Now that more people are taking PrEP, studies are beginning to document the impact that Truvada PrEP can have on kidney function in HIV-negative people.
PrEP clinical trials did not find significant negative effects on kidney function, but these studies largely excluded people with any pre-existing kidney impairment. Also, sometimes uncommon side effects only show up after many more people are using a drug. At this year's Conference on Retroviruses and Opportunistic Infections (CROI), a few studies revealed that PrEP can impair kidney function in some people -- supporting regular kidney function monitoring for people who may be at risk.
Kidneys filter our blood and then reabsorb useful components such as amino acids, sugars, and minerals. Drugs like tenofovir, which are excreted by the kidneys, can build up and damage the delicate kidney tubules. Minor declines in filtration and reabsorption capacity are often subclinical, or without symptoms, but more serious tubule damage (tubulopathy) can lead to disruption of the body's pH balance and bone loss.
Monica Gandhi, M.D., presented results from a study showing that kidney function changed among participants in an open-label continuation of the iPrEx trial -- and that older people and people with greater exposure to PrEP were more likely to have kidney function declines.
The study team measured cumulative drug exposure by analyzing the levels of tenofovir and emtricitabine in hair samples. They assessed kidney function with a serum creatinine test and by estimating how quickly the kidneys were working to filter the blood (eGFR).
Measures of eGFR greater than 90 mL/min are normal, 60 mL/min indicates moderate impairment, and less than 30 mL/min indicates severe impairment.
Overall, creatinine clearance decreased slightly after starting Truvada, by an average of 2.5% over 18 months. There was a consistent relationship between eGFR decline and increasing levels of tenofovir or emtricitabine in hair samples: eGFR fell by 5.6% among people with the highest quartile of hair drug levels (indicating daily dosing).
Older people were more likely to experience a clinically significant decrease (i.e., have their eGFR fall below 70 mL/min). About a quarter of people over age 50 with high drug levels fell below this threshold, but among participants under age 40 the proportion never rose above 5% even with daily dosing. People with slightly low eGFR at baseline (less than 90 mL/min) were also more likely to fall below the threshold.
This excerpt was cross-posted with the permission of BETAblog.org. Read the full article.