Propylene glycol (CAS: 57-55-6), also known as 1,2-propanediol, is an organic compound (a diol alcohol), usually a tasteless, odourless, and colourless clear oily liquid that is hygroscopic and miscible with water, acetone, and chloroform. It is manufactured by the hydration of propylene oxide. Propylene glycol is used as a solvent for intravenous, oral, and topical pharmaceutical preparations It is generally considered safe. However, in large doses, it can be toxic, especially if given over a short period of time. Intravenous lorazepam contains the largest amount of propylene glycol of commonly used drugs. In adults with normal liver and kidney function, the terminal half-life of propylene glycol ranges from 1.4 to 3.3 hours. Propylene glycol is metabolized by the liver to form lactate, acetate, and pyruvate. The nonmetabolized drug is excreted in the urine mainly as the glucuronide conjugate, approximately 12 to 45 percent is excreted unchanged in urine. Renal clearance decreases as the dose administered increases (390 ml/minute/173 m2 at a dose of 5 g/day but only 144 ml/minute/173 m2 at a dose of 21 g/day). These data suggest that renal clearance declines at higher propylene glycol doses because of the saturation of proximal tubular secretion of the drug. As an acceptable level of propylene glycol has not been defined, the clinical implication of a propylene glycol level is unclear. The World Health Organization (WHO) recommends a maximum consumption of 25 mg/kg/day (1.8 g/day for a 75 kg male) of propylene glycol when used as a food additive, but this limit does not address its use as a drug solvent. No maximum dose is recommended in the literature for intravenous therapy with propylene glycol. Intoxication occurs at much higher doses than the WHO dose limit and is exclusive to pharmacologic exposure. Propylene glycol toxicity includes the development of serum hyperosmolality, lactic acidosis, and kidney failure. It has been suggested that proximal tubular necrosis is the cause of acute kidney injury from propylene glycol. Along these lines, proximal tubular cell injury occurs in cultured human cells exposed to propylene glycol. Acute tubular necrosis was described with propylene glycol toxicity in a case of concomitant administration of intravenous lorazepam and trimethoprim sulfamethoxazole. Propylene glycol induced intoxication can also mimic sepsis or systemic inflammatory response syndrome (SIRS). Patients suspected of having sepsis with negative cultures should be evaluated for propylene glycol toxicity if they have been exposed to high dose lorazepam or other medications containing this solvent (PMID:17555487).