Metabolic acidosis isoniazid

Coma Increase/decrease Seizures, metabolic acidosis Isoniazid... 

Normally, the sum of the cations exceeds the sum of the anions by no more than 12-16 mEq/L (or 8-12 mEq/L if the formula used for estimating the anion gap omits the potassium level). A larger-than expected anion gap is caused by the presence of unmeasured anions (lactate, etc) accompanying metabolic acidosis. This may occur with numerous conditions, such as diabetic ketoacidosis, renal failure, or shock-induced lactic acidosis. Drugs that may induce an elevated anion gap metabolic acidosis (Table 58-1) include aspirin, metformin, methanol, ethylene glycol, isoniazid, and iron. 

Isoniazid Isoniazid is incompatible with sugars. Isoniazid overdose may be severe to fatal, and treatment is symptomatic and supportive, including stomach wash for control of convulsions and treating metabolic acidosis. Administration of pyridoxine and hemodialysis may be needed. Isoniazid interacts with carba-mazepine, phenytoin, diazepam, triazolam, chlorzoxazone, theophylline, ethosux-imide, enflurane, cycloserine, and warfarin. 

Acute poisoning with isoniazid in children (48) and adults (13,26,35) causes recurrent seizures, profound metabolic acidosis, coma, and even death. In adults, toxicity can occur with the acute ingestion of as little as 1.5 g of isoniazid. Doses larger than 30 mg/kg often produce seizures and 80-150 mg/kg or more can be rapidly fatal. The first signs and symptoms of isoniazid toxicity usually appear 0.5-2.0 hours after ingestion, by which time peak absorption occurs (49), and include nausea, vomiting, slurred speech, dizziness, tachycardia, and urinary... 

When taken or administered in overdose to dogs, isoniazid produces seizures, metabolic acidosis, and, if untreated, death. 

This gap is normally 12-16 meq/L. A significant increase may be produced by diabetic ketoacidosis, renal failure, or drug-induced metabolic acidosis. Drugs that may cause metabolic acidosis include ethanol, ethylene glycol, isoniazid, iron, methanol, phenelzine, salicylates, tranylcypromine, and verapamil. 

Isoniazid (INH), a hydrazide derivative of isonicotinic acid, is the bactericidal drug of choice for tuberculosis. INH is well known for its propensity to cause hepatitis with chronic use. Acute isoniazid overdose is a common cause of drug-indued seizures and metabolic acidosis. 

The significance of the metabolic acidosis which occurs following ingestion of large amounts of isoniazid is emphasized in a paper by Bear et al. in which the point is made that the diagnosis of isoniazid overdose should always be considered in patients presenting with unexplained seizures together with a metabolic acidosis (10 -). 

---