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Raltegravir Pharmacokinetics in Neonates Following Maternal Dosing

Clarke, Diana F. PharmD*; Acosta, Edward P. PharmD; Rizk, Matthew L. PhD; Bryson, Yvonne J. MD§; Spector, Stephen A. MD; Mofenson, Lynne M. MD; Handelsman, Edward MD#; Teppler, Hedy MD; Welebob, Carolee MS; Persaud, Deborah MD**; Cababasay, Mae P. MS††; Wang, JiaJia MS††; Mirochnick, Mark MD‡‡for the International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) P1097 Study Team

JAIDS Journal of Acquired Immune Deficiency Syndromes: November 1st, 2014 - Volume 67 - Issue 3 - p 310–315
doi: 10.1097/QAI.0000000000000316
Brief Report: Clinical Science

Abstract: International Maternal Pediatric Adolescent AIDS Clinical Trials P1097 was a multicenter trial to determine washout pharmacokinetics and safety of in utero/intrapartum exposure to raltegravir in infants born to HIV-infected pregnant women receiving raltegravir-based antiretroviral therapy. Twenty-two mother–infant pairs were enrolled; evaluable pharmacokinetic data were available from 19 mother–infant pairs. Raltegravir readily crossed the placenta, with a median cord blood/maternal delivery plasma raltegravir concentration ratio of 1.48 (range, 0.32–4.33). Raltegravir elimination was highly variable and extremely prolonged in some infants; [median t1/2 26.6 (range, 9.3–184) hours]. Prolonged raltegravir elimination likely reflects low neonatal UGT1A1 enzyme activity and enterohepatic recirculation. Excessive raltegravir concentrations must be avoided in the neonate because raltegravir at high plasma concentrations may increase the risk of bilirubin neurotoxicity. Subtherapeutic concentrations, which could lead to inadequate viral suppression and development of raltegravir resistance, must also be avoided. Two ongoing International Maternal Pediatric Adolescent AIDS Clinical Trials studies are further investigating the pharmacology of raltegravir in neonates.

*Section of Pediatric Infectious Diseases, Boston Medical Center, Boston, MA;

Division of Clinical Pharmacology, University of Alabama at Birmingham, Birmingham, AL;

Merck & Co., Inc., Whitehouse Station, NJ;

§Department of Pediatric Infectious Diseases, David Geffen School of Medicine at University of California at Los Angeles, Los Angeles, CA;

Department of Pediatrics, University of California, San Diego and Rady Children's Hospital San Diego, La Jolla, CA;

Eunice Kennedy Shriver National Institute of Child Health and Human Development,

#Division of AIDS, National Institute of Health, Bethesda, MD;

**Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD;

††Statistical and Data Analysis Center, Harvard School of Public Health, Boston, MA; and

‡‡Department of Pediatrics, Boston University School of Medicine, Boston, MA.

Correspondence to: Diana F. Clarke, PharmD, Section of Pediatric Infectious Diseases, Department of Pediatrics, Boston University School of Medicine/Boston Medical Center, 670 Albany Street, 6th Floor, Boston, MA 02118 (e-mail: diana.clarke@bmc.org).

Supported by the International Maternal Pediatric Adolescent AIDS Clinical Trials Group (IMPAACT). Overall support for IMPAACT was provided by the National Institute of Allergy and Infectious Diseases (NIAID) (U01 AI068632), the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), and the National Institute of Mental Health (NIMH) (AI068632); and the Statistical and Data Analysis Center at Harvard School of Public Health, under the NIAID cooperative agreement #1 U01 AI068616 with the IMPAACT Group. Support of the sites was provided by the NIAID and the NICHD International and Domestic Pediatric and Maternal HIV Clinical Trials Network funded by NICHD (contract number: N01-DK-9-001/HHSN267200800001C).

H.T., M.L.R., and C.W. are employees of Merck Sharp & Dohme Corp, a subsidiary of Merck & Co, Inc, and may own stock and/or stock options in the company. The remaining authors have no conflicts of interest to disclose.

Presented in part at the 13th International Workshop on Clinical Pharmacology of HIV Therapy, April, 16–18, 2012, Barcelona, Spain [Abstract O_22; Raltegravir pharmacokinetics and safety in neonates: Washout PK of transplacental RAL (IMPAACT P1097)], and abstract presented at Conference on Retroviruses and Opportunistic Infections (CROI), Atlanta, GA (Raltegravir Pharmacokinetics and Safety in Neonates: IMPAACT P1097, 2013).

