Abstract
Background:
There are few data on tenofovir-diphosphate (TFV-DP) concentrations in pregnant and postpartum women on Tenofovir Disoproxil Fumarate-Emtricitabine (TDF-FTC) or Tenofovir Alafenamide-Emtricitabine (TAF-FTC).
Methods:
Eligible pregnant women were randomized to TDF-FTC or TAF-FTC and followed for 16 weeks (8-weeks pregnant, 8-weeks postpartum) with weekly collection of dried blood spot (DBS) and 4-weekly peripheral blood mononuclear cells (PBMC). PrEP dosing was observed daily via asynchronous videos sent via cell phone. We report geometric means (GM) and their ratios (GMR) with 95% confidence intervals (CIs) for TFV-DP in PBMC and DBS from pregnancy and postpartum.
Results:
We enrolled N=39 participants (n=19 TDF-FTC, n=20 TAF-FTC): median age was 28 years (IQR:25-34); median gestational age was 24-weeks (IQR:21-28). For TDF-FTC, TFV-DP DBS concentrations at 8-weeks did not differ significantly between pregnancy (GM: 675; 95%CI:537-849) and postpartum (GM: 583; 95%CI:471-722; GMR-TDF=1.16; 95%CI:0.74-1.80). For TAF-FTC, TFV-DP DBS concentrations at 8-weeks were 44% higher in postpartum (GM: 1199; 95%CI:929-1549) versus pregnancy (GM: 832; 95%CI:751-922; GMR-TAF=1.44; 95% CI: 1.01-2.06). In PBMC analysis of TDF-FTC, 8-week median TFV-DP (pmol/10^6 cell) was 71 (IQR 44-112) in pregnancy and 73 (IQR 50-102) in postpartum (GMR=1.04; 95%CI:0.44-2.44). In TAF-FTC, median PBMC at 8-weeks was 580 (IQR:341-985) in pregnancy and 666 (IQR:396-1123) in postpartum (GMR=1.15; 95%CI:0.30-2.49).
Conclusion:
TFV-DP concentrations were overall lower during pregnancy than postpartum for TAF-FTC. We found high concentrations of TFV-DP in PBMC in pregnancy and postpartum on TAF-FTC, suggesting PrEP efficacy is maintained. Efficacy and safety studies are warranted to evaluate TAF-FTC for PrEP in pregnant and postpartum women.
Keywords: pregnancy, PrEP, TDF/FTC, TAF/FTC, pharmacokinetics, prevention
INTRODUCTION
Oral pre-exposure prophylaxis (PrEP) using Tenofovir Disoproxil Fumarate-Emtricitabine (TDF-FTC) is currently one of the most efficacious biomedical interventions for HIV prevention available, along with injectable PrEP.1-3 New formulations of oral PrEP include 25mg tenofovir alafenamide (TAF) with 200mg emtricitabine (FTC).3-5 When used consistently, oral PrEP is over 95% effective at preventing HIV infection.1,6-8 Although oral PrEP has been shown to be effective across a variety of settings, effectiveness is highly dependent on daily use of the regimen and may differ when pregnant or postpartum.9-12 TAF-FTC is not yet approved for cisgender women to use for exposures related to vaginal intercourse and studies are ongoing to demonstrate efficacy.
PrEP adherence can be assessed through blood concentrations of drugs or drug metabolites, including tenofovir diphosphate (TFV-DP) and emtricitabine triphosphate (FTC-TP).13,14 Most pharmacological methods, such as measurement of tenofovir concentrations in plasma and urine or FTC-TP concentrations in dried blood spots (DBS), primarily provide information on recent drug dosing (i.e., dosing in the past 3-5 days)15, while usage to assess adherence is limited by “white coat adherence” or dosing prior to medical visits.16,17 Alternate methods measuring longer-term cumulative adherence, such as TFV-DP concentrations in peripheral blood mononuclear cells (PBMC) and DBS, offer an assessment of average and dynamic adherence over a longer period (6-8 weeks).15 TFV-DP concentrations, measured in femtomole (fmol)/punch, have strong associations with PrEP efficacy to date.16,17
A recent study of men who have sex with men found that ≥4 doses of TDF-FTC a week on average was associated with high PrEP efficacy.18 This relationship is consistent with the IPERGAY trial, which showed an average of 86% efficacy for 3.75 doses/week, as well as iPrEx, which suggested 90% efficacy for approximately 3 doses/week on average.19,20 In terms of oral TAF/FTC PrEP, a 2020 study established adherence interpretations based on steady state TFV-DP concentrations as follows: <450 fmol/punch = <2 doses/week, 450-949 fmol/punch = 2-3 doses/week, 950-1799 fmol/punch = 4-6 doses/week, and ≥1800 = 7 doses/week.21
While previous literature has evaluated TDF-FTC concentrations and adherence/efficacy relationships, pharmacokinetic research is limited in women and especially in women who are pregnant or postpartum.22,23 One such study, the IMPAACT 2009 study in Malawi, South Africa, Uganda, and Zimbabwe, found that among N=40 (n=20 pregnant and n=20 postpartum) African adolescent girls and young women, TFV-DP was 31-37% lower in pregnant women compared to postpartum women – indicating that strict adherence to PrEP is needed in pregnancy.23 There are limited data on TAF-FTC for PrEP efficacy nor pharmacokinetics in pregnant and postpartum women. Pregnancy and postpartum are periods of profound physiological change. Altered metabolism, volume changes, and increased renal clearance during these periods may result in reduced tenofovir concentrations in plasma and DBS. Given the gaps identified from the literature, this study aims to describe the pharmacokinetics of TFV-DP and FTC-TP in pregnant women followed through postpartum period and randomized to TDF-FTC or TAF-FTC for PrEP.
