CL/F were similarly related to age. Mean calculated doses (0.61 mg kg(-1) for children less than 2 weeks, 1.23 mg kg(-1) for children more than 2 weeks with bodyweight less than 30 kg, and 31.5 mg for children with a bodyweight between 30 and 60 kg) were in agreement with the current paediatric doses (0.5 mg kg(-1), 1 mg kg(-1), and 30 mg, respectively).

CONCLUSIONS

Our findings support the current recommended paediatric dosage regimens for stavudine, as they result in the same exposure to the drug as in adults.

Antiviral Activity of Nucleoside Analogues During Short-Course Monotherapy or Dual Therapy

BACKGROUND

This is the first report on the preliminary efficacy of 4 different short-course nucleoside analogue regimens (stavudine [d4T], didanosine [ddI], d4T+ddI, and zidovudine [ZDV]) for the prevention of mother-to-child transmission of HIV-1 (MTCT) in a resource-limited setting.

DESIGN

This prospective open-label, randomized 4-arm study (May 1999 to May 2000) conducted in South Africa enrolled 373 women from 34 weeks of gestation; medication was continued through delivery and for 6 weeks to infants. MTCT rates were ascertained at birth, 6, 12, and 24 weeks of age.

RESULTS

Mean maternal HIV-1 RNA levels decreased rapidly on treatment in all groups. At week 4, the mean decrease was 1.91 log10 copies/mL (c/mL) in the d4T+ddI group, 1.33 log10 c/mL in the ddI group, 1.12 log10 c/mL in the d4T group, and 0.76 log10 c/mL in the ZDV group. Among the 362 evaluable mother-infant pairs, 11 infants in the d4T group, 10 in the ddI group, 5 in the ZDV group, and 4 in the d4T+ddI group were infected by 24 weeks of age. Eleven infections occurred in utero. Treatment with d4T and ddI was not associated with lactic acidosis or hepatic steatosis.

CONCLUSIONS

The abbreviated use of nucleoside analogues for the prevention of MTCT appears safe and effective.

Impact of pregnancy on abacavir pharmacokinetics

OBJECTIVE

To describe abacavir pharmacokinetics during pregnancy and postpartum; physiological changes during pregnancy are known to affect antiretroviral drug disposition.

DESIGN

The Pediatric AIDS Clinical Trials Group P1026s study is an on-going, prospective, non-blinded pharmacokinetic study of pregnant women receiving one or more antiretroviral drugs for routine clinical care, including a cohort receiving abacavir 300 mg twice daily.

METHODS

Serial plasma samples (predose, 1, 2, 4, and 6 h postdose) obtained antepartum (30-36 weeks of gestation) and again postpartum (6-12 weeks after delivery) were assayed for abacavir concentration by reversed-phase high-performance liquid chromatography.

RESULTS

Antepartum evaluations were available for 25 women [mean age, 28.6 years (SD, 6); mean third-trimester weight 92 kg (SD, 35.4); and race/ethnicity 52% black, 28% Hispanic, 16% white, 4% Asian], with geometric mean abacavir area under the concentration-time curve (AUC) of 5.9 mg.h/l [90% confidence interval (CI), 5.2-6.8] and maximum plasma concentration (Cmax) of 1.9 mg/l (90% CI, 1.6-2.2). Seventeen women completed postpartum sampling, and the ratios of antepartum to postpartum AUC and Cmax were 1.04 (90% CI, 0.91-1.18) and 0.79 (90% CI, 0.65-0.98), respectively.

CONCLUSIONS

Abacavir AUC during pregnancy was similar to that at 6-12 weeks postpartum and to that for non-pregnant historical controls (5.8 mg.h/l). Consequently, pregnancy does not appear to affect overall abacavir exposure significantly or to necessitate dose adjustments.

Treating HIV During Pregnancy

The expanded use of multiple antiretroviral drugs during pregnancy has led to a reduction in the occurrence of perinatal transmission of HIV to <2%, but has led to concerns regarding both short-term toxicity and the long-term impact on the woman and her child. Enhanced toxicity of nevirapine has been noted among women with CD4+ lymphocyte counts >250 cells/microL at treatment initiation and among pregnant women on long-term didanosine and stavudine. These drugs should be avoided in such situations if alternatives are available. Efavirenz has been associated with birth defects in monkeys, and several cases of neural tube defects have been reported in humans after first trimester exposure, so treatment with this drug should be avoided during the first trimester. Protease inhibitors have been associated with an increased risk of maternal glucose intolerance, pre-eclampsia and preterm birth in some, but not all, studies. Pregnancies exposed to antiretroviral therapy should be registered with the Antiretroviral Pregnancy Registry as early in pregnancy as possible in order to provide data on the risk of birth defects after exposure. The pharmacokinetics of nucleoside and non-nucleoside reverse transcriptase inhibitors are not significantly changed in pregnancy, so standard dosing may be used. However, concentrations of several protease inhibitors are lower in pregnancy, so ritonavir-boosting or increased doses are required. Of great theoretical concern is the impact of resistance mutations that develop following single-dose nevirapine therapy on the response to later therapy among women and their infected infants. The use of dual nucleoside therapy for 3-7 days after single-dose nevirapine in the mother reduces but does not eliminate the risk of nevirapine resistance; alternative regimens for prevention of resistance are under study, as are the subsequent responses of the mother and her infant to therapy. Short courses of prophylactic zidovudine and nevirapine have been well tolerated in neonates. Concern has been raised, however, that these exposures may lead to persistent mitochondrial dysfunction or later cancers, underscoring the need for long-term surveillance of antiretroviral-exposed, HIV-uninfected infants.