Isoniazid overdose treated with high-dose pyridoxine

Extracorporeal treatments for isoniazid poisoning: Systematic review and recommendations from the EXTRIP workgroup

Isoniazid toxicity from self-poisoning or dosing errors remains common in regions of the world where tuberculosis is prevalent. Although the treatment of isoniazid poisoning is centered on supportive care and pyridoxine administration, extracorporeal treatments (ECTRs), such as hemodialysis, have been advocated to enhance elimination of isoniazid. No systematic reviews or evidence-based recommendations currently exist on the benefit of ECTRs for isoniazid poisoning. The Extracorporeal Treatments in Poisoning (EXTRIP) workgroup systematically collected and rated the available evidence on the effect of and indications for ECTRs in cases of isoniazid poisoning. We conducted a systematic review of the literature, screened studies, extracted data on study characteristics, outcomes, and measurement characteristics, summarized findings, and formulated recommendations following published EXTRIP methods. Forty-three studies (two animal studies, 34 patient reports or patient series, and seven pharmacokinetic studies) met inclusion criteria. Toxicokinetic or pharmacokinetic analysis was available for 60 patients, most treated with hemodialysis (n = 38). The workgroup assessed isoniazid as "Moderately Dialyzable" by hemodialysis for patients with normal kidney function (quality of evidence = C) and "Dialyzable" by hemodialysis for patients with impaired kidney function (quality of evidence = A). Clinical data for ECTR in isoniazid poisoning were available for 40 patients. Mortality of the cohort was 12.5%. Historical controls who received modern standard care including appropriately dosed pyridoxine generally had excellent outcomes. No benefit could be extrapolated from ECTR, although there was evidence of added costs and harms related to the double lumen catheter insertion, the extracorporeal procedure itself, and the extracorporeal removal of pyridoxine. The EXTRIP workgroup suggests against performing ECTR in addition to standard care (weak recommendation, very low quality of evidence) in patients with isoniazid poisoning. If standard dose pyridoxine cannot be administered, we suggest performing ECTR only in patients with seizures refractory to GABA_A receptor agonists (weak recommendation, very low quality of evidence).

Neurological and Psychiatric Adverse Effects of Antimicrobials

Antimicrobials are a widely used class of medications, but several of them are associated with neurological and psychiatric side effects. The exact incidence of neurotoxicity with anti-infectives is unknown, although it is estimated to be < 1%. Neurotoxicity occurs with all classes of antimicrobials, such as antibiotics, antimycobacterials, antivirals, antifungals and antiretrovirals, with side effects ranging from headaches, anxiety and depression to confusion, delirium, psychosis, mania and seizures, among others. It is important to consider these possible side effects to prevent misdiagnosis or delayed treatment as drug withdrawal can be associated with reversibility in most cases. This article highlights the different neurotoxic effects of a range of antimicrobials, discusses proposed mechanisms of onset and offers general management recommendations. The effects of antibiotics on the gut microbiome and how they may ultimately affect cognition is also briefly examined.

Oral pyridoxine can substitute for intravenous pyridoxine in managing patients with severe poisoning with isoniazid and rifampicin fixed dose combination tablets: a case report

Background

Fixed drug combination of isoniazid and rifampicin is a rare cause of poisoning even in endemic countries for tuberculosis infection. Severe poisoning can cause severe morbidity and mortality if not treated promptly. Though intravenous pyridoxine is the preferred antidote for severe standard isoniazid poisoning it is not freely available even in best of care centers. We describe a case of severe poisoning with fixed drug combination of isoniazid and rifampicin successfully managed with oral pyridoxine at national hospital of Sri Lanka.

