Sharon, Theophylline and other methylxanthines work by incapacitating the machinery that "shuts off" cell energy metabolism (ATP cycle, adenyl cyclase is the enzyme incapacitated if I remember correctly, I might not). Therefore, at the cellular level, the body never gets a rest. For an infant, who clears methylxanthines slowly, this effect would be especially acute. When it is a choice between breathing or growing, most peds will opt for the baby breathing! Catherine Watson Genna, IBCLC