NRTI-related dosing issues

Nucleoside reverse transcriptase inhibitors (NRTIs) are primarily eliminated by the kidneys (exceptions are abacavir and AZT, excreted via hepatic route). NRTIs may reach high concentrations in people with impaired kidney function, increasing the risk of side-effects. Patients with kidney impairment can still use NRTIs, but dosing may need to be reduced.¹

Kidney toxicity has been reported in patients taking ddI (didanosine, Videx / VidexEC). In addition to increasing the risk of kidney toxicity by raising tenofovir (Viread) levels by as much as 50%, ddI may conceivably contribute independently to kidney damage, possibly related to mitochondrial toxicity.ref]

A university-based outpatient HIV clinic that monitored NRTI prescriptions issued over a two-year period found a 6% overall rate of NRTI prescribing errors, but a 31% rate when prescribing NRTIs for patients with renal impairment. Many of the mistakes came from the use of fixed dose combinations (e.g. FTC/tenofovir ± efavirenz). Common errors were failing to dose adjust for patient weight, impaired creatinine clearance, and/or co-administration with ddI; use of non-standard doses was also an issue.²