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The methods used for assessing adherence and exposure to ARV drugs include self-reported missed doses, monitoring pharmacy refills and conducting pill counts, use of electronic monitoring devices, measuring ARV concentration in plasma or hair. It is desirable to have a routine assessment of adherence and exposure to ARV drugs available for use by healthcare providers. It has been estimated that between 20 to 50% of adolescents experience adherence-related antiretroviral (ARV) drug treatment failure.
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Poor adherence to treatment leads to sub-optimal drug exposure limiting treatment efficacy. Zimbabwe has a prevalence of 13.3%, with 1.3 million people living with HIV including 77,000 children and adolescents. Of these, approximately 3 million were children and adolescents under 20 years of age. Measuring drug concentration in hair is feasibly accomplished and could be more accurate for monitoring ARV drugs exposure.Ībout 36.9 million people were living with Human Immunodeficiency Virus (HIV) worldwide in 2017. The determinants of increased ATV/r concentrations in hair found in our analysis are monitoring at follow up event, body mass index, and caregiver status. Adolescents receiving care from fellow siblings had atazanavir in hair at least 54% less compared to other forms of care. Thinner participants had 54% higher while overweight had 21% lower atazanavir in hair compared to normal weight participants. We associated a unit increase in adherence score with 2% increase in hair concentration both ATV/r. At follow-up, we estimated an increase of 30% /42% of respective ATV/r in hair. There is 16% / 18% of the respective ATV/r in hair as a ratio of steady-state trough plasma concentrations. We performed model development in NONMEM (version 7.3) ADVAN 13. We based the study on secondary data analysis whereby data from a previous study on Zimbabwean adolescents which collected hair samples at enrolment and 3 months follow-up was used in model development. We aimed at developing and validating a pharmacokinetic model based on atazanavir/ritonavir (ATV/r) in hair and identify factors associated with variabilities in hair accumulation. Pharmacokinetic modelling can explore utility of drug in hair. Drug concentration in hair promises to be reliable for assessing exposure to antiretroviral (ARV) drugs. Adolescents experience higher levels of non-adherence to HIV treatment.