Seizures, Metabolic Acidosis and Coma Resulting from Acute Isoniazid Intoxication

Isoniazid is an anti-tuberculosis drug, used commonly for treatment and prophylaxis of tuberculosis. Acute isoniazid intoxication is characterized by a clinical triad consisting of metabolic acidosis resistant to treatment with sodium bicarbonate, seizures which may be fatal and refractory to standard anticonvulsant therapy, and coma. Treatment requires admission to the intensive care unit for ventilatory support, management of seizures and metabolic acidosis. Pyridoxine, in a dose equivalent to the amount of isoniazid ingested, is the only effective antidote. We report the successful treatment of two isoniazid intoxication cases: the case of a child developing an accidental acute isoniazid intoxication and an adult case of isoniazid intoxication with the intent of suicide.

Near Fatal Poisoning by Isoniazid and Rifampicin

Since six decades, Isoniazid and Rifampicin are used as first line drugs for treatment of tuberculosis. The minimum acute lethal or toxic dose of Rifampicin is not well established. However, non-fatal acute overdoses in adults have been reported with doses ranging from 9 to 12 gm and fatal acute overdoses with doses ranging from 14 to 60 gm. Isoniazid, if acutely ingested, even 1.5 to 2 gram may cause toxicity in adults. We report a case of Pott's spine on ATT, who took massive overdose of Rifampicin (>18 gm) and Isoniazid (>12 gm) and reported late (almost 36 hours) after ingestion. He was treated successfully with pyridoxine, hemodialysis and supportive care.

Rhabdomyolysis due to isoniazid poisoning resulting from the use of intramuscular pyridoxine

Isoniazid is an effective antituberculosis drug. Isoniazid poisoning produces a characteristic clinical syndrome that occurs 30 to 120 minutes after ingestion and includes seizures, metabolic acidosis, and in severe cases, coma. Rhabdomyolysis is one of the reported complications of isoniazid poisoning, but relevant data are limited. Parenteral pyridoxine is the antidote of isoniazid. In this case, a 16-year-old male patient admitted to the Pediatric Emergency Department two hours after isoniazid poisoning. For treatment, intramuscular pyridoxine was used, but he developed serious rhabdomyolysis.

Fatal suicidal poisoning with antituberculosis agents with ST elevation and acute coronary syndrome symptoms--a case report

A 19-years old, previously healthy male, ingested the higher amount of rifampicin, isoniazyd, pyrazinamide, ketoprofene and alcohol. Within less than 20 hours he developed dyspnoe, pruritus, red man syndrome, and ECG changes suggesting acute coronary syndrome appeared - ST interval elevation. In the next few hours chest pain appeared and troponin I concentration was elevated (13.54 ng/ml). The performed echocardiography revealed global hypokinesis with the decreased left ventricular ejection fraction (approx. 30%). There was no significant pathological changes in coronarography, except for slowed blood flow. Further patient developed cardiogenic shock, pulmonary oedema and died within 32 hours from medication overdose.

Toxic optic neuropathy

Toxic optic neuropathy (TON) is a disease entity which is not only underdiagnosed, but also often diagnosed at a stage when recovery of vision is not possible. This article gives an overview of common causes, clinical features, and management of TON.

Suicidal Isoniazid poisoning

Accidental or intentional Isoniazid poisoning may manifest within half to three hours as intractable seizure, acidosis, and coma. Single high dose of pyridoxine was used as an antidote with good response as reported earlier. Ingestion of more than 80 mg/kg body weight produces severe central nervous system symptoms and a dose of 125 mg/kg is potentially lethal if not promptly treated. We report a case of suicidal attempt with use of Isoniazid, who developed grand mal seizures and was controlled with diazepam and symptomatic treatment.

Accidental isoniazid poisoning--a report

Eight patients who had taken accidental overdose of Isoniazid were followed in relation to its clinical manifestations, EEG changes and management. All cases survived without any residual effect.

Acute isoniazid toxicity and the need for adequate pyridoxine supplies

A 25-year-old, 54-kg Hispanic man who had recently started multidrug therapy for pulmonary tuberculosis presented in status epilepticus after ingesting 9 g of isoniazid in a suicide attempt. Successful management of this patient required collaboration between several institutions to provide the large amount of necessary intravenous pyridoxine. Ultimately, this single overdose depleted the supply of intravenous pyridoxine for a significant region of the state of Nebraska. Isoniazid is commonly used to treat tuberculosis, but it is encountered relatively infrequently as the cause of an acute overdose. Severe isoniazid overdoses may present as seizure activity that is refractory to conventional antiepileptic therapy. Although intravenous pyridoxine is an effective antidote for isoniazid overdoses in patients presenting with status epilepticus, this agent has few indications and is typically stocked in limited quantities. In regions with large populations of patients who receive antituberculosis therapy, collaborative networks must be created to ensure that adequate supplies of intravenous pyridoxine (> or = 20 g) are available for effective treatment of isoniazid poisonings.

