Cyanide intoxication in sheep; therapeutics

Various cyanide antidotes were evaluated by comparing the effects of delay in time of therapy following oral administration of sodium cyanide in sheep. Successful therapy of lethal doses of sodium cyanide could be accomplished with the more potent antidotes for up to 30 minutes following administration of sodium cyanide. Either 660 mg/kg sodium thiosulfate or 1 mg/kg p-aminopropriophenone were effective antidotes for moderate lethal doses (7.6 mg/kg) of sodium cyanide. The conventional low dosage nitrite/thiosulfate (6.7 mg/kg and 67 mg/kg) was much less effective. Larger doses (15.2 mg/kg) of sodium cyanide were effectively antagonized by either 660 mg/kg sodium thiosulfate alone or in combination with 1.5 mg/kg p-aminopropriophenone or 22 mg/kg sodium nitrite. At high cyanide dosage, p-aminopropriophenone alone was less effective than sodium thiosulfate alone. Sodium thiosulfate at high dosage appears to be the antidote of choice. This more closely satisfies the requirements of high efficacy and low toxicity for an antidote. Sodium nitrate or other antidotes may be used in conjunction with sodium thiosulfate, but their use is not necessary for high efficacy.     

The efficacy of alpha-ketoglutaric acid in the antagonism of cyanide intoxication

It has been reported that compounds containing carbonyl groups can readily react with cyanide. Pyruvic acid, an alpha-ketocarboxylic acid, has been shown to antagonize the lethal effects of cyanide. It is suggested that its mechanism of action rests in its ability to react with or "bind" cyanide. In this study, alpha-ketoglutaric acid, also an alpha-ketocarboxylic acid, was evaluated for its ability to counteract the lethal effects of cyanide. alpha-Ketoglutaric acid increased the LD50 value of cyanide (6.7 mg/kg) by a factor of five, a value statistically equivalent to that ascertained in mice pretreated with sodium thiosulfate and sodium nitrite. The combination of alpha-ketoglutaric acid and sodium thiosulfate increased the LD50 value of cyanide to 101 mg/kg. Addition of sodium nitrite to the alpha-ketoglutaric acid/sodium thiosulfate regimen increased the LD50 value of cyanide to 119 mg/kg. Unlike sodium nitrite, no induction of methemoglobin formation was observed with alpha-ketoglutaric acid pretreatment. It is apparent from these studies that the administration of alpha-ketoglutaric acid in conjunction with sodium thiosulfate resulted in fewer animal deaths than sodium nitrite and sodium thiosulfate without the dangerous formation of methemoglobin.     

Zur Beurteilung der Blausäure-Antidote

The effect of various antidotes on the exhalation of hydrocyanic acid has been measured in guinea pigs and cats poisoned with cyanide. This procedure permits evaluation of both the speed of action and the capacity of the agents tested to detoxify hydrocyanic acid, and therefore allows an exact judgement as to therapeutic value of various antidotes to cyanide poisoning. The results were as follows:

1. Cobaltous histidine at a dose of 20 mg/kg was distinguished among the compounds tested by its rapid action in both species. Its detoxifying capacity was not adequate however. Treatment of severe cyanide poisoning in man with Co (his)₂ would appear to be reasonable, but only when combined with sodium thiosulfate.
2. The same rapid action as with cobaltous histidine was achieved in cats by intravenous injection of 2.25 mg/kg p-dimethylaminophenole (DMAP) leading to a methemoglobin formation of 30%. A dose of 0.75 mg/kg DMAP forming 10% methemoglobin reduced HCN-exhalation by an equivalent amount only after a 2.4 min delay. The capacity of DMAP to detoxify hydrocyanic acid was considerably greater than that of cobaltous histidine but still was far inferior to that of sodium thiosulfate.
3. The high capacity of sodium thiosulfate to detoxify hydrocyanic acid was likewise demonstrated by the new method employed here in both animal species. However, the onset of its effect was always very delayed. In clinical practice, this agent should never be omitted, but in treatment of severe poisonings it will only be successful when combined with a more rapid-acting antidote such as cobaltous histidine or DMAP.
4. Sodium nitrite, even when applied in relatively high doses, did not act rapidly enough nor did it demonstrate a satisfactory capacity to detoxify hydrocyanic acid. Therefore, it no longer fulfills the requirements that presently should be demanded of an antidote to hydrocyanic acid.