METHODS
Study Design and Participants
This study was conducted between June 2022 and April 2023. The study enrolled participants from a large, urban clinic outside of Cape Town, South Africa. Participation was strictly voluntary and required written informed consent. Overall, 60 consecutive eligible pregnant women presenting for antenatal care were enrolled between June 2022 and October 2022. Inclusion criteria required the women to: (1) be ≥18 years old; (2) test HIV-negative (via rapid HIV 4th generation antigen and antibody test); (3) be between 20-30 weeks of gestation; (4) own a smart phone; (5) agree to daily video observations of taking a PrEP pill; (6) have no psychiatric or medical contraindications to PrEP; (7) have an estimated creatinine clearance (CrCI) greater than 60mL/min; (8) have a negative Hepatitis B surface antigen test (HBsAg); (9) reside close to the clinic (<10km); and (10) intend to give birth at the facility of study enrolment.
Sample size
A target sample size of at least 15 women per group was consistent with similar studies of directly observed PrEP that estimated steady-state concentrations of TFV-DP, providing adequate precision for outcome estimates of steady-state concentrations of TFV-DP when comparing pregnancy vs. postpartum samples [12]. We increased the sample size to 30 participants per group to account for potential attrition and pregnancy loss (total N=60 women). This study was not powered to assess for safety or efficacy.
Study procedures
Once enrolled, participants were randomized 1:1 to receive a particular formulation of PrEP, i.e., assigned to either to TDF-FTC or TAF-FTC. Participants were then observed for 16 weeks of daily PrEP dosing, including 8 weeks during pregnancy and 8 weeks in postpartum. Once participants had completed their 8 weeks of in-pregnancy observation, observation of therapy was paused until they entered the first week of the postpartum phase (median 7 days from infant birth date to the start of the postpartum study phase, IQR 5-12 days postpartum). PrEP dosing was not observed or measured during this pause, but participants were supplied with sufficient pills during this time and were encouraged to continue with daily PrEP use.
Participants were observed daily via video observed therapy (VOT) during the periods of observation from study weeks 1 to 8 in pregnancy and again in postpartum period to confirm daily dosing. Participants had a choice to record themselves taking their PrEP pill and send this video to study staff via WhatsApp or to receive a video call from the study staff at a pre-decided time daily. Study staff then recorded each dose as either observed or unobserved via REDCap, an electronic data platform.24 If an asynchronous video was sent, the participant would verbally confirm the date of recording in the video. Additionally, staff members would also compare a newly received video to previous ones to ensure that videos were not reused. As part of the quality control, each VOT observer was assigned a maximum of 10 participants at a given time. Study staff observed the videos of these participants and also conducted the study interviews with them during study visits. This enabled each staff member to have a good recognition of the participant and to ensure that the video was from that participant (and recorded on a separate date).
Demographic information such as age, gestational age, socioeconomic status, and education was recorded at baseline. Safety laboratory testing (e.g., liver function, creatinine, haematocrit) was conducted at baseline, at first postpartum visit and end of study.