Intoxikation mit Isoniazid

HISTORY AND ADMISSION FINDINGS

A 55-year-old woman presented with sustained convulsions after the ingestion of an at first unknown amount of isoniazid, rifampin, ethambutol and alcohol.

INVESTIGATION

At admission the patient had a severe metabolic acidosis. Blood tests showed changes caused by the hepatotoxicity of isoniazid.

TREATMENT AND COURSE

Because diazepam was not efficacious in controlling the convulsions the patient was intubated. In response to the therapautic measures the convulsions stopped and metabolic acidosis was quickly compensated. Pyridoxine was given intravenously as an antidote.

CONCLUSION

The rare intoxication with isoniazid demands immediate administration of pyridoxine and aggressive treatment of the convulsions.

Pyridoxine in clinical toxicology: a review

Pyridoxine (vitamin B6) is a co-factor in many enzymatic pathways involved in amino acid metabolism: the main biologically active form is pyridoxal 5-phosphate. Pyridoxine has been used as an antidote in acute intoxications, including isoniazid overdose, Gyromitra mushroom or false morrel (monomethylhydrazine) poisoning and hydrazine exposure. It is also recommended as a co-factor to improve the conversion of glyoxylic acid into glycine in ethylene glycol poisoning. Other indications are recommended by some sources (for example crimidine poisoning, zipeprol and theophylline-induced seizures, adjunct to d-penicillamine chelation), without significant supporting data. The value of pyridoxine or its congener metadoxine as an agent for hastening ethanol metabolism or improving vigilance in acute alcohol intoxication is controversial. This paper reviews the various indications of pyridoxine in clinical toxicology and the supporting literature. The potential adverse effects of excessive pyridoxine dosage will also be summarized.

Do not overlook acute isoniazid poisoning in children with status epilepticus

A previously healthy 2-year-old girl was admitted with generalized convulsive status epilepticus. She was in a stupor and could respond only to painful stimuli. She also had severe metabolic acidosis. Although initial liver function tests were normal, they were found to be moderately high on the fifth day of admission; however, they dropped to their normal ranges on the twelfth day of admission. Initially, the patient was diagnosed as having idiopathic status epilepticus, and classic anticonvulsant agents, including diazepam, phenytoin, and then phenobarbital, were given. However, her seizures did not subside, and diazepam infusion was initiated. After initiation of diazepam infusion, the seizures were completely controlled. On the fourth day of admission, her parents said that she had accidentally received 20 tablets (a total dose of 2000 mg) of isoniazid just before admission to our hospital. Later, we injected 200 mg of pyridoxine intravenously. During follow-up, her general condition improved, and anticonvulsant agents were discontinued because an electroencephalogram was found to be norma. She was discharged from the hospital on the twelfth day of admission. At the fourth month of follow-up, she was seizure free. Because of this case, we would like to re-emphasize that acute isoniazid poisoning should also be considered in a child with unexplained status epilepticus.

Prevalence and interaction of hepatitis B and latent tuberculosis in Vietnamese immigrants to the United States

OBJECTIVES

Southeast Asian immigrants, with a high prevalence of both hepatitis B and latent tuberculosis, constitute a large proportion of immigrants to the United States. Isoniazid hepatotoxicity may be associated with hepatitis B. This study was conducted to document the prevalence and interaction of hepatitis B, latent tuberculosis, and isoniazid toxicity.

METHODS

Hepatitis B surface antigen (HBsAg) and tuberculin skin testing was done on 743 Vietnamese immigrants to the Midwest between January, 1991 and December, 1999. HBsAg positive cases were tested for hepatitis B e antigen (HBeAg). All tuberculin skin test-positive patients were treated with isoniazid, unless contraindicated. Complications of isoniazid treatment and compliance with hepatitis B virus immunization recommendations were evaluated.

