ever, because it was self-administered and to be taken only when ordered by the unit commander (PAC, 1996). Thus, actual veterans’ exposures to PB are not known, and there are few examples of documentation in either individual health records or unit records, making it difficult to assess any potential contribution of this drug to the current unexplained illnesses (PAC, 1996).

DoD noted that at the recommended dosage levels, soldiers reported acute but transient side effects. Keeler and colleagues (1991) conducted an uncontrolled retrospective survey of the medical officers of the XXVIII Airborne Corps. The unit’s 41,650 soldiers were instructed to take PB at the onset of Operation Desert Storm in January 1991. Usage varied from 1 to 21 tablets taken over 1–7 days; 34,000 soldiers reported taking the medication for 6–7 days. Reported side effects of PB were estimated to have been present in half the troops; they were not incapacitating, however, and were primarily gastrointestinal in nature. An estimated 1 percent of the soldiers believed they had symptoms that warranted medical attention, but less than 0.1 percent had effects sufficient to warrant discontinuation of the drug (Keeler et al., 1991).

PB, alone and in combination with other exposures, has been suggested as one of several possible causative factors associated with illnesses in Gulf War veterans (Abou-Donia et al., 1996a,b; Chaney et al., 1997; Fukuda et al., 1998; Unwin et al., 1999). The remainder of this chapter examines the scientific literature on the potential adverse health effects of PB.

The committee begins its review with a discussion of the toxicology and pharmacokinetics of PB, based primarily on findings from animal studies and other experimental test systems. The committee then turns its attention to studies in humans. These include clinical studies, related principally to the use of PB in the treatment of myasthenia gravis and its use as a test of hypothalamic pituitary function or growth hormone response. In addition to these clinical studies, the committee reviewed studies in healthy volunteers and epidemiologic studies. The healthy-volunteer studies were conducted among healthy military and nonmilitary populations to evaluate the tolerance of prophylactic doses of PB. Unfortunately, there is a paucity of epidemiologic studies on PB and adverse health effects in the peer-reviewed literature. Although there have been a number of descriptive epidemiologic studies of Gulf War veterans (see Chapter 2), those investigations generally sought to characterize the nature and frequency of the symptoms and illnesses reported by returning soldiers and did not examine the association of PB with the illnesses reported. Studies that attempted to evaluate the association of PB and symptoms among Gulf War veterans are reviewed.

TOXICOLOGY

There is an extensive toxicologic literature on PB, which was reviewed by the committee. The studies discussed below were designed to assess the pharmacologic and toxic properties of PB in animals and other test systems.



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