BACKGROUNDSimplified maintenance therapy with ritonavir-boosted atazanavir (ATV/RTV) alone is attractive because of nucleoside reverse-transcriptase inhibitor (NRTI)-sparing benefits, low pill burden, once-daily dosage, and safety.METHODSSubjects with virologic suppression after > or = 48 weeks of initial antiretroviral therapy with 2 NRTIs and a protease inhibitor (PI) were enrolled. Subjects switched to ATV/RTV at entry and discontinued NRTIs after 6 weeks. The primary end point was time to virologic failure (confirmed HIV-1 RNA level > or = 200 copies/mL). Drug resistance at virologic failure was evaluated by standard genotyping and single-genome sequencing (SGS). Residual viremia (1.1-49 copies/mL) was measured by single-copy assay.RESULTSThirty-four subjects simplified to ATV/RTV alone, of whom 30 (88%) did not experience virologic failure by 48 weeks after simplification. Residual viremia did not change significantly after NRTI discontinuation among those without virologic failure but did increase 4-12 weeks before confirmed virologic failure. No major PI-resistance mutations were identified at virologic failure by standard genotyping or SGS.CONCLUSIONSIn this pilot study, simplified maintenance therapy with ATV/RTV alone maintained viral suppression in most subjects through 48 weeks. PI resistance was not detected among subjects experiencing virologic failure. Larger, randomized trials are warranted to further define the efficacy and safety of this strategy.

When fully suppressive regimens are not available, incompletely suppressive regimens also provide immunologic benefits. In this study, with stable background therapy, human immunodeficiency virus (HIV)-infected patients who were randomized to receive atazanavir or boosted atazanavir, compared with those who continued boosted protease inhibitor therapy, maintained similar virologic and immunologic control, resistance-mutation patterns, and replication capacities with reduced use of lipid-lowering medication.

To the Editor: Further data on the use of atazanavir (ATV) with H2-receptor antagonists and proton pump inhibitors (PPIs) have become available since the letter published by Drs. Homayoun Khanlou and Charles Farthing.1 Previously, ATV and PPI interaction studies demonstrated that ATV exposures were reduced by more than 70%, leading to a recommendation that PPIs should not be used concomitantly with ATV.2,3 Studies to evaluate other dosing strategies with ATV and PPIs are planned. More recently, data have become available on the interaction between ATV and H2-receptor antagonists, indicating that reduced exposures to ATV resulting from an interaction with H2-receptor antagonists may be attenuated by concurrent use of low-dose ritonavir (RTV) or by temporal separation from an H2-receptor antagonist.4 In 2 drug interaction studies of 108 HIV-negative subjects, the effect of the commonly used H2-receptor antagonist famotidine at 40 mg twice daily on ATV at 400 mg and ATV/RTV at 300/100 mg was evaluated.4 Relative to a control arm of ATV at 400 mg alone, coadministration of famotidine at 40 mg twice daily decreased ATV exposures by approximately 40%. Temporal separation (dosing ATV 10 hours after and 2 hours before the famotidine dose) attenuated the reduction in ATV exposures. Furthermore, ATV at 300 mg coadministered with RTV at 100 mg led to a 79% and 4.5-fold increase in area under the curve and Cmin, respectively, with Cmax values similar to ATV at 400 mg alone. Relative to a control arm of ATV/RTV at 300/100 mg alone, coadministration with famotidine at 40 mg twice daily modestly reduced ATV exposures by 18%, 14%, and 28% for area under the curve, Cmax, and Cmin, respectively. These exposures were similar to an antiretroviral regimen of ATV/RTV with 2 nucleosides including tenofovir, the efficacy of which has been established in a well-controlled study in HIV-infected subjects relative to a standard of care regimen.5 Thus, ATV/RTV at 300/100 mg may be given concomitantly in combination with H2-receptor antagonists. Atazanavir/RTV at 300/100 mg is recommended with H2-receptor antagonists, although the reductions in ATV exposures with maximal doses of famotidine could be overcome by increasing the dose of ATV to 400 mg while keeping the dose of RTV steady at 100 mg. Atazanavir/RTV at 400/100 mg is not recommended because there is a potential for increased risk of ATV intolerability, resulting from increased ATV exposures that could occur with less potent, lower doses, or sporadic dosing of H2-receptor antagonists in combination with higher doses of ATV. To further minimize any reduction in ATV exposures, an alternative to simultaneous dosing of H2-receptor antagonists with ATV/RTV at 300/100 mg is temporal separation, which may be attained by administering ATV/RTV at 300/100 mg at least 10 hours after and at least 2 hours before an H2-receptor antagonist; temporal separation should be considered in treatment-experienced patients. In summary, although H2-receptor antagonists increase intragastric pH and have been shown to reduce ATV absorption, H2-receptor antagonists are less potent than PPIs in suppressing intragastric acid secretion and may be used with ATV. Atazanavir/RTV at 300/100 mg may be administered concomitantly with H2-receptor antagonists. Alternatively, ATV at 400 mg or ATV/RTV at 300/100 mg may be temporally separated by administering ATV at least 10 hours after and at least 2 hours before an H2-receptor antagonist to minimize the interaction; temporal separation of ATV/RTV at 300/100 mg should be considered in treatment-experienced patients. Local prescribing information may vary; therefore, clinicians using ATV with H2-receptor antagonists should consult their local package inserts for specific information. Additional studies to evaluate alternative dosing strategies with ATV and H2-receptor antagonists are ongoing. Sangeeta Agarwala, PhD* Gary Thal, MD† Richard Nettles, MD* Richard Bertz, PhD* *Bristol-Myers Squibb Co, Princeton, NJ and †Bristol-Myers Squibb Co, Plainsboro, NJ [email protected]

