Theophylline, a methylated
xanthine closely resembling
caffeine and
theobromine, is a widely used
pharmaceutical agent for the treatment of respiratory disorders and certain acute cardiovascular conditions. The National Toxicology Program has conducted 13-week subchronic toxicity studies in F344 rats and B6C3F1 mice (10 animals/group) following administration of
theophylline via the diet or by gavage. Administration of
theophylline in the feed (0, 1000, 2000, and 4000 ppm) resulted in no mortality or
body weight effects in F344 rats, but did induce periarteritis of the arteries adjacent to mesenteric lymph nodes and the pancreas, particularly arterioles in the latter. Also observed in rats dosed with
theophylline via the diet was an increased severity of chronic nephropathy in males, especially at the high dose. Administration of
theophylline at the same concentrations in the feed to B6C3F1 mice resulted in no mortality, but terminal
body weights were significantly decreased in all dosed groups. An increased incidence of hepatocellular
glycogen depletion was observed in male and female mice, and this change is believed to represent a physiological alteration exacerbated by the administration of
theophylline. Administration of
theophylline by gavage to F344 rats (0, 37.5, 75, and 150 mg/kg) resulted in the early death of one high-dose male and female and significantly decreased or increased terminal
body weights of high-dose males and females, respectively. Similar to the results of the dosed-feed study, male and female rats receiving
theophylline by gavage demonstrated a dose-related increase in the incidence and severity of perivascular
inflammation of mesenteric arteries. Gavage administration of
theophylline to B6C3F1 mice (0, 75, 150, and 300 mg/kg) resulted in the early death of all high-dose females and 3/10 high-dose males and significant depression of terminal
body weights in high- and mid-dose males and low-dose females. As in the dosed-feed study, the primary histopathologic change in the mouse subchronic gavage study was hepatocellular
glycogen depletion, although in this case it was seen only in females. In summary, the major target organs for orally administered
theophylline in 13-week subchronic toxicity studies appear to be the mesenteric arteries in F344 rats and the liver in B6C3F1 mice. On the basis of organ weight changes and/or minor histopathologic effects, many other tissues were also affected, particularly the kidneys in dosed-feed male rats and the uterus in gavage-dosed female rats.