Comparison of the hemodynamic effects of hydroxocobalamin and cobalt edetate at equipotent cyanide antidotal doses in conscious dogs

High-Dose Vitamin B12 in Vasodilatory Shock: A Narrative Review

Vasodilatory shock, as observed in postoperative states and sepsis, is hallmarked by low systemic vascular resistance and low blood pressure compensated by increased cardiac output. Gasotransmitters, such as nitric oxide and hydrogen sulfide, are implicated in the development and perpetuation of vasodilatory shock. Established therapies do not target these physiologic drivers of vasodilation. Due to their nontoxic and pleotropic effects, micronutrients are being used as rescue therapy in postoperative vasoplegia and septic shock. Here, we outline the pathophysiology of vasodilatory shock, describe the rationale for vitamin B12 (hydroxocobalamin) in vasodilatory shock, and identify literature evaluating its use in vasoplegic states.

Cyanide: critical issues in diagnosis and treatment

The concern of a terrorist attack using cyanide, as well as the gradual awareness of cyanide poisoning in fire victims, has resulted in a renewed interest in the diagnosis and treatment of cyanide poisoning. The formerly academic presentation of cyanide poisoning must be replaced by more useful knowledge, which will allow emergency physicians and rescue workers to strongly suspect cyanide poisoning at the scene. Human cyanide poisonings may result from exposure to cyanide, its salts, or cyanogenic compounds, while residential fires are the most common condition of exposure. In fire victims, recognition of the cyanide toxidrome has been hampered by the short half-life in blood and poor stability of cyanide. In contrast, carboxyhemoglobin, as a marker of carbon monoxide poisoning, is easily measured and long-lasting. No evidence supports the assumption of the arbitrary fixed lethal thresholds of 50% for carboxyhemoglobin, and 3 mg/L for cyanide, in fire victims. Preliminary data, drawn when comparing pure carbon monoxide and pure cyanide poisonings, suggest that a cyanide toxidrome can be defined considering signs and symptoms induced by cyanide and carbon monoxide, respectively. Prospective studies in fire victims may provide value in clarifying signs and symptoms related to both toxicants. Cyanide can induce a lifethreatening poisoning from which a full recovery is possible. A number of experimentally efficient antidotes to cyanide exist, whose clinical use has been hampered due to serious side effects. The availability of potentially safer antidotes unveils the possibility of their value as first-line treatment, even in a complex clinical situation, where diagnosis is rapid and presumptive.

The efficacy and adverse effects of dicobalt edetate in cyanide poisoning

INTRODUCTION

Dicobalt edetate is one of a number of cobalt compounds that have been studied in the treatment of cyanide poisoning, their efficacy being based upon the fact that cyanide combines with cobalt to form relatively non-toxic complexes. Inorganic cobalt salts are quite toxic (cyanide and cobalt antagonise one another's toxicity) and complexes such as dicobalt edetate were studied with the aim of identifying compounds that were less acutely toxic, but which retained the antidotal properties of cobalt salts. The proprietary preparation, Kelocyanor™, contains free cobalt and glucose as well as dicobalt edetate.

OBJECTIVE

The aim of this study was to evaluate the published evidence for the efficacy and adverse effects of dicobalt edetate.

METHODS

A Pubmed search was undertaken for the period 1961-September 2015. The search terms were "dicobalt edetate", "cobalt edetate" and "Kelocyanor", which produced 24 relevant citations. A review of the references in four relevant books (L'intoxication cyanhydrique et son traitement, Clinical and Experimental Toxicology of Cyanides, Antidotes for Poisoning by Cyanide and Antidotes) produced three further relevant papers, making a total of 27 papers. Efficacy of dicobalt edetate: There is evidence from animal pharmacodynamic studies that dicobalt edetate is an effective cyanide antidote in experimental animals. Some 39 cases of human poisoning treated with dicobalt edetate have been reported, but in only nine cases were blood cyanide concentrations measured, although administration of dicobalt edetate procured survival in four of the seven patients with concentrations in the lethal range (>3.0 mg/L). It is unlikely that death in any of the adequately documented fatal cases was attributable to treatment failure with dicobalt edetate, as it is probable that they all had suffered anoxic brain damage before treatment could be initiated. Furthermore, in one case, acute gold toxicity contributed substantially to death. Adverse effects of dicobalt edetate: Adverse effects reported have included hypertension, tachycardia, nausea, retrosternal pain, sweating, palpebral, facial and laryngeal oedema, vomiting, urticaria and/or a feeling of impending doom. Such effects appear to be more prevalent where the antidote has been administered without evidence of substantial systemic poisoning or where other antidotes have been used which might have been expected also to combine with cyanide. Although the adverse effects observed were doubtless unpleasant, and some were severe, no fatal reactions were found.

