Antihistamines and birth defects

Antihistamines - Antihistamines are, by the very nature of their pharmacological activity, immunosuppressant. An allergic reaction occurs when a foreign antigen activates T-cells passing through the site of the allergic response. These activated T-cells stimulate B-cells to produce high levels of IgE antibodies. At the same time, the T-cells release chemotactic factors which attract basophils into the affected tissue. The basophils, bind with the newly produced IgE and when these cells come in contact with the allergen, they release stores of histamine, heparin and other mediators amplifying the allergic response. Antihistamines block the effects of histamine on blood vessels and smooth muscle, thus they help to suppress the body's reaction to a foreign antigen.

Standard adverse reaction warnings on most antihistamines include many symptoms which are also characteristic of chemically-induced immune dysfunction: rash, photosensitivity, fatigue, dizziness, disturbed coordination, insomnia, tinnitus, paresthesia, neuritis, blurred vision, headache, gastrointestinal problems, hemolytic anemia, thrombocytopenia and so on. Like other immune modulators, antihistamines can also produce the paradoxical effects of sedation in some people, restlessness and excitation in others. (PDR 1988)

Doxylamine succinate, an antihistamine in a number of over-the-counter products as well as the controversial morning sickness remedy Bendectin, has been associated with a statistically significant increase in acute nonlymphoblastic leukemia in children whose mothers took Bendectin for eleven weeks or more during pregnancy. (Robinson et al 1988) In 90-day chronic toxicity studies at the National Toxicology Program, doxylamine was associated with toxic lesions of the livers and parotid glands of mice and rats. (NTP 1986)

Bendectin has been associated with limb reduction defects, heart defects, oral clefts and other serious birth defects in animal and human studies. (ABDC 1988) Other antihistamines, diphenhydramine (Benadryl), meclizine and cyclizine have also been associated with birth defects in animal and human studies.

However, The Centers for Disease Control and Department of Social and Health Services studied the use of antihistamines by pregnant women and the potentiality of birth defects. Their presentation (with notes) revealed "Limited evidence of association between antihistamine use and selected birth defects."