Atazanavir plus raltegravir 300/400 mg twice daily is being explored as a ritonavir-and nucleoside-sparing treatment strategy. The pharmacokinetics and safety of this combination in healthy individuals were evaluated. Methods: A total of 22 healthy individuals received raltegravir 400 mg on days 1-5, atazanavir 300 mg on days 6-12 and atazanavir plus raltegravir 300/400 mg on days 13-26, twice daily with a light meal. Serial blood samples were collected 12 h after the morning dose on days 5, 12

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... and 26; safety assessments, clinical laboratory data and serial electrocardiograms (ECGs) at 0, 2 and 6 h were obtained. Results: Raltegravir coadministration reduced atazanavir geometric mean maximum plasma concentration (C max ), area under the plasma concentration-time curve from 0 to 12 h post-dose (AUC 0-12 ) and trough plasma concentration (C min ) by 11%, 17% and 29%, respectively, compared with atazanavir alone. Geometric mean atazanavir C min was 817 ng/ml (range 250-1,550) with raltegravir coadministration. Atazanavir increased raltegravir geometric mean C max , AUC 0-12 and C min by 39%, 54% and 48%, respectively. All adverse events were of mild or moderate intensity. Hyperbilirubinaemia and ECG PR increases with atazanavir were similar to those of atazanavir/ritonavir once daily. No corrected QT prolongations were noted. Mean QRS increase from baseline was 11.0 ms (range 2-25) after receiving atazanavir for 7 days; no further QRS increase was noted and no QRS interval was >120 ms with raltegravir coadministration. No ECG changes were observed with raltegravir alone. Conclusions: Coadministration of atazanavir and raltegravir 300/400 mg twice daily decreased atazanavir AUC 0-12 and C min relative to atazanavir alone, and increased AUC 0-12 of raltegravir relative to raltegravir alone. Atazanavir and raltegravir alone and coadministered appeared safe and well-tolerated.