Introduction
Five trials compared the effectiveness of pyridoxine (vitamin B6) for the treatment of NVP.41,59,100,107,112 Two trials compared doses of vitamin B6 against placebo tablets,41,100 and they were at low41 and unclear100 risk of bias, respectively. Tan and colleagues107 examined the effect of vitamin B6 and metoclopramide combination versus metoclopramide alone and was at an unclear risk of bias, mainly due to the use of a dubious placebo (Tic Tac®, Ferrero UK Ltd, Greenford, UK). The trial of Wibowo and colleagues112 compared high and low doses of vitamin B6, and was at low risk of bias. Babaei and Foghaha59 compared the effectiveness of vitamin B6 against dimenhydrinate in the treatment of NVP and was at an unclear risk of bias.
In all five studies,41,59,100,107,112 women were described as experiencing mild to moderate symptoms at baseline (). However, as previously described (see Chapter 3, Meta-analysis of included randomised controlled trials), given the differences between trials in patient populations, settings, interventions and, in particular, the heterogeneous nature of the reported outcomes across trials, we did not attempt to perform meta-analyses. Thus we reported a narrative summary only for each intervention and comparator set.
Results for vitamin B6 interventions for NVP
Vitamin B6 versus placebo
Pregnancy-Unique Quantification of Emesis and Nausea scale
Wibowo and colleagues112 measured the change in overall symptom severity using the PUQE scale for lower versus higher doses of vitamin B6. They found a higher mean change for the high dosage compared with lower, and there was a statistically significant improvement in PUQE score with the higher dose.
Nausea outcomes
The trial of Vutyavanich and colleagues41 used the 10-point VAS to assess mean change in nausea symptoms.41 The study determined a higher mean change in the pyridoxine group [2.9 (SD 2.2) vs. placebo 2.0 (SD 2.7)], and this difference was significant (p < 0.001). The Sahakian and colleagues100 trial also employed the VAS to assess mean change in nausea. Overall, the study did not detect a significant difference between groups. However, for patients experiencing severe nausea, a significant mean change was observed in favour of the pyridoxine group (p < 0.001).
Vomiting outcomes
The change in the number of vomiting episodes was measured by Vutyavanich and colleagues.41 However, although a greater reduction was observed in the pyridoxine group, this was not significant (p = 0.055). Sahakian and colleagues100 also assessed vomiting outcomes via number of vomiting episodes.100 They observed a significant improvement both in the pyridoxine group as a whole (p < 0.05), and for the subgroup of women experiencing severe symptoms (p < 0.055).
Retching outcomes
No independent retching outcomes reported.
Safety outcomes
None of the included trials reported on pregnancy outcomes or adverse events. UKTIS data on vitamin B6 enquiries are provided in Appendix 7.
Vitamin B6 and metoclopramide combination versus metoclopramide alone
The trial of Tan and colleagues107 used the 10-point VAS to assess median nausea scores in women with severe nausea and vomiting during pregnancy with clinical features. The trial also reported the mean number of daily vomiting episodes.107
Combined severity score
No combined score reported.
Nausea outcomes
Tan and colleagues107 reported no significant difference in nausea score after 2 weeks between the pyridoxine (vitamin B6) and metoclopramide as a combination treatment and metoclopramide alone [combination median 2 (IQR 3), metoclopramide alone median 2.5 (IQR 4); p = 0.69].
Vomiting outcomes
Tan and colleagues107 reported no significant difference in the mean number of daily vomiting episodes after 2 weeks between the vitamin B6 and metoclopramide as a combination treatment and metoclopramide alone [combination mean 1.4 (SD 1.3), metoclopramide alone mean 1.4 (SD 1.6); p = 0.98].
Retching outcomes
No independent retching outcomes reported.
Safety outcomes
Tan and colleagues107 did not report on pregnancy outcomes or adverse events. UKTIS data on vitamin B6 enquiries are provided in Appendix 7.
Vitamin B6 versus serotonin antagonist
The trial of Babaei and Foghaha59 compared effectiveness of vitamin B6 against dimenhydrinate in the treatment of NVP in a double-blind RCT which was adjudged as being at unclear risk of bias.
Rhodes Index of Nausea, Vomiting and Retching
Babaei and Foghaha59 compared nausea and vomiting scores at baseline and post treatment using the RINVR. Results showed that both vitamin B6 and dimenhydrinate groups decreased nausea and vomiting scores from baseline. However, the average score change in the vitamin B6 group was less than that in the dimenhydrinate group [mean 4.4 (SD 1.6) vs. mean 5.7 (SD 5.5); p < 0.05].
Nausea outcomes
No independent nausea outcomes reported.
Vomiting outcomes
No independent vomiting outcomes reported.
Retching outcomes
No independent retching outcomes reported.
Safety outcomes
Babaei and Foghaha59 did not report on pregnancy outcomes. Occurrence of drowsiness was significantly lower in the vitamin B6 group compared with the dimenhydrinate group [5 (4.5%) as opposed to 36 (53%); p < 0.01]. No other adverse effect was observed in either group during the 1-week follow-up. UKTIS data on vitamin B6 enquiries are provided in Appendix 7.
Summary
The evidence available for vitamin B6 was predominantly at low risk of bias or the risk of bias was unclear.
Participants in the five studies
41,59,100,107,112 had symptoms categorised as mild to moderate at baseline.
Comparisons of vitamin B6 preparations with placebo generally reported evidence of a reduction in symptoms of nausea, especially in women with more severe symptoms, and vomiting.
Higher doses of vitamin B6 preparations resulted in a greater improvement in NVP symptoms.
There was no evidence to suggest that vitamin B6 and metoclopramide as a combination treatment had an advantage over metoclopramide alone.
Overall, there is a suggestion that vitamin B6 might be better than placebo in reducing the severity of symptoms especially at higher doses, but more studies are required using a range of comparators.
