Tenofovir plus FTC reduce NNRTI resistance following single dose nevirapine
Polly Clayden, HIV i-Base
Single dose nevirapine (NVP) still remains an important component in prevention of mother to child transmission (PMTCT). With short course AZT and tail coverage it is considered to be a reasonable option for women who do not need antiretroviral treatment to protect their own health.
Four presentations at CROI and a recent Lancet paper looked at using tenofovir (TDF) and emtricitabine (FTC) added to single dose NVP to reduce the emergence of resistance to non-nucleoside reverse transcriptase inhibitors (NNRTI). Two of the presentations describe TDF and FTC maternal and infant pharmacokinetics.
Both drugs have long half-lives (approx 17 hours for TDF and 8 hours for FTC in plasma) and are category B for use in pregnancy.
Reduction in NNRTI resistance with one dose of TDF/FTC
A paper authored by Benjamin Chi and coworkers, published in the November 17, 2007 edition of the Lancet reported findings from a Zambian study to investigate whether the addition one dose of the co-formulation of 300mg TDF and 200mg FTC (Truvada) to single dose NVP in labour would be effective in reducing resistance .
In this study, conducted at two primary health care facilities in Lusaka, women screened that met WHO maternal criteria for antiretroviral therapy were referred and not enrolled.
All enrolled women received standard of care of AZT from 32 weeks gestation plus single dose NVP in labour. The women were randomised to receive TDF/FTC or no additional intervention above the standard of care.
All infants received single dose NVP plus seven days of AZT. The majority of women opted to breastfeed for six months.
The primary endpoint of the study was maternal NNRTI resistance at 6 weeks post partum. The secondary endpoints were NNRTI resistance at two weeks, other antiretroviral resistance (particularly to TDF, FTC and AZT) at two and six weeks post partum, HIV transmission rates and drug safety.
The investigators reported: 627 women were enrolled in the study, of those 227 were not eligible, 397 women were randomised between March 2005 and February and three others were excluded from the analysis, two due to incorrect dispensing of the study drug according to protocol and the third due to the randomisation envelope being incorrectly opened.
The mean maternal CD4 was 464 cells/mm3 (SD±208) in the intervention arm (n=198) and 490 cells/mm3 (SD±200) in the control arm. 83% and 79% received antenatal AZT, and the length of time on AZT was 39 (SD±25) and 34 (SD±20) days in the intervention and control arms respectively. 28% and 29% of women had a viral load <400 copies/mL at delivery. Among those not suppressed at delivery the mean log viral loads were 3.9 (SD, 0.8) and 3.7 (SD, 0.6) logs in the intervention and control arms.
Using a genotype test with thresholds for detection to detect a mutant viral subpopulation of 20%, they found that women receiving the intervention were less likely than controls to have an NNRTI mutation at 2 weeks post partum: 6/187 (3%) vs 21/169 (12%) (RR, 0.27; 95% CI, 0.11-0.66), p=0.002; at 6 weeks, 20/173 (12%) vs 41/166 (25%), (RR, 0·47, 95% CI 0·290·76), p=0.002 and cumulatively, 22/167 (13%) vs 49/163 (30%), (RR, 0.44, 95% CI, 0.28-0.69), p<0.0001.
The investigators noted that when they stratified the women according to maternal viral load at delivery, they found the protective effect was greatest in women whose viral load was >10,000 copies/mL.
They did not detect any mutations associated with resistance to TDF, FTC or AZT.
The overall transmission rate at 6 weeks was similar in the two groups 10/180 (5-6%) and 14/175 (8%) in the intervention and control group respectively, p=0.403. this was consistent for in utero, 8/180 (4.4%) vs 10/175 (5.7%), p=0.635, and intrapartum/early post partum, 2/127 (1.6%), p=0.44.
Serious maternal adverse events were also similar in both groups, 7/198 and 9/199 in the intervention and control groups. The most common was postpartum anaemia, which was reported for four women in each group. 20/198 (10%) of infants in the intervention group and 23/199 (12%) in the control group had a serious adverse event, mostly septicaemia (n=22) or pneumonia (n=8), there was no difference between the groups and none were considered to be associated with the study intervention.
The investigators concluded that addition of a single dose of combined TDF and FTC to the prophylaxis regimen of short course AZT and single dose NVP was associated with a 73% reduction in resistance at two weeks and a 53% reduction at six weeks. They noted that in this setting the intervention did not result in a reduction of mother to child transmission compared to controls.