     

Effect of oxygen on the antagonism of cyanide intoxication--cytochrome oxidase, in vivo

The inhibition and recovery of brain and liver cytochrome oxidase in mice pretreated in an air or oxygen atmosphere were measured after the administration of KCN with and without sodium nitrite and sodium thiosulfate pretreatment. Inhibition of cytochrome oxidase in both brain and liver reached a maximum within 5 min after cyanide administration, and cytochrome oxidase activity was restored more rapidly in liver than in brain. Also, this enzymatic activity returned more rapidly in oxygen than in air. In the animals pretreated with sodium nitrite and sodium thiosulfate, brain but not liver cytochrome oxidase was inhibited by cyanide. The effect of administering varying doses of KCN to mice maintained in air or oxygen resulted in a dose-dependent inhibition of both brain and liver cytochrome oxidase. Oxygen treatment produced a shift to the right in the dose-response curve when compared to the air treatment group. No significant difference was detected in rhodanese activity in air and oxygen in mice receiving varying doses of cyanide.     

Acute, sublethal cyanide poisoning in mice is ameliorated by nitrite alone: complications arising from concomitant administration of nitrite and thiosulfate as an antidotal combination

Sodium nitrite alone is shown to ameliorate sublethal cyanide toxicity in mice when given from ～1 h before until 20 min after the toxic dose as demonstrated by the recovery of righting ability. An optimum dose (12 mg/kg) was determined to significantly relieve cyanide toxicity (5.0 mg/kg) when administered to mice intraperitoneally. Nitrite so administered was shown to rapidly produce NO in the bloodsteam as judged by the dose-dependent appearance of EPR signals attributable to nitrosylhemoglobin and methemoglobin. It is argued that antagonism of cyanide inhibition of cytochrome c oxidase by NO is the crucial antidotal activity rather than the methemoglobin-forming action of nitrite. Concomitant addition of sodium thiosulfate to nitrite-treated blood resulted in the detection of sulfidomethemoblobin by EPR spectroscopy. Sulfide is a product of thiosulfate hydrolysis and, like cyanide, is known to be a potent inhibitor of cytochrome c oxidase, the effects of the two inhibitors being essentially additive under standard assay conditions rather than dominated by either one. The findings afford a plausible explanation for an observed detrimental effect in mice associated with the use of the standard nitrite-thiosulfate combination therapy at sublethal levels of cyanide intoxication.     

Application of a hepatocyte-erythrocyte coincubation system to studies of cyanide antidotal mechanisms

A coincubation system composed of hepatocytes in primary monolayer culture and erythrocytes suspended in the culture medium was developed and used as a model for investigations of mechanisms of cyanide antidote action at the cellular level. Hepatocyte ATP was used as the cytotoxicity indicator. Treatment of rat hepatocytes in the coincubation system with KCN (1.0 mM) for 10 min at 37 degrees C selectively reduced hepatocyte ATP levels to 33 +/- 15% of control (no KCN added) levels. 4-dimethylaminophenol (DMAP), cobalt(II) chloride, sodium nitrite, sodium thiosulfate, or a combination of the last two antidotes added to the KCN-containing medium significantly reversed ATP depression and the response was concentration dependent. The relative effectiveness, on a molar basis, was estimated to be DMAP greater than CoCl2 much greater than NaNO2 congruent to Na2S2O3. NaNO2 and DMAP induced methemoglobin formation in the absence of cyanide and cyanmethemoglobin formation in its presence; erythrocytes were required in the medium for effectiveness. CoCl2 produced neither cyanmethemoglobin nor thiocyanate in appreciable quantities nor required erythrocytes for antagonism. Na2S2O3 converted cyanide to thiocyanate and reversed ATP depression without erythrocytes in the medium. The addition of erythrocytes increased these rates significantly and to a greater extent than albumin. The overall results are consistent with previously proposed modes of action for these antidotes. However, the enhancement in cyanide metabolism and ATP recovery with Na2S2O3 and erythrocytes in the system was unexpected and raises the possibility that erythrocytes may contribute to cyanide disposition and antagonism in vivo when this antidote is administered.     

