**3.1. Calcium channel blockers**

The main drug of this class used in preterm birth inhibition is nifedipine, and many dosing regimens were proposed. Among tocolytics, nifedipine was the only drug that seems to statistically reduce neonatal morbidity and to increase gestational age at birth [38, 39].

In addition to being inexpensive, nifedipine is also administered orally and has less adverse maternal effects when compared to beta-agonists. When present, hypotension, flush, and headaches usually are not severe [37, 39].

The recommendation in UNIFESP is an initial dose of 10 mg orally every 20 minutes (maximum of 30 mg in 1 hour) until inhibition is reached, followed by 20 mg orally every 8 hours for up to 48 hours [40].