The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Received April 06, 2014

Accepted July 17, 2014

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INTRODUCTION

Safe and effective combination antiretroviral drug regimens for use in the first days of life are needed to prevent, treat, and possibly cure HIV infection in neonates.1 Administration of multiple antiretroviral drugs to neonates who are at high risk of acquiring HIV has been shown to reduce peripartum HIV transmission.2 Only 5 antiretrovirals (zidovudine, lamivudine, emtricitabine, stavudine, and nevirapine), are currently approved by the Food and Drug Administration for use in neonates aged less than 14 days. Raltegravir, a potent antiretroviral and the first HIV integrase inhibitor to be licensed and approved by the Food and Drug Administration for use in children, blocks the establishment of postintegration HIV latency and has the potential to play an important role in both prophylaxis and treatment of neonates.3 Both raltegravir and bilirubin are metabolized by uridine diphosphate gluronosyltransferase (UGT) 1A1, and they compete for albumin-binding sites.4 This raises the possibility that raltegravir elimination could be prolonged in neonates and that elevated plasma raltegravir concentrations could increase the plasma concentration of free unconjugated bilirubin, posing an increased risk of acute bilirubin toxicity and its sequela, kernicterus.5–7 The goal of this study was to describe washout pharmacokinetics of raltegravir acquired through transfer across the placenta in infants born to mothers receiving raltegravir for the treatment of HIV infection during pregnancy.

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METHODS

The International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) P1097 was a multicenter trial designed to describe the washout pharmacokinetics and safety of in utero/intrapartum exposure to raltegravir in full-term neonates born to HIV-infected pregnant women who received raltegravir-based antiretroviral therapy during pregnancy. The study was conducted at sites participating in the IMPAACT Network in the United States. HIV-infected mothers and their neonates were enrolled before delivery if the mother had received raltegravir 400 mg twice daily for at least 2 weeks before delivery as part of a combination antiretroviral regimen and had a singleton gestation. Local institutional review boards approved the protocol at all participating sites, and signed informed consent was obtained from the mothers of all study subjects before participation.

Maternal medical histories were abstracted from the medical record, and maternal plasma and cord blood for raltegravir assay were obtained at the time of delivery. Infant physical examinations were performed shortly after birth, and neonatal medical histories were obtained. Serial neonatal plasma samples were collected at 1–5, 8–14, 18–24, and 30–36 hours after birth if birth weight was above 2 kg, gestational age was more than 37 weeks, and no medications that might induce UGT1A1 activity were received, in addition to the absence of any serious or life-threatening medical condition. Dried blood spots were obtained from newborns for determination of UGT1A1 genetic polymorphisms. Study neonates had blood drawn for total and direct bilirubin, liver transaminases, and creatinine at 8–14 hours, 30–36 hours, and 1–2 weeks after birth and for complete blood counts at 8–14 hours and 1–2 weeks after birth. Infants were monitored until 20 weeks after birth for signs of raltegravir toxicity. The target sample size was 15 infants with collection of 4 postnatal pharmacokinetic samples for raltegravir assay.

Raltegravir plasma concentrations were measured using a previously published validated, isocratic, reverse-phase high-performance liquid chromatography–tandem mass spectrometry method.8 The linear calibration range was 10–10,000 ng/mL from a 200 μL plasma sample. Polymorphisms in UGT1A1 (rs5839491) were determined by real-time polymerase chain reaction on DNA extracted from dried blood spots using QIAamp DNA Mini Kit (Qiagen, Valencia, CA). Descriptive statistics were determined for maternal delivery, cord blood, and neonatal raltegravir concentrations. Regression analysis was used to determine the neonatal raltegravir terminal elimination half-life (t1/2). The terminal t1/2 was calculated using Excel, 2010 (Microsoft, Redmond, WA). Following natural log transformation, the last 2–3 measured concentration–time points were used to determine the slope of the elimination curve to estimate the elimination rate constant. The t1/2 was calculated as ln2 divided by the rate constant. Seventeen participants had a t1/2 estimated; 8 of these data sets used 3 terminal phase points to determine the rate constant.

