Therapeutic Drug Monitoring · 1987 · 14 citations · 0 references
For assessing the clinical impact of nonlinearity in theophylline elimination, we examined the incidence of individuals with an apparent Michaelis-Menten kinetics (percent change in plasma concentration exceeding that in dose by at least 50%) among asthmatic children (n = 122) and adults (n = 50) screened through a two-step chart review. Forty-nine children and 21 adults had the apparent nonlinearity. When compared overall between the two groups, the maximum elimination rate (Vmax) differed significantly (mean +/- SD, 32.2 +/- 11.5 versus 21.8 +/- 6.7 mg/kg/day, p less than 0.001). The Vmax correlated with age (r = -0.459, p less than 0.001). Such a trend as found in Vmax was not observed in Km. Our results imply that a disproportionate relationship between dose and concentration of theophylline appears to be relatively common in asthmatic children and adults; the metabolic capacity in children is greater than in adults, if the nonlinearity could occur; and caution is needed with these certain susceptible individuals when using linear kinetics for the dosage modification of theophylline.