Effects of oxygen on the antagonism of cyanide intoxication: cytochrome oxidase, in vitro

Since oxygen was reported to be an effective cyanide antagonist in vivo, particularly in the presence of the classic antidotal combination of sodium nitrite and sodium thiosulfate, in vitro studies were initiated in an attempt to investigate the mechanism of oxygen-mediated cyanide antagonism. The effect of oxygen on cyanide-inhibited cytochrome oxidase with and without cyanide antagonist(s) was investigated in a purified membraneous enzyme system prepared from rat liver mitochondria. Cyanide produced a concentration dependent inhibition of cytochrome oxidase, and 100% oxygen did not alter the inhibition produced by KCN either in the presence or absence of sodium thiosulfate. However, the addition of sodium thiosulfate and rhodanese to the assay reactivated the cyanide-inhibited cytochrome oxidase. Kinetic analysis indicated rhodanese competes with cytochrome oxidase for cyanide, and oxygen had no effect on this coupled reaction. In conclusion, the in vivo antidotal properties of oxygen cannot be attributed to oxygen-mediated reactivation of cyanide-inhibited cytochrome oxidase or an oxygen-mediated acceleration of rhodanese detoxification.     

Antagonism of cyanide poisoning by chlorpromazine and sodium thiosulfate

Anti-cyanide action by sodium thiosulfate (ST) was enhanced by prior administration of chlorpromazine (CPZ). However, CPZ (alone) provided no protection against cyanide lethality. To investigate the possibility that CPZ enhances thiocyanate formation in ST-pretreated mice, the effects of CPZ on rhodanese activity and the time course of plasma thiocyanate concentrations were investigated. CPZ did not alter hepatic rhodanese kinetics nor did it enhance plasma thiocyanate concentrations in ST-pretreated mice. The effect of CPZ and ST on the time course of cytochrome oxidase inhibition and recovery, in vivo, was also investigated. At 4 mg KCN/kg, maximal inhibition of brain (40%) and heart (60%) cytochrome oxidase occurred 10 to 20 min post-challenge in control and CPZ-pretreated mice, while no inhibition occurred in ST- and CPZ/ST-pretreated mice. Twenty milligrams KCN/kg caused 100% lethality in control and CPZ-pretreated mice and 6/25 and 4/20 deaths were observed in ST- and CPZ/ST-pretreated mice, respectively. No significant inhibition of brain, heart, and liver cytochrome oxidase activities was observed in surviving ST- and CPZ/ST-pretreated mice challenged with 20 mg KCN/kg. Control and CPZ-pretreated mice died within 5 min of KCN challenge and had almost the same degree of inhibition of brain (35 and 29%, respectively) and heart (60 and 55%, respectively) cytochrome oxidase as did similarly pretreated mice 5 min after challenge with a nonlethal cyanide dose (4 mg/kg). Our results suggest that CPZ does not enhance the formation of thiocyanate in ST-pretreated mice. In addition, the similar degree of cytochrome oxidase inhibition noted after both lethal and nonlethal KCN treatments raises questions as to the ultimate target in cyanide-induced lethality.     