CONTEXTThe long-term adverse effects, expense, and difficulty of adherence to antiretroviral regimens have led to studies of simpler maintenance therapies. Maintenance therapy with ritonavir-boosted atazanavir alone is a possible option because of low pill burden, once-daily dosing, safety, and unique resistance profile.OBJECTIVETo assess whether simplified maintenance therapy with atazanavir-ritonavir alone after virologic suppression increases the risk of virologic failure (2 consecutive human immunodeficiency virus type 1 [HIV-1] RNA measurements of > or =200 copies/mL).DESIGN, SETTING, AND PARTICIPANTSSingle-group, open-label, multicenter, 24-week pilot study of 36 HIV-infected adults with virologic suppression for 48 weeks or longer receiving their first protease inhibitor (PI)-based regimen. The study was conducted between September 1, 2004, and April 18, 2006, at 12 participating AIDS clinical trial units in the United States.INTERVENTIONParticipants switched PIs to atazanavir-ritonavir at entry and discontinued nucleoside analog reverse transcriptase inhibitors (NRTIs) after 6 weeks.MAIN OUTCOME MEASURESVirologic failure within 24 weeks of discontinuing NRTIs. Other measures included HIV-1 drug resistance, plasma atazanavir concentrations, adverse events, CD4 cell counts, plasma lipid levels, and HIV-1 RNA levels in seminal plasma.RESULTSThirty-six participants enrolled and 2 discontinued before simplification to atazanavir-ritonavir alone. Thirty-four patients were included in the analysis of the primary end point after 24 weeks: 1 withdrew voluntarily, and 33 continued the regimen. Virologic success (absence of failure) through 24 weeks of simplified therapy occurred in 91% (31 of 34 patients; lower 90% confidence interval limit = 85%). Three participants experienced virologic failure 12, 14, and 20 weeks after simplification, with plasma HIV-1 RNA levels of 4730, 1285, and 28 397 copies/mL, respectively. Resistance testing at failure did not identify PI resistance mutations. Plasma atazanavir concentrations at failure were low or below detection in 2 of 3 participants experiencing failure. There were no treatment discontinuations for adverse events after simplification; no significant changes in CD4 cell counts or plasma lipid levels; and no detectable HIV-1 RNA in seminal plasma from all 8 participants tested.CONCLUSIONSThese preliminary data suggest that simplified maintenance therapy with atazanavir-ritonavir alone may be efficacious for maintaining virologic suppression in carefully selected patients with HIV infection. These findings require confirmation in larger, randomized trials of this strategy.TRIAL REGISTRATIONclinicaltrials.gov Identifier: NCT00084019.

