Yeah-- older first-gen stuff is both H1/H2 blocking, but shorter acting, and as ndw notes above, the second generation meds are more selective for H1 receptors, which tend to exclude the CNS H2 sites (thus making them "non-drowsy" or at least better for most people). They work FAR better (for most people) on the irritating peripheral symptoms like skin, eyes, nasal congestion. They're also a lot more idiosyncratic in terms of individual action, however. (So if loratidine does nothing, the advice is often for patients to try cetirizine, or fexofenadine, for example...)
One thing which is useful to recall when using first-gen versus second-gen antihistamines is that they do various things selectively, and one may sometimes make use of those properties.
Diphenhydramine is useful for GI reactivity in particular-- to the point that it often works as a mild anti-emetic.
Ranitidine is also a histamine blocker, though it's got nowhere near the efficacy of something that hits systemic H1 and H2 receptors like diphenhydramine.
Just recall that those older generation antihistamines that indiscriminately hit both receptor types can cause drowsiness that masks neurological/cardiovascular effects of a systemic reaction.
All this pharmacology-- better living through chemistry at my house, anyway!