Effect of chlorpromazine on cyanide intoxication

Previous reports from our laboratory indicated that prophylactic protection against cyanide intoxication in mice can be enhanced by administration of chlorpromazine when it is given with sodium thiosulfate. The mechanism of potentiation of sodium thiosulfate by chlorpromazine was studied alone and in combination with sodium nitrite. Although chlorpromazine was found to induce a hypothermic response, the mechanism of enhancement of the antagonism of cyanide by chlorpromazine does not correlate with the hypothermia produced. Various other possible mechanisms were investigated, such as rate of methemoglobin formation, enzymatic activity of rhodanese and cytochrome oxidase, and alpha-adrenergic blockade. The alpha-adrenergic blocking properties of chlorpromazine may provide a basis for its antidotal effect, since this protective effect can be reversed with an alpha-agonist, methoxamine.     

Clinical features and management of cyanide poisoning

The pathophysiology, clinical features, and management of cyanide toxicity are reviewed and sources of cyanide are listed. Cyanide is a deadly poison that is found in many foods and household and industrial products, including some that are readily available. Cyanide binds with cytochrome oxidase, the enzyme responsible for oxidative phosphorylation, and paralyzes cellular respiration. Because the tissues cannot use oxygen that is delivered, aerobic metabolism ceases. The signs and symptoms of cyanide poisoning reflect the extent of cellular hypoxia. Manifestations may include respiratory abnormalities (progressing from tachypnea and dyspnea to respiratory depression and apnea), hemodynamic instability, metabolic acidosis, and, possibly, local irritant effects after oral ingestion of cyanide. The mainstays of therapy are 100% oxygen and specific antidotes to cyanide. Sequential treatment with amyl nitrite by inhalation, intravenous sodium nitrite 3%, and intravenous sodium thiosulfate 25% is directed toward decreasing the amount of cyanide available for cellular binding. Nitrites convert hemoglobin to methemoglobin, which reacts with cyanide to form cyanomethemoglobin. Sodium thiosulfate serves as a source of sulfur groups, which are needed for conversion of cyanide to thiocyanate, a compound that is relatively less toxic and is excreted renally. Supportive care also is important. Cobalt EDTA, hydroxocobalamin, and aminophenols have also been used but are not considered standard treatments. Cyanide poisoning is a medical emergency that requires prompt recognition and immediate and aggressive treatment.     

Effect of cyanide antidotes on the metabolic conversion of cyanide to thiocyanate

The excretion of thiocyanate following the administration of equitoxic doses of cyanide to unprotected mice and to animals pretreated with various cyanide antidotes has been studied.The results demonstrate that cyanide given alone or to animals pretreated with thiosulfate is extensively converted to thiocyanate. Animals pretreated with sodium nitrite or a combination of nitrite and sodium thiosulfate excreted even higher amounts of thiocyanate. This demonstrates that cyanide originally detoxified by combination with methemoglobin is ultimately converted to thiocyanate in the animal body.Pretreatment of animals with cobalt compounds (cobaltous chloride or dicobalt-EDTA) or a combination of cobalt compounds and thiosulfate resulted, on the other hand, in a less efficient conversion of cyanide to thiocyanate. The cyanide detoxified by trapping as highly undissociated cobalt-cyanide complexes is instead excreted in the urine, as demonstrated by detection of high amounts of cobalt ions and strongly complex-bound cyanide in the urine from animals treated with cobalt compounds and cyanide. A method for the determination of cyanide present as cobalt-cyanide complexes is described and its forensic application is proposed.     

Stereospecific effect of naloxone hydrochloride on cyanide intoxication

Cyanide intoxication in mice can be antagonized by the opiate antagonist, (-)naloxone HCl, alone or in combination with sodium thiosulfate and/or sodium nitrite. Potency ratios, derived from LD50 values, were compared in groups of mice pretreated with sodium nitrite (sc, 100 mg/kg), sodium thiosulfate (ip, 1 g/kg), and (-)naloxone HCl (sc, 10 mg/kg) either alone or in various combinations. These results indicate that naloxone HCl provides a significant protection against the lethal effects of potassium cyanide. The protective effect of sodium thiosulfate, but not sodium nitrite, was enhanced with (-)naloxone HCl. The combined administration of sodium nitrite and sodium thiosulfate was further enhanced with (-)naloxone HCl. This protective effect of naloxone HCl against the lethal effect of cyanide appears to be restricted to the (-)stereoisomer, as the (+)stereoisomer, the inactive opiate antagonist, is also inactive in protecting against the lethal effects of cyanide. The mechanism of antagonism is discussed.     

