New antidote
A NEW ANTIDOTE FOR CYANIDE POISONING By Dr. Mohammad Ali kavianpour Kermanshah medical university Iran May,2008
INTRODUCTION This paper describes a study of the antidotal actions of nickel nitrate against cyanide poisoning. Hydrocyanic acid acts as a poison because it combines with, and stops the function of, the iron atom in cytochrome oxidase, so blocking the electron transfer through the cytochrome system, and checking the final oxidations involving oxygen uptake of the tricarboxylic acid cycle. It also inhibits many other enzymes.Attempts to find an antidote for cyanide have usually been in the direction of breaking down the cyanide-cytochrome complex, and have looked for substances with a stronger affinity for cyanide ions than has the oxidase.One such method is to convert some of the blood haemoglobin into methaemoglobin,for example,by injection of a nitrite; the methaemoglobin combines with the cyanide ion to form the very stable cyanmethaemoglobin. This has the drawback that it involves the loss of oxygen-carrying power of the blood, so that, for example, to antidote twice the LD50 of cyanide would be equivalent to the loss of about 12% (or in an adult man 550 ml.) of the blood. METHODS
The LD50 of hydrocyanic acid, by various routes of administration, was determined for mice and rabbits. A solution of sodium cyanide was neutralized with acetic acid to about pH 7,the content of hydrocyanic acid was estimated by silver titration, and the subsequent dilution to the required concentration was made with 0.9% saline.At pH 7 the hydrocyanic acid is about 1% ionized. In some experiments pure hydrocyanic acid was used, but this had no advantage and was more difficult to handle. Owing to the volatility of hydrocyanic acid, the solutions were kept in special vessels and, when any doubt existed as to the final concentration, were again titrated at the end of the day’s experiments. It was usually found that after 6 hr the concentration had fallen, often by 5%, and sometimes in hot weather by as much as 12%. Intravenous injections were made into the tail layer in mice and an ear layer in rabbits; intramuscular injections were into the thigh muscles. Doses are expressed usually in terms of umoles/kg of body weight, and for hydrocyanic acid sometimes also in terms of LD50. Owing to the rapidity of action of hydrocyanic acid when large doses are given, and to the difficulty of giving intravenous injections when the animal is convulsing, it was more usual to give the antidote first, intravenously, and then to follow this in a matter of seconds by the hydrocyanic acid, usually by intramuscular injection, but in some experiments that order was reversed; the antidotal effects were at least as great, and often greater, when that was done, provided the antidote was given soon enough. In order to indicate the molar relationship between the hydrocyanic acid and the antidote in each experiment, the ratio between them was usually expressed (moles of hydrocyanic acid per kg divided by moles of nickel compound per kg) and is called the cyanide/nickel ratio. RESULTS The effectiveness of a nickel nitrate, against hydrocyanic acid was examined mainly on mice and rabbits.for rabbits (4 x LD50), was effective at a molar cyanide/nickel ratio of 4. and for mice (3 x LD50 at a molar ratio of 2), with no apparent side effects. At a molar ratio of 1, it was slightly more effective than on rabbits. Nickel nitrate by mouth was effective against orally administered hydrocyanic acid. The oxygen uptake of the body, reduced by cyanide, improved when nickel antidotes has been successfully administered. Relatively small amounts of nickel salts would be needed for the neutralization of several fatal doses of cyanide. By intravenous injection.The LD50 for mice was found to be about 42 umoles/ kg, and for rabbits 33 umoles/kg. Mice given two to three times the LD50 convulse in a few seconds and die in 50 seconds.By intraperitoneal injection,the results showed a rather large spread, the mean LD50 for rabbits being 52 ,umoles/kg, and for mice 107 umoles/ kg, so that by this route mice were only about half as sensitive as rabbits.This is probably due to a more rapid detoxification by the mouse liver.It will be expected that toxicity would be maximal when the cyanide is given quickly into a vein which drains into the inferior vena cava, so that it is quickly delivered to the central nervous system, less toxic when it enters more slowly, as by intramuscular injection, and least toxic when it enters the circulation slowly, as when given intraperitoneally, subcutaneously or orally. the descending order of toxicity proved to be intravenous intramuscular-intraperitoneal-subcutaneous-oral, The results of inhalation are more vague, but are probably comparable with those by intravenous injection.A method of administration often used, but not employed in the present investigation, is to anaesthetize the animal and to inject the cyanide intravenously at a constant slow rate of about 0.1 mg/kg/min.The results so obtained do not seem to differ greatly from those of the usual procedure for intravenous injection. The nickel ion is known to be toxic to some micro-organisms, to