Hypersensitivity reactions during therapy with the nucleoside reverse transcriptase inhibitor abacavir.

BACKGROUND: Hypersensitivity reactions consist of a variable group of clinical findings and have been described for a wide variety of chemical compounds. OBJECTIVE: This review characterizes the clinical profile of hypersensitivity to the nucleoside reverse transcriptase inhibitor abacavir sulfate. METHODS: We performed a retrospective medical review of pooled adverse events data from approximately 200,000 patients who received abacavir in clinical trials, through expanded-access programs, or by prescription from 1996 through 2000. Screened cases of hypersensitivity were classified as either definitive or probable. Definitive cases were identified when initial symptoms resolved on interruption of abacavir therapy and returned on reintroduction of abacavir therapy. RESULTS: A total of 1803 cases were identified, 1302 in the 30,595 patients participating in clinical trials or the expanded-access program and 501 in patients from the post-marketing experience. On review, 176 (9.8%) of these cases were considered definitive and the remainder probable. Based on the 1302 cases identified in clinical trials or the expanded-access program, the calculated incidence of hypersensitivity was 4.3%. Symptoms reported in > or = 20% of cases of this multiorgan reaction included fever, rash, malaise/fatigue, and gastrointestinal symptoms such as nausea, vomiting, and diarrhea, among others. Respiratory symptoms occurred in 30% of cases and included dyspnea (12%), cough (10%), and pharyngitis (6%). In 90% of cases, hypersensitivity reactions occurred within the first 6 weeks after initiation of abacavir (median time, 11 days); after an initial reaction, rechallenge with abacavir resulted in the reappearance of symptoms within hours of reexposure. Hypotension was present in 25% of these rechallenge reactions. Among patients who received abacavir in clinical trials, the mortality rate was 0.03% (3 per 10,000 patients). CONCLUSIONS: Hypersensitivity to abacavir is an idiosyncratic reaction and a distinct clinical syndrome characterized predominantly by systemic involvement. It can be expected to appear as a treatment-limiting event in approximately 5% of patients. The appearance of clinical symptoms consistent with this syndrome mandates immediate discontinuation of abacavir. Hypersensitivity to abacavir is an absolute contraindication to subsequent treatment with any formulation that includes this agent.

Intensification of stable background therapy with abacavir in antiretroviral therapy experienced patients: 48-week data from a randomized, double-blind trial.

OBJECTIVES: To evaluate antiretroviral efficacy of abacavir (ABC) in antiretroviral-experienced patients, by intensifying current antiretroviral therapy (CART) in patients with stable, detectable plasma HIV-1 RNA. METHODS: Thirty-two European centres recruited HIV-1 positive patients with < or = 36 months of CART experience. Patients were randomized to receive either ABC (300 mg twice daily) plus CART (ABC + CART) or ABC placebo plus CART (CART). We assessed efficacy as measured by plasma HIV-1 RNA and CD4+ cell counts and safety at baseline, weeks 2, 4 and every 4 weeks thereafter until week 48. Protocol-defined criteria enabled patients to switch to open-label ABC from week 8 onwards. RESULTS: Ninety-two patients with a median plasma of 3.66 log10 HIV-1 RNA copies/mL and a median CD4+ cell count of 408 cells/microL were randomized to ABC + CART and 93 patients with a median plasma of 3.52 log10 HIV-1 RNA copies/mL and a median CD4+ cell count of 411 cells/microL were randomized to CART. From weeks 8-48, 11 (12%) patients in the ABC + CART group and 34 (37%) patients in the CART group switched to open-label ABC. At week 48, significantly more patients on ABC + CART (23/92, 25%) than on CART (5/93, 5%) had plasma < or =400 HIV-1 RNA copies/mL (P < 0.001, intent-to-treat switch = failure population). Neither duration of previous nucleoside reverse transcriptase inhibitor treatment (up to 18 months) nor prior lamivudine therapy affected ABC efficacy. In the ABC + CART group, 16/25 (64%) patients with the M184V mutation at baseline had < or = 400 copies/mL or a decrease > or = 1 log10 copies/mL at week 16. More patients (19/46, 41%) with baseline viral load < or = 5000 copies/mL had plasma < 400 HIV-1 RNA copies/mL at 48 weeks than those > 5000 copies/mL (4/44, 9%). CD4+ cell counts increased by 102 cells/microL and 57 cells/microL at week 48 for the ABC + CART and CART groups, respectively (intent-to-treat, switch included). ABC addition had minimal impact on the CART safety profile. CONCLUSIONS: ABC intensification, in CART-experienced patients with low viral loads and limited reverse transcriptase mutations, most of whom had previously been on double-therapy, resulted in a significant and durable plasma HIV-1 reduction and concomitant increase in CD4+ cell count. The presence of M184V at baseline had minimal impact on the efficacy of ABC.

