Tenofovir substitution in Namibia based on an analysis of the antiretroviral dispensing database

Objectives: In the management of HIV infection, tenofovir is preferred to its predecessors - zidovudine and stavudine - in the antiretroviral therapy (ART) nucleoside backbone. Tenofovir's (TDF) preference is based on its safety profile. Nevertheless, TDF causes adverse reactions, some of which warrant its substitution for patients. The rate of TDF-substitution is suggestive of the rate of occurrence of TDF-related adverse reactions. However, the rate of substitution of TDF with another nucleoside reverse transcriptase inhibitor (NRTI) in Namibia was unknown. The objective of this review was to measure the rate of TDF's substitution for the period of January 1, 2008 to November 30, 2011, and to compare the gender difference in the rates of TDF's substitution.

Methods: We accessed antiretroviral medicine dispensing records from the national antiretroviral dispensing database (NDB). We selected patients who were started on a TDF-containing conventional ART regimen - 2NRTI+1NNRT. We used the initial and current ART regimens to identify records of TDF's substitution with another NRTI.

Results: A total of 84,741 patients were initiated on ART (Jan-1-2008 to Nov-30-2011). A total of 52,612 patient-records were excluded from the analysis because they did not meet the criteria for inclusion. Of the 32,129 included records, 59.4% (n=19 096) and 40.6% (n=13 033) were for female and male patients, respectively. Of these, 1.2% (n=380) of the patients had their TDF substituted with another NRTI. Of the females and males, respectively, 1.1% (95% CI: 0.9-1.3; n=210) and 1.3% (95% CI: 1.1-1.5; n=170) had TDF substituted with another NRTI. No gender difference was observed (p-value = 0.11).

Conclusion: The percentage of patients for whom TDF was substituted with another NRTI, possibly due to TDF-related adverse reactions, was within the current published limits. However, 1.2% is likely not a true representation of the percentage of patients who experience adverse events because some patients could have been maintained on TDF even in the presence of adverse events. Further investigation is required to determine the clinical reasons for TDF's withdrawal.