Cyanide intoxication: protection with chlorpromazine.

Protection against cyanide intoxication in mice can be enhanced by the administration of chlorpromazine, providing it is given with sodium thiosulfate, or the sodium thiosulfate-sodium nitrite antidotal combination. Protency ratios which were derived from the LD50 values were compared in groups of mice premedicated with chlorpromazine (10 mg/kg) and/or sodium thiosulfate (1 g/kg) and/or sodium nitrite (100 mg/kg). These results indicate that the administration of chlorpromazine alone provides no protection against the lethal effects of cyanide. Chlorpromazine also does not enhance the protective effect of sodium nitrite; however, it strikingly potentiates the effectiveness of sodium thiosulfate either alone or in combination with sodium nitrite.     

Comparison of hydroxylamine, 4-dimethylaminophenol and nitrite protection against cyanide poisoning in mice

Intraperitoneal doses of 4-dimethylaminophenol hydrochloride (DMAP), hydroxylamine hydrochloride (H₂NOH) and sodium nitrite (NaNO₂) were found where each converted a maximum of about 37% of the total circulating hemoglobin in mice to methemoglobin. Those doses in mmol/kg were: 0.29 for DMAP, 1.1 for H₂NOH, and 1.1 for NaNO₂. For DMAP and H₂NOH the peak was sharp and at about 7 min after injection whereas for NaNO₂ the peak was much broader and at about 40 min. The i.p. LD₅₀'s in mmol/kg were: 0.48 for DMAP, 1.8 for H₂NOH and 2.3 for NaNO₂. When mice pretreated with each of the methemoglobin-generating agents were challenged with sodium cyanide, the ratios of the LD₅₀'s in protected mice to those in control mice (protection index, PI) were 1.5 for H₂NOH, 2.0 for DMAP and 3.1 for NaNO₂. When sodium thiosulfate was also given in combination with each of the three methemoglobin-generating agents, the protective effect was at least additive. The PI against sodium sulfide was also significantly greater in mice pretreated with NaNO₂ than in mice given H₂NOH. Methemoglobins generated from human and mouse hemoglobins by either NaNO₂ or by H₂NOH had identical binding affinities (dissociation constants) for cyanide. When human red cells containing methemoglobin generated by exposure to either NaNO₂ or H₂NOH were injected into the peritoneal cavity of mice and then followed by cyanide challenges, there was no difference in the PI for the two kinds of methemoglobin. Not only was the PI the same in each case with human cells, but it was also identical with that in mice given NaNO₂ systemically to generate the same total amount of methemoglobin. The difference in PI between NaNO₂ and H₂NOH (or DMAP) in mice appears to be related to the high rate of methemoglobin reductase activity in mouse RBC. It appears likely that cyanmethemoglobin is a substrate for mouse methemoglobin reductase activity, and that NaNO₂ is an inhibitor of mouse methemoglobin reductase. No differences in cyanide antagonism between NaNO₂ and H₂NOH would be anticipated in humans because of the slow rates of methemoglobin reduction in human red cells.     