Case presentation

A 22 year old, Sri Lankan female presented to a local hospital 1 h after self-ingestion of 28 tablets of fixed drug combination of isoniazid and rifampicin which contained 4.2 g of standard isoniazid and 7.2 g of rifampicin. One and half hours after ingestion she developed generalized tonic–clonic seizure with loss of consciousness. She was given intravenous diazepam 5 mg immediately and transferred to national hospital of Sri Lanka, for further care. Upon arrival to tertiary care hospital in 3.5 h of poisoning she had persistent vomiting, dizziness and headache. On examination, she was drowsy but arousable, orange–red discoloration of the body was noted even with the dark skin complexion. She also had orange–red colour urine and vomitus. Pulse rate was 104 beats/min, blood pressure 130/80 mmHg, respiratory rate was 20 breaths/min. The arterial blood gas analysis revealed compensated metabolic acidosis and mildly elevated lactic acid level. Considering the clinical presentation with neurological toxicity and the large amount of isoniazid dose ingested, crushed oral tablets of pyridoxine 4.2 g (equal to standard isoniazid dose ingested) administered immediately via a nasogastric tube since intravenous preparation was not available in the hospital. Simultaneously forced diuresis using intravenous 0.9% saline was commenced in order to enhance excretion of toxic metabolites via kidneys. She had no recurrence of seizures but had acute liver injury subsequently which gradually improved with supportive care. Her liver functions found to be completely normal 1 week after the discharge.

Conclusions

Poisoning with fixed drug combination of isoniazid and rifampicin tablets is rare but can cause severe morbidity and mortality if not treated promptly. Oral pyridoxine can substitute for intravenous pyridoxine with almost similar efficacy at a low cost in managing patients with acute severe standard isoniazid poisoning in resource poor setting.

PdxH proteins of mycobacteria are typical members of the classical pyridoxine/pyridoxamine 5'-phosphate oxidase family

Pyridoxal 5'-phosphate (PLP) biosynthesis is essential for the survival and virulence of Mycobacterium tuberculosis (Mtb). PLP functions as a cofactor for 58 putative PLP-binding proteins encoded by the Mtb genome and could also act as a potential antioxidant. De novo biosynthesis of PLP in Mtb takes place through the 'deoxyxylulose 5'-phosphate (DXP)-independent' pathway, whereas PdxH enzymes, possessing pyridoxine/pyridoxamine 5'-phosphate oxidase (PNPOx) activity, are involved in the PLP salvage pathway. In this study, we demonstrate that the annotated PdxH enzymes from various mycobacterial species are bona fide members of the classical PNPOx enzyme family, capable of producing PLP using both pyridoxine 5'-phosphate (PNP) and pyridoxamine 5'-phosphate (PMP) substrates.

Antidotes to coumarins, isoniazid, methotrexate and thyroxine, toxins that work via metabolic processes

Some toxins cause their effects by affecting physiological processes that are fundamental to cell function or cause systemic effects as a result of cellular interaction. This review focuses on four examples, coumarin anticoagulants, isoniazid, methotrexate and thyroxine from the context of management of overdose as seen in acute general hospitals. The current basic clinical pharmacology of the toxin, the clinical features in overdose and evidence base for specific antidotes are discussed. The treatment for this group is based on an understanding of the toxic mechanism, but studies to determine the optimum dose of antidote are still required in all these toxins except thyroxine, where treatment dose is based on symptoms resulting from the overdose.

Seizures caused by pyridoxine (vitamin B6) deficiency in adults: A case report and literature review

Pyridoxine (vitamin B6) deficiency is a recognised cause of intractable seizures in neonates. However, pyridoxine deficiency related seizures in adults were rarely reported. This article reports a case of a 79 year old lady who suffered from new-onset seizures and was successfully treated with vitamin B6. The patient had chronic renal disease and weight loss due to anepithymia following a pelvic fracture. This article also reviews literatures of seizures caused by pyridoxine deficiency in adults. Seizures caused by vitamin B6 deficiency in adults may result from dietary deficiency, liver disease, pregnancy and certain medications and can be easily treated by vitamin B6 with excellent outcome. Clinicians should consider vitamin B6 deficiency as a potential aetiology of seizures, even in patients who suffer from other underlying diseases which can cause seizures.

