Recently, the Centers for Disease Control reported an alarming outbreak of bone marrow toxicity in multiple U.S. States, primarily in the southwest (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5849a3.htm). The potentially life-threatening problem manifest as a paucity of infection-fighting white blood cells, a condition called agranulocytosis. This is a common and expected side-effect of cancer chemotherapy and can also occur following the use of certain prescription medications.
In three of the first six in the initial cluster of agranulocytosis cases (all from New Mexico), there was no history of such therapies, although one case did report using herbals obtained outside the U.S. The two other atypical cases did share a common link, though: illicit use of cocaine. Such abuse had not been known previously to cause agranulocytosis. In the months that followed, additional cases were reported and the suspected link to cocaine was confirmed, yet remained unexplained.
Approximately 6 months into the investigation, laboratory testing of cocaine samples from Canada revealed contamination with a pharmaceutical called levamisole. Although levamisole has had some allowed human uses in the U.S., it is now restricted to veterinary applications. The drug fell out of favor after agranulocytosis was found to be a common side-effect of its use. Once public health authorities knew what to look for, they began to detect levamisole in the blood of drug users with otherwise unexplained agranulocytosis.
Although one part of the mystery was solved, the reason why this veterinary medicine is being added to cocaine remains obscure. What is clear is that the practice is common, with nearly 7 in 10 samples seized at U.S. borders testing positive for the additive. Now levamisole toxicity can be added to the long list complications that injection-users of illicit drugs face. Many of these problems are infectious in nature, even including botulism and anthrax, but this is not the first outbreak of toxic chemical-caused disease in drug users either, for example a recent epidemic of manganese poisoning in drug abusers in Eastern Europe.
There is a larger lesson here, too. Agranulocytosis is part of a spectrum of abnormalities. In particular, it is related to an even more devastating condition called aplastic anemia, in which all of the bone marrow cells fail. Worldwide, the frequencies of both conditions vary widely. Curiously, data suggest that this variation may not be random - where agranulocytosis is more common, aplastic anemia is less frequent, and vice-versa. A potential key is that both problems can be brought on by exogenous exposures to chemicals, including prescription medications. For aplastic anemia, one of the strongest links is to the solvent benzene. Recognized as a cause of such disease for more than 100 years, this toxic agent was only subject to more stringent workplace controls in the U.S. in the late 1980s and its use in consumer products such as household glues persisted for years after that. Benzene is still widely used across the world. A recent investigation from South America, for example, found that 1 in 20 of all the aplastic anemia cases were caused by frequent benzene exposure.
Inherently toxic industrial chemicals and pharmaceuticals with potential severe side-effects share a lot more in common than may be generally appreciated. But one major difference is worth remembering too: unlike toxic chemicals used in the workplace or put into consumer products, pharmaceuticals have to be extensively tested for safety in humans before they are ever approved. Moreover, once allowed, they are subject to swift action to take them of the market if unsuspected adverse effects are noted. If benzene were a drug, it would have been banned long ago.