depress metabolism in tissue slices and, under certain conditions, metallic nickel can be carcinogenic, though this last action has not been demonstrated for the nickel ion. In acute experiments, nickel salts given intravenously cause a fall, followed by a rise and a later fall, of arterial pressure, an increase in breathing, cramps, vomiting and acute diarrhea with intestinal inflammation. These effects have been analyzed and shown to be partly due to central action and partly to peripheral effects. Death is due to respiratory failure when the administration is rapid, to cardiac failure when more slowly given. In more chronic administrations the principal effects are polycythaemia, porphyrinuria, increase in the size of the adrenals, and goitre.Nickel salts have been given orally to human subjects in doses up to 140 mg daily without clearly pronounced harmful effects. Orally administered nickel is very slightly absorbed, and mainly excreted in the faeces; injected intravenously it is mainly, and rapidly, excreted in the urine; according to experiments what remains in the body is to be found mainly in liver, kidneys, pancreas and spleen.In the present experiments, no evidence could be found that nickel was present in any tissues or organs 14 hr after intravenous injection. Post mortem examination showed intense congestion of the mucosa of the intestinal tract.On the rabbit isolated ileum preparation the effect was relaxation, with diminution of the rhythmic contractions on the rectum in situ intravenous injection caused powerful rhythmic contractions, and these probably account for the colic and diarrhea which often follow administration of nickel salts. The toxicity of nickel compounds is related to the ease with which they yield nickel ions, and hence is greatest in salts of nickel. Nickel nitrate yields ions readily; and the compound would be expected to be somewhat toxic. Exactly what occurs when nickel and cyanide ions are introduced into the body is uncertain; while being at the same time only slightly toxic (LD50=1,000 mg/kg). nickel ions can reach the brain, that is they can penetrate the blood-brain barrier, have no precipitating action on proteins, and, when introduced into the blood stream, are eliminated by the kidney, which is not damaged.The opposition between nickel and cyanide ions can be illustrated by experiments with isolated tissues. Some experiments were made to find whether nickel ions were able to reverse the inhibition of the cytochrome oxidase system produced by cyanide.using p-phenylenediamine as the oxidation substrate.Only about 10% of the initial oxidase activity was restored, Since the lethal dose of nickel salts is around 110 umoles/kg, the amount given as an antidote has mostly been lower than that; but that dose should be able to antidote 550 umoles of hydrocyanic acid, if the theoretical ratio holds good, and the mutual antidotal action should in theory reduce any risk of nickel poisoning. This would mean that, for a safe dose of a nickel salt, some 10 x LD50 of hydrocyanic acid intraperitoneally for rabbits, and 5 x LD50 intraperitoneally for mice,should be the maximum amounts that could be antidoted.In experiments done the maximum dose antidoted was 10 x LD50, in a goat.The present series, using mice and rabbits, gave results which are satis- factory for rabbits, but for mice fall short of the theoretical predictions mentioned above. When the molecular ratios of cyanide and nickel are calculated, it is seen that, in rabbits, the ratios are spread over the range 1.5 to 13. then in all cases there should be no hydrocyanic acid left free. In the instances where an excess would be left it would be only a fraction of an LD50, and this should have been nonlethal, but in one instance (cyanide/nickel ratio of 12) was not, which indicates that the case is not so simple as it first seemed.The results show that the nickel salt was more effective as an antidote for rabbits than for mice. For rabbits, provided the molar cyanide/ nickel ratio does not exceed 6, it seems that at least 6 x LD50 can be neutralized, while at a ratio of 12 even twice the LD50 is not antidoted. It should be noted, however, that, in the rabbit series, hydrocyanic acid was usually given intravenously, whether before or after the nickel. With mice that are less sensitive to hydrocyanic acid, and about as sensitive to nickel, as are rabbits, and the results are less regular. It appears from the results that, under the most favorable conditions, only upwards of twice the LD50 can be antidoted, and then only when the cyanide/nickel ratio is below 5. The hydrocyanic acid was given intraperitoneally and the nickel solution intravenously in this species, which might have affected the results. Thiosulphate alone had antidotal action which varied; for mice the value was around 2 x LD50 at the best, but was irregular, and in rabbits it was also around twice the LD50. The results are rather irregular, but show that, for mice, 3 x LD50 can be antidoted when the nickel compound is given with glucose, and when thiosulphate is also given. Some of the cyanide/nickel ratios were very high, as much as 20, but, as thiosulphate was also given, much of