Effects of pyridoxine on the intestinal absorption and pharmacokinetics of isoniazid in rats

Pyridoxine is always simultaneously administered orally with isoniazid for tuberculosis patients in the clinic to prevent or treat the nervous system side effects induced by isoniazid. So the aim of this research was to investigate the effects of pyridoxine on the intestinal absorption and pharmacokinetics of isoniazid. The intestinal absorption of isoniazid with or without pyridoxine was investigated by the rat single-pass intestinal perfusion model in situ, and a high-performance liquid chromatographic method was applied to study the pharmacokinetics of isoniazid with or without pyridoxine. The results suggested that the intestinal apparent permeability (P app) and intestinal absorption rate constant (K a) for isoniazid (30 μg/ml) were decreased by 43.7 and 36.4 %, respectively, by co-perfused pyridoxine (40 μg/ml). In vivo, the effect of pyridoxine on isoniazid pharmacokinetic correlated with the doses of pyridoxine. The blood concentrations of isoniazid at the absorption phase were affected by co-administered pyridoxine, but the AUC and C max of isoniazid were not greatly affected by pyridoxine as expected from the inhibition by pyridoxine of the intestinal absorption of isoniazid, which could be caused by its rapid absorption phase. Therefore, although the intestinal absorption of isoniazid could be significantly inhibited by pyridoxine, the pharmacokinetics of isoniazid oral administration was not greatly affected by the decreased intestinal absorption of isoniazid due to its rapid absorption.

Isoniazid-induced status epilepticus in a pediatric patient after inadequate pyridoxine therapy

BACKGROUND

Isoniazid (INH) is an effective treatment for tuberculosis and among the most common causes of drug-induced seizures in the United States. Isoniazid intoxication produces a characteristic clinical syndrome including seizures, metabolic acidosis, and, in severe cases, respiratory depression and coma.

CASE

A 10-month-old male infant was presented after being found with his father's INH. The patient was brought to a local hospital where he had a witnessed generalized seizure and was given 650 mg pyridoxine intravenously, which was based on a 70 mg/kg recommendation. Five hours after the time of ingestion, the patient developed recurrent generalized seizures. He was given diazepam and then loaded with phenobarbital 20 mg/kg, while awaiting more pyridoxine from the pharmacy. He received an additional 2 g pyridoxine for a suspected ingestion of approximately 2.7 g INH (290 mg/kg total dose), and his seizures subsequently resolved.

DISCUSSION

Treatment of INH toxicity must address correction of gamma-aminobutyric acid deficiency with pyridoxine replacement and management of life-threatening events. For poisonings in which the amount of INH ingested is known, pyridoxine is dosed on a gram-for-gram basis. Several reference textbooks recommend pyridoxine dosing in children to be 70 mg/kg. This was the justification for the initial pyridoxine dose administered in our case. However, after review of the referenced literature, the rationale supporting this recommendation remains unclear. Benzodiazepines should also be given with pyridoxine as they have been shown to have a synergistic effect in terminating seizures in animal models.

CONCLUSIONS

As soon as possible after INH overdose is suspected or diagnosed, pyridoxine should be administered in a dose approximately equal to the estimated amount of INH ingested regardless of the age of the patient.

Antitubercular drug poisoning in a pregnant woman

A 20-year-old female in her third month of pregnancy, presented with generalised tonic clonic seizures, metabolic acidosis and coma following suicidal ingestion of antitubercular medication. We successfully managed the case with pyridoxine, sodium bicarbonate and mechanical ventilation.

Management of the critically poisoned patient

BACKGROUND

Clinicians are often challenged to manage critically ill poison patients. The clinical effects encountered in poisoned patients are dependent on numerous variables, such as the dose, the length of exposure time, and the pre-existing health of the patient. The goal of this article is to introduce the basic concepts for evaluation of poisoned patients and review the appropriate management of such patients based on the currently available literature.

