I am quoting from a useful book entitled Drugs and Breastfeeding Guide 1994/5 produced by the Royal Women's Hospital in Melbourne Australia. They suggest that "short and medium acting antihistamines eg chlorpheniramine, dexchlorpheniramine, dimenhydrinate, diphenhydramine, doxylamine, tripolidine may be used for treatment as long as therapeutic doses are not exceeded. Avoid slow release preparations." I also agree with the person who suggested that antihistamines are often not indicated or useful in infections (i'm sure they're put in children's 'flu' mixtures more for their sedative effect). As with all treatment, sometimes simple things like steam inhalations, lemon and honey etc do just as good a job (plus antibiotics only if felt necessary).