Antiretroviral activity and safety of abacavir in combination with selected HIV-1 protease inhibitors in therapy-naive HIV-1-infected adults.

OBJECTIVE: To assess antiretroviral efficacy and safety of abacavir in combination with selected HIV-1 protease inhibitors. DESIGN: A 48-week, open-label study. MATERIALS AND METHODS: Eighty-two antiretroviral naive HIV-1-infected adults (CD4 cell count > or = 100 cells/mm3, plasma HIV-1 RNA > or = 5,000 copies/ml) were randomly assigned to receive abacavir (300 mg twice daily) in combination with standard doses of one of five protease inhibitors: indinavir, saquinavir soft-gel, ritonavir, nelfinavir or amprenavir. Adults who met protocol-defined switch criteria at or after week 8 could modify their randomized therapy. Antiretroviral activity was assessed by the proportion of subjects with plasma HIV-1 RNA < or = 400 and < or = 50 copies/ml, and by changes in plasma HIV-1 RNA levels and CD4 cell counts. Safety was assessed by monitoring clinical adverse events and laboratory abnormalities. RESULTS: At week 48, the proportion of subjects in the indinavir, saquinavir, ritonavir, nelfinavir and amprenavir groups with plasma HIV-1 RNA < or = 400 copies/ml was 53, 50, 50, 41 and 56%, respectively, and the proportion with HIV-1 RNA < or = 50 copies/ml was 47, 56, 50, 47, and 44%, respectively (by intent-to-treat analysis). Median reductions from baseline in plasma HIV-1 RNA for each group ranged from 1.7 to 2.4 log10 copies/ml. The median CD4 cell count increase from baseline was 195, 131, 116, 136 and 259 cells/mm3 in the indinavir, saquinavir, ritonavir, nelfinavir, and amprenavir groups, respectively. Overall, the most common adverse events attributed to study drugs were diarrhoea, nausea, malaise/fatigue, headache and perioral paresthesia. The frequency of treatment-limiting adverse events did not differ between groups. CONCLUSIONS: Abacavir is safe and effective when used in combination with a protease inhibitor.

Abacavir-lamivudine-zidovudine vs indinavir-lamivudine-zidovudine in antiretroviral-naive HIV-infected adults: A randomized equivalence trial.

