Venom Concentrations and Clotting Factor Levels in a Prospective Cohort of Russell's Viper Bites with Coagulopathy.

BACKGROUND: Russell's viper envenoming is a major problem in South Asia and causes venom induced consumption coagulopathy. This study aimed to investigate the kinetics and dynamics of venom and clotting function in Russell's viper envenoming. METHODOLOGY/PRINCIPAL FINDINGS: In a prospective cohort of 146 patients with Russell's viper envenoming, we measured venom concentrations, international normalised ratio [INR], prothrombin time (PT), activated partial thromboplastin time (aPTT), coagulation factors I, II, V, VII, VIII, IX and X, and von Willebrand factor antigen. The median age was 39 y (16-82 y) and 111 were male. The median peak INR was 6.8 (interquartile range [IQR]: 3.7 to >13), associated with low fibrinogen [median,<0.01 g/L; IQR: <0.01-0.9 g/L), low factor V levels [median,<5%; IQR: <5-4%], low factor VIII levels [median,40%; IQR: 12-79%] and low factor X levels [median, 48%; IQR: 29-67%]. There were smaller reductions in factors II, IX and VII over time. All factors recovered over 48 h post-antivenom. The median INR remained >3 at 6 h post-antivenom but had reduced to <2, by 24 h. The aPTT had also returned to close to normal (<50 sec) at 24 h. Factor VII, VIII and IX levels were unusually high pre-antivenom, median peak concentrations of 393%, 307% and 468% respectively. Pre-antivenom venom concentrations and the INR (r = 0.20, p = 0.02) and aPTT (r = 0.19, p = 0.03) were correlated (non-parametric Spearman analysis). CONCLUSIONS: Russell's viper coagulopathy results in prolonged aPTT, INR, low fibrinogen, factors V, VIII and X which recover over 48 h. Severity of clotting abnormalities was associated with venom concentrations.

Population Pharmacokinetics of an Indian F(ab')2 Snake Antivenom in Patients with Russell's Viper (Daboia russelii) Bites.

BACKGROUND: There is limited information on antivenom pharmacokinetics. This study aimed to investigate the pharmacokinetics of an Indian snake antivenom in humans with Russell's viper bites. METHODS/PRINCIPAL FINDINGS: Patient data and serial blood samples were collected from patients with Russell's viper (Daboia russelii) envenoming in Sri Lanka. All patients received Indian F(ab')2 snake antivenom manufactured by VINS Bioproducts Ltd. Antivenom concentrations were measured with sandwich enzyme immunoassays. Timed antivenom concentrations were analysed using MONOLIXvs4.2. One, two and three compartment models with zero order input and first order elimination kinetics were assessed. Models were parameterized with clearance (CL), intercompartmental clearance (Q), central compartment volume (V) and peripheral compartment volume (VP). Between-subject-variability (BSV) on relative bioavailability (F) was included to account for dose variations. Covariates effects (age, sex, weight, antivenom batch, pre-antivenom concentrations) were explored by visual inspection and in model building. There were 75 patients, median age 57 years (40-70 y) and 64 (85%) were male. 411 antivenom concentration data points were analysed. A two compartment model with zero order input, linear elimination kinetics and a combined error model best described the data. Inclusion of BSV on F and weight as a covariate on V improved the model. Inclusion of pre-antivenom concentrations or different batches on BSV of F did not. Final model parameter estimates were CL,0.078 L h(-1), V,2.2L, Q,0.178 L h(-1) and VP,8.33L. The median half-life of distribution was 4.6 h (10-90%iles:2.6-7.1 h) and half-life of elimination, 140 h (10th-90th percentilesx:95-223h). CONCLUSION: Indian F(ab')2 snake antivenom displayed biexponential disposition pharmacokinetics, with a rapid distribution half-life and more prolonged elimination half-life.

Detection of venom after antivenom is not associated with persistent coagulopathy in a prospective cohort of Russell's viper (Daboia russelii) envenomings.

BACKGROUND: Venom recurrence or persistence in the circulation after antivenom treatment has been documented many times in viper envenoming. However, it has not been associated with clinical recurrence for many snakes, including Russell's viper (Daboia spp.). We compare the recovery of coagulopathy to the recurrence or persistence of venom in patients with Russell's viper envenoming. METHODOLOGY/PRINCIPAL FINDINGS: The study included patients with Russell's viper (D. russelii) envenoming presenting over a 30 month period who had Russell's viper venom detected by enzyme immunoassay. Demographics, information on the snake bite, and clinical effects were collected for all patients. All patients had serum collected for venom specific enzyme immunoassay and citrate plasma to measure fibrinogen levels and prothrombin time (international normalised ratio; INR). Patients with venom recurrence/persistence were compared to those with no detectable recurrence of venom. There were 55 patients with confirmed Russell's viper envenoming and coagulopathy with low fibrinogen concentrations: 31 with venom recurrence/persistence, and 24 with no venom detected post-antivenom. Fibrinogen concentrations increased and INR decreased after antivenom in both the recurrence and non-recurrence patients. Clinical features, laboratory parameters, antivenom dose and length of hospital were similar for both groups. Pre-antivenom venom concentrations were higher in patients with venom recurrence/persistence with a median venom concentration of 385 ng/mL (16-1521 ng/mL) compared to 128 ng/mL (14-1492 ng/mL; p = 0.008). CONCLUSION: Recurrence of Russell's viper venom was not associated with a recurrence of coagulopathy and length of hospital stay. Further work is required to determine if the detection of venom recurrence is due to the venom specific enzyme immunoassay detecting both venom-antivenom complexes as well as free venom.

Immune response to snake envenoming and treatment with antivenom; complement activation, cytokine production and mast cell degranulation.

