Small, occasional doses of pyrilamine are probably acceptable during breast feeding. Larger doses or more prolonged use may cause effects in the infant or decrease the milk supply, particularly, in combination with a sympathomimetic such as pseudoephedrine or before lactation is well established. The nonsedating antihistamines are preferred alternatives.
One early study that used a biologic assay system reported that after a 100 mg intramuscular dose of diphenhydramine in 3 women, drug levels in milk ranged from 50 to 2.3 mg/L at 1 to 2 hours after the dose and 220 mcg/L to 4 mg/L 5 hours after the dose. Eight hours after the dose, levels were 200 mcg/L and 1.16 mg/L in two mothers, respectively, and not measured in the third. No studies using modern assay methods have been reported.
Relevant published information was not found as of the revision date.
Effects in Breastfed Infants:
In one telephone follow-up study, mothers reported irritability and colicky symptoms in 10% of infants exposed to various antihistamines and drowsiness was reported in 1.6% of infants. None of the reactions required medical attention and none of the infants were exposed to pyrilamine.
Possible Effects on Lactation:
Antihistamines in relatively high doses given by injection can decrease basal serum prolactin in nonlactating women and in early postpartum women. However, suckling-induced prolactin secretion is not affected by antihistamine pretreatment of postpartum mothers. Whether lower oral doses of antihistamines have the same effect on serum prolactin or whether the effects on prolactin have any consequences on breastfeeding success have not been studied.
1. Rindi V. La eliminazione degli antistaminici di sintesi con il latte e l'azione latto-goga de questi. Riv Ital Ginecol. 1951;34:147-57. 2. Ito S, Blajchman A, Stephenson M et al. Prospective follow-up of adverse reactions in breast-fed infants exposed to maternal medication. Am J Obstet Gynecol. 1993;168:1393-9. PMID:8498418 3. Messinis IE, Souvatzoglou A, Fais N et al. Histamine H1 receptor participation in the control of prolactin secretion in postpartum. J Endocrinol Invest. 1985;8:143-6. PMID:3928731 4. Pontiroli AE, De Castro e Silva E, Mazzoleni F et al. The effect of histamine and H1 and H2 receptors on prolactin and luteinizing hormone release in humans: sex differences and the role of stress. J Clin Endocrinol Metab. 1981;52:924-8. PMID:7228996
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