The group of esters called phthalates are used in an array of products ranging from pill capsules to children's toys to shower curtains. A research group in Korea has found a strong positive correlation between ADHD behavioral characteristics and phthalate metabolites in the urine of Korean school children. This is a particularly important study for two reasons: 1) a correlation between ADHD and phthalate exposure during critical periods of development has never been shown, and 2) the metabolite levels found in these children indicates the amount of exposure that can now be replicated in animal models.
"Previous animal studies (6,15,16) have shown that phthalate related metabolites induce hyperactivity in rats. These studies reported that pups treated with phthalate demonstrated 1.4 times the level of hyperactivity at night compared with control subjects. Such hyperactivity was dose-dependent, which is consistent with the results of our study."
"It is possible that the toxicity of phthalates is attributable to degeneration of dopaminergic neurons, leading to the hyperkinetics observed in rats in cases of 6-hydroxydopamine (OHDA) procedures (27). Well-known animal models of ADHD like the OHDA rat model suggest that the dopamine neuronal damage can provoke hyperactivity and impulsivity. Many structural magnetic resonance imaging studies showed striatal volume loss suggesting the dopamine neuronal loss in ADHD patients (28)."
"With DNA macroarray data, researchers have found that phthalate metabolites change
the expression patterns of various genes, including both the dopamine receptor D4 (DRD4) and the dopamine transporter in the midbrain (6). The dopamine receptor D4 and dopamine transporter gene expression modulation can induce changes in extracellular dopamine and neuronal dopamine sensitivity, resulting in hyperactivity and impulsivity in rats."
Here is something particularly interesting: if excessive exposure to phthalates is linked causally to ADHD phenotypes -- which has yet to be explored -- perhaps the time-release medications used to treat ADHD such as Wellbutrin and Ritalin should cease to use phthalates in the enteric coating of their medications. It seems odd that they are so widely used in films of pharmaceutical capsules if for no other reason than their heavy reputation as endocrine disruptors. Capsules can contain in the range of 3600 ug phthalates, while most studies estimate that the "safe" exposure range is near 20 ug per kilogram body weight. That means the "safe" range for most young children is about 750 ug. Note that phthalates do not bioaccumulate, so exposure levels are dailies.
"The bupropion (Wellbutrin® SR) release rate has been improved by the introduction of two types of film coated active pellets that release the drug at different pH resulting in novel dissolution profiles. Inert spheres are initially coated with bupropion and hydroxypropyl methylcellulose. The active pellets containing bupropion comprise 70-75 weight % of the dosage form. An enteric coating, applied to about one third of the active drug pellets, is comprised of a film insoluble at low pH, such as hydroxypropyl methylcellulose phthalate. The second coating applied to the other two thirds of active drug pellets is comprised of a combination of a hydrophobic coating agent and methyl acrylic acid copolymer. The two pellet types are then combined in a capsule."
"The novel dosage forms are used to administer methylphenidate (Ritalin) in a pulsatile release manner... Suitable membrane coating materials for effecting delayed release include, but are not limited to: cellulosic polymers such as hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, cellulose acetate, cellulose acetate phthalate, cellulose acetate trimellitate, hydroxypropylmethyl cellulose phthalate, cellulose ester-ether phthalate, hydroxypropylcellulose phthalate, alkali salts of cellulose acetate phthalate, alkaline earth salts of cellulose acetate phthalate, hydroxypropylmethyl cellulose hexahydrophthalate, cellulose acetate hexahydrophthalate..."