The diagnosis of lactic acidosis is made when the serum lactate level is greater than 4 mmol/L. Type A lactic acidosis is due to impaired tissue oxygenation, while type B lactic acidosis is caused by a variety of disorders and can be neoplastic or drug or toxin induced.

In drug-induced lactic acid production, the pathogenesis is partially due to drug-induced mitochondrial dysfunction, which causes decreased energy production and increased lactate accumulation. Drugs such as metformin, linezolid, propofol, intravenous epinephrine, inhaled beta agonists (eg, albuterol), and nucleoside reverse transcriptase inhibitors (NRTIs), which are used for treatment of human immunodeficiency virus (HIV), have been linked to lactic acidosis.

Diagnosis of drug-induced lactic acidosis should be considered in patients taking high-risk medications. In the case of metformin-associated lactic acidosis (MALA), a secondary condition such as cirrhosis or sepsis is often necessary to cause lactic acid buildup. Patients with renal and hepatic insufficiency should not be prescribed metformin. Risk factors for NRTI-associated lactic acidosis include reduced creatinine clearance, low CD4 count, and female sex.

The diagnosis is made by checking serum lactic acid levels. Clinical manifestations vary and can include altered mental status, respiratory distress, abdominal pain, nausea, and vomiting. Untreated lactic acidosis can be fatal, leading to cardiac arrhythmias and organ failure.