RESULTS

One hundred three subjects (13.86%) had HBsAg, and 43 (5.7%) HBeAg. Prevalences of latent tuberculosis were similar in HBsAg positive (53%) and HBsAg negative (45%) subjects. Sixty-two percent of HBeAg positive versus 19% of HBeAg negative subjects had hepatotoxic side effects requiring discontinuation of treatment (relative risk [RR] = 11.38, CI = 5.49 < RR < 23.59, p < 0.001). Three cases of severe isoniazid hepatitis occurred in 21 HBeAg positive subjects, versus no cases in 121 HBeAg negative cases treated with isoniazid (RR = 7.72, CI = 5.02 < RR < 11.88, p < 0.001). Only 58% of subjects at risk of developing hepatitis B virus infection were appropriately immunized.

CONCLUSIONS

Vietnamese immigrants have a high prevalence of hepatitis B and latent tuberculosis. HBeAg positive cases have a 7.7-fold increased risk of serious isoniazid toxicity and an 11.3-fold increased risk of isoniazid side effects requiring discontinuation of treatment. HBeAg represents an important risk factor for severe isoniazid hepatitis.

Acute isoniazid neurotoxicity in childhood

Acute isoniazid (INH) poisoning is uncommon in children. Although most physicians are aware of INH hepatotoxicity, acute INH poisoning and its treatment are not well recognized. INH is increasingly being used to control the spread of tuberculosis, and physicians should know its potentially fatal effects. INH overdose is known to result in rapid onset of seizures, metabolic acidosis and prolonged obtundation. We report two cases of obtundation secondary to INH overdose that was immediately reversed by pyridoxine. Parenteral pyridoxine administration is an effective method in INH intoxication. The intravenous form of pyridoxine must be available in the emergency care units, and INH toxicity should be suspected in any patient with refractory seizures and metabolic acidosis.

Rhabdomyolysis in isoniazid poisoning

BACKGROUND

Rhabdomyolysis is one of the reported complications of isoniazid poisoning, but relevant data are limited.

METHODS

A retrospective study was conducted on isoniazid poisoning cases seen at the Philippine General Hospital over 5 years (1992-1997). Patients excluded from the study were those who coingested other substances, including hepatotoxic and nephrotoxic drugs, those with underlying medical illnesses, and those without creatine phosphokinase muscle fraction determinations.

RESULTS

Out of the 270 cases of isoniazid poisoning, 52 patient records were reviewed. Common clinical manifestations were seizures (100%), depressed sensorium (53%), and vomiting (45%). Laboratory results showed leukocytosis (74.5%), metabolic acidosis (29%), and impaired liver function tests (21%). Creatine phosphokinase muscle fraction was elevated in 59.6% of cases, beginning at a dose of 2.4 g. Values peaked on days 5 and 6 and declined on days 7 and 8. Statistically significant correlations were observed for the elevation of creatine phosphokinase muscle fraction with the duration/amount of drug ingested and the frequency of seizure. No correlation was observed between the frequency of seizures and elevated creatine phosphokinase muscle fraction nor between the time delay in consultation and elevation of creatine phosphokinase muscle fraction.

CONCLUSIONS

The incidence of rhabdomyolysis in isoniazid poisoning was 3/100 cases a year. The findings suggesting its direct toxic effect on the muscles may not be clinically relevant.

[Acute isoniazid poisoning presenting convulsion and liver dysfunction]

A-19-year-old girl ingested 7.4 g of Isoniazid (INH) and 14.5 g of Ethambutol (EB) intentionally. She presented repetitive generalized convulsions with metabolic acidosis, treated with diazepam and 7.5 g of Pyridoxine (Vitamin B6). During day 4 and 5, liver dysfunction worsened and prothrombin time declined below 5%. She was treated with infusion of fresh frozen plasma and fully recovered on day 13. Serum concentration of INH and EB at 5 hours after ingestion was 7.6, 0.94 micrograms/ml respectively.

Acute isoniazid intoxication: seizures, acidosis and coma

Isoniazid (INH) is the most widely used of the antituberculosis drugs. An acute overdose is potentially fatal and is characterized by the clinical triad of repetitive seizures unresponsive to the usual anticonvulsants, metabolic acidosis with a high anion gap and coma. The diagnosis of INH overdose should be considered in any patient who presents with an unexplained metabolic acidosis and convulsions. The cornerstone of therapy consists in pyridoxine (vitamin B6) and the dose should be equal to the amount of INH ingested. When conservative therapy fails or in case of renal insufficiency, dialysis must be considered. Severe central nervous toxicity can also be caused by chronic ingestion of higher than therapeutic doses of INH. In those cases pyridoxine-therapy can be useful as well. In the present paper a case of acute overdose of INH is reported, followed by a review of the literature.

Acute isoniazid exposures and antidote availability

BACKGROUND

Over the past 10 years the reported incidence of acute isoniazid (INH)-related poisonings has increased, with 507 cases reported in 1996. Parenteral pyridoxine is the antidote for INH-induced seizures, but 5-g aliquot recommended to treat an ingestion of unknown quantity of INH is not always readily available to emergency physicians.

