Assessment of blood clot formation and platelet receptor function ex vivo in patients with primary Sjogren's syndrome.

OBJECTIVES: Primary Sjögren's syndrome (pSS) shares clinical features and pathogenetic mechanisms with systemic lupus erythematosus (SLE). SLE is associated with an increased thromboembolic risk; however, it is unclear whether pSS patients are susceptible to thromboembolic diseases. In this study, we examined ex vivo blood clot formation (clot strength, rates of clot formation and lysis) in pSS using thromboelastography (TEG) and platelet aggregation to common agonists using multiple electrode aggregometry (MEA). We also investigated the relationship between TEG/MEA parameters and clinical/laboratory features of pSS. DESIGN: Case control. SETTING: Secondary care, single centre. PARTICIPANTS: 34 pSS patients, 11 SLE patients and 13 healthy volunteers (all women) entered and completed the study. PRIMARY OUTCOMES: TEG and MEA parameters between three subject groups. SECONDARY OUTCOMES: The relationships between TEG/MEA and clinical/laboratory parameters analysed using bivariate correlation analysis with corrections for multiple testing. RESULTS: All TEG and MEA parameters were similar for the three subject groups. After corrections for multiple testing, interleukin (IL)-1α and Macrophage inflammatory proteins (MIP)-1α remain correlated inversely with clot strength (r=-0.686, p=0.024 and r=-0.730, p=0.012, respectively) and overall coagulability (r=-0.640, p=0.048 and r=-0.648, p=0.048). Stepwise regression analysis revealed that several cytokines such as MIP-1α, IL-17a, IL-1α and Interferon (IFN)-γ may be key predictors of clot strength and overall coagulability in pSS. CONCLUSIONS: Clot kinetics and platelet receptor function are normal in pSS. Several cytokines correlate with clot strength and overall coagulability in pSS.

Pharmacokinetics of the hypoxic cell cytotoxic agent tirapazamine and its major bioreductive metabolites in mice and humans: retrospective analysis of a pharmacokinetically guided dose-escalation strategy in a phase I trial.

Tirapazamine (3-amino-1,2,4-benzotriazine-1,4-di-N-oxide; SR 259075) is a selective hypoxic cell cytotoxic agent that is bioreductively activated in tumours to a reactive-drug free radical. Preclinically the agent has been shown to possess additive and synergistic anti-tumour activity in combination with radiotherapy and chemotherapy regimens. In the present study the pharmacokinetics and metabolism of tirapazamine were investigated in mice and patients as part of pre-clinical and phase I investigations. The objectives of this work were twofold; firstly, to evaluate retrospectively the utility of a pharmacokinetically guided dose-escalation (PGDE) strategy for tirapazamine, and secondly, to investigate if pharmacologically relevant plasma concentrations could be achieved at tolerable doses. Pharmacokinetic studies for PGDE were conducted in mice at four dose levels ranging from one-tenth of the LD10 to the LD50. The AUC at the LD10 (2932 micrograms ml-1 min) was used to determine a target AUC value of 1173 micrograms ml-1 min (equivalent to 40% of the mouse LD10 AUC) for clinical studies. A phase I study to investigate the tolerance of a single i.v. infusion of tirapazamine (once every 3 weeks) was initiated with close pharmacokinetic monitoring. The starting dose (36 mg/m2) was based on toxicity data obtained in the mouse, rat and dog. Doses were escalated by increases in the volume and duration of infusion. A retrospective analysis of the pharmacokinetic and toxicity data was then made to determine the utility of a PGDE approach. The drug exhibited a steep dose-lethality relationship in mice (LD10 294 mg/m2, LD50 303 mg/m2). The major gross toxicities were body-weight loss (15-20%), pilo-erection and hypoactivity at all dose levels. Sporadic ptosis and conjunctivitis were observed at doses of > 300 mg/m2. The plasma elimination of tirapazamine fitted a monoexponential open model, with rapid elimination from the plasma (t1/2 = 36 +/- 0.65 min) occurring at the LD10 dose of 294 mg/m2. A 10.3-fold increase in dose resulted in a 25.0-fold increase in AUC. Clinically, doses were escalated over the range of 36-450 mg/m2. Ototoxicity (tinnitus and reversible hearing loss) was dose-limiting at 450 mg/m2 and the MTD was 390 mg/m2 for this schedule. Pharmacokinetic analyses in patients revealed that the elimination of tirapazamine in patients was generally bi-phasic, with low inter-patient variability being found in clearance. A 12.5-fold increase in dose resulted in a 19.0-fold increase in AUC. There was good quantitative agreement in metabolite formation between mice and humans with respect to the two- and four-electron bioreductive metabolites. AUC values recorded for tirapazamine at the MTD of 390 mg/m2 (range 1035-1611 micrograms ml-1 min) were similar to the target AUC in mice. Importantly, these levels are consistent with the levels required for radiation-dose enhancement and effective combination with cisplatin in mice. Given (a) the similarities in plasma pharmacokinetics and metabolism observed at the target AUC/MTD in mice, rats, dogs and humans, (b) the similar degree of plasma protein binding seen between species and (c) the relatively low inter-patient variability noted in drug clearance, a successful PGDE approach should have been feasible. The results also indicate that potentially therapeutic levels of tirapazamine are achievable in patients at tolerable doses.

Dose regimen adjustment for milrinone in congestive heart failure patients with moderate and severe renal failure.

This study was designed to test a proposed dose modification for intravenous milrinone in congestive heart failure patients (CHF, NYHA I-II) with either moderate or severe renal impairment. All the patients were administered an intravenous loading dose of drug at 50 micrograms kg-1 over 10 min. This was followed by an 18 h maintenance infusion of milrinone at 0.45 or 0.35 micrograms kg-1 min-1 for the moderate (chromium-EDTA clearance of 31-75 mL min-1, n = 10) and severe renally impaired subjects (chromium-EDTA of clearance 10-30 mL min-1, n = 11), respectively. Plasma and urine samples were collected for up to 34 h and analysed for parent drug by validated HPLC methods. The mean (+/- s.d.) steady-state plasma concentrations of milrinone were within the therapeutic range (100-300 ng mL-1) for both groups, with values of 239 +/- 71 ng mL-1 and 269 +/- 32 ng mL-1 for the moderate and severe patients, respectively. No statistical differences were observed between the steady-state values for the two groups. With the exception of two patients per group, individual steady-state levels were also within the therapeutic range. Those outside the nominal range showed steady-state levels, ranging between 308 and 353 ng mL-1, that were not associated with any serious adverse events.(ABSTRACT TRUNCATED AT 250 WORDS)