Question

It has been stated (Henceles L., Weinberger M. Am J Hosp Pharm. 1980; 37:49-50) that an initial loading dose of 1 mg/kg of theophylline will produce an increase in serum theophylline of 2mcg/ml.

(1) What is the weighted volume of distribution of theophylline?

(2) Since aminophylline, which is the only intravenous form of theophylline, is 80% theophylline, what would be the IV loading dose required to produce an initial plasma concentration of 10mcg/ml of theophylline?

Answer 1

• Volume of distribution = dose/plasma concentration

= 1mg/kg ÷ 2mcg/ml

= 500ml

• Loading dose = volume of distribution × plasma concentration = .8×500 × 10 = 4000mcg/kg