Alan H. Hall

Clinical toxicology of cyanide

Cyanide poisoning causes a high incidence of severe symptomatology and fatality. There are numerous sources of potential cyanide exposure. Without the history of cyanide exposure, diagnosis is often difficult. Treatment with supportive measures and available specific and efficacious antidotes frequently allows survival. The toxicology of cyanide, including sources, clinical features, diagnosis, and treatment, is reviewed.

HYDROXOCOBALAMIN AS A CYANIDE ANTIDOTE: SAFETY, EFFICACY AND PHARMACOKINETICS IN HEAVILY SMOKING NORMAL VOLUNTEERS

The safety, efficacy and pharmacokinetic parameters of 5 g of hydroxocobalamin given intravenously, alone or in combination with 12.5 g of sodium thiosulfate, were evaluated in healthy adult men who were heavy smokers. Sodium thiosulfate caused nausea, vomiting, and localized burning, muscle cramping, or twitching at the infusion site. Hydroxocobalamin was associated with a transient reddish discoloration of the skin, mucous membranes, and urine, and when administered alone produced mean elevations of 13.6% in systolic and 25.9% in diastolic blood pressure, with a concomitant 16.3% decrease in heart rate. No other clinically significant adverse effects were noted. Hydroxocobalamin alone decreased whole blood cyanide levels by 59% and increased urinary cyanide excretion. Pharmacokinetic parameters of hydroxocobalamin were best defined in the group who received both antidotes: t1/2 (alpha), 0.52 h; t1/2 (beta), 2.83 h; Vd (beta), 0.24 L/kg; and mean peak serum concentration 753 mcg/mL (560 mumol/L) at 0-50 minutes after completion of infusion. Hydroxocobalamin is safe when administered in a 5 gram intravenous dose, and effectively decreases the low whole blood cyanide levels found in heavy smokers.

Acetaminophen Hepatotoxicity in Alcoholics

Excerpt To the editor: Seeff and colleagues (1) presented the cases of 6 patients and reviewed those of 19 others reported in the literature describing the possible development of hepatotoxicity in...

Ibuprofen overdose: 126 cases

In this study of ibuprofen overdose, symptoms developed in 19% of patients (24 of 126) — in 7% of children (6 of 88) and in 47% of adlts (18 of 38). Central nervous system depression, seizures, gastrointestinal disturbances, bradycardia, hypotension, apnea, abnormal renal functions, hematuria, nystagmus, and blurred vision were observed. No patients became symptomatic more than four hours after ingestion. There was no significant difference ( P > .05) between symptomatic and asymptomatic adult groups in either total milligrams or milligram-per-kilogram amounts ingested by history. Pediatric patients who became symptomatic had a mean ingestion by history of 440 mg/kg; those who remained asymptomatic had a mean ingestion by history of 114 mg/kg ( P

Toxic Effects of Nonsteroidal Anti-Inflammatory Drugs in Overdose

SummaryNonsalicylate, nonsteroidal anti-inflammatory drugs (NSAIDs) can be divided into 4 chemical classes: acetic acids, fenamic acids, oxicams and propionic acids. Most NSAID overdoses result in a benign outcome. Of 50 614 exposures reported to poison centres in the United States in a 2-year period, 131 (0.26%) had a major outcome, with 10 deaths. Despite the generally mild effects reported in large patient series, isolated case reports have documented serious toxicity, such as seizures, hypotension, apnoea, coma and renal failure. The majority of these consequences occur after ingestion of substantial quantities by adults attempting suicide. Rarely, with ibuprofen and piroxicam, children who ingest small amounts in accidental exposure develop serious toxicity.Typical signs and symptoms of NSAID overdose include nausea, vomiting, headache, drowsiness, blurred vision and dizziness. Seizures are rarely documented across all NSAID classes, with the exception of mefenamic acid (where seizures occur in over one-third of cases), or following massive ingestion of other agents. Drugs in the propionic acid group have produced metabolic acidosis, respiratory depression and coma in severe cases. Ibuprofen is the agent with the most published data on overdose, probably because it is available without a prescription in many countries. Symptoms are unlikely after ingestion of 100 mg/kg or less, and are usually not life-threatening unless more than 400 mg/kg is ingested. There is some relationship between plasma concentrations and the potential for development of symptoms, but plasma concentrations have no impact on treatment decisions. Treatment of NSAID overdose is entirely supportive. Recent trends in emergency department procedures regarding gastric decontamination are evolving towards the recommended administration of activated charcoal without gastric emptying in patients presenting more than 1 hour after ingestion, although gastric lavage, followed by administration of activated charcoal, may be advisable in patients who present earlier. Home administration of syrup of ipecac is still recommended if treatment is given shortly after ingestion, with a few exceptions: for example, ipecac is contraindicated after ingestion of mefenamic acid or ibuprofen in amounts greater than 400 mg/kg.Urine alkalinisation and diuresis have been recommended to enhance the elimination of NSAIDs, based on a pKa in the range of 3 to 5. However, because the drugs are universally highly protein bound, with little unchanged renal excretion, this technique is not likely to be beneficial. Haemodialysis is also unlikely to enhance elimination, but may be required if oliguric renal failure develops. Multiple dose activated charcoal may be useful in enhancing elimination of NSAIDs with long half-lives, such as piroxicam and sulindac.

