Blastomycosis in dogs: itraconazole vs fluconazole — MAYBE (weak evidence)

In dogs with blastomycosis, does itraconazole give higher remission and survival than fluconazole, and at what cost/toxicity trade-off?

Shelf #143 · gate-verified and approved by the developer

MAYBE (weak evidence): There is no randomised head-to-head trial of itraconazole versus fluconazole for canine blastomycosis — the draft premise of a randomised Legendre-programme comparison does not exist in the record; the genuine comparison is a retrospective case review (Mazepa 2011, 144 dogs, 1998-2008). In it, clinical remission was 90% on itraconazole versus 75% on fluconazole — a 15-percentage-point gap that was not significant (P = .13) in a non-randomised comparison where sicker dogs may have been channelled to either drug; relapse was 18% versus 22% (P = .75) (no demonstrated difference). The clear trade-offs were time and money: fluconazole needed a significantly longer median treatment duration (183 vs 138 days; P = .001) but cost a median of $1,223 versus $3,717 for itraconazole (P < .001) — roughly one-third the drug cost. Raised ALT activities were similar (26% itraconazole, 17% fluconazole; P = .71, on small tested subsets), so the record does not support the hope that fluconazole is clearly gentler on the liver. Tier C (survival/remission claim). The older Legendre itraconazole series (112 dogs) anchors itraconazole's absolute performance — about 54% cured with a 60-day course and about 25% mortality — but compares doses, not fluconazole. Drafted Nov 10, 2026 (VetMed build, topic #143); all figures from abstracts fetched and verified at drafting.

Mazepa 2011: remission 90% itraconazole vs 75% fluconazole (P = .13, not significant); fluconazole cheaper but slower

Retrospective comparison (record's own title wording: 'Retrospective comparison'; publication type: Comparative Study)

Who: Dogs: 144 dogs with systemic blastomycosis treated with itraconazole or fluconazole from 1998 to 2008, in a retrospective case review (per-arm denominators are not stated in the record's abstract).

Result: Neither treatment efficacy between fluconazole (75% remission) and itraconazole (90% remission) nor relapse rate (18% for itraconazole, 22% for fluconazole) was significantly different (P = .13, .75, respectively). Treatment duration was significantly longer for fluconazole (median 183 days) than for itraconazole (138 days; P = .001). Costs for fluconazole (median $1,223) were significantly less than for itraconazole ($3,717; P < .001). Incidence of increased ALT activities was not significantly different between groups (17% [3/18] for fluconazole, 26% [6/23] for itraconazole; P = .71). The authors conclude fluconazole is associated with survival to clinical remission in 75% of dogs with blastomycosis, and that although dogs receiving fluconazole were treated longer, drug costs were one-third those of itraconazole.

Watch out: Retrospective and non-randomised: drug choice over a 10-year span (1998-2008) reflects clinician preference, era and case mix, so the non-significant 15-point remission gap could hide confounding in either direction — randomisation is not established for this claim-carrying record. ALT was measured in only 18 fluconazole and 23 itraconazole dogs, so the hepatotoxicity comparison rests on small subsets. Costs are US drug costs of that era and will not transfer directly to current prices.

Mazepa AS, Trepanier LA, Foy DS. Retrospective comparison of the efficacy of fluconazole or itraconazole for the treatment of systemic blastomycosis in dogs. J Vet Intern Med. 2011;25(3):440-5. PMID: 21418325. Registry ID: none in the record. MeSH: Animals · Antifungal Agents · Blastomycosis · Dog Diseases · Dogs · Female · Fluconazole · Itraconazole · Male · Retrospective Studies

Legendre 1996: itraconazole in 112 dogs — ~54% cured with a 60-day course, ~25% mortality, 5 mg/kg as effective as 10 mg/kg

Non-randomised case series with sequential dose cohorts (publication type: Clinical Trial; no randomisation stated in the record)

Who: Dogs: 112 client-owned dogs with blastomycosis treated with itraconazole — a first group of 70 dogs treated in 1987-1988 received 10 mg/kg/d (group 1), and a second group of 42 dogs treated after October 1988 received 5 mg/kg/d (group 2); a historical group treated with amphotericin B is reported for comparison.

Result: The proportion of dogs cured with a 60-day course of itraconazole was similar for both dose groups (53.6% versus 54.3%) and for the historical amphotericin B group (57%); the recurrence rate was also similar (20%, 21.4%, and 20%, respectively). Dogs treated with itraconazole had similar mortality rates (25.7% at 5 mg/kg/d; 25% at 10 mg/kg/d) to those treated with amphotericin B (23%). Seventeen of the 23 dogs that died (74%) did so during the first week of treatment, usually attributed to respiratory failure. The only site of infection significantly associated with failure (death or recurrence) was the brain. Dogs in group 1 (10 mg/kg/d) had significantly more adverse effects than group 2 (P = .046); anorexia was the most common adverse effect, in 14.9% of group 1, while only 8% of group 2 dogs had adverse effects. The authors conclude itraconazole at 5 mg/kg/d is the drug of choice for blastomycosis in dogs.

Watch out: Context card only: this series never compares itraconazole with fluconazole, and its dose groups were treated in different eras (sequential cohorts, not randomised), with amphotericin B as a historical control — it anchors itraconazole's absolute cure and mortality figures, nothing comparative. Most deaths occurred in the first week from respiratory failure, i.e. disease severity at presentation dominates early mortality whatever the drug.

Legendre AM, Rohrbach BW, Toal RL, Rinaldi MG, Grace LL, Jones JB. Treatment of blastomycosis with itraconazole in 112 dogs. J Vet Intern Med. 1996;10(6):365-71. PMID: 8947868. Registry ID: none in the record. MeSH: Alanine Transaminase · Alkaline Phosphatase · Animals · Antifungal Agents · Blastomycosis · Brain Diseases · Dog Diseases · Dogs · Dose-Response Relationship, Drug · Female · Itraconazole · Liver · Lung Diseases · Male · Skin Diseases

Synthesis: no randomised comparison exists — itraconazole is the default on weak evidence, fluconazole the cheaper, slower alternative

Synthesis

Who: Synthesis of the cards above: Mazepa 2011 (retrospective comparison, 144 dogs with systemic blastomycosis) and Legendre 1996 (non-randomised itraconazole series, 112 dogs).

Result: The honest answer to the shelf question is that it is untested by any randomised trial. The retrospective comparison numerically favours itraconazole on remission (90% vs 75%) without reaching significance, shows no difference in relapse or in raised ALT, and shows fluconazole's real advantages and costs plainly: about one-third the drug cost ($1,223 vs $3,717 median) in exchange for about 45 more days of treatment (183 vs 138 days median). Legendre's series supports itraconazole 5 mg/kg/d as an effective standard (~54% cured on a 60-day course, ~25% mortality, fewer adverse effects than 10 mg/kg/d). A clinician choosing fluconazole for cost reasons is not contradicted by this evidence; a clinician expecting it to be clearly less hepatotoxic is not supported by it either.

Watch out: All comparative figures come from one retrospective review spanning 1998-2008; treatment-era, formulation and pricing changes since then limit how far the cost and duration numbers travel. Neither carded record is randomised, and no blinded comparison exists — the stamp stays MAYBE (weak evidence).

Synthesis of Mazepa AS et al. PMID: 21418325 and Legendre AM et al. PMID: 8947868. Registry ID as on the individual cards.

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