The frequency of the K103N mutation increased from 2 weeks to 6 weeks postpartum as has been described in other studies. The frequency of Y181C/I remained stable. None of the women in the intervention group developed a mutation at codon 181 and the investigators were unable to explain this finding.
The investigators suggested that further reductions in resistance might be possible with the addition of a second dose of tenofovir and FTC but would also preserve the simplicity of the regimen.
A poster authored by the same group, showed findings from a secondary analysis from this study, in which they evaluated 122 random maternal samples using an oligonucleotide ligation assay (OLA) . This assay can detect a mutant sub-population as low as 5% of circulating virus. Mutations found at codons 103, 106, 181, and 190 were considered to be NNRTI resistant.
Of the 122 maternal samples evaluated, 38 were taken at two weeks post partum (15 in the intervention arm and 23 in the control arm) and 84 were taken at six weeks post partum (43 in the intervention arm and 41 in the control arm). The investigators reported that the median log10 viral load was not different between the study arms at two weeks post partum (3.53 vs 3.67; p=0.27), nor at six weeks postpartum (4.61 vs 4.54; p=0.44).
When NNRTI resistance was assessed by OLA, they found a 69% reduction at two weeks post partum, 2/15 (13%) vs 10/23 (44%), (RR 0.31, 95%CI 0.08-1.21), and a 58% reduction in NNRTI at six weeks post partum, 8/43 (19%) vs 18/41 (44%), (RR 0.42, 95%CI 0.21- 0.87).
The investigators concluded that the efficacy of single-dose TDF and FTC in reducing NNRTI drug resistance by population genotyping was confirmed with the more sensitive OLA. These findings further emphasise the role of this simple intervention in settings that rely heavily on intrapartum NVP, alone or in combination with other drugs, for perinatal HIV prevention they wrote.
Further reduction with seven days TDF/FTC postpartum
In an oral presentation, Elise Arrive from the TEmAA French National Agency for AIDS Research (ANRS) 12109 study conducted in Ivory Coast, Cambodia and South Africa presented findings from a similar strategy but using seven days TDF/FTC tail coverage .
This is an open label, phase II trial to look at safety in which all HIV-positive pregnant women received AZT from 28-38 weeks of gestation (median 33) single dose NVP at the onset of labour with two doses of TDF/FTC followed by once daily TDF/FTC for seven days post partum.
All infants received single-dose NVP syrup and AZT syrup for 7 days.
The study enrolled 38 women with a median age of 27, a median CD4 count 450 cells/mm3, and a median viral load of 4.08 log10 copies/mL. The women received TDF/FTC at a median of 4.9 hours before delivery.
The investigators reported 9/38 (24%) women experienced Grade 3/4 biological events (anemia, leucopenia) postpartum. 9/39 (23%) live births (1 set of twins), had serious adverse events, including 4 deaths (meningitis, gastroenteritis, intestinal obstruction, and severe encephalopathy of unknown aetiology) and 2 had transient grade 3 anemia (5%).
They found that the mothers viral load decreased by a median of 0.90 log copies/mL at 2 days postpartum, and returned to baseline at 4 weeks. 2/39 (5.1%) infants had detectable virus at 3 days (confirmed at 4 weeks), suggesting in utero transmission. No genotypic viral resistance to AZT, NVP, FTC, or TDF was detected in either the mothers or infants in this small study.
The investigators wrote: A TDF/FTC combination for PMTCT appears to be well tolerated in women and exposed newborns: 7 days of postpartum TDF/FTC exposure seem to extend the suppression of viral replication avoiding NVP-resistance mutations.
Tenofovir and FTC pharmacokinetics
In a pharmacokinetc substudy presented as an oral late breaker, Deborah Hirt and coworkers from the ANRS group evaluated tenofovir pharmacokinetics in pregnant women and in their infants. 
In this study, they measured maternal, cord blood, and neonatal tenofovir plasma concentrations.
The authors noted that absorption was faster and greater for women with caesarian section than with vaginal delivery (they suggested this was due to fasting administration of TDF before delivery). Following a 600-mg TDF administration, median population tenofovir AUC, Cmax and Cmin in pregnant women were 2.73 mg.L-1.h, 0.31 and 0.056 mg/L, respectively.
They found at delivery, maternal and cord blood median tenofovir concentrations were 0.13 and 0.10 mg.L-1 respectively. Neonatal plasma half-life was 8.3 hours (45%), suggesting low neonatal concentrations quickly after birth.
