Upper respiratory disease in shelter cats: doxycycline-first vs alternative first-line antibiotics — POSSIBLE

POSSIBLE: In shelter-housed cats with clinical upper respiratory tract disease (URTD), the one randomised head-to-head trial found doxycycline at least as effective as the alternative first-line antibiotics and better on some sign scores, so a doxycycline-first protocol is supported — but the advantage over amoxicillin-clavulanate was narrow. In Litster 2012 (PMID: 22765368; randomised prospective clinical trial, 48 shelter cats, 16 per group), cats received amoxicillin-clavulanic acid (12.5 mg/kg PO q12h for 14 days), cefovecin (8.0 mg/kg SC, once) or doxycycline (10.0 mg/kg PO q24h for 14 days), with signs scored twice daily for 14 days on a 0–3 scale: doxycycline cats had significantly lower overall oculonasal discharge scores than either other group, amoxicillin-clavulanate and doxycycline cats had significantly lower overall sneezing scores than cefovecin cats, both oral-drug groups had significantly increased body weight by day 14, and the authors conclude oral amoxicillin-clavulanic acid or doxycycline appeared more effective than a single subcutaneous cefovecin injection. The second card (Kompare 2013, PMID: 23246249; randomised masked trial, 40 shelter cats with Mycoplasma felis URTD) does not compare drugs — both arms are doxycycline — but it defines the doxycycline-first course: a 14-day course beat a 7-day course microbially (day-14 PCR-positive 5 of 20, 25%, vs 11 of 20, 55%; mean Mycoplasma load lower at day 14, P = 0.01) while the authors state the 14-day course produced superior microbial but not clinical results, with nasal discharge and sneezing scores lower in the 14-day group only on individual days in the day 8–14 period (P < 0.05). Design class (b): randomisation is established by Litster 2012, the carded record that answers this shelf's own comparison in this shelf's own population, but blinding is not established — the record states random assignment and does not state masked scoring, and twice-daily sign scores are subjective. Kompare 2013 is randomised and masked on its own course-length question, but class is never borrowed across comparisons, so it does not raise this shelf to class (a). The stamp is POSSIBLE, not LIKELY, because the head-to-head evidence is a single 48-cat trial (16 per arm) with subjective scores, and doxycycline's edge over amoxicillin-clavulanate rests on one sign score (oculonasal discharge). One-home cross-points: Vernau 2024 (PMID: 39485362, doxycycline with or without famciclovir in 373 kittens) homes on shelf #146 — a different population (kittens with infectious ophthalmic/respiratory disease) and a different comparison (antiviral add-on, not antibiotic choice) — and is not re-carded here. Hartmann 2008 (PMID: 18289288, pradofloxacin vs doxycycline in 39 non-shelter cats with pathogen-confirmed Chlamydophila felis/Mycoplasma URTD or conjunctivitis treated for 42 days) is not carded: it is not a shelter population and not an empirical first-line comparison, and shelf #747 likewise records it as deliberately not carded as a claim-carrier. Tier C is not engaged: no mortality or survival claim is made. Drafted Nov 10, 2026 (VetMed build, topic #748); figures from the abstracts, fetched and verified at drafting.