[Simple Formula to Predict Residual Amount of Continuously Infused Rocuronium in the Body]

When antagonism is performed using sugammadex after continuous infusion of rocuronium, if the total amount of residual rocuronium can be esti- mated prior to performing antagonism, antagonism without excess or deficiency of sugammadex will be made possible. We therefore prepared a simple formula to predict residual amount of rocuronium in the body, which can be easily applied in clinical setting, and veri- fied it using Tivatrainer©.

1. Pharmacokinetics of rocuronium was simulated, using a 3-compartment model. The following assumptions were made to derive the simple for- mula : when rocuronium is continuously infused to reach the steady state plasma concentration, an equal concentration in each compartment is reached. Only the amounts of rocuronium infused to the central com- partment and rocuronium excreted from there are thus considered, and these two amounts are in balance. For pharmacokinetic parameters, we referred to V. Saldien, Anesth Analg 2003 ; 97 : 44-9. 2. The prepared simple formula was verified using Tivatrainero. We considered a model in which initial boluses of 0.3, 0.6, 0.9, and 1.2 mg · kg(-1) were adminis- tered, and continuous infusion began at 30 minutes at the rate of 0.2, 0.3, 0.4, 0.5, 0.6, and 0.8 mg - kg-1 - hr-1. Patients with body weight of 50, 60, 70, and 80 kg were investigated.

1. The derived simple formula was as fol- lows : Q=0.74 X R Q Total residual amount of rocuronium (mg) R Dose per hour (mg · hr(-1)) 2. The predicted value of the total residual amount obtained from the simple formula was consistent with the value predicted by Tivatrainer© with a high preci- sion within the error of 1.4%. Convergence time until the stable state was reached varied depending on the condition. However, it took approximately 150 minutes after the beginning of continuous infusion.for the error between values predicted by the simple formula and Tivatrainer© to stabilize within 5 mg.

We prepared a simple formula to esti- mate the total residual amount of rocuronium at a steady state. The value predicted by the simple for- mula agreed with the value predicted by Tivatrainer) with a high precision.