The authors review the basic pharmacology and potential for adverse drug-drug interactions (DDIs) of bosentan and ambrisentan, the 2 endothelin receptor antagonists currently approved for pulmonary arterial hypertension (PAH) treatment. Bosentan, an endothelin (ET) receptor-type ET(A) and ET(B) antagonist, is metabolized to active metabolites by and an inducer of cytochrome P450 (CYP)2C9 and CYP3A. Ambrisentan, a selective ET(A) receptor antagonist, is metabolized primarily by uridine 5'diphosphate glucuronosyltransferases (UGTs) 1A9S, 2B7S, and 1A3S and, to a lesser extent, by CYP3A and CYP2C19. Drug interactions observed with bosentan DDI studies have demonstrated a potential for significant clinical implications during PAH management: bosentan is contraindicated with cyclosporine A and glyburide, and additional monitoring/dose adjustments are required when coadministered with hormonal contraceptives, simvastatin, lopinavir/ritonavir, and rifampicin. As bosentan carries a boxed warning regarding risks of liver injury and showed dose-dependant increases in serum aminotransferase abnormalities, drug interactions that increase bosentan exposure are of particular clinical concern. Ambrisentan DDI studies performed to date have shown only one clinically relevant DDI, an interaction with cyclosporine A that requires ambrisentan dose reduction. As the treatment of PAH moves toward multimodal combination therapy, scrutiny should be placed on ensuring that drug combinations achieve maximal clinical benefit while minimizing side effects.
Renal transplant recipients exhibit variability in mycophenolic acid (MPA) and MPA glucuronide (MPAG) pharmacokinetics, which are influenced by clinical and demographic factors. Racial influence on MPA and MPAG pharmacokinetics was investigated in 53 patients: 17 African American males, 22 Caucasian males, and 14 females receiving mycophenolate mofetil (MMF) and cyclosporine. A 12-hour steady-state pharmacokinetic study was conducted. Enterohepatic circulation of MPA was characterized by a second plasma concentration peak and was included in a novel statistical model with MPAG. MPA clearance in African American males was 26.5 ± 14.4 L/h versus 17.9 ± 6.1 L/h in Caucasian males (P = .035) and 16.1 ± 4.6 L/h in Caucasian females (P = .024) with no difference noted in MPA troughs. Enterohepatic circulation occurred less frequently in African American males (23%) compared with Caucasian males (42%) and Caucasian females (50%) (P > .05). Cyclosporine exposure was correlated with MPA and MPAG pharmacokinetics, whereas creatinine clearance influenced MPAG pharmacokinetics. A racial difference was noted with more rapid MPA clearance in African American males compared with Caucasians. The results support differential MPA dosing and the role of therapeutic drug monitoring in addition to considering the influence of renal function and concurrent immunosuppressives on MPA and MPAG pharmacokinetics.
GS-9667, a new selective, partial agonist of the A(1) adenosine receptor (AR), may represent an effective therapy for Type 2 diabetes (T2DM) and dyslipidemia via lowering of free fatty acids (FFA). The objectives of the studies were to evaluate the effects of single and multiple doses of GS-9667 on plasma FFA concentrations, its pharmacokinetics (PK) and safety/tolerability. Two studies were conducted. In the single ascending dose study, healthy, non-obese, and obese subjects received a single oral dose of GS-9667 (30-1,800 mg). In the multiple, ascending dose study, healthy, obese subjects received GS-9667 (600-2,400 mg QD, 1,200 mg BID, or 600 mg QID) for 14 days. Blood and urine samples were collected for lipid profiling and PK analyses. The ECG, vital signs, and subject tolerability were monitored. Doses of GS-9667 ≥300 mg caused dose-dependent reductions in FFA levels that were reproducible over 14 days without evidence of desensitization or rebound. All doses were well tolerated. GS-9667 was rapidly absorbed and distributed; Steady-state concentrations were achieved within 3-5 days. The A(1) AR partial agonist GS-9667 reduced plasma FFA, exhibited linear kinetics, and was well-tolerated in healthy non-obese and obese subjects.
Systemic candidiasis causes significant mortality in patients despite amphotericin B (AMB) therapy. Mycograb C28Y variant, a human recombinant antibody fragment to heat shock protein 90, is closely related to Mycograb, which showed a survival advantage in combination with AMB in a phase III human trial. The Mycograb C28Y variant could potentially increase the antifungal effect of AMB. In our study, the interaction between AMB-desoxycholate (DAMB) and the Mycograb C28Y variant was characterized in vitro by using a checkerboard method. Quantitative cultures of kidneys, livers, and spleens of neutropenic mice with systemic Candida albicans infections were used to assess the in vivo interaction between 1.4 mg/kg of body weight/day of DAMB and 0.15, 1.5, and 15 mg/kg/day of the Mycograb C28Y variant after 1, 3, and 5 days of therapy. DAMB and Mycograb C28Y variant monotherapies, vehicle, and a no-treatment arm served as controls. Also, singleand multidose pharmacokinetics for the Mycograb C28Y variant were determined. Indifference or synergy between DAMB and the Mycograb C28Y variant was seen in two trials by the checkerboard method. The pharmacokinetics of the Mycograb C28Y variant was best described by a 2-compartment model with a median serum t 1/2␣ of ϳ0.198 h and a t 1/2 of ϳ1.77 h. In mice, DAMB together with the Mycograb C28Y variant was no more effective than AMB alone (P > 0.05 by analysis of variance). The Mycograb C28Y variant alone had no antifungal activity. We therefore conclude that the Mycograb C28Y variant in combination with DAMB offered no benefit over DAMB monotherapy in a neutropenic murine model of systemic candidiasis.Despite antifungal mono-and combination therapies with azoles, echinocandins, and polyene formulations, the mortality associated with systemic candida infections in humans remains above 29% (3,8,9,(11)(12)(13). Studies have shown that the attributable mortality associated with humans with systemic candidal infections in intensive care units of hospitals can exceed 49% (2, 15). Thus, there is a need to identify adjunct compounds that will improve the efficacy of current antifungal drug therapies.Heat shock protein 90 (HSP90) is found in the cell wall of Candida species and other fungal pathogens (5). In fungi, HSP90 functions as a molecular chaperone that guides the normal folding, intracellular disposition, and proteolytic turnover of many of the key regulators of cell growth (4). HSP90 is critical to the survival of fungi (14). Further, HSP90 is believed to be involved in the development of resistance to antifungal drugs (5). Observational studies found that patients with high titers of serum antibodies against HSP90 of Candida species had a higher probability for survival. Falling or nondetectable serum antibody levels were associated with a higher probability of death in subjects with candidemia (6, 7).Mycograb is a 28-kDa human recombinant antibody fragment that binds to the HSP90 of fungi (5). Mycograb consists of the antigen-binding domains of antibody heavy and light chain...
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