Blood for PBMC samples was collected every 4 weeks (twice in pregnancy, twice postpartum), whereas plasma and fingerpick DBS samples were collected weekly. For DBS, 50 μL blood was applied to Whatman 903 protein saver cards. Cards were dried at room temperature, stored in labelled plastic bags with desiccant at −80°C. DBS and PBMC samples were assayed with validated liquid chromatography tandem mass spectrometry methods.14,16,21 Breast milk samples were collected at the final study visit via 5mL aliquots.25,26 Breastmilk was also spotted onto Whatman 903 protein saver cards for dried milk samples (DMS). DMS and milk aliquots were stored at −80°C. FTC-TP concentrations in PBMC at week 8 were analysed for pregnancy and postpartum periods within both study arms. Supplementary Figure 1 depicts the study visit schedule and sample schedule.
Statistical Methods
In each of the TDF-FTC and TAF-FTC arms, clinical characteristics and safety lab results from participants were summarized and compared at baseline during pregnancy and after 4-weeks of postpartum follow-up. A paired t-test was used to estimate the differences between the continuous clinical measures during pregnancy and postpartum.
At each 4-week interval, geometric means and 95% CIs were reported for TFV-DP and FTC-TP measures obtained using PBMC and DBS. Geometric mean ratios (GMR) were then used to compare TFV-DP and FTC-TP measures during pregnancy and postpartum after 4- and 8-weeks of follow-up. The GMR is a parameter of the observed effect size between all concentrations in each group. GMR and 95% confidence intervals (CIs) were used to interpret if there is a clinically significant difference in drug exposure between the two phases. Participants with concentrations below the limit of quantification (BLQ) due to poor adherence at 4- and 8-week follow-up were excluded from the GMR calculations, which represented an “as treated” analysis.
TFV-DP measures were obtained by DBS once a week for 16 weeks. The midpoint of the lower limit quantification value of TFV-DP concentrations (15.7) was allocated to participants with BLQ TFV-DP concentrations from DBS samples as to include all participants in subsequent analysis, which represented an “intention to treat” analysis. Non-linear regression, specifically a one-phase exponential model, was used to describe the pattern of TFV-DP concentrations over time by the equation; observed TFV-DP concentration = Css x (1 – e(-k x time)).
This pharmacokinetic modelling was used to determine fitted values of steady-state concentrations at the 25th-75th percentiles as well as the half-life of TFV-DP. Comparisons were only made between pregnancy and postpartum states within each arm and no concentration comparisons were made across arms. We adjusted for participants’ body mass index (BMI), haematocrit, and creatinine levels at baseline and for haematocrit and creatinine only at 4-week follow-up in postpartum. The model provided steady-state concentration estimates (Css) and an elimination rate constant (k). Half-life in weeks was calculated by dividing 0.693 by k. The exponential model projections were fitted on a scatter plot of TFV-DP concentration over time in pregnant and postpartum groups within each arm. Fitted 25th and 75th percentiles were generated using bootstrap resampling with initial Css and k estimates as starting points, resulting in a distribution of Css estimates. All analyses were performed in RStudio version 4.3.1.
Ethics
The PrEP-PP PK study was approved by the University of Cape Town Human Research Ethics Committee (UCT HREC:108/2021). The study was also granted provincial approval by the Western Cape government to conduct study activities at a public health care facility (WC_202103_029).
RESULTS
Between June 2022 and October 2022, we enrolled N=60 eligible, consenting pregnant women in the study. Over the course of the study, n=21 participants were censored due to pregnancy loss, loss to follow up or withdrawal from the study and were excluded from analysis. Overall, n=39 participants completed all 16 weeks of observation, with 19 participants in the TDF-FTC arm and 20 participants in TAF-FTC arm. Whilst 19 participants in the TDF-FTC arm completed the study period, for the pharmacokinetic analysis of TFV-DP metabolite concentrations, participants that had a ‘below limit of quantification’ (BLQ) measure in either the PBMC or DBS samples were excluded based on nonadherence to the protocol. This resulted in a sample size of n=13 at week 4 and n=16 at week 8 within the TDF-FTC arm. For the TAF-FTC arm, although 20 participants had completed the study, for pharmacokinetic analysis of TFV-DP metabolite concentrations, participants that had a BLQ measure in either the PBMC or DBS samples were similarly excluded. This resulted in a sample size of n=18 at week 4 and n=18 at week 8 for the TAF-FTC arm. The consort diagram in Figure 1 illustrates the flow of participants through screening, enrolment and completion of analysis per study arm.
Figure 1.
Consort diagram illustrating the patient flow through screening, recruitment, enrollment and follow-up in PrEP-PP PK randomized control trial, Cape Town, South Africa (2022-2023)
The baseline sociodemographic characteristics of these participants are presented in Table 1. All participants were Black/African females, median age was 28 years (IQR: 25, 34), and median gestational age at enrolment was 24 weeks (IQR: 21, 28 weeks). The majority (74%) of all participants had only completed a primary education and most (64%) were unemployed at the time of enrolment. There were no significant differences in baseline characteristics between participants randomized to the TDF-FTC and TAF-FTC arms.