The relationship between raltegravir t1/2 and neonatal UGT1A1 polymorphisms [wild-type (TA)6/(TA)6 vs. other 3 genotypes: heterozygous (TA)6/(TA)7 and (TA)5/(TA)6 or homozygous (TA)7/(TA)7 genotypes] was analyzed using the Wilcoxon rank-sum test.

Infant safety data, including adverse birth outcomes, signs and symptoms, diagnoses, and laboratory test results from evaluations specified in the protocol and additional evaluations performed as part of the infant's clinical care, were evaluated. In addition, the number and proportion of infants who received any therapy to treat elevated bilirubin were determined.

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RESULTS

Twenty-two mother–infant pairs were enrolled and all infants were included in the safety analyses. Maternal plasma and cord blood samples were available from 19 mothers. Nineteen infants had evaluable plasma collections. Of the 22 infants enrolled in the study, 6 (27%) were female, 13 (59%) were African American, and 8 (36%) were Hispanic. The median gestational age at birth was 38 (range, 37–40) weeks, and the median birth weight was 3080 (range, 2200–4100) g.

The median maternal raltegravir concentration at delivery was 540 (range, 12–5809) ng/mL collected at a median of 4.6 (range, 1.1–21.0) hours after dosing. The median cord blood raltegravir concentration was 957 (range, 24–3974) ng/mL, and the median ratio of cord blood to maternal delivery concentration was 1.48 (range, 0.32–4.33). The relationship between the time interval from maternal dosing to delivery and maternal delivery concentration, cord blood concentration, and the cord blood to maternal delivery concentration ratio are presented in Figure 1A, B.

FIGURE 1

FIGURE 1

Individual infant raltegravir concentration–time plots are presented in Figure 2 and individual raltegravir elimination t1/2, UGT1A1 genotype, and need for phototherapy are presented in Table 1. Median (range) infant concentrations and the time of collection after birth were 671 (13–2672) ng/mL at 1.9 (0.9–4.4) hours, 507 (<10–2280) ng/mL at 9.3 (7.9–13.3) hours, 481 (<10–2106) ng/mL at 20.5 (18.1–23.9) hours, and 291 (<10–1402) ng/mL at 33.8 (30.3–35.8) hours. In 9 of 19 (47%) infants, raltegravir concentration increased over the initial 12–24 hours after birth before declining. Raltegravir concentrations remained above the IC95 (14 ng/mL) for wild-type HIV through the last time point for all but 1 infant, who was born within an hour of maternal dosing and had a low concentration of raltegravir detected only in the initial postnatal sample. Elimination t1/2 could not be determined for another infant who had no decline in the raltegravir concentration in the last 3 samples. For the 17 subjects for whom an elimination t1/2 could be determined, the median elimination t1/2 was 26.6 hours, with a minimum of 9.3 hours, a maximum of 184 hours, and an interquartile range of 22.0–69.2 hours.

FIGURE 2

FIGURE 2

TABLE 1

TABLE 1

UGT1A1 genotyping was an optional evaluation in this study and was obtained for 17 of 22 infants enrolled. Of the 17 infants with UGT1A1 genotyping, pharmacokinetic evaluations were performed on 16 infants. Eight infants (47.1%) were (TA)6/(TA)6 homozygotes, 7 (41.2%) were (TA)6/(TA)7 heterozygotes, 1 (5.9%) was a (TA)5/(TA)6 heterozygote, and 1 (5.9%) was a (TA)7/(TA)7 homozygote. There were no differences in median raltegravir concentrations at any time point or in elimination t1/2 when the (TA)6/(TA)6 infants were compared with the infants with other 3 UGT1A1 genotypes.

Five (22.7%) infants had grade 3 or 4 laboratory events (total bilirubin, creatinine, hemoglobin, neutrophil count, and glucose), 2 (9.1%) had grade 3 or 4 signs and symptoms (fever and neonatal respiratory discomfort), and 1 (4.6%) had a grade 3 or 4 diagnosis (metabolic/endocrine disorder). There was 1 (4.6%) infant with low birth weight (2200 g). No infant death or still birth was reported. None of the adverse events reported in infants were determined to be related to maternal raltegravir use. Only 1 infant received phototherapy for the treatment of hyperbilirubinemia. This infant was heterozygous (TA)6/(TA)7 and had a raltegravir t1/2 of 75.4 hours. None of the infants received an exchange transfusion therapy.