BACKGROUND: Snake bite is one of the most neglected public health issues in poor rural communities worldwide. In addition to the clinical effects of envenoming, treatment with antivenom frequently causes serious adverse reactions, including hypersensitivity reactions (including anaphylaxis) and pyrogenic reactions. We aimed to investigate the immune responses to Sri Lankan snake envenoming (predominantly by Russell's viper) and antivenom treatment. METHODOLOGY/PRINCIPAL FINDINGS: Plasma concentrations of Interleukin (IL)-6, IL-10, tumor necrosis factor α (TNFα), soluble TNF receptor I (sTNFRI), anaphylatoxins (C3a, C4a, C5a; markers of complement activation), mast cell tryptase (MCT), and histamine were measured in 120 Sri Lankan snakebite victims, both before and after treatment with antivenom. Immune mediator concentrations were correlated with envenoming features and the severity of antivenom-induced reactions including anaphylaxis. Envenoming was associated with complement activation and increased cytokine concentrations prior to antivenom administration, which correlated with non-specific systemic symptoms of envenoming but not with coagulopathy or neurotoxicity. Typical hypersensitivity reactions to antivenom occurred in 77/120 patients (64%), satisfying criteria for a diagnosis of anaphylaxis in 57/120 (48%). Pyrogenic reactions were observed in 32/120 patients (27%). All patients had further elevations in cytokine concentrations, but not complement activation, after the administration of antivenom, whether a reaction was noted to occur or not. Patients with anaphylaxis had significantly elevated concentrations of MCT and histamine. CONCLUSIONS/SIGNIFICANCE: We have demonstrated that Sri Lankan snake envenoming is characterized by significant complement activation and release of inflammatory mediators. Antivenom treatment further enhances the release of inflammatory mediators in all patients, with anaphylactic reactions characterised by high levels of mast cell degranulation but not further complement activation. Anaphylaxis is probably triggered by non allergen-specific activation of mast cells and may be related to the quality of available antivenom preparations, as well as a priming effect from the immune response to the venom itself.

A randomised controlled trial of two infusion rates to decrease reactions to antivenom.

BACKGROUND: Snake envenoming is a major clinical problem in Sri Lanka, with an estimated 40,000 bites annually. Antivenom is only available from India and there is a high rate of systemic hypersensitivity reactions. This study aimed to investigate whether the rate of infusion of antivenom reduced the frequency of severe systemic hypersensitivity reactions. METHODS AND FINDINGS: This was a randomized comparison trial of two infusion rates of antivenom for treatment of non-pregnant adult patients (>14 y) with snake envenoming in Sri Lanka. Snake identification was by patient or hospital examination of dead snakes when available and confirmed by enzyme-immunoassay for Russell's viper envenoming. Patients were blindly allocated in a 11 randomisation schedule to receive antivenom either as a 20 minute infusion (rapid) or a two hour infusion (slow). The primary outcome was the proportion with severe systemic hypersensitivity reactions (grade 3 by Brown grading system) within 4 hours of commencement of antivenom. Secondary outcomes included the proportion with mild/moderate hypersensitivity reactions and repeat antivenom doses. Of 1004 patients with suspected snakebites, 247 patients received antivenom. 49 patients were excluded or not recruited leaving 104 patients allocated to the rapid antivenom infusion and 94 to the slow antivenom infusion. The median actual duration of antivenom infusion in the rapid group was 20 min (Interquartile range[IQR]:20-25 min) versus 120 min (IQR:75-120 min) in the slow group. There was no difference in severe systemic hypersensitivity reactions between those given rapid and slow infusions (32% vs. 35%; difference 3%; 95%CI:-10% to +17%;p = 0.65). The frequency of mild/moderate reactions was also similar. Similar numbers of patients in each arm received further doses of antivenom (30/104 vs. 23/94). CONCLUSIONS: A slower infusion rate would not reduce the rate of severe systemic hypersensitivity reactions from current high rates. More effort should be put into developing better quality antivenoms. TRIAL REGISTRATION: www.slctr.lk SLCTR/2007/005.

A phase II clinical trial to assess the safety of clonidine in acute organophosphorus pesticide poisoning.

BACKGROUND: An estimated 2-3 million people are acutely poisoned by organophosphorus pesticides each year, mostly in the developing world. There is a pressing need for new affordable antidotes and clonidine has been shown to be effective in animal studies. Our aim was to determine the safety of clonidine given as an antidote in adult patients presenting with signs or symptoms of acute organophosphate ingestion. METHODS: This study was a dose finding, open-label, multicentre, phase II trial. Forty eight patients with acute organophosphate poisoning were randomized to receive either clonidine or placebo: Four to receive placebo and twelve to receive clonidine at each dose level. The first dose level was an initial loading dose of 0.15 mg followed by an infusion of 0.5 mg of clonidine over 24 hours. The initial loading dose was increased to 0.3 mg, 0.45 and 0.6 mg. at all dosing levels however the subsequent infusion remained at 0.5 mg of clonidine over 24 hours. RESULTS: The baseline characteristics of both groups were similar. The trial was stopped after completion of the 3rd dosing level. At the 1st and 2nd dosing level there were no reported adverse drug reactions. At the 3rd dosing level 5 patients (42%) developed significant hypotension during clonidine treatment that responded to intravenous fluids. There were no statistical differences in ventilation rate, pre and post GCS, and mortality rates over all levels. CONCLUSION: Our findings suggest use of moderate doses of clonidine in acute organophosphate poisoning can be used without causing frequent clinical problems but that higher doses are associated with a high incidence of hypotension requiring intervention. Further studies are needed to study the efficacy of clonidine as an antidote in organophosphate poisoning.