CONTEXT: Abacavir, a nucleoside analogue, has demonstrated suppression of human immunodeficiency virus (HIV) replication alone and in combination therapy. However, the role of abacavir in a triple nucleoside combination regimen has not been evaluated against a standard protease inhibitor-containing regimen for initial antiretroviral treatment. OBJECTIVE: To evaluate antiretroviral equivalence and safety of an abacavir-lamivudine-zidovudine regimen compared with an indinavir-lamivudine-zidovudine regimen. DESIGN AND SETTING: A multicenter, phase 3, randomized, double-blind trial with an enrollment period from August 1997 to June 1998, with follow-up through 48 weeks at 73 clinical research units in the United States, Canada, Australia, and Europe. PATIENTS: Five hundred sixty-two antiretroviral-naive, HIV-infected adults with a plasma HIV RNA level of at least 10 000 copies/mL and a CD4 cell count of at least 100 x 10(6)/L. INTERVENTIONS: Patients were stratified by baseline HIV RNA level and randomly assigned to receive a combination tablet containing 150 mg of lamivudine and 300 mg of zidovudine twice daily plus either 300 mg of abacavir twice daily and indinavir placebo or 800 mg of indinavir every 8 hours daily plus abacavir placebo. After 16 weeks, patients with confirmed HIV RNA levels greater than 400 copies/mL were eligible to continue receiving randomized treatment or receive open-label therapy. MAIN OUTCOME MEASURE: Virologic suppression, defined as HIV RNA concentration of 400 copies/mL or less at week 48. RESULTS: The proportion of patients who met the end point of having an HIV RNA level of 400 copies/mL or less at week 48 was equivalent in the abacavir group (51% [133/262]) and in the indinavir group (51% [136/265]) with a treatment difference of -0.6% (95% confidence interval [CI], -9% to 8%). In patients with baseline HIV RNA levels greater than 100 000 copies/mL, the proportion of patients achieving less than 50 copies/mL was greater in the indinavir group than in the abacavir group with 45% (45/100) vs 31% (30/96) and a treatment diference of -14% (95% CI, -27% to 0%). The 2 treatments were comparable with respect to their effects on CD4 cell count. There was no difference between groups in the frequency of treatment-limiting adverse events or laboratory abnormalities. One death in the abacavir group was attributed to hypersensitivity reaction, which occurred following rechallenge with abacavir, approximately 3 weeks after initiating study treatment. CONCLUSIONS: In this study of antiretroviral-naive HIV-infected adults, the triple nucleoside regimen of abacavir-lamivudine-zidovudine was equivalent to the regimen of indinavir-lamivudine-zidovudine in achieving a plasma HIV RNA level of less than 400 copies/mL at 48 weeks.

A randomized, double-blind study of triple nucleoside therapy of abacavir, lamivudine, and zidovudine versus lamivudine and zidovudine in previously treated human immunodeficiency virus type 1-infected children. The CNAA3006 Study Team.

OBJECTIVES: Abacavir (ABC) is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. We compared the efficacy, safety, and tolerability of combination therapy with ABC, lamivudine (3TC), and zidovudine (ZDV) versus 3TC and ZDV in antiretroviral experienced HIV-1-infected children over 48 weeks. METHODS: Two hundred five HIV-1-infected children who had received previous antiretroviral therapy and had CD4(+) cell counts >/=100 cells/mm(3) were stratified by age and by previous treatment. Participants were randomly assigned to receive ABC (8 mg/kg twice daily [BID]) plus 3TC (4 mg/kg BID) and ZDV (180 mg/m(2) BID; ABC/3TC/ZDV group) or ABC placebo plus 3TC (4 mg/kg BID) and ZDV (180 mg/m(2); 3TC/ZDV group). Participants who met a protocol-defined switch criteria (plasma HIV-1 RNA >0.5 log(10) copies/mL above baseline at week 8 or >10 000 copies/mL after week 16) had the option to switch to open-label ABC plus any antiretroviral combination or continue randomized therapy or withdraw from the study. RESULTS: The Kaplan-Meier estimates (95% confidence interval) of the proportion of participants who maintained HIV-1 RNA levels 10 000 copies/mL, a significantly higher proportion of participants in the ABC/3TC/ZDV group had HIV-1 RNA

Cellular restoration in HIV infected persons treated with abacavir and a protease inhibitor: age inversely predicts naive CD4 cell count increase.