Table 1.
Baseline socio-demographic and clinical characteristics of pregnant women randomized to study arm in pharmacokinetic study of TDF-FTC and TAF-FTC in Cape Town, South Africa (June 2022 – June 2023; N = 39)
| All women N (%) |
TDF-FTC Arm n, % |
TAF-FTC Arm n, % |
p-value 1 | |
|---|---|---|---|---|
| Total participants | 39 | 19 (49%) | 20 (51%) | |
| Socio-demographic characteristics | ||||
| Maternal age (median, IQR) years | 28 (25, 34) | 29 (25, 34) | 28 (25, 32) | > 0.9 |
| 18 – 25 | 12 (31%) | 6 (32%) | 6 (30%) | > 0.9 |
| > 25 | 27 (69%) | 13 (68%) | 14 (70%) | |
| BMI (median, IQR) kg/m2 | 32 (28, 37) | 30 (28, 36) | 34 (28, 39) | 0.5 |
| Gravidity | 0.7 | |||
| Primigravida | 7 (18%) | 4 (21%) | 3 (15%) | |
| Multigravida | 32 (82%) | 15 (79%) | 17 (85%) | |
| Education level completed | > 0.9 | |||
| Primary | 29 (74%) | 14 (74%) | 15 (75%) | |
| Secondary or Tertiary | 10 (26%) | 5 (26%) | 5 (25%) | |
| Employment | 0.2 | |||
| Employed | 14 (36%) | 9 (47%) | 5 (25%) | |
| Unemployed / Student | 25 (64%) | 10 (53%) | 15 (75%) | |
| Socioeconomic status | 0.3 | |||
| Low SES | 12 (31%) | 4 (21%) | 8 (40%) | |
| Moderate/high SES | 27 (69%) | 15 (79%) | 12 (60%) |
TDF-FTC, tenofovir disoproxil fumarate and emtricitabine; TAF-FTC, tenofovir alafenamide-emtricitabine; μmol/L, micromole per Liter; UL, units per Liter; L/L, litre of cells per litre of blood; GA: gestational age; BMI, body mass index; kg, kilograms; m, meters
Wilcoxon rank sum test or Fisher’s exact test
Participant baseline pregnancy and postpartum clinical measurements are summarized in Table 2. In both TDF-FTC and TAF-FTC arms, the median creatinine (μmol/L) was significantly higher postpartum compared to during pregnancy (TDF/FTC: 69 vs. 40, p<0.001; TAF/FTC: 70 vs. 43, p<0.001). Median haematocrit (L/L) was lower during pregnancy in the TDF/FTC arm (median= 0.33; IQR: 0.32, 0.35) than postpartum (0.37; IQR: 0.35, 0.40; p-value <0.001), but no significant difference was found in pregnancy versus postpartum in the TAF/FTC arm. Platelet count was also lower in pregnancy than postpartum in both arms. These changes reflect expected physiological changes from pregnancy to postpartum and were expected. No differences were found in alanine transaminase.
Table 2.
Clinical characteristics of pregnant women at baseline and postpartum women in TDF-FTC or TAF-FTC study arm in Cape Town, South Africa (PrEP-PP PK Study, June 2022 – June 2023; N = 39)
| TDF Arm | p-value1 | TAF-FTC Arm | p-value1 | |||
|---|---|---|---|---|---|---|
| Pregnancy | Postpartum | Pregnancy | Postpartum | |||
| Total participants | N = 19 | N = 20 | ||||
| N = 19, 100% Baseline |
N = 19, 100% 4 weeks postpartum |
N = 20, 100% Baseline |
N = 20, 100% 4 weeks postpartum |
|||
| GA (median, IQR) weeks | 24 (23, 26) | 4.1 (3.5, 4.6) | 24 (21, 28) | 4.1 (3.8, 5.6) | ||
| Creatinine (μmol/L) | 40 (38, 46) | 69 (61, 75) | <0.001 | 43 (40, 48) | 70 (65, 73) | <0.001 |
| Alanine transaminase (U/L)* | 12 (10, 16) | 17 (15, 22) | 0.2 | 12 (9, 23) | 14 (11, 19) | 0.4 |
| Haemoglobin (g/dL) | 11.1 (10.4, 11.9) | 12.4 (11.1, 13.0) | 0.4 | 11.4 (10.8, 11.8) | 11.70 (11.4, 13.3) | 0.017 |
| Haematocrit (%) | 33 (32, 36) | 37 (35, 41) | <0.001 | 35 (33, 37) | 37 (35, 40) | 0.3 |
| Platelet Count (×109/L) | 279 (215, 296) | 303 (276, 351) | 0.010 | 210 (197, 259) | 312 (237, 351) | 0.011 |
TDF-FTC, tenofovir disoproxil fumarate and emtricitabine; TAF-FTC, tenofovir alafenamide-emtricitabine; PBMC, peripheral blood mononuclear cells; DBS, dried blood spots; fmol, femtomole; pmol, picomole
Paired t-test
One participant missing Alanine result at baseline
Bold: p<0.05
Daily PrEP dosing was asynchronously observed via video recordings or video calls (depending on participant preference). Overall, out of 4077 total expected video doses, 3749 (92%) videos were received by study staff. A further 241 (6%) doses were not observed but were reported by participants as having been taken. In the TDF-FTC arm, 1828 (92%) doses were observed out of an expected 1979. Similarly, in the TAF-FTC arm, 1921/2098 (92%) of videos were received. Overall, 1981/2181 (91%) videos were received during pregnancy and 1768/1896 (93%) during postpartum observation.
