A loading-dose infusion scheme for intravenous tocolysis with ritodrine: a pilot study.

A loading-dose infusion scheme for intravenous ritodrine therapy was tested in twelve patients with preterm labour. We started with a rather high (386 micrograms/min) infusion rate, but the moment tocolysis was reached this infusion rate was reduced to a level needed to maintain the plasma concentration then found. Plasma samples of ritodrine were taken the moment tocolysis was reached and in the steady state, and compared with each other and with expected and calculated plasma concentrations. In the dynamic loading phase we found a half-life for ritodrine of 1 h. This half-life of 1 h can be explained by cumulation of ritodrine in the central compartment and is therefore called cumulation t1/2. In developing an infusion scheme with a loading dose for ritodrine, this cumulation t1/2 of 1 h should be taken into account.