METHODS

An unsystematic review of the medical literature was performed and articles pertaining to human poisoning were obtained. The literature selected was based on the preference and clinical expertise of authors.

DISCUSSION

If a poisoning is recognized early and appropriate testing and supportive care is initiated rapidly, the majority of patient outcomes will be good. Judicious use of antidotes should be practiced and clinicians should clearly understand the indications and contraindications of antidotes prior to administration.

Pyridoxine therapy in a patient with severe hydrazine sulfate toxicity

OBJECTIVE

To report hydrazine sulfate as a cause of severe encephalopathy and to report its response to high-dose pyridoxine therapy.

DESIGN

Case report.

SETTING

An adult six-bed medical/surgical intensive care unit of a general hospital.

PATIENT

One patient who developed severe encephalopathy after hydrazine sulfate.

INTERVENTION

5 g i.v. pyridoxine.

MEASUREMENTS AND MAIN RESULTS

After 180 mg/day for 2 wks followed by 360 mg/day of hydrazine sulfate ingestion, our patient suffered severe encephalopathy. He received mechanical ventilation with attendant supportive measures and high-dose pyridoxine. The patient's encephalopathy resolved 24 hrs after receiving pyridoxine.

CONCLUSION

Severe encephalopathy could result from hydrazine sulfate toxicity. High-dose pyridoxine is an effective treatment to reverse this encephalopathy.

Acute isoniazid neurotoxicity during preventive therapy

OBJECTIVE

To describe rare side effects of treatment with isoniazid.

DESIGN

Descriptive case report.

SETTING

Medical intensive care unit in a university medical center.

PATIENT

A 14-yr old previously healthy girl receiving preventive isoniazid therapy who suddenly developed generalized tonic-clonic seizures and coma.

INTERVENTIONS

Patient was sedated and mechanically ventilated. She also received pyridoxine intravenously.

MEASUREMENTS AND MAIN RESULTS

An isoniazid overdose was not confirmed. Computed tomography of the brain and electroencephalogram revealed nothing abnormal. Seizures gradually disappeared within 2 hrs after sedation and treatment with pyridoxine. The patient was discharged on day 14 without consequences and has been well for 10 mos. No seizures reappeared after isoniazid was discontinued.

CONCLUSIONS

We caution against possible isoniazid neurotoxicity in healthy individuals using recommended preventive doses.

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.

Update on Antidotal Therapy

Antidotal therapy is useful for only a meager number of poisonous agents in which reversal of the effects of the toxin, or treatment of the toxin-induced pathophysiologic derangements, is possible. This review of selected antidotes is meant to acquaint the reader with some of the new and/or controversial uses for a few of our older agents, to introduce two new agents recently marketed, and to refresh information on antidotes not often used.

Treatment of a potentially lethal dose isoniazid ingestion

A seven-year-old boy ingested 3,000 mg (125 mg/kg) of isoniazid. Initial blood levels of isoniazid were 250 micrograms/mL approximately six hours after ingestion. Despite IV treatment in the emergency department with 3,000 mg pyridoxine and a repeat of the same antidote one hour later in the intensive care unit, the high isoniazid blood levels and persistent metabolic acidosis and coma prompted a decision to increase drug clearance by hemodialysis. Clearance data confirmed the effectiveness of hemodialysis in removing the poison, and the clinical response was dramatic.

Advances in clinical toxicology

New data are reviewed in two areas in the management of the acute overdose: gastrointestinal decontamination and systemic antidotes. The mechanism and effectiveness of Ipecac syrup, gastric aspiration and lavage, activated charcoal, gastrointestinal dialysis, and saline cathartics are discussed. Special problems posed by disc batteries and packet ingestion of cocaine (in transporting contraband) are highlighted. The pharmacology and uses of pyridoxine and naloxone as antidotes are detailed.