CONCLUSIONS

Dicobalt edetate is an effective cyanide antidote when given to patients with systemic cyanide poisoning, but it has the potential to give rise to adverse reactions, particularly when administered in the absence of intoxication.

Hydroxocobalamin in cyanide poisoning

INTRODUCTION

On theoretical grounds, hydroxocobalamin is an attractive antidote for cyanide poisoning as cobalt compounds have the ability to bind and detoxify cyanide. This paper reviews the pharmacokinetic and pharmacodynamic aspects of hydroxocobalamin, its efficacy in human cyanide poisoning and its adverse effects.

METHODS

PubMed was searched for the period 1952 to April 2012. A total of 71 papers were identified in this way; and none was excluded. PHARMACOKINETICS AND PHARMACODYNAMICS: Pharmacokinetic studies in dogs and humans suggest a two-compartment model, with first order elimination kinetics. Pharmacodynamic studies in animals suggest that hydroxocobalamin would be a satisfactory antidote for human cyanide poisoning. EFFICACY IN HUMAN POISONING: There is limited evidence that hydroxocobalamin alone is effective in severe poisoning by cyanide salts. The evidence for the efficacy of hydroxocobalamin in smoke inhalation is complicated by lack of evidence for the importance of cyanide exposure in fires and the effects of other chemicals as well as confounding effects of other therapeutic measures, including hyperbaric oxygen. Evidence that hydroxocobalamin is effective in poisoning due to hydrogen cyanide alone is lacking; extrapolation of efficacy from poisoning by ingested cyanide salts may not be valid. The rate of absorption may be greater with inhaled hydrogen cyanide and the recommended slow intravenous administration of hydroxocobalamin may severely limit its clinical effectiveness in these circumstances.

ADVERSE EFFECTS

Both animal and human data suggest that hydroxocobalamin is lacking in clinically significant adverse effects. However, in one human volunteer study, delayed but prolonged rashes were observed in one-sixth of subjects, appearing 7 to 25 days after administration of 5 g or more of hydroxocobalamin. Rare adverse effects have included dyspnoea, facial oedema, and urticaria.

CONCLUSIONS

Limited data on human poisonings with cyanide salts suggest that hydroxocobalamin is an effective antidote; data from smoke inhalation are less clear-cut. Although clinically important reactions to hydroxocobalamin have not been seen, some, non-life threatening, adverse reactions can occur.

Safety of Hydroxocobalamin in Healthy Volunteers in a Randomized, Placebo-Controlled Study

INTRODUCTION

This randomized, double-blind, placebo-controlled, ascending-dose study was conducted in healthy volunteers to evaluate the safety of the investigational cyanide antidote hydroxocobalamin.

METHODS

Four ascending dosing groups received intravenous doses of 2.5, 5, 7.5 or 10 g hydroxocobalamin over 7.5 to 30 minutes at a constant infusion rate. Volunteers (n = 136) randomized 3:1 to receive hydroxocobalamin or placebo underwent a 4-day in-house observation after infusion on Day 1 and follow-up visits on Days 8, 15, and 28.

RESULTS

The most common drug-related adverse events were asymptomatic and self-limiting chromaturia and reddening of the skin, which are attributed to the red color of hydroxocobalamin. Other adverse events included pustular/papular rash, headache, erythema at the injection site, decrease in lymphocyte percentage, nausea, pruritus, chest discomfort, and dysphagia. Hydroxocobalamin was associated with an increase in blood pressure in some volunteers. Blood pressure changes peaked toward the end of hydroxocobalamin infusion and typically returned to baseline levels by 4 hours postinfusion. Maximum mean changes from baseline in systolic blood pressure ranged from 22.6 to 27.0 mmHg across hydroxocobalamin doses compared with 0.2 to 6.7 mmHg in the corresponding placebo groups. Maximum mean change from baseline in diastolic blood pressure ranged from 14.3 to 25.4 mmHg across hydroxocobalamin doses compared with -3.0 to 3.8 mmHg in the corresponding placebo groups. Two allergic reactions that occurred within minutes after start of the 5- and 10-g hydroxocobalamin infusions were successfully managed with dexamethasone and/or dimethindene maleate.