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DISCUSSION

Previously published data on peripartum raltegravir pharmacokinetics are limited to several case reports describing cord blood and maternal delivery raltegravir concentrations in a total of 7 term and preterm infants.9–11 Although these reports suggest that raltegravir readily crosses the placenta, they provide limited data describing the postnatal elimination of transplacentally acquired raltegravir in the infant. One preterm infant has been described as having raltegravir concentrations present 1 month after delivery, suggesting very prolonged elimination.11

This study, to the best of our knowledge, is the first to describe the elimination of transplacentally acquired raltegravir in infants. In this study, we found that raltegravir readily crossed the placenta so that by 3 hours after maternal dosing, the umbilical cord raltegravir concentration equaled or exceeded the maternal plasma concentration at the time of delivery. In the first 12–24 hours after delivery, raltegravir concentrations increased in almost half of the study infants, although they received no postnatal raltegravir doses. Once raltegravir concentrations started to decline, the rate of elimination was highly variable. Although several of our subjects had elimination t1/2 in the range similar to that reported in adults (7–12 hours), most demonstrated very slow elimination, with the longest t1/2 being 184 hours.5 As a result of the excellent placental transport and slow neonatal elimination of raltegravir, infant raltegravir concentrations remained above the IC95 (14 ng/mL) for wild-type HIV through 30–36 hours after delivery, the time of collection of the last sample, in all but one of the study infants.

A limitation of our study is the limited pharmacokinetic sampling time. We did not anticipate that the half-life would be so prolonged and that the plasma concentrations would continue to increase in the absence of raltegravir dosing in some infants. Because these were healthy full-term infants delivered to pregnant women on combination antiretroviral therapy (cART), many were discharged from the hospital within a few days. The study was designed to be completed before discharge from the hospital to not inconvenience the study families. Another limitation of our study is that no raltegravir was directly administered to study neonates, therefore we can provide no data describing neonatal raltegravir absorption. Follow-up IMPAACT studies that are now underway include direct administration of raltegravir to neonates and more extensive pharmacokinetic sampling.

Raltegravir is primarily eliminated through hepatic glucuronidation by UGT1A1 followed by biliary and renal excretion of the glucuronide conjugate.3 Bilirubin is also primarily metabolized by UGT1A1, and its metabolism is known to be slow immediately after birth and to increase dramatically over the first weeks of life. It is therefore not surprising that raltegravir elimination was found to be prolonged in most neonates in the first days of life.6 Genetic variations in the number of TA repeats in the promoter region of the UGT1A1 gene are associated with reduced gene expression and enzyme activity, leading to elevated bilirubin concentrations in the neonate and later in life.12 The wild-type allele (UGT1A1*1) has 6 TA repeats in the promoter of UGT1A1. Alleles with 5 or 7 TA repeats are associated with decreased gene transcription and expression of UGT1A1 and reduced enzyme activity.12 In our small group of infants, no relationship was found between raltegravir concentrations or elimination when infants with the wild-type (TA)6/(TA)6 genotype were compared with those with other UGT1A1 genotypes. It is likely that immaturity of neonatal UGT1A1 enzyme activity accounts for much of the variability in the observed raltegravir pharmacokinetics rather than the infant genotype. The relationship between UGT1A1 genotype and neonatal raltegravir pharmacokinetics and bilirubin metabolism will be explored further in the enrolling IMPAACT follow-up studies.

Nearly half of the study subjects demonstrated an initial increase in the raltegravir concentration over the first 12–24 hours after birth in the absence of any directly administered infant raltegravir dosing. This increase is likely explained by enterohepatic recirculation, where beta-glucuronidase present in the brush border of the fetal and neonatal gut breaks down luminal substrate–glucuronide complexes and allows intestinal reabsorption of the now unconjugated substrates.13 It is likely that immediately after birth when gut motility and raltegravir metabolism are slow, raltegravir glucuronide present in meconium undergoes deconjugation followed by reabsorption of the unconjugated raltegravir resulting in the initial increases in raltegravir plasma concentrations seen in nearly half of the study infants.