OBJECTIVE

To determine the hospital availability of pyridoxine.

METHODS

One hundred thirty questionnaires were distributed nationwide to the pharmacies and emergency departments (ED) of hospitals containing pediatric emergency medicine (PEM) fellowships and/or emergency medicine (EM) residencies. Questions were posed regarding the availability, quantity, location, and deemed importance of pyridoxine at each institution.

RESULTS

Responses were received from 81% of the hospitals with fellowships and 80% of the hospitals with residencies. Half of the former and one third of the latter reported not having the recommended 5-g aliquot available. Eighty percent of the hospitals with PEM programs and 71% with EM residencies with an adequate stock store it in the hospital's pharmacy, as opposed to in the ED. Thirty-four states were represented, 18 of which have experienced an increase in tuberculosis (TB) from 1993 to 1994; 6/18 (33%) of those did not have the pyridoxine available, and 7/18 (39%) did not deem it necessary.

CONCLUSIONS

Our results imply that between one third and one half of the respondents would be ill-equipped to treat acute INH neurotoxicity. Establishing regional distribution centers may alleviate this deficiency, specifically in urban areas with a high incidence or a positive percent increase in TB.

Isoniazid poisonings in New York City

We identified 41 New York City residents who had been hospitalized at least overnight between January 1992 and September 1993 because of a toxic isoniazid (INH) exposure. Review of the available medical charts of 33 patients revealed that median age was 19 years, 27 (82%) were females, and 24 (83%) were taking INH chemoprophylaxis for tuberculosis infection. Twenty-two patients had seizures. Twenty-seven (82%) patients had attempted suicide using INH, and another three patients had intentionally misused INH by making up missed doses at one time. All patients survived. Physicians should be aware of the potential for INH toxicity and should assess their patients' current mental and psychosocial status when prescribing it. INH toxicity should be considered when young patients, particularly females, present with unexplained intractable seizures, and treatment with pyridoxine should be given.

Acute isoniazid poisoning: presenting as seizure

A case of young female who was brought in status epilepticus with history of isoniazid poisoning is discussed. Early institution of treatment with pyridoxine saves the patient's life.

Management of isoniazid poisoning--case report

A young girl was admitted with generalized tonic clonic seizures and unconsciousness, four hours after ingestion of 12 gm of isoniazid (INH). In the absence of injectable preparation of pyridoxine, she was treated with oral pyridoxine and made a complete recovery.

Intentional overdosage with isoniazid: case report and review of literature

Isoniazid (INH) is widely used in most prophylactic and therapeutic anti-tuberculosis regimens because of its effectiveness and low cost. Yet, INH poisoning appears to be rare. We report the first case of intentional INH overdosage in Singapore. A 26-year-old Filipino male presented with mental obtundation, recurrent seizures, metabolic acidosis and hepatic dysfunction. He was successfully treated with large doses of pyridoxine (vitamin B6). Recommendations for the management of acute INH toxicity are highlighted.

Acute isoniazid intoxication: a case report

Since its introduction in 1952, isoniazid has remained one of the drugs of choice in the treatment and prophylaxis of tuberculosis. In populations with a high prevalence rate of tuberculosis or suicide rate, acute ingestion of isoniazid has occasionally been reported. Acute intoxication by isoniazid is known to cause symptoms of seizures, metabolic acidosis, coma, and even death. These clinical symptoms, however, are not well recognized by physicians in Taiwan, even though the prevalence rate of tuberculosis is relatively high here. This report concerns the case of a 25-year-old female with a past history of tuberculosis who presented with the symptoms of refractory seizures, metabolic acidosis and deep coma after intentional ingestion of some unknown drug. Although implicating agents were not recognized initially, she was successfully revived with basic resuscitation, anticonvulsants and correction of metabolic acidosis. A review of her history revealed that her ingestion of five grams of isoniazid in this case was responsible for the entire clinical spectrum. Given easy access to isoniazid in Taiwan, a diagnosis of isoniazid poisoning should always be considered in patients who present with the classical symptoms of refractory seizures, metabolic acidosis and coma.