CONCLUSION

Timely intervention for acute cyanide poisoning could entail administration of an antidote in the prehospital setting based on a presumptive diagnosis. Results of this placebo-controlled study in healthy volunteers corroborate previous studies and French postmarketing experience in cyanide-exposed patients in suggesting that the safety profile of hydroxocobalamin is consistent with prehospital or hospital use.

Nitric Oxide Scavenging by Hydroxocobalamin May Account for Its Hemodynamic Profile

BACKGROUND

Antidotal doses of hydroxocobalamin are associated with transient increases in blood pressure in some animals and humans. These studies in anesthetized rabbits were undertaken to explore the possible mechanisms underlying the hemodynamic effects of hydroxocobalamin by investigating 1) possible hemodynamic effects of cyanocobalamin, which is formed on a molar-to-molar basis when hydroxocobalamin binds cyanide, and 2) the interference of hydroxocobalamin with the endothelial nitric oxide system.

METHODS

Study 1 investigated the hemodynamic effects of cyanocobalamin. This study included two treatment arms: 1) cyanocobalamin (75 mg/kg, IV) followed by saline (n = 7) and 2) saline followed by cyanocobalamin (n = 7). Study 2 assessed the hemodynamic effects of hydroxocobalamin (75 mg/kg, IV) in the presence and absence of the nitric oxide synthase inhibitor L-Nomega-nitro-L-arginine methyl ester (L-NAME; 30 mg/kg, IV). Nitric oxide synthase inhibition itself increases blood pressure. Thus, as part of Study 2, the hemodynamic effects of hydroxocobalamin were also investigated in the presence of an equipressor dose of angiotensin II (ANGII; 0.05 microg/kg/min, IV) in order to determine whether elevated blood pressure per se could interfere with hydroxocobalamin's hemodynamic effects. This study included six treatment arms (designated as first treatment + second treatment): saline + saline (n = 5), L-NAME + saline (n = 7), saline + hydroxocobalamin (n = 7), L-NAME + hydroxocobalamin (n = 7), ANGII + hydroxocobalamin (n = 7), and ANGII + saline (n = 7).

RESULTS

In Study 1, the effects of cyanocobalamin on hemodynamic parameters were indistinguishable from those of saline. In Study 2, hydroxocobalamin infusion was associated with moderate hemodynamic effects, including an increase in systemic vascular resistance, an increase in blood pressure, and a decrease in cardiac output. Administration of L-NAME abolished the effects of hydroxocobalamin on all hemodynamic parameters. ANGII at a dose producing a pressor response comparable to that of L-NAME did not influence the hydroxocobalamin-associated hemodynamic changes.

CONCLUSION

These studies in anesthetized rabbits demonstrate that the moderate pressor effect of hydroxocobalamin is not related to the formation of cyanocobalamin but is very likely related to the scavenging of nitric oxide by hydroxocobalamin.

Chemical Terrorism Attacks: Update on Antidotes

There is well-founded concern that a chemical or radioactive agent will at some point be used as a weapon of terror. There are several antidotes that, if used correctly in a timely fashion, can help lessen the harm caused by these agents. This article is meant to introduce the clinician to several such agents, along with the antidotes useful in the management of exposure to these. It covers the indications, administration, and precautions for using these antidotes.

Efficacy of hydroxocobalamin for the treatment of acute cyanide poisoning in adult beagle dogs

INTRODUCTION

The efficacy of hydroxocobalamin for acute cyanide poisoning was compared with that of saline vehicle in dogs.

METHODS

Anesthetized adult beagle dogs were administered potassium cyanide (0.4 mg/kg/min, IV) until 3 min after the onset of apnea. Hydroxocobalamin (75 mg/kg [n = 19] or 150 mg/kg [n = 18], IV) or saline vehicle [n = 17] was then infused over 7.5 min while animals were ventilated with 100% oxygen, which was stopped after 15 min.

RESULTS

In vehicle-treated animals cyanide produced deterioration that culminated in a moribund state requiring euthanasia within 4 h in 10 of 17 animals and in neurological deficits necessitating euthanasia within 2-4 d in an additional 4 animals (mortality rate 82%). Survival through 14 d was observed in 15 of 19 animals administered hydroxocobalamin 75 mg/kg (mortality rate 21%), and 18 of 18 administered hydroxocobalamin 150 mg/kg (mortality rate 0%).

CONCLUSION

Hydroxocobalamin reversed cyanide toxicity and reduced mortality in a canine model.