They concluded: TDF 600 mg before delivery produces similar concentrations to those of HIV infected people taking 300 mg daily. If time elapsed between maternal administration and delivery is >12 hours, 2 tablets of TDF/FTC should be re-administered. Tenofovir was shown to have good placental transfer. Administering 13 mg/kg of TDF as soon as possible after birth should produce neonatal concentrations comparable to those observed in adults.
A poster from the same group presented findings from a similar pharmacokinetic study with FTC.
They report, after the 400 mg FTC administration, median population AUC, T max, C max and C min in pregnant women were 15.5 mg.L1.h, 3.0 hours, 1.60 and 0.14 mg/L, respectively. At delivery, median (range) FTC maternal and cord concentrations were respectively 1.02 (0.035 to 2.04) and 0.74 (0.005 to 1.46) mg.L1.
They conclude: FTC was shown to have good placental transfer. Administering 2 mg/kg of FTC 12 hours after birth or 1 mg/kg 6 hours after birth should produce neonatal concentrations comparable to those observed in adults.
These preliminary studies looking at TDF and FTC are useful in extending the possibilities to reduce the risk of maternal NNRTI resistance following single dose NVP. In the Chi et al study the investigators excluded women with CD4<200 cells mm3 (who, quite rightly, received HAART), and 81% of women evaluated received antepartum AZT for a median of about 37 days, with 30% having undetectable viral load at delivery.
In contrast, in TOPS (which looked at AZT/3TC tail coverage and provided evidence for this strategy to be included in the WHO guidelines), there was no AZT and all women received single dose NVP regardless of CD4 . It is possible that the longer TOPS regimens were more successful in reducing resistance (from nearly 60% to 10% vs 30% to 14% in the Chi study) but there is no head-to-head comparison. TEmAA also evaluated healthy women who received AZT from a median of 33 weeks so,again, it is difficult to compare results between studies.
Chis findings suggest that the single dose addition of TDF/FTC would be valuable where the WHO guidelines are being fully implemented ie where those indicated for HAART receive it. But perhaps some will caution, not yet known to the question of whether this strategy will be as effective where only single dose NVP is viable. But the simplicity would make it even more attractive for those programmes with very limited capacity.
Shahin Lockman and James McIntyre write in an accompanying editorial to the Lancet paper: Chis results do provide strong evidence that addition of single-dose tenofovir/FTC to short-course zidovudine and single-dose nevirapine in women with higher CD4 cell counts is a new, effective, and feasible approach to reducing maternal nevirapine resistance, and one that should be seriously considered for implementation. 
Unless otherwise stated, all references are from the Programme and Abstracts from the 15th Conference on Retroviruses and Opportunistic Infections, 2-6 February 2008, Boston, USA.
- Chi B, Sinkala M, Mbewe F et al. Single dose tenofovir and emtricitabine for reduction of viral resistance to non-nucleoside reverse transcriptase inhibitor drugs in women given intrapartum nevirapine for perinatal HIV prevention: an open-label randomised trial. Lancet. Vol 370:1698-705.
- Chi B, Frenkel L, Aldrovandi G et al. Intrapartum tenofovir and emtricitabine reduces development of low-level NNRTI resistance following Ingestion of single-dose nevirapine for perinatal HIV prevention. Poster abstract 631.
- Arrive E, M L Chaix ML, Nerrienet E et al. The TEmAA ANRS 12109 phase II trial, step 1: Tolerance and viral resistance after single-dose nevirapine and short-course of tenofovir disoproxil fumarate and emtricitabine to prevent mother-to-child transmission of HIV-1. Oral abstract 45b.
- Hirt D, Urien S, Rey E et al. Population pharmacokinetics of tenofovir in HIV-1-infected pregnant women and their neonates: TEmAA ANRS 12109. Oral abstract 47LB.
- Hirt D, S Urien S, E Rey E et al. Population pharmacokinetics of emtricibine in HIV-infected women and their neonates: TEmAA ANRS 12109. Poster abstract 626.
- McIntyre JA, Martinson N, Gray GEfor the Trial 1413 Investigator Team. Single dose nevirapine combined with a short course of combivir for prevention of mother to child transmission of HIV-1 can significantly decrease the subsequent development of maternal and infant resistant virus. Antivir Ther 2005; 10 (suppl 1): S4.
- Lockman S and McIntyre J. Reduction of HIV-1 drug resistance after intrapartum single-dose nevirapine. Lancet 2007; 370:1668-1670.