Fact check: What is the concentration of ivermectin in horse paste?

1. Conflicting headlines: one percentage versus a per‑kilogram dose

The most direct claim about paste concentration is that an oral paste formulation used in a 2010 equine pharmacokinetic study contained ivermectin at 1.87%, described alongside excipients titanium dioxide and propylene glycol ^[1]. By contrast, several entries frame ivermectin in terms of dose administered as 0.2 mg/kg bodyweight (200 µg/kg) in clinical or efficacy contexts; this is a per‑weight dose, not a concentrate figure for the paste itself ^{[2] [3]}. The two descriptions can coexist: a paste with a given percent concentration can be dosed to deliver a mg/kg payload, but the provided materials do not always make that conversion explicit ^{[1] [2]}.

2. Where the record is silent: many sources do not report a concentration

Multiple analyses explicitly note no concentration is provided for the horse paste in their texts, even when discussing ivermectin efficacy or pharmacokinetics in equines and humans ^{[4] [6] [5] [7]}. These summaries indicate a literature emphasis on pharmacokinetic outcomes, efficacy, and comparative formulations rather than standardized reporting of percent content for commercially available pastes. The absence of concentration statements in several items means any single concentration claim should be treated as study‑specific rather than universally representative ^{[4] [6]}.

3. Dose statements vs. formulation content — a crucial technical distinction

Some materials report ivermectin in mg/kg dosing terms (0.2 mg/kg), which are clinical dose targets used in trials and practice; these do not by themselves specify the percent concentration of a commercially supplied paste ^{[2] [3]}. Translating a percent concentration into a per‑kilogram dose requires knowing the paste’s density and the administered volume per kilogram, details not supplied in the summaries. Thus, a 1.87% paste could deliver 0.2 mg/kg if administered in an appropriate volume, but the reviewed items do not provide enough data to confirm that conversion for any given product ^{[1] [2]}.

4. Date and provenance issues that affect trustworthiness

The dataset contains a range of publication dates from 2010 through 2024, including several clearly erroneous medieval dates ^[8] in metadata that signal indexing problems and reduce confidence in those entries ^{[1] [2] [7] [6]}. The most recent relevant analyses include a 2024 pharmaco-metrics summary and a 2023 equine formulation study summarized here; the 2010 study explicitly naming 1.87% remains the only entry in this set that gives a percent concentration ^{[1] [7] [2]}. Where dates are modern (2010–2024), the documents address pharmacokinetics and dosing strategies, which is useful context but not conclusive about retail paste concentrations ^{[1] [7]}.

5. Multiple viewpoints and potential agendas in the summaries

The available summaries reflect different research priorities: some aim to report formulation composition for pharmacokinetic experiments (leading to the 1.87% figure), while others emphasize dosing strategies and bioavailability across populations (producing mg/kg dose statements) ^{[1] [5] [7]}. The presence of entries warning about extra‑label use and underdosing signals an animal‑welfare and veterinary practice agenda focused on correct dosing rather than brand concentration disclosure ^[6]. These differing emphases explain why some documents specify concentration and others do not ^{[1] [6]}.

6. What can be reliably concluded from these sources

From the assembled analyses, the defensible facts are: one published equine study reports a 1.87% ivermectin oral paste formulation ^[9], and several clinical descriptions report administration at 0.2 mg/kg in equine contexts (200 µg/kg), which is a standard therapeutic dose referenced in the summaries ^{[1] [2] [3]}. No single provided document establishes that all commercial horse pastes are 1.87% or that a specific product will deliver 0.2 mg/kg without knowing dose volume and product concentration ^{[1] [2]}.

7. Practical implication — why the distinction matters

The difference between percent concentration and mg/kg dose matters for safe, effective use: percent describes the formulation; mg/kg describes the therapeutic target. Administering a paste without matching the paste concentration and volume to the animal’s weight risks overdosing or underdosing, a concern explicitly raised in the extra‑label use discussions ^[6]. Therefore, when planning treatment, practitioners must translate product concentration into an administered volume appropriate to the horse’s weight, information not consistently provided in these summaries ^{[6] [2]}.

8. Bottom line for readers seeking a definitive number

Within this dataset the clearest concentration claim is 1.87% ivermectin in an oral horse paste used in a 2010 study, while several other items report the common therapeutic dose of 0.2 mg/kg without listing paste concentration. Given the mixed reporting and metadata anomalies, treat the 1.87% figure as study‑specific evidence rather than a universal commercial standard, and rely on product labels or manufacturer data to determine the concentration of any particular paste before calculating mg/kg dosing ^{[1] [2] [6]}.