With a few exceptions as noted below, one should avoid using all medications in pregnant and lactating (nursing) dogs. There may be instances in which a medication not recommended for use during pregnancy may need to be used to save the life of the bitch, even though it may potentially harm the fetuses.
NOTE: According to the Merck Veterinary Manual , this is only a partial listing of drugs that should be avoided in pregnant or nursing dogs. A listing of all such drugs is beyond the scope of this article. If you have concerns regarding a specific drug, make sure you do an internet search for that particular drug or purchase a copy of the Merck Vet Manual to have on-hand.
Glucocorticoids are potent anti-inflammatories, regardless of the inflammation's cause; their primary anti-inflammatory mechanism is lipocortin-1 (annexin-1) synthesis. Lipocortin-1 both suppresses phospholipase A2 , thereby blocking eicosanoid production, and inhibits various leukocyte inflammatory events ( epithelial adhesion , emigration , chemotaxis , phagocytosis , respiratory burst , etc.). In other words, glucocorticoids not only suppress immune response, but also inhibit the two main products of inflammation, prostaglandins and leukotrienes . They inhibit prostaglandin synthesis at the level of phospholipase A2 as well as at the level of cyclooxygenase /PGE isomerase (COX-1 and COX-2),  the latter effect being much like that of NSAIDs , potentiating the anti-inflammatory effect.