the beneficial effect must have been due to that. For rabbits the results were similar, but were also improved by giving thiosulphate. The most favorable condition for the action of the nickel antidotes would be expected to be if they were mixed with the hydrocyanic acid before administration.It would be expected that, if the resulting compound were not toxic and held the cyanide firmly enough in competition with cytochrome oxidase, the effect of the hydrocyanic acid would be entirely eliminated if enough antidote were present, and that, for instance, nickel salts would be able to fix more molar equivalents of hydrocyanic acid, A simple experiment shows that the complex formed by nickel salts though not harmless is not very toxic.Solutions of nickel nitrate and sodium cyanide were mixed in such proportions that the mixture contained 260 ,umoles of cyanide and 45 ,umoles of nickel salt per ml. This was injected into an ear vein of a rabbit in a dose of 1 ml./kg. This would be, in terms of hydrocyanic acid, about 8.5-times the LD50. For some minutes after injection there was panting and convulsions, followed by paresis of the hind limbs, and loss of consciousness, as would have been the effects of, say, half a lethal dose of hydrocyanic acid; but after 5 min, apart from a little panting, the animal was apparently normal and made an uninterrupted recovery, with no subsequent diarrhea. We might suppose, since the cyanide/nickel ratio was less than 6 that these transitory symptoms of cyanide poisoning were to be attributed to slight dissociation of the nickelocyanide, but in any case the experiment shows that there are grounds for the belief that the nickel ion can, under the most favorable conditions, antidote the theoretical amount of cyanide. These expectations were only in part borne out by experiment on mice, These results show that when the dose of hydrocyanic acid is low (3 x LD50 or less) and the cyanide/nickel ratio is 6 or less, the expectations from theory hold approximately, but with four or more times the LD50 and cyanide/ nickel ratios above 4 the results are less good. In the experiments the oxygen utilization of rats anaesthetized with a mixture of allobarbitone and urethane was measured by the use of a small-scale respirometer, and the effect of an intraperitoneal dose of hydrocyanic acid, as large as possible without causing arrest of respiration, was observed; nickel derivatives of various kinds were then injected intravenously, and the subsequent oxygen usage measured over a sufficient period. In several experiments, the nickel injection was given too late, but when the animal survived the nickel injection restoration of oxygen usage was prompt and complete and was often followed by increased usage, presumably the expression of oxygen lack.Interaction between nickel salt and hydrocyanic acid given orally when hydrocyanic acid or a cyanide is taken by mouth, one obvious line of treatment would be to give a nickel salt by mouth immediately, or as soon as possible after any appropriate intravenous therapy had been applied. An experiment was carried out by giving hydrocyanic acid by stomach tube to mice, and then following this up after an interval of time by administering by the same route a dilute nickel nitrate solution. It would seem that nickel nitrate solution, given by mouth within a short time of ingestion of cyanide, might be helpful; it would normally be followed by a wash-out of the stomach, or by chelating any excess of nickel and there would then be little danger from toxic effects due to absorption of nickel into the blood stream DISCUSSION The consequences of administration of cyanide depend mainly on the rate at which it enters the blood stream, maximum effect resulting when the dose is high and the rate of entry rapid, as for example, when a high concentration of hydrocyanic acid vapor is breathed or when a large dose is injected into a systemic vein, in either of which cases serious symptoms ensue in a matter of seconds and death within minutes. Even if attempts at recovery appear to be successful, permanent damage to the central nervous system may remain if the period of tissue anoxia has been more than a few minutes. As the rate of entry of cyanide into the circulation is slowed, by slower administration , another factor enters into consideration, namely, the rate of destruction of cyanide in the body by conversion into thiocyanate, a change which takes place mainly in the liver by the action of the enzyme rhodanese. The use of thiosulphate depends on the provision by it of available sulphur for this reaction; the change seems to be somewhat slow, so it is better as a prophylactic than as an antidote. Since cyanide when given orally or intraperitoneally enters initially into the portal circulation, it will go direct to the liver, so that destruction is facilitated and larger doses can therefore be tolerated. If the rate of eventual entry into the systemic circulation is slow enough, as on subcutaneous, oral or respiratory administration.of small doses, the effects are less serious, or may even be absent altogether. The mode of administration therefore has a definite effect on the LD50, and as