Wednesday, September 24, 2008

Melamine Milk Poisoning and Kidney Stones

Nephrology rears its ugly head in the news cycle.

The NYT weighs in. China Says Complaints About Milk Began in 2007

The top food official resigns. I bet he is happy to get away with a forced resignation compared to Zheng Xiaoyu, former head of the chinese FDA who was executed for corruption following the tainted phamaceutical debacle last year.

The interesting is that the same toxin, melamine, was implicated in the pet food renal failure problem in 2007. At that time, the US FDA provided lots of assurances that malamar is not that toxic. Is this a pediatric issue? In some of the articles following the pet food issue a second compound, cyanuric acid, was implicated in the pathophysiology. I have not read anything about cyanuric acid.

More on this as it develops.

The only data I could find on the concentration of melamine in the milk products comes from this ChinaDaily article.

The highest concentration of melamine was found in Sanlu products. Tests show every kg of Sanlu milk food contains 2.56 g of melamine, which can make milk appear rich in protein in quality tests. The chemical is usually used to make plates, bowls, mugs and sundry other products, but is banned from being used in the food industry.

The other tainted products contain between 0.09 mg to 619 mg of melamine per kg.

During the pet food scare of 2007, there was concern that some of the melamine contaminated pet-food reached live-stock and ended up contaminating the food supply. The FDA estimated the tolerable daily intake of melamine at 0.63 mg/kg.

The point of departure (POD) is the NOAEL of 63 mg/kg/day from the rodent subchronic bioassay. This POD was then divided by two 10-fold safety/uncertainty factors (SF/UF) to account for inter- and intra-species sensitivity, for a total SF/UF of 100. The resulting Tolerable Daily Intake (TDI) is 0.63 mg/kg bw/day. The TDI is defined as the estimated maximum amount of an agent to which individuals in a population may be exposed daily over their lifetimes without an appreciable health risk with respect to the endpoint from which the NOAEL is calculated.

Using the concentrations from the China Daily article and the FDA limits on tolerability a 7 kg baby would need to ingest 1.7 liters of Sanlu milk to exceed this safe limit (of note, at the highest concentration only 7 mL would exceed the safe limit). Either the safety estimate was off or there is an additional compound causing the toxicity.

Google search for melamine
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