Pharmacokinetics of TFV-DP
Concentrations accumulated to steady state concentrations at week 8 of observation in both the pregnancy and postpartum periods in the same women. Observed concentrations of TFV-DP in DBS and PBMC at weeks 4 and 8 among those in both the TDF-FTC and TAF-FTC arm are shown in Table 3. How these concentrations compare to the previously published IMPAACT 2009 adherence categories23 for TDF-FTC in pregnancy and postpartum are reflected in Supplementary Table 1.
Table 3.
Geometric mean levels of TFV-DP and FTC-TP in TAF-FTC and TDF arms in pregnant vs. postpartum periods with log transformed geometric mean ratios (GMR) in Cape Town, South Africa (June 2022 – June 2023
| Pregnancy (4-week follow- up) GM (95% CI) |
Postpartum (4-week follow- up) GM (95% CI) |
GMR (95% CI) comparing log transformed Postpartum vs. Pregnant concentrations (4 week follow- up) |
Pregnancy (8-week follow- up) GM (95% CI) |
Postpartum (8-week follow- up) GM (95% CI) |
GMR (95% CI) comparing log transformed Postpartum vs. Pregnant concentrations (8 week follow- up) |
|
|---|---|---|---|---|---|---|
| TDF-FTC Arm (N = 19) |
n = 13 | n = 13 | n = 16 | n = 16 | ||
| GA (median, IQR) weeks | 28 (27-30) | 4.1 (3.5-4.6) | 32 (31-34) | 8.43 (7.50-9.00) | ||
| TFV-DP PBMC (fmol/10^6cells) | 67 (47-94) | 69 (48-98) | 1.04 (0.51, 2.09) | 71 (44-112) | 73 (50-108) | 1.04 (0.44, 2.44) |
| FTC-TP in PBMC (pmol/10^6 cell) | 7 (5-10) | 5.1 (3.3-7.9) | 0.76 (0.33, 1.73) | 8 (5-13) | 4.9 (2.9-8.2) | 0.60 (0.22, 1.60) |
| TFV-DP DBS (fmol/3mm punch) | 431 (358-517) | 579 (465-721) | 1.34 (0.90, 2.01) | 583 (471-722) | 675 (537-849) | 1.16 (0.74, 1.80) |
| TAF-FTC Arm (N = 20) |
n = 18 | n = 18 | n = 18 | n = 18 | ||
| GA (median, IQR) weeks | 28 (25-31) | 4.1 (3.8-5.6) | 31 (29-35) | 8.71 (7.96-9.93) | ||
| TFV-DP PBMC (fmol/10^6 cells) | 712 (537-944) | 996 (797-1 245) | 1.40 (0.84, 2.32) | 580 (341-985) | 666 (396-1 123) | 1.15 (0.30, 2.49) |
| FTC-TP in PBMC (pmol/10^6 cells) | 8 (6-11) | 12 (10-14) | 1.49 (0.89, 2.51) | 7 (4-13) | 9 (6-12) | 1.25 (0.49, 3.21) |
| TFV-DP DBS (fmol/7mm punch) | 632 (575-694) | 1032 (887-1202) | 1.63 (1.28, 2.51) | 832 (751-922) | 1199 (929-1549) | 1.44 (1.01, 2.06) |
Bold: p<0.05
TDF/FTC arm
The geometric mean TFV-DP concentrations in DBS (fmol/3mm punch) at week 8 were 583 during pregnancy (95% CI: 71, 722) and 675 in postpartum (95% CI: 537, 849), with a geometric mean ratio (GMR) of 1.16 (95% CI 0.74, 1.80) at 8-week follow-up (Table 3). TFV-DP PBMC sampling showed a similar pattern, with geometric mean concentrations of TFV-DP also being lower during pregnancy (71; 95% CI: 44, 112) compared to postpartum (73; 95% CI: 50, 108; GMR=1.04; 95% CI: 0.44, 2.44), (Table 3). Geometric mean concentrations of FTC-TP in PMBC (picomole[pmol]/10^6 cell) were 8 in pregnancy (95% CI: 5, 13) compared to 4.9 in postpartum (95% CI: 2.9, 8.2; GMR=0.60, 95% CI: 0.22, 1.60).
