Norepinephrine more potent than phenylephrine for hypotension during C-section
Norepinephrine is a more potent choice than phenylephrine for postspinal hypotension during elective caesarean section, a recent study has found.
The study included 100 patients with postspinal hypotension, who were treated with a predetermined dose of either phenylephrine or norepinephrine. Resolution of hypotension within 1 minute of administration was considered a success. The corresponding 95 percent (ED95) and 50 percent (ED50) effective doses for norepinephrine and phenylephrine, as well as the potency ratio, were calculated.
There were 50 participants each in the norepinephrine (mean age, 25.9±3.6 years) and phenylephrine (mean age, 25.7±3.7 years) groups. Probit analysis revealed that ED95 and ED50 values were 43.1 and 33.2 µg for phenylephrine, respectively, and 3.7 and 3.2 µg for norepinephrine, respectively.
The resulting potency ratio was 11.3:1, suggesting that norepinephrine is at least 11 times more potent than phenylephrine.
There were also more patients in the phenylephrine than norepinephrine group who developed further hypotension episodes after the delivery of the baby and required rescue phenylephrine. However, the difference was not statistically significant (42 percent vs 38 percent; p=0.838).
Neonatal Apgar scores at 1 and 5 minutes (p=1.00) and birth weights (2.7±0.4 vs 2.6±0.4 kg; p=0.214) were also statistically comparable between the phenylephrine and norepinephrine groups.
In terms of safety, 10 percent in the phenylephrine group complained of nausea, as opposed to only 6 percent in the norepinephrine group. On the other hand, 6 percent and 2 percent reported vomiting in the respective treatment arms.