Hydroxocobalamin: improved public health readiness for cyanide disasters

The United States is under the constant threat of a mass casualty cyanide disaster from industrial accidents, hazardous material transportation incidents, and deliberate terrorist attacks. The current readiness for cyanide disaster by the emergency medical system in the United States is abysmal. We, as a nation, are simply not prepared for a significant cyanide-related event. The standard of care for cyanide intoxication is the cyanide antidote kit, which is based on the use of nitrites to induce methemoglobinemia. This kit is both expensive and ill suited for out-of-hospital use. It also has its own inherent toxicity that prevents rapid administration. Furthermore, our hospitals frequently fail to stock this life-saving antidote or decline to stock more than one. Hydroxocobalamin is well recognized as an efficacious, safe, and easily administered cyanide antidote. Because of its extremely low adverse effect profile, it is ideal for out-of-hospital use in suspected cyanide intoxication. To effectively prepare for a cyanide disaster, the United States must investigate, adopt, manufacture, and stockpile hydroxocobalamin to prevent needless morbidity and mortality.

Hydroxocobalamin vs cobalt toxicity on rat cardiac and diaphragmatic muscles

BACKGROUND

Hydroxocobalamin has been shown to be a rapid and powerful antidote in acute cyanide poisoning and to prevent cyanide poisoning during sodium nitroprusside administration. This cobalt-containing compound has been shown to be devoid of significant immediate side effects during acute administration. However, its potential delayed toxicity related to cobalt accumulation in tissue remains unknown. Therefore, we evaluated the toxicity of hydroxocobalamin as compared with that of cobalt salts on rat cardiac and diaphragmatic muscles.

METHODS

For a 21-day period, rats were treated intraperitoneally with either hydroxocobalamin (70 mg kg-1 per day, n = 14), cobalt chloride hexahydrate (12 mg kg-1 per day, n = 14) or saline (n = 10). Hydroxocobalamin and cobalt chloride groups received equimolar doses of cobalt. We studied: (1) the mechanical properties of isolated left ventricular papillary muscles and diaphragmatic strips, (2) the cardiac and diaphragmatic cobalt tissue concentrations, and (3) the myocardial histological aspect.

RESULTS

During the study period, no significant increase in body weight was noted in the cobalt-treated group (-4 +/- 1%), which was in contrast to the hydroxocobalamin-treated group (+21 +/- 2%) and the saline-treated group (22 +/- 2%). Compared with controls, the mechanical properties of cardiac and diaphragmatic muscles were unchanged after either hydroxocobalamin or cobalt salt treatments, and myocardial histological characteristics were similar in all groups. Conversely, large amounts of cobalt deposit were observed in the cobalt-treated group in both the diaphragm (41.90 +/- 16.30 vs 0.70 +/- 0.40 mu mol mu g-1 in the control group, P < 0.001) and the myocardium (16.90 +/- 6.40 vs 0.14 +/- 0.01 mu mol mu g-1 in the control group, P < 0.001). After hydroxocobalamin administration, cobalt concentrations were significantly lower in the diaphragm (25.10 +/- 16.50 mu mol mu g-1, P < 0.001 vs cobalt-treated group) and the myocardium (4.50 +/- 1.20 mu mol mu g, P < 0.001 vs cobalt-treated group).

CONCLUSION

These results indicate that repeated administration of hydroxocobalamin was devoid of significant diaphragmatic and cardiac muscle toxicity and therefore remains a safe antidote for acute cyanide poisoning.

Pharmacokinetics of hydroxocobalamin in smoke inhalation victims

OBJECTIVE

Hydroxocobalamin has been proposed as a cyanide antidote. Little is known, however, about its pharmacokinetics in human cyanide poisoning.

METHODS

We prospectively studied the pharmacokinetics of hydroxocobalamin in 11 smoke inhalation victims of whom all but one had objective evidence of cyanide exposure. Serum hydroxocobalamin levels were followed from just before drug administration to six days after a single 5 g dose of hydroxocobalamin.

RESULTS

The results (mean +/- standard error) suggest a two compartment model. Distribution half-life is on the order of 1.86 +/- 0.34 h and the elimination half-life 26.2 +/- 2.7 h. The apparent volume of distribution is 0.45 +/- 0.03 L/kg. Renal and total body clearance are 0.31 +/- 0.06 and 0.83 +/- 0.07 L/h, respectively.

CONCLUSION

The apparent volume of distribution suggests a predominantly extracellular partitioning of the antidote, even in the presence of cyanide, an important factor in terms of its antidotal effect. Hydroxocobalamin's elimination half-life in these cyanide-exposed patients far exceeds those found in previous studies of dogs and minimally-exposed humans. If confirmed, this half-life suggests that a single dose of hydroxocobalamin, sufficiently large enough to bind the cyanide present, should be adequate.