The fitted 8-week median TFV-DP steady-state concentration was 603 (IQR 549-672) fmol/3mm punch in pregnancy compared to 611 (IQR 555-646) fmol/3mm punch in postpartum, indicating 1.3% increase postpartum (Table 4). TFV-DP accumulated with a median (IQR) half-life of 2.8 weeks (2.4–3.4) in pregnancy and 1.4 weeks (1.2 – 1.8) postpartum.
Table 4.
Tenofovir diphosphate (TFV-DP) in dried blood spots (DBS) at steady state during pregnancy and postpartum (N = 39)
| Pregnancy (8 weeks follow-up) 1 | Postpartum (8 weeks follow-up) 2 | |||
|---|---|---|---|---|
| Observed TFV-DP concentration |
Fitted 50th (25th and 75th percentiles |
Observed TFV-DP concentration |
Fitted 50th (25th and 75th percentiles |
|
| TDF-FTC Arm TFV-DP DBS (fmol/3mm punch) |
n = 19 | n = 19 | ||
| Css | 602 | 603 (549 – 672) | 613 | 611 (555 – 646) |
| Half-life (weeks) | 2.8 | 2.8 (2.4 – 3.4) | 1.4 | 1.4 (1.2 – 1.8) |
| Median | 410.0 | - | 518.3 | - |
| Min / Max | 8.3 / 1 208.0 | - | 8.3 / 1 377.4 | - |
| Q1 / Q3 | 271.0 / 571.1 | - | 285.7 / 780.1 | - |
| TAF-FTC Arm TFV-DP DBS (fmol/7mm punch) |
n = 20 | n = 20 | ||
| Css | 754 | 754 (704 – 813) | 1 154 | 1 149 (1 086 – 1 231) |
| Half-life (weeks) | 2.4 | 2.4 (2.1 – 2.8) | 1.6 | 1.5 (1.4 – 1.9) |
| Median | 611.3 | - | 940.5 | - |
| Min / Max | 8.3 / 1 282.7 | - | 8.3 / 2 481.1 | - |
| Q1 / Q3 | 396.6 / 754.5 | - | 630.2 / 1 259.3 | - |
Adjusted for BMI, haematocrit, and creatinine at baseline.
Adjusted for haematocrit and creatinine at 4 weeks of postpartum follow-up.
Participants with levels below limit of quantification (BLQ) replaced with midpoint of LLQ (16.6 / 2 = 8.3)
TDF-FTC: 19 participants with 16 observations = 304 total observations. BLQ replacement of 10 observations (3%)
TAF-FTC: 20 participants with 16 observations = 320 total observations. BLQ replacement of 23 observations (7%)
TAF-FTC arm
The geometric mean of TFV-DP DBS concentrations (fmol/7mm punches) at 8-week follow-up during pregnancy (832; 95%CI: 751, 922) was lower than in postpartum (1199; 95% CI: 929, 1549; GMR: 1.44m95%CI: 1.01, 2.06) (Table 3). The geometric mean of TFV-DP concentrations measured in PBMC samples at 8-week follow-up were580 (95%CI: 341, 985) compared to 666 in postpartum (95% CI: 396, 1123: GMR=1.15; 95%CI: 0.30, 2.49). In contrast to the TDF-FTC arm, the geometric mean of FTC-TP concentrations in PBMC (pmol/10^6 cell) samples at 8-week follow-up were 7 pregnancy (95% CI: 4, 13) compared to 9 in postpartum (95% CI: 6, 12), with a GMR of 1.25 (95% CI: 0.49, 3.21). In adjusted pharmacokinetic modelling, the 8-week median TFV-DP steady state concentration was 52% higher postpartum (1149 fmol/3mm punch; IQR: 1086,1231) compared to pregnancy (754 fmol/3mm punch; IQR: 704, 813). TFV-DP accumulated with a median half-life of 2.4 weeks (2.1 – 2.8) in pregnancy and 1.5 weeks (1.4 – 1.9) postpartum.
