A B S T R A C TAims: The aim of this study was to evaluate the onset, duration of sensory and motor block, hemodynamic effects (if any), duration and quality of postoperative analgesia, and adverse effects of magnesium or fentanyl given intrathecally with hyperbaric 0.5% bupivacaine in patients with mild preeclampsia undergoing elective caesarean sections. Materials and Methods: A total of 60 women with mild preeclampsia undergoing elective cesarean section were included in a prospective, double-blind, controlled trial. Patients were randomly assigned to receive spinal anesthesia with 2 mL 0.5% hyperbaric bupivacaine with 12.5 µg fentanyl (Group F) or 0.1 mL of 50% magnesium sulfate (50 mg) (Group M) with 0.15 ml preservative free distilled water. Onset, duration and recovery of sensory and motor block, time to maximum sensory block, duration of spinal anesthesia and postoperative analgesia requirements were studied. Statistical comparison was carried out using the Chi-square or Fisher's exact tests and independent Student's t-test where appropriate. Results: The onset of both sensory and motor block was slower in the magnesium group. The duration of spinal anesthesia (246 min ± 11 min vs. 284 min ± 15 min; P < 0.001) and motor block (186.3 ± 12 min vs. 210 ± 10 min; P < 0.001) were significantly longer in the magnesium group. Total analgesic dose requirement was less in Group M. Hemodynamic parameters were comparable in the two groups. Intrathecal magnesium caused minimal side effects. Conclusions: The addition of magnesium sulfate 50 mg to bupivacaine for sub-arachnoid block in patients with mild preeclampsia undergoing elective cesarean section prolongs the duration of analgesia and reduces postoperative analgesic requirements without additional side effects and adverse neonatal outcomes

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