values in rats and rabbits of 7 ml/kg bw. ruddick (1972) also summarized intramuscular ld50 data for rat as 13-20 ml/kg bw, and 6 ml/kg bw for the rabbit. adverse effects to intravenous administration of drugs that use propylene glycol as an excipient have been seen in a number of people, particularly with large bolus dosages. responses may include cns depression, "hypotension, bradycardia, qrs and t abnormalities on the ecg, arrhythmia, cardiac arrhythmias, seizures, agitation, serum hyperosmolality, lactic acidosis, and haemolysis". a high percentage (12% to 42%) of directly-injected propylene glycol is eliminated or secreted in urine unaltered depending on dosage, with the remainder appearing in its glucuronide-form. the speed of renal filtration decreases as dosage increases, which may be due to propylene glycol's mild anesthetic / cns-depressant -properties as an alcohol. in one case, intravenous administration of propylene glycol-suspended nitroglycerin to an elderly man may have induced coma and acidosis. however, no confirmed lethality from propylene glycol was reported. animals propylene glycol is an approved food additive for dog and sugar glider food under the category of animal feed and is generally recognized as safe for dogs, with an ld50 of 9 ml/kg. the ld50 is higher for most laboratory animals (20 ml/kg). however, it is prohibited for use in food for cats due to links to heinz body formation and a reduced lifespan of red blood cells. heinz body formation from mpg has not been observed in dogs, cattle, or humans. pg has been used in the dairy industry since the 1950s for cows showing signs of ketosis. the negative energy balance during the early stages of lactation can cause the animal's body to have lower glucose levels, inducing the liver to make up for this by the conversion of body fat, leading to several health conditions, e.g. displaced abomasum. pg "reduces the propionate ratio of acetate to acetaminophen, while increasing conversion of ruminal pg to propionate, and aid in the closure of energy deficit in cattle." allergic reaction estimates on the prevalence of propylene glycol allergy range from 0.8% (10% propylene glycol in aqueous solution) to 3.5% (30% propylene glycol in aqueous solution). the north american contact dermatitis group (nacdg) data from 1996 to 2006 showed that the most common site for propylene glycol contact dermatitis was the face (25.9%), followed by a generalized or scattered pattern (23.7%). investigators believe that the incidence of allergic contact dermatitis to propylene glycol may be greater than 2% in patients with eczema or fungal infections, which are very common in countries with lesser sun exposure and lower-than-normal vitamin d balances. therefore, propylene glycol allergy is more common in those countries. because of its potential for allergic reactions and frequent use across a variety of topical and systemic products, propylene glycol was named the american contact dermatitis society's allergen of the year for 2018. recent publication from the mayo clinic reported 0.85% incidence of positive patch tests to propylene glycol (100/11,738 patients) with an overall irritant rate of 0.35% (41/11,738 patients) during a 20-year period of 1997–2016. 87% of the reactions were classified as weak and 9% as strong. the positive reaction rates were 0%, 0.26%, and 1.86% for 5%, 10%, and 20% propylene glycol respectively, increasing with each concentration increase. the irritant reaction rates were 0.95%, 0.24%, and 0.5% for 5%, 10%, and 20% propylene glycol, respectively. propylene glycol skin sensitization occurred in patients sensitive to a number of other concomitant positive allergens, most common of which were: myroxylon pereirae resin, benzalkonium chloride, carba mix, potassium dichromate, neomycin sulfate; for positive propylene glycol reactions, the overall median of 5 and mean of 5.6 concomitant positive allergens was reported. environmental impacts propylene glycol occurs naturally, probably as the result of anaerobic catabolism of sugars in the human gut. it is degraded by vitamin b12-dependent enzymes, which convert it to propionaldehyde. propylene glycol is expected to degrade rapidly in water from biological processes, but is not expected to be significantly influenced by hydrolysis, oxidation, volatilization, bioconcentration, or adsorption to sediment. propylene glycol is readily biodegradable under aerobic conditions in freshwater, in seawater and in soil. therefore, propylene glycol is considered as not persistent in the environment. propylene glycol exhibits a low degree of toxicity toward aquatic organisms. several guideline studies available for freshwater fish with the lowest observed lethal concentration of 96-h lc50 value of 40,613 mg/l in a study with oncorhynchus mykiss. similarly, the lethal concentration determined in marine fish is a 96-h lc50 of >10,000 mg/l in scophthalmus maximus. although propylene glycol has low toxicity, it exerts high levels of biochemical oxygen demand (bod) during degradation in surface waters. this process can adversely affect aquatic life by consuming oxygen needed by aquatic organisms for survival. large quantities of dissolved oxygen (do) in the water column are consumed when microbial populations decompose propylene glycol.: 2–23