Figures 2 and 3 demonstrate the one-phase exponential formula for the TFV-DP measured ruing DBS in the TDF-FTC arm (fmol/3mm punch) and TAF-FTC arm (fmol/7mm punches) during pregnancy (blue) and postpartum (green) and the linear relationship adjusted for age and haematocrit at baseline by pregnancy vs postpartum periods in both study arms.
Figure 2.
TFV-DP (fmol/3mm punch) measured using DBS during a) pregnancy and b) postpartum in the TDF-FTC arm. In TAF-FTC arm is measured in TFV-DP (fmol/7mm punch) during c) pregnancy and d) postpartum over an observational period of 16 weeks in total. A one-phase exponential formula is shown during pregnancy (blue) and postpartum (green).
Figure 3.
Linear relationship, adjusted for age and haematocrit at baseline, of: a) TFV-DP (fmol/3mm punch) in the TDF-FTC arm and b) TFV-DP (fmol/7mm punch) in the TAF-FTC arm
TFV concentrations in breastmilk
Breastmilk samples were obtained at the final study visit at week 8 of postpartum observation. Dried milk spot samples were obtained from 36 participants. Across both study arms TFV-DP concentrations in breast milk were found to be <0.25 pmol/30μL (or <8.3 pmol/mL). Sample concentrations were all classified as either below the limit of detection where the TFV-DP chromatographic peak was not distinguishable from the assay background or as below the limit of quantification (i.e., samples where the TFV-DP is detectable, but is not resolved from the interfering peak and has a signal response below our lowest calibrator of 0.25 pmol/sample).
DISCUSSION
Our study assessed the pharmacokinetics of two different formulations of PrEP (i.e., TDF-FTC and TAF-FTC) in women during pregnancy and postpartum periods in an urban setting in South Africa. Comparisons were made between concentrations of TFV-DP measured in women during pregnancy and postpartum phases. We found that the geometric mean TFV-DP concentration in DBS did not differ statistically when compared to postpartum, among women taking a daily dose of TDF-FTC and were slightly higher in postpartum compared to pregnancy (GMR=1.44; 95% CI=1.01-2.06) among women taking TAF-FTC. We found similar patterns of TFV-DP concentrations in PBMC samples in both study arms, but differing patterns of FTC-TP concentrations, in that geometric mean concentrations did not differ in pregnancy compared to postpartum in the TDF-FTC arm, but higher in postpartum versus pregnancy in the TAF-FTC arm. We did not observe any appreciable accumulation of TFV-DP in breast milk. Our findings of women having lower concentrations of tenofovir metabolite in the TAF-FTC arm during pregnancy compared to postpartum are consistent with previous literature.22 These findings are also supported by the fact that women have an altered metabolism and increased volume and renal clearance during pregnancy which may result in reduced tenofovir concentrations in plasma, PBMC, and DBS as observed.14 Whilst the TFV-DP concentration findings of this study was expected due to the previous IMPAACT 2009 study23, the reductions during pregnancy were generally not statistically significant (except for TFV-DP in DBS arising from TAF). Thus the implication for PrEP efficacy require further study as it is still unclear if pregnancy reduces efficacy levels of daily oral PrEP and requires stricter adherence measures.
Our study was not designed to compare FTC-TP between the TDF and TAF arms. In the TAF arm the concentrations of FTC-TP are increased postpartum, as might be expected. No significant differences were found in FTC-TP concentrations in the TDF arm between pregnancy and postpartum. This may be due to issues with adherence and not necessarily a biological difference in FTC-TP levels, which this study was not powered to determine.
A strength of this study the combined use of pharmacologic measures (DBS and PBMC) with daily video observed therapy which allowed assessment of average adherence whilst also providing detail of dosing patterns (e.g., when doses were missed or resumed) for both TDF-FTC and TAF-FTC. The high proportion of expected doses that were observed (94%) indicate good adherence over the 16 weeks of observation with similar proportion of doses observed during pregnancy and postpartum periods; however, we noted several cases of DBS or PBMC TFV-DP that were below the limit of quantification, highlighting some possible weakness of the video DOT method compared to traditional DOT observed by a clinician that will be discussed in a later manuscript.
Women in this study were recruited during pregnancy and then observed through to their postpartum phase, so participants were their own comparators for the two phases of observation. This reduced the potential for inter-individual variability to act as a confounder. Although studies commonly focus on DBS measurements to assess TFV-DP metabolite concentrations, red blood cells are not the target site for tenofovir drug action14. We included assessment of PBMC concentrations to provide insight into PrEP pharmacokinetics in target cells in pregnancy and postpartum.