OBJECTIVE: To characterize early and later indices of cellular restoration among HIV-1 infected persons treated with abacavir and one protease inhibitor and to identify predictors of CD4 cell increases. METHODS: Flow-cytometric analyses of lymphocyte phenotypes among 71 antiretroviral treatment naive adults in a 48 week treatment trial. RESULTS: During the first 4 weeks of therapy, increases in naive and memory CD4 cells and in B cells were seen; naive CD8 cells increased while CD8 cells remained stable as memory CD8 cells decreased. During the second phase total CD4 and naive CD4 and CD8 cells increased while total CD8 and memory CD8 cells decreased. The numbers of CD4 cells that expressed CD28 increased from a median of 308 x 10(6)/l at baseline to 477 x 10(6)/l at week 48. Higher baseline plasma HIV-1 RNA levels predicted the magnitude of early CD4 (r = 0.35; P = 0.01), memory CD4 (r = 0.38; P = 0.001) and CD28 CD4 cell (r = 0.29; P = 0.01) restoration but was not related to second phase changes. Younger age predicted a greater second phase (but not first phase) increase in naive CD4 cells (r = -0.31; P = 0.03). CONCLUSIONS: Higher baseline levels of HIV-1 replication determine the magnitude of first phase CD4 cell increases after suppression of HIV-1 replication. Second phase (primarily naive) CD4 cell increases are not related to HIV-1 replication but are inversely relate to age suggesting that thymic potential is a major determinant of long term cellular restoration in HIV-1 infected persons receiving antiretroviral therapy.

The role of abacavir (ABC, 1592) in antiretroviral therapy-experienced patients: results from a randomized, double-blind, trial. CNA3002 European Study Team.

OBJECTIVE: To compare the antiviral activity of abacavir (ABC) with stable background therapy (SBG) and SBG alone in antiretroviral therapy-experienced subjects as demonstrated by the proportion of subjects with plasma HIV-1 RNA < or = 400 copies/ml, plasma HIV-1 RNA and CD4 cell count profiles, and safety and tolerance of the two regimens over 16 weeks. DESIGN: One-hundred and eighty-five HIV-1 infected adults, with CD4 cell counts > or = 100 x 10(6)/l and plasma HIV-1 RNA of 400-50,000 copies/ml and who had received SBG therapy for at least 12 weeks, were randomized to receive ABC (300 mg twice daily) or placebo in a double blind, multi-centre study. METHODS: Antiretroviral activity was assessed by measuring changes in plasma HIV-1 RNA levels and CD4 cell counts. Genotypic and phenotypic resistance was determined at baseline and week 16. Evaluation of safety and tolerance was based on clinical adverse events and laboratory analyses. RESULTS: At week 16 significantly more subjects receiving ABC + SBG had plasma HIV-1 RNA < or = 400 copies/ml (36/92, 39%) than subjects receiving SBG alone (7/93, 8%; P < 0.001). A similar response was observed in both the lamivudine naive and lamivudine-experienced subjects. The presence of the M184V mutation did not preclude an antiviral response to ABC; 73% of subjects with the M184V mutation alone experienced a > or = 1.0 log10 copies/ml reduction in plasma HIV-1 RNA or had a value of < or = 400 copies/ml by week 16. CONCLUSIONS: ABC was generally well tolerated and exerted significant antiviral effect when added to combination antiretroviral therapy over 16 weeks.

HIV-1 reverse transcriptase (RT) genotype and susceptibility to RT inhibitors during abacavir monotherapy and combination therapy.

OBJECTIVE: To examine changes in HIV-1 susceptibility (genotype and phenotype) during an initial abacavir monotherapy phase followed by the addition of zidovudine and lamivudine. DESIGN: Sixty HIV-1 infected, antiretroviral therapy-naive subjects were randomized to receive 100, 300 or 600 mg abacavir twice daily. Subjects completing 24 weeks of randomized therapy or meeting a protocol defined switch criterion could switch to open label abacavir/zidovudine/lamivudine. METHODS: Plasma HIV-1 reverse transcriptase was genotyped at baseline, week 12, and at the last time point on ABC monotherapy. Drug susceptibility was analysed at baseline and on subsequent samples with sufficient HIV-1 RNA levels using the recombinant virus assay. Virological responses (week 24) were correlated to week 24 genotypes. RESULTS: Mutant viruses were not detected before week 12 with the exception of one subject. At the latest time point on abacavir monotherapy (range, weeks 6-48), 21 out of 43 subjects harboured virus with resistance conferring mutations including single, double and triple combinations of K65R, L74V, Y115F and M184V. The most common mutational pattern was L74V + M184V (11/21 cases). Twenty of the 21 subjects with isolates containing abacavir-associated mutations reached week 48, and upon addition of lamivudine/zidovudiine, 16 out of 20 (80%) had week 48 plasma HIV-1 -RNA below 400 copies/ml. At week 48, 16 out of 46 genotypes were obtained; one of these was wild-type; 15 contained M184V either alone, in combination with K65R and/or L74V and/or Y115F or with thymidine analogue-associated mutations. Week 48 viral load levels for these 15 subjects was low (median 3.43 log10 copies/ml or -1.99 log10 copies reduction from baseline). Genotype correlated well with phenotypic resistance to ABC; four samples with three abacavir-associated mutations had high level abacavir resistance (> 8-fold) and six samples with two or three mutations showed intermediate (4-8-fold) resistance. All samples with single mutations retained full ABC susceptibility. CONCLUSIONS: Resistance conferring mutations to abacavir were relatively slow to develop during the monotherapy phase, and did not preclude durable efficacy of abacavir/lamivudine/zidovudine up to 48 weeks.

