A 44-year-old man with previously undiagnosed HIV infection was hospitalized in August 2011 for the treatment of Pneumocystis jirovecii pneumonia and multiple other opportunistic infections. His CD4 cell count was 50 per μl and his HIV viral load (VL) was 330 000. After initial therapy for pneumonia, he was started on once-daily tenofovir, emtricitabine and ritonavir-boosted atazanavir (100/300 mg). Over the ensuing 20 weeks, the patient did well with no signs, symptoms or laboratory test results indicating toxicity, and his repeated assertions of strict adherence to treatment were corroborated by decline in HIV viral load to 200 copies/ml and a rise in CD4 lymphocytes (Fig. 1). His initial genotype showed wild-type HIV subtype B.Fig. 1: Patient's time course of HIV viral load (RNA copies/ml), CD4 number, and CD4 percentage (multiply the latter by 0.1 for real value) in relation to antiretroviral therapy.Unlabeled arrows – timing of HIV genotypes obtained.Starting after 30 weeks of therapy, his HIV viral load rose progressively. The patient repeatedly affirmed his adherence to treatment; he was not taking any other medications and he had been counseled extensively about not taking complementary therapies. A second genotype was ordered when his VL rose to 2000 (at 38 weeks) which showed new, high-level resistance to only emtricitabine and lamivudine. At this juncture, the patient admitted that he had been eating approximately six stir-fried garlic cloves three times per week after starting treatment. Although garlic is not mentioned in the latest (03/2012) atazanavir prescribing information, one study showed that garlic ingestion reduced the AUC for boosted saquinavir by ∼50%, with effects persisting for more than 10 days after discontinuation [1]; some sources suggested that atazanavir absorption might be affected by garlic, without citations [2]. Consequently, the patient was advised to stop taking garlic. Two trough atazanavir concentrations were ordered, one when garlic was being taken and another 10 days later, with the results (returning 1 month later) showing sub-optimal levels [3] of 178 and 121 ng/ml. By week 40, his viral load had risen to 20 000 and another genotype showed no change (high-level FTC and 3TC resistance). Therefore, atazanavir was discontinued and twice-daily, ritonavir-boosted darunavir was initiated. On this regimen, his HIV viral load rapidly became undetectable and remained so. After 16 weeks, he skipped an evening dose of DRV/r, taking one dose of ATV/r instead; a trough serum ATV concentration obtained the following day was 609 ng/ml. To our knowledge, this is the first instance of virologic failure of a boosted atazanavir regimen almost certainly caused by ingestion of garlic, acting by lowering serum atazanavir concentrations. In this patient, garlic appeared to reduce atazanavir blood levels by more than 70%, with the effect persisting for more than 10 days. Alternative explanations for virologic failure, such as poor adherence or effects of garlic on metabolism of tenofovir or emtricitabine, seemed unlikely for a variety of obvious reasons. The mechanism by which garlic affects HIV protease inhibitor concentrations is highly complex, as garlic contains many biologically active compounds, which can affect intestinal absorption as well as metabolism by the cytochrome system [4–7]. The course of the patient's viral load on this garlic-vitiated regimen was interesting. The initial response to therapy was relatively good, with the VL falling from over 300 000 to 200 over the space of about 20 weeks, although, in retrospect, the decline might have been slower than with a fully-effective regimen. One could speculate that much of the early antiviral activity from this regimen was due to the tenofovir and emtricitabine components, and that the viral load began to rise when resistance to the emtricitabine component had developed. Acknowledgements The authors gratefully acknowledge the patient who assisted in resolving the cause of his virologic failure and who gave permission for us to share this experience. Conflicts of interest There are no conflicts of interest.