In addition to sharing major elimination pathways, raltegravir and bilirubin also compete for plasma albumin-binding sites. Circulating unconjugated bilirubin binds to plasma albumin, so that at low bilirubin concentrations, there is minimal free unbound bilirubin in the circulation. If the unconjugated bilirubin concentration rises above the plasma albumin-binding capacity, then circulating unbound bilirubin is available to cross the blood–brain barrier and cause bilirubin-associated central nervous system toxicity. Administration of a competitor to bilirubin binding to albumin may enhance the potential for bilirubin toxicity by decreasing bilirubin–albumin binding. In the 1950s, administration of sulfisoxazole, which at therapeutic concentrations displaces bilirubin from albumin-binding sites, to low birth weight infants resulted in an increased incidence of kernicterus and mortality.14 Because raltegravir also competes with bilirubin for albumin-binding sites, its use in neonates poses the risk of a similar effect. However, the binding affinity of bilirubin to albumin is much greater that than of raltegravir; and in an in vitro study in neonatal serum, raltegravir was shown to significantly displace bilirubin from albumin only at concentrations 50–100 fold higher than typical therapeutic concentrations.4

Our data suggest that a safe and effective neonatal raltegravir dosing regimen must take into account developmental changes in raltegravir elimination over the first weeks of life. Excessive raltegravir concentrations must be avoided in the neonate, because raltegravir at high plasma concentrations may increase the risk of bilirubin neurotoxicity. Also, subtherapeutic concentrations, which could lead to inadequate viral suppression and development of raltegravir resistance, must be avoided. Raltegravir administration to preterm infants poses heightened risk of toxicity, because raltegravir and bilirubin elimination are prolonged, plasma albumin binding is reduced, and the blood–brain barrier is more permeable in preterm infants. As a result, administering raltegravir to preterm infants is likely to carry a greater risk of causing central nervous system bilirubin toxicity and should be avoided until raltegravir has been well-studied in term and preterm infants.

Two ongoing IMPAACT studies will investigate the safety of raltegravir administered directly to term infants and washout raltegravir pharmacokinetics in low birth weight infants. IMPAACT P1110 is a dose-finding pharmacokinetic study to evaluate the safety and tolerability of raltegravir oral granules for suspension when administered during the first 6 weeks of life with standard prevention of mother-to-child transmission (PMTCT) antiretroviral (ARV) prophylaxis to HIV-1–exposed infants who are at high risk of HIV infection. P1110 will enroll an initial cohort receiving 2 single doses approximately 1 week apart, followed by a second cohort receiving daily dosing. The study design allows for adjustment of cohort 2 dosing based on analysis of the cohort 1 data. Version 2 of P1097 will investigate raltegravir washout pharmacokinetics in low birth weight infants, and P1110 may be expanded to include low birth weight infants. The goal of these studies is to provide the data necessary to develop regimens that will allow for the safe administration of raltegravir in the first month of life for prevention, treatment, and possibly cure of HIV infection.

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ACKNOWLEDGMENTS

The authors acknowledge the expertise of the P1097 protocol team members and thank the women and infants who participated in the protocol and the staff of the participating International Maternal Pediatric Adolescent AIDS Clinical Trials centers. This article is dedicated to Catherine Kneut, PNP, field representative for the protocol, who provided compassionate care for many children with HIV and their families. In addition to the authors, members of the IMPAACT 1097 protocol team include: Elizabeth Hawkins, MA, Social Scientific Systems, Silver Springs, MD; Bobbie Graham, BS, Frontier Science and Technology Research Foundation, Amherst, NY; John Gaeddert, MPH, Frontier Science and Technology Research Foundation, Amherst, NY; Linda Marillo, BA, Frontier Science and Technology Research Foundation, Amherst, NY; Terence Fenton, EdD, Statistical and Data Analysis Center, Harvard School of Public Health, Boston, MA; Derek Weibel, BS, Frontier Science and Technology Research Foundation, Amherst, NY; Catherine Kneut, CPNP, MS, Boston Children's Hospital, Boston, MA; Debra McLaud, RN, Boston Medical Center, Boston, MA; Larissa Wenning, PhD, Merck & Co., Inc.,,Whitehouse Station, NJ; Elizabeth Rhee, MD, Merck & Co., Inc., Whitehouse Station, NJ.

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Keywords:

raltegravir pharmacokinetics; neonates

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