shown, the LD50 in increasing order is intravenous-intramuscular-intraperitoneal -subcutaneous-oral, with inhalation, which is a common industrial risk, comparable with administration by the intravenous route. Another factor which influences the outcome is whether the antidote precedes or follows the administration of the cyanide and, if the latter, after what interval of time. It would be expected that the maximum antidotal effect would be seen when poison and antidote were mixed before administration,and next to this when the two were injected simultaneously into the circulation, or when antidote preceded the cyanide by a very short time; the minimum effect would be seen when the antidote was given slowly, for example subcutaneously, and at a time when the animal was near to death, when it would be all but useless. In nearly every instance in the present experiments, the antidote was administered intravenously, but intraperitoneal injection has also been found effective. For practical reasons the nickel antidote was usually given to mice intravenously a few seconds before the dose of hydrocyanic acid, intraperitoneally or intramuscularly. The toxic action of nickel ions is the probable reason for this, but this is not great and would largely be offset by the mutual detoxification of the two reactants. The number of mean lethal doses of hydrocyanic acid which can be antidoted by nickel ions is greater for rabbits than for mice, namely five to six for rabbits and two for mice, with maximal cyanide/nickel ratios of 5 and 4 respectively. One reason for this is that mice are less sensitive to hydrocyanic acid than are rabbits, while to nickel ions they are about equal in sensitivity. Doses of nickel nitrate greater than 50 umoles/kg, though lowering the cyanide/nickel ratio, were unsatisfactory for mice. Another reason in most of the present experiments is that in rabbits both substances were given intravenously, and so had more opportunity of reacting. The fact that the cyanide/nickel ratio can be, with rabbits, effective at ratios as high as 5, indicates that the changes involved in the antidotal reaction are much as expected from theoretical considerations; and the fact that, with high doses of hydrocyanic acid the effective cyanide/nickel ratio is usually lower, is probably to be explained on the basis that the difference between the affinities of the cyanide ions for cytochrome and for nickel are not very large. The results of the present experiments indicate that in that respect there is not much to choose between the two.The more favorable results which have been obtained with the compound by present a disagreement which must be explained; one explanation being that in those experiments cyanide and antidote were given almost simultaneously by intravenous injection, which, gives very favorable conditions for reaction.One fact is against the view that the compound is to be regarded as an ionizable salt of nickel, despite the similarity of their respective toxicities when expressed in terms of molarity; Ratio at effectivity when no thiosulphate is given is much lower than with nickel. This is also shown for the experiments with previous mixing, and bears out the findings of that the reaction is complete at a molar ratio of about 2, , then the compound is not an ordinary ionizable nickel salt, or it reacts with some blood constituent, or else it was not obtainable in as pure a state. The object of this investigation was to form an opinion as to the best antidote and method of treatment for cyanide poisoning. First, as to the amounts of the various antidotes which would be required for the treatment of a man who had received one LD50 of cyanide, say 50 mg of hydrocyanic acid, The question is, whether a dose of nickel nitrate of the order of 100 mg would be safe to give intravenously, taking into account the probability that most of its toxicity would be neutralized by the cyanide. The balance of evidence is that it would be a reasonably safe dose under the circumstances. And then to give an intravenous injection of hypertonic glucose.The use of oxygen administration has been advised,although the only explanation of its value which is offered is that it helps to overcome the large oxygen debt which is seen on recovery from the immediate effects of the poison; at all events, it should be tried. So also should the administration of nickel nitrate by mouth, in cases where cyanide has been ingested.
ABSTRACT
The effectiveness of a nickel nitrate, against hydrocyanic acid was examined mainly on mice and rabbits.For rabbits (4 xLD50),was effective at a molar cyanide/nickel ratio of 4. For mice (3 x LD50 at a molar ratio of 2), with no apparent side effects.
At a molar ratio of 1, it was slightly more effective than on rabbits.Nickel nitrate by mouth was effective against orally administered hydrocyanic acid. The oxygen uptake of the body, reduced by cyanide, improved when nickel antidotes has been successfully administered.Relatively small amounts of nickel salts would be needed for the neutralization of several fatal doses of cyanide.
KEY WORDS Antidote / Nickel nitrate / Cyanide poisoning
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