Although atazanavir pharmacokinetics and pharmacodynamics are related, atazanavir plasma trough concentrations in patients taking the unboosted drug may not be high enough to maintain adequate suppression of HIV.

To address the question of the potency of unboosted vs boosted atazanavir when used in routine clinical practice, Spanish researchers looked at the percentage of HIV patients with atazanavir trough concentrations lower than the proposed minimum effective concentration, comparing subjects receiving ritonavir-boosted atazanavir (n = 31) or unboosted atazanavir (n= 54).

Blood samples were drawn 21 to 25 hours after the last atazanavir dose. Plasma drug concentrations were determined by high-performance liquid chromatography. Atazanavir concentrations were considered suboptimal if they were below 0.15 mg/L, and potentially toxic if they were higher than 0.85 mg/L.

Study results were published in the October 2007 issue of Therapeutic Drug Monitoring.

Results

Conclusion

In conclusion, the study authors wrote, “Atazanavir trough concentrations may be lower than the proposed minimum effective concentration in a considerable percentage of HIV-infected patients receiving antiretroviral therapy with unboosted atazanavir.”

“Therapeutic drug monitoring may be useful in this setting,” they added.

Lluita contra la SIDA Foundation, Hospital Universitari Germans Trias i Pujol, Badalona, Spain; Universidad Autónoma de Barcelona, Barcelona, Spain; Centre d’Investigació del Medicament, Institut de Recerca de l’Hospital de la Santa Creu i Sant Pau, Barcelona, Spain; and IrsiCaixa Foundation, Hospital Universitari Germans Trias i Pujol, Badalona, Spain.

12/11/07

Reference
J Molto, JR Santos, M Valle, and others. Monitoring Atazanavir Concentrations with Boosted or Unboosted Regimens in HIV-infected Patients in Routine Clinical Practice. Therapeutic Drug Monitoring 29(5): 648-651. October 2007.