Treatment of acute isoniazid overdose in dogs

The National Animal Poison Control Center received 28 calls of isoniazid (INH) exposures in dogs and cats between 1987 and 1993. The ingestion of a single 300 mg INH tablet was the most common complaint. Isoniazid has a low therapeutic margin and produces life threatening signs in dogs ingesting single 300 mg human tablets. The LD50 of INH in dogs is estimated at 50 mg/kg bw, which is probably similar to that for humans. However, rodents are among the species most resistant to INH and thus are not good animal models for toxic dose extrapolation. The more consistent clinical signs reported were recurrent clonic-tonic seizures followed by a stuporous state with poor response to stimulus. Ideal treatment combines vitamin B6 given as a single i.v. bolus at an equivalent dose to the amount of INH ingested and anticonvulsants such as 1 mg diazepam/kg bw. This combination acts synergistically to improve GABAergic transmission in the CNS and has proved effective in protecting animals from further convulsions and death, even after several seizure episodes, as often encountered in clinical situations.

Isoniazid-associated rhabdomyolysis

We report the occurrence of rhabdomyolysis and hepatitis in a 17-year-old girl after the ingestion of up to 10.8 g of isoniazid. The initial isoniazid concentration in the blood was 1,230 mmol/L. There were no findings indicating the ingestion of other substances known to be associated with rhabdomyolysis. In addition to rhabdomyolysis (peak creatine phosphokinase 88,000 U/L), the patient had a significant elevation of her liver enzymes (peak aspartate aminotransferase 1,980 U/L). She recovered completely without evidence of liver or renal damage. Rhabdomyolysis and isoniazid-induced hepatitis are complications that should be considered when caring for patients with acute isoniazid ingestion.

Isoniazid overdose: four case reports and review of the literature

OBJECTIVES

To review the pathophysiology, presentation and treatment of isoniazid (INH) intoxication.

DATA SOURCES

Human, animal and modeling studies published since 1940 identified through MEDLINE and a review of the bibliographies of relevant articles.

STUDY SELECTION AND DATA EXTRACTION

The studies identified were reviewed with emphasis on the most recent. Earlier studies were selected for their historical value and relevance to the clinical setting.

DATA SYNTHESIS

Isoniazid overdose is a potentially fatal intoxication. The incidence of tuberculosis has recently increased in the United States and therefore the frequency of INH overdose may also increase. Patients with INH overdose may present with nausea, vomiting, ataxia, symptoms reminiscent of atropine intoxication, coma and grand mal seizures. Lactic acidosis is revealed by laboratory evaluation. Treatment requires admission to the ICU for ventilatory support, and management of seizures and acid-base abnormalities. Pyridoxine, in a dose equivalent to the amount of INH ingested, is the only effective antidote.

CONCLUSIONS

INH overdose should be suspected in any patient presenting with seizures and metabolic acidosis. Prognosis is good when treatment is instituted early.

Acute isoniazid neurotoxicity in an urban hospital

OBJECTIVES

To describe the presentation and treatment of acute isoniazid (INH) neurotoxicity appearing at an inner-city municipal hospital.

DESIGN

Case series.

PARTICIPANTS

Seven patients (eight patient visits) with an age range of 5 days to 14.9 years.

RESULTS

At our institution, no children appeared with acute INH neurotoxicity in the period 1985 through 1990, whereas seven patients were treated from 1991 through 1993. This paralleled the rise in the number of children with tuberculous infection and disease seen at our institution, from an average 96 per year to 213 per year during these two time periods. All seven patients were receiving INH daily for tuberculosis (TB) prophylaxis. Accidental ingestion (five episodes) and suicidal attempts (three episodes) accounted for these visits. The total amount ingested range from 14.3 to 99.3 mg/kg (mean, 54 mg/kg). All but one patient presented with afebrile seizures. One patient presented twice with seizures. Acute INH neurotoxicity was not suspected on the first admission; however, when readmitted 4 weeks later with another seizure, the diagnosis of acute INH neurotoxicity was made.

INTERVENTION

Intravenous pyridoxine was used in five episodes. Because it was not a stocked item in our pediatric emergency cart (as well as at another hospital, necessitating a transfer of a patient with refractory seizures to our hospital), the average delay was 5.8 hours (range, 1.3 to 13 hours) before it was given. Two patients with refractory seizures failed to respond to anticonvulsants, and their seizures were controlled only after parenteral pyridoxine.

CONCLUSIONS

We have seen an increased incidence of acute INH neurotoxicity because of the resurgence of TB in New York City. Others as well may see a similar rise based on local trends in TB infection and disease. Acute INH toxicity should be suspected in children presenting with seizures with or without fever. In patients with a known access to INH, seizures should be considered to be caused by INH toxicity unless proved otherwise. Parenteral pyridoxine, the specific antidote for INH-induced refractory seizures, should be readily available in every emergency department in the areas similarly experiencing increasing trends of TB.