Our study found lower concentrations of TFV-DP in DBS among pregnant women when compared to the IMPAACT 2009 study in Malawi, South Africa, Uganda, and Zimbabwe. The IMPAACT 2009 study found that TFV-DP in DBS was 31-37% lower in pregnant women compared to postpartum women.22 Their benchmark concentrations were also higher in pregnancy and postpartum, highlighting better adherence to the video DOT protocol, population variation or BMI differences. For context, Supplemental Table 1 compares our results to the IMPAACT 2009 adherence categories.
We found high concentrations of TFV-DP in PBMC in pregnancy and postpartum on TAF-FTC (above TDF-FTC levels), suggesting PrEP efficacy may be retained. Efficacy and safety studies are warranted to evaluate TAF-FTC for PrEP in pregnant and postpartum women. The PURPOSE-1 trial results demonstrated equivalent efficacy of TAF compared to TDF in cisgender women, including some pregnant women. There was no evidence of a meaningful difference in HIV incidence was observed between TAF and TDF (incidence rate ratio, 1.20; 95% CI, 0.67 to 2.14), though adherence to TAF and TDF was low and declined over time. Pregnant women were included in the study follow up and we expect that safety and efficacy will be reported in women using TAF in a sub-analysis.
A limitation of this study was nonadherence to the VOT protocol as observed in some participants. This increased variability in the benchmark estimates. Additionally, participants were advised to continue PrEP after birth prior to the postpartum PK assessment. This could result in slightly higher TFV-DP accumulation during the postpartum phase, although 8 weeks of dosing represents 90% of eventual steady-state. Our modelling suggested that fitted Css values were similar to observed week 8 values indicating that Css was essentially reached, and the half-lives were consistent with previous studies.14,21 Another limitation of this study is that the sample consisted entirely of lower-income pregnant women in an urban setting. This limits the generalizability of results to higher-income settings and limits the ability to characterize associations between demographic characteristics and TFV-DP pharmacokinetics. We acknowledge that the high percentage of successfully observed videos (92%) is incongruous with the number of participants excluded from analysis due to BLQ. Some possible reasons include: participants taking their tablets in the video but spitting them out once they have stopped recording, some degree of drug instability as participants often decant their PrEP pills (to avoid the stigma of the packaging) resulting in sub-optimal storage conditions. Another consideration might be variation in lab equipment sensitivity as TFV-DP from the TDF/FTC and TAF/FTC arms were analysed in different laboratories which may account for the disproportional BLQs in the TDF/FTC arm. Finally, this study was not powered to assess safety or efficacy of either formulation of PrEP when used to prevent HIV in pregnant and postpartum women.
CONCLUSION
In conclusion, we found that TFV-DP concentrations were not significantly different during pregnancy than postpartum, in both DBS as well as PBMC, and for TDF-FTC, while TAF-FTC formulations of oral PrEP were slightly higher in postpartum in DBS measures. We found high concentrations of TFV-DP in PBMC in pregnancy and postpartum on TAF, suggesting PrEP efficacy is retained. Further research is needed to explore the implications of lower PrEP levels in pregnant women on the efficacy of PrEP and levels of protection afforded during this time. Efficacy and safety studies are warranted to evaluate TAF-FTC for PrEP in pregnant and postpartum women.
Supplementary Material
Highlights.
We analyze TDF-FTC and TAF-FTC for PrEP in pregnant and postpartum women in a pharmacokinetic study in South Africa
Our study found that tenofovir diphosphate (TFV-DP) concentrations were overall lower during pregnancy than postpartum for TAF-FTC, but not with TDF-FTC samples.
We found high concentrations of TFV-DP in PBMC in pregnancy and postpartum on TAF-FTC, suggesting PrEP efficacy is maintained.
Efficacy and safety studies are warranted to evaluate TAF-FTC for PrEP in pregnant and postpartum women.
ACKNOWLEDGEMENTS:
The authors thank the study participants, the personnel at the University of Cape Town Gugulethu clinical site, the University of Cape Town Division of Pharmacology laboratory and the University of Colorado Antiviral Pharmacology Bioanalytical Laboratory for their support and contributions to this work.
FUNDING
This study is an investigator driven study, sponsored by Gilead Sciences Inc. The donor was not involved in data collection, analysis nor interpretation of the study findings. CW is supported by a Wellcome Clinical Research Career Development Fellowship, 222075/Z/20/Z.
Footnotes
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Declaration of interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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