Antihistamines - Cyclizine and Promethazine

Brand names for these antihistamines are:

• Valoid (cyclizine)
• Avomine (promethazine)

A wide body of evidence suggests that H1 receptor antagonist antihistamines have no human teratogenic potential (teratogenic means harmful defects in the foetus). Pooled data from 7 randomised controlled trials indicate that these antihistamines are effective in the treatment of nausea and vomiting in pregnancy. These antihistamines can cause drowsiness and should not be taken without medical advice, although they are available over the counter. It can take a couple of weeks to become accustomed to the drowsy effect.

By using either cyclizine or promethazine in combination with pyridoxone (B6) it is very similar to the Canadian drug Diclectin which can be very effective if used as a prophylactic for women who have previously had hyperemesis gravidarum. This is the basic first line treatment in the UK.