A dose-ranging study to evaluate the safety and efficacy of abacavir alone or in combination with zidovudine and lamivudine in antiretroviral treatment-naive subjects.

OBJECTIVE: To compare antiretroviral efficacy, safety and tolerance of three dosing regimens of the novel nucleoside reverse transcriptase inhibitor, abacavir (1592U89) over 24 weeks and its efficacy in open-label combination with zidovudine and lamivudine. DESIGN: Sixty HIV-1-infected antiretroviral therapy naive subjects (entry criteria; CD4+ cell count > or = 100 cells/mm(3), plasma HIV-1 RNA > or = 30 000 copies/ml), randomized into 20 subjects per cohort received 100, 300 or 600 mg abacavir twice daily. Subjects successfully completing 24 weeks' randomized therapy could switch to open label therapy (abacavir, zidovudine, lamivudine at 300, 300 and 150 mg twice daily, respectively) for a further 24 weeks of studly, as could subjects meeting one or more switch criteria. METHODS: Subjects were assessed for antiretroviral activity by measuring changes in plasma HIV-1 RNA load and CD4+ cell counts. Evaluation of safety and tolerance was based on clinical adverse events and laboratory analyses. RESULTS: At week 4, subjects receiving 300 or 600 mg abacavir twice daily had greater reductions in plasma HIV-1 RNA (median changes -1.55 and -1.61 log10) copies/ml, respectively); differences (P = 0.007 and P < or = 0.001, respectively) than subjects receiving 100 mg abacavir twice daily (median change, -0.63 log10 copies/ml). Differences between the 300 and 600 mg twice daily groups were not clinically or statistically significant. At 24 weeks, analysis showed a median change in plasma HIV-1 RNA of -0.70 and -1.30 log10 copies/ml in the 300 and 600 mg twice daily groups, respectively. During the open label phase in which zidovudine/lamivudine was added to 300 mg abacavir twice daily, a further median reduction in plasma HIV-1 RNA of 1.74 log10 copies/ml was seen. At 48 weeks pooled data from all abacavir-treated subjects showed a sustained reduction in plasma HIV-1 RNA of 2.8 log10) copies/ml; 65% and 43% of subjects had < or = 400 and < or = 50 HIV-1 RNA copies/ml, respectively, and a further median increase of 111 CD4+ cells/mm3 were seen. Abacavir was generally well tolerated with few clinically significant adverse events. Two subjects (3.3%) developed hypersensitivity reactions to abacavir. There were no differences between the groups with regard to serious adverse events. CONCLUSIONS: In terms of antiretroviral therapy naive subjects, treatment with 300 or 600 mg abacavir twice daily was statistically superior to a 100 mg twice daily dose at 4 weeks. Combinations therapy containing abacavir-zidovudine-lamivudine was a highly effective antiretroviral regimen, resulting in substantial reductions in plasma HIV-1 RNA which may be comparable to combinations containing protease inhibitors. Abacavir was generally tolerated.