Antagonism of cyanide intoxication with sodium pyruvate

Cyanide intoxication in mice can be effectively antagonized by sodium pyruvate, particularly if it is administered in combination with the antidotes, sodium nitrite and sodium thiosulfate. Potency ratios derived from the LD50 data were compared in groups of mice treated with sodium nitrite, sodium thiosulfate, and sodium pyruvate either alone or in various combinations. These results indicate that the administration of sodium pyruvate alone does provide minimal, but statistically significant, protection against the lethal effects of cyanide. Sodium pyruvate does not enhance the effect of sodium nitrite; however, it does potentiate the antidotal effect of sodium thiosulfate. The sodium thiosulfate and sodium pyruvate combination is not as effective as the sodium nitrite and sodium thiosulfate combination, but the addition of sodium pyruvate to the sodium nitrite-sodium thiosulfate combination further enhances the antidotal effect. No further enhancement is observed when sodium nitrite, sodium thiosulfate, and sodium pyruvate are combined with oxygen.     

对二甲氨基酚治疗急性失血合并氰中毒对血液动力学及血液内环境的影响

本实验用犬制备了轻(10％)、中(15％)、重度(20％)急性失血合并ⅳ NaCN 2.5 mg/kg中毒的动物模型,观察了ⅳ DMAP 2.5mg/kg治疗时血液动力学及血液内环境的变化。结果发现,DMAP治疗轻度急性失血合并氰中毒能使心血管功能迅速恢复正常并维持稳定,随失血程度加重DMAP对心血管功能兴奋作用减弱;血气分析及HbFe~(3+)测定结果表明,DMAP治疗急性失血合并氰中毒可造成机体严重缺氧及代谢性酸中毒,并随失血程度的加重而加剧。     

Antagonism of cyanide poisoning by dihydroxyacetone

Dihydroxyacetone (DHA) effectively antagonized the lethal effect of cyanide in mice and rabbits, particularly if administered in combination with thiosulfate. Oral DHA (2 and 4 g/kg) given to mice 10 min before injection (i.p.) of cyanide increased the LD50 values of cyanide from 5.7 mg/kg to 12 and 17.6 mg/kg, respectively. DHA prevented cyanide-induced lethality most effectively, if given orally 10-15 min before injection of cyanide. A combination of pretreatment with oral DHA (4 g/kg) and post-treatment with sodium thiosulfate (1 g/kg) increased the LD50 of cyanide by a factor of 9.9. Furthermore, DHA given intravenously to rabbits 5 min after subcutaneous injection of cyanide increased the LD50 of cyanide from 6 mg/kg to more than 11 mg/kg, while thiosulfate (1 g/kg) given intravenously 5 min after cyanide injection increased the LD50 of cyanide only to 8.5 mg/kg. DHA also prevented the convulsions that occurred after cyanide intoxication.     

Cyanide intoxication: protection with cobaltous chloride

Protection against the lethal effects of cyanide can be elicited by administration of cobaltous chloride, either alone or in combination with sodium nitrite and/or sodium thiosulfate. Potency ratios derived from the LD50 values were compared in groups of mice premedicated with cobaltous chloride and/or sodium thiosulfate and/or sodium nitrite. Under the conditions of our experiment cobaltous chloride alone is slightly more effective than sodium nitrite; when it is combined with sodium nitrite, an additive effect is obtained. When cobaltous chloride is administered in combination with sodium thiosulfate, a dramatic antagonism of the lethal effects of potassium cyanide is observed. The synergistic antidotal effect of cobaltous chloride may be related to the physiological disposition of the cobaltous ion and its ability to chelate both cyanide and thiocyanate ions.     

Sodium thiosulfate for acute cyanide poisoning: study in a rat model

Unlike practices in the United States where it is associated with other antidotes, sodium thiosulfate is not used for emergency therapy for cyanide poisoning in France. The purpose of this study was to develop a rat model using intraperitoneal injections of sodium thiosulfate at a dose of 225 mg/kg to test its therapeutic efficacy for acute cyanide poisoning. Efficacy was assessed directly by quantifying arterial blood cyanide and indirectly using markers of hypoxia: serum lactate and arteriolization of venous blood gases. Cyanide poisoning induced intense biological anomalies which were persistent (serum lactate) or transient (blood gases). Sodium thiosulfate was found to be an effective antidote in the rat enabling rapid normalization of hypoxia markers and clearing of cyanide from arterial blood.