Tenofovir in Pregnancy to Prevent Mother to Child Transmission of Hepatitis B.

Participants with HBV mono infection and a measurable HBV DNA viral load attending SMRU antenatal clinics (ANC) on the Myanmar-Thailand border will be invited if they have a gestational age of at least 20 weeks. A total of 24 women: 12 participants enrolled in 2nd trimester (EGA 20-\<24 weeks) and 12 enrolled in 3rd trimester (EGA 28-\<36) with complete samples are required. Women, identified by routine antenatal care screening for HBV will be invited to participate if they are HBsAg positive and meet the inclusion and exclusion criteria. Participants will be provided TDF 300mg daily and will continue TDF treatment until one month after delivery. The TFV concentrations will be measured monthly before delivery, at delivery, in cord blood and 1 and 2 months postpartum. Additional dense PK blood sampling will be done in the second and third trimester and postpartum. Breast milk samples timed with mother blood and infant blood samples will be included to measure drug concentrations in breastmilk as possible presence of HBV DNA viral in breastmilk following cessation of TDF. The dense sampling for pharmacokinetics assessments will occur at least after 2 weeks of TDF treatment in second trimester between 22-26 weeks gestation, in third trimester between 30-38 weeks gestation, and 4 weeks postpartum. The dense sampling will entail twelve blood samples in a 24 hour period (24ml of blood in total). Women will be counseled about the importance of adherence. Direct Observed Treatment (DOT) in the 3 days prior to the dense blood sampling will be performed. The woman can choose to be admitted for these days or if a home visitor lives close enough be supervised at home. The follow-up for women will be until 6 months post-partum, to check for flares. TFV concentrations will be collected by venous blood testing but an indwelling catheter can be used during the rich sampling 24 hour period. Infants will be followed up from delivery, and at 1, 2, 4 and 6 months of age for vaccination and growth. Infant drug exposure is measured at month 1 and HBV DNA will be measured at birth from cord blood and HBsAg by venepuncture at 2 months of age. Funder \& grant reference number: iTPA Award (grant ref. no. WT-iTP-2019/006)