Chick limb buds at stages 22-23 largely consist of replicating presumptive chondroblasts and presumptive myoblasts. To study the influence that different medium compositions may have on the survival, replication, and terminal differentiation of these dissociated cells in vitro, micromass cultures were reared in either standard Dulbecco's modified Eagle's medium containing fetal calf serum (SC-DMEM) or in serum-free DMEM. By day 4, approximately 80% and 50% of the original cell inoculum had been lost in DMEM and SC-DMEM cultures, respectively, as estimated from the recovery of incorporated 3H-thymidine. Between days 1 and 4, the total-DNA content remained virtually constant in DMEM cultures, while it increased five- to sixfold in SC-DMEM cultures. In both media, definitive myoblasts and chondroblasts first emerged on day 1 and day 2, respectively, as determined by immunofluorescence staining using antibodies against muscle light meromyosin (LMM) or the major cartilage proteoglycan. In both media, the chondroblasts increased in number and, by day 4, had formed sizable chondroblast nodules. The number of chondroblasts in SC-DMEM cultures exceeded that observed in DMEM cultures. In DMEM, the LMM-positive myoblasts had an atypical morphology and failed to fuse into elongated myotubes; these cells began to degenerate on about day 4, being undetectable by day 8. In SC-DMEM, the numerous LMM-positive myoblasts located in the center of the micromasses also had an atypical morphology, failed to form multinucleated myotubes, and were absent by day 8.(ABSTRACT TRUNCATED AT 250 WORDS)

Transverse frozen sections from the postcephalic region of stage 9–16 chick embryos and from the wing bud region of stage 17–31 embryos were stained with antibodies to the major extracellular matrix components of cartilage. These probes included unfractionated A1 and A2 antisera to the major cartilage proteoglycan, affinity-purified antibodies to the proteoglycan core protein and to Type II collagen, and a monoclonal antibody to keratan sulfate. In embryos as early as stage 10, notochord stained specifically with the keratan sulfate monoclonal antibody. At this stage the notochord, as well as surrounding tissues, were negative to cartilage proteoglycan and collagen antibodies. Positive staining with the latter probes was coordinately acquired by notochord cells and their accompanying sheath around stage 15, while surrounding tissues remained negative. At this stage, the ventral region of the perispinal cord sheath exhibited light staining with the proteoglycan and keratan sulfate antibodies though failing to react to Type II collagen antibodies. Positive staining of notochord and ventral spinal cord persisted through later developmental stages. As revealed by immunofluorescence, definitive vertebral chondroblasts first emerged at approximately stage 23 and definitive limb chondroblasts at stage 25. The results are discussed in terms of the possible multiple roles of notochord in early embryogenesis.

Polyclonal antibodies were raised in a rabbit against the major proteoglycan of chick sternal cartilage. A total of six antisera was obtained, three after the first booster injection (A1, A2, and A3) and three after the second booster injection (A4, A5, and A6). The A1 antiserum, which was characterized in most detail, immunoprecipitated native as well as chondroitinase ABC-digested or chondroitinase ABC/keratanase-digested cartilage proteoglycan synthesized by cultured chick chondroblasts, but failed to immunoprecipitate the major proteoglycan synthesized by chick skin fibroblasts. This antiserum was also able to immunoprecipitate the cartilage proteoglycan core protein newly synthesized by cultured chondroblasts, but no other major cell protein. However, the late bleed antisera obtained from the same rabbit after a second booster injection reacted with a new chondroblast- specific polypeptide(s) of approximately 60,000 mol wt in addition to the cartilage proteoglycan. By immunofluorescence procedures, the A1 antiserum stained the extracellular proteoglycan matrix of cultured chondroblasts but not that of skin fibroblasts. Following enzymatic removal of the extracellular matrix and cell membrane permeabilization, this antiserum stained primarily a large, juxtanuclear structure. Additional radioautographic evidence suggests that this structure represents the Golgi complex. Similar immunofluorescent staining with antibodies to the cartilage-characteristic Type II collagen revealed that type II procollagen was localized in numerous cytoplasmic, vacuole- like structures which were scattered throughout most of the chondroblast cytoplasm but were notably scanty in the Golgi complex area. In conclusion, our data suggest the transit of the major cartilage proteoglycan through the Golgi complex of cultured chondroblasts and possible differences in the intracellular distribution of newly synthesized cartilage proteoglycan and Type II procollagen.