Drug- and Chemical-Induced Methaemoglobinaemia

SummaryMethaemoglobin is haemoglobin with the iron oxidised to the ferric (Fe+++) state from the normal (or reduced) ferrous (Fe++) state. Methaemoglobinaemia refers to the presence of greater than the normal physiological concentration of 1 to 2% methaemoglobin in erythrocytes.Methaemoglobin is incapable of transporting oxygen. It has an intense dark blue colour; thus, clinical cyanosis becomes apparent at a concentration of about 15%. The symptoms are manifestations of hypoxaemia with increasing concentrations of methaemoglobin. Concentrations in excess of 70% are rare, but are associated with a high incidence of mortality.Methaemoglobinaemia may be congenital but is most often acquired. Congenital methaemoglobinaemia is of two types. The first is haemoglobin M disease (several variants) which is due to the presence of amino acid substitutions in either the a or β chains. The second type is due to a deficiency of the NADH-dependent methaemoglobin reductase enzyme. This deficiency has an autosomal dominant transmission, and both homozygous and heterozygous forms have been reported. The heterozygous form is not normally associated with clinical cyanosis, but such individuals are more susceptible to form methaemoglobin when exposed to inducing agents.A wide variety of chemicals including several drugs, e.g. the antimalarials chloroquine and primaquine, local anaesthetics such as lignocaine, benzocaine and prilocaine, glyceryl trinitrate, sulphonamides and phenacetin, have been reported to induce methaemoglobinaemia.An intense ‘chocolate brown’coloured blood and central cyanosis unresponsive to the administration of 100% oxygen suggests the diagnosis. A simple bedside test using a drop of the patient’s blood on filter paper helps to confirm the clinical suspicion. Methaemoglobin can be quantitated rapidly by a spectrophotometric method.The intravenous administration of methylene blue (tetramethylthionine chloride) is a specific treatment for acquired methaemoglobinaemia, but may be ineffective in chlorate poisoning. Chlorate poisoning and severe cases of methaemoglobinaemia require exchange transfusion. Hyperbaric oxygen can sustain life during preparations for exchange transfusion.

Hydroxycobalamin/sodium thiosulfate as a cyanide antidote

Severe, acute cyanide poisoning is uncommon and can be very difficult to diagnose if a history of exposure is unavailable. Victims of smoke inhalation may have significant cyanide poisoning as well as carbon monoxide toxicity. The Lilly Cyanide Antidote Kit currently available in America unfortunately has its own inherent toxicity. An efficacious antidote lacking toxicity is desirable, especially in cases where the diagnosis of cyanide poisoning cannot be made with certainty. Hydroxycobalamin/sodium thiosulfate has been used in France since 1970. Both components have been shown to be safe and efficacious in animal studies. Case reports of human cyanide poisoning treated with hydroxycobalamin/sodium thiosulfate have been published only in French. Animal and human data on the use of this antidotal combination are reviewed. Hydroxycobalamin/sodium thiosulfate is an efficacious cyanide antidote with little inherent toxicity.

Which cyanide antidote

Cyanide has several antidotes, with differing mechanisms of action and diverse toxicological, clinical, and risk–benefit profiles. The international medical community lacks consensus about the antidote or antidotes with the best risk–benefit ratio. Critical assessment of cyanide antidotes is needed to aid in therapeutic and administrative decisions that will improve care for victims of cyanide poisoning (particularly poisoning from enclosed-space fire-smoke inhalation), and enhance readiness for cyanide toxic terrorism and other mass-casualty incidents. This paper reviews preclinical and clinical data on available cyanide antidotes and considers the profiles of these antidotes relative to properties of a hypothetical ideal cyanide antidote. Each of the antidotes shows evidence of efficacy in animal studies and clinical experience. The data available to date do not suggest obvious differences in efficacy among antidotes, with the exception of a slower onset of action of sodium thiosulfate (administered alone) than of the other antidotes. The potential for serious toxicity limits or prevents the use of the Cyanide Antidote Kit, dicobalt edetate, and 4-dimethylaminophenol in prehospital empiric treatment of suspected cyanide poisoning. Hydroxocobalamin differs from these antidotes in that it has not been associated with clinically significant toxicity in antidotal doses. Hydroxocobalamin is an antidote that seems to have many of the characteristics of the ideal cyanide antidote: rapid onset of action, neutralizes cyanide without interfering with cellular oxygen use, tolerability and safety profiles conducive to prehospital use, safe for use with smoke-inhalation victims, not harmful when administered to non-poisoned patients, easy to administer.

Hydrogen sulfide poisoning from toxic inhalations of roofing asphalt fumes

Hydrogen sulfide poisoning from inhalation of roofing asphalt fumes is a rare but devastating injury. Two cases of toxic inhalation involving exposure to several gases, including hydrogen sulfide, evolved from cooling asphalt, are presented. Both victims were treated with supportive measures, including 100% normobaric oxygen, and one also received sodium nitrite. In one patient rapid, complete recovery was temporally associated with nitrite administration. The patient not treated with sodium nitrite survived with apparently permanent severe neurological sequelae.

Acute ingestions of boric acid

Four patients with elevated serum boric acid levels after single, acute ingestions of 10 to 297 grams were reported to the Rocky Mountain Poison and Drug Center (RMPDC) between January 1983 and August 1985. Systemic effects were absent. In 1983-4, 364 cases of boric acid exposure were reported to the RMPDC with only one fatality from a probable chronic ingestion. Vomiting, nausea, diarrhea, and abdominal cramps were rather common. Systemic effects were notably absent in acute ingestions. Five of three hundred sixty-four patients had measured serum levels and were the only ones hospitalized. These observations suggest that significant poisoning is unlikely to result from a single, acute ingestion of boric acid. Serum boric acid levels appear to correlate poorly with clinical toxicity following acute ingestion.