For low-dose canine heartworm prophylaxis tablets, micronized ivermectin is incorporated by direct compression at label claims of 68 µg, 136 µg, and 272 µg. The primary processing constraint in this solid oral dosage form is not tabletability but rather blend homogeneity at an extremely low active pharmaceutical ingredient load. A pre-blend trituration is prepared by geometric dilution of the micronized API with lactose monohydrate NF in 1:10 increments until the drug concentration is reduced to approximately 0.1% w/w. The resulting pre-blend is screened through a 600 µm stainless-steel sieve and charged to a bin blender with microcrystalline cellulose PH102, croscarmellose sodium, and colloidal silicon dioxide. Tablet compression is performed on a rotary tablet press with 8 mm and 10 mm round flat-faced bevel-edged tooling. Compression force is maintained between 6 kN and 12 kN, and friability is tested according to USP <1216>. Content uniformity is evaluated by USP <905>, with the acceptance value controlled below 15.0. Dissolution is assessed using USP <711> Apparatus 2 at 50 rpm with a medium containing 0.1 M hydrochloric acid and 0.1% sodium lauryl sulfate; the Q value at 45 minutes is not less than 75% based on label claim. The tablets are film-coated with an opaque hydroxypropyl methylcellulose coating to limit photodegradation because ivermectin exhibits light sensitivity in the solid state. Stability batches are packaged in polyvinyl chloride/polyvinylidene chloride blister cavities with aluminum foil lidding and placed under VICH GL3 long-term storage at 25°C/60% RH and intermediate storage at 30°C/65% RH. The terminal product is administered monthly at a dose of 0.006 mg/kg body weight.

What Limits Terminal Sterilization of Non-Aqueous Ivermectin Injectables?

A 1% w/v injectable solution contains 10 mg/mL ivermectin in a non-aqueous vehicle of glycerol formal and propylene glycol. The API is practically insoluble in water; aqueous formulations are not used for this route because the required concentration exceeds the aqueous solubility limit by several orders of magnitude. Sterilization is the principal process boundary. Terminal steam sterilization is generally avoided because the non-aqueous solvent system has a high vapor pressure and the filled vials may distort under autoclave load. Aseptic filtration through a 0.45 µm polypropylene pre-filter followed by a 0.22 µm polyvinylidene fluoride membrane is therefore the standard manufacturing route. The filter train is integrity-tested before and after filtration by bubble point and diffusion flow per ASTM F838-20. Filling is performed under Grade A laminar airflow with a nitrogen overlay to reduce oxidative degradation. The solution is filled into Type I borosilicate glass vials with coated chlorobutyl elastomer closures. Sterility is confirmed according to USP <71>, and bacterial endotoxin limits are set at not more than 0.5 EU/mg using USP <85>. Subvisible particulate matter is controlled by USP <788>, with not more than 6000 particles per container at ≥10 µm and not more than 600 particles per container at ≥25 µm. Container closure integrity is verified using USP <1207> methodology. The terminal product is administered subcutaneously at 200 µg/kg body weight, which corresponds to 1 mL per 50 kg body weight for the 1% w/v solution. The packaging includes 50 mL, 200 mL, and 500 mL vials stored at controlled room temperature not exceeding 30°C and protected from light.

Oral Drench Stability in Hard Water Dilution Depends on Surfactant Selection

In ovine and caprine anthelmintic programs, an oral drench solution at 0.08% w/v ivermectin is manufactured as a micelle-based rather than a true aqueous solution. The vehicle consists of propylene glycol, benzyl alcohol, polysorbate 80, and purified water. The non-ionic surfactant load must prevent API precipitation when the drench is diluted with hard water. Water hardness at 300 mg/L calcium carbonate equivalent is used as a stress condition during development; the diluted solution is inspected after 24 hours and nephelometric turbidity is maintained below 10 NTU. Manufacturing proceeds by dissolving ivermectin in propylene glycol at 35°C to 40°C, adding the surfactant and benzyl alcohol, and then introducing purified water under high-shear mixing at 3000 rpm to 5000 rpm for 15 minutes. The finished solution is passed through a 100 µm nylon filter before filling into amber high-density polyethylene drench containers. Assay is performed by reverse-phase high-performance liquid chromatography with ultraviolet detection at 245 nm. The drench is administered at 200 µg/kg body weight, equivalent to 2.5 mL per 10 kg body weight. Drench gun calibration is verified by dispensing ten consecutive doses into a graduated cylinder; the relative standard deviation for delivered volume should not exceed 2.0%. Stability is evaluated under VICH GL3 at 25°C/60% RH and 30°C/65% RH for 24 months in the commercial container.

Feed Premix Carryover and Cleaning Validation Boundaries

In feed mill operations, a Type A medicated article is prepared by dispersing ivermectin onto soybean hulls, corn cob fractions, or a blend of both carriers with light mineral oil as a binder. The concentrate is produced at 0.6% w/w and 1.0% w/w ivermectin. The API is pre-blended with a portion of the carrier in a paddle mixer at 20 rpm for 10 minutes, then the remaining carrier is added and mixed for an additional 15 minutes. Light mineral oil is sprayed through a single-nozzle spray bar at 0.5% to 1.0% of total batch weight while mixing continues. The finished premix is discharged through a 1000 µm screen to remove agglomerates. Homogeneity is verified by sampling ten 100 g increments from different zones of the mixer. The coefficient of variation for ivermectin content should not exceed 5.0% across the batch. The medicated feed is prepared by adding the premix to complete swine feed at an inclusion rate that delivers 100 µg/kg body weight per day for 7 days as the sole ration. A step-wise mixing sequence is used: a working premix is prepared at 2.0% premix in ground corn and then diluted into the final feed. The feed mill equipment is cleaned according to 21 CFR 225.1 and VICH GL18 principles; carryover of ivermectin into non-medicated feed is controlled to either the analytical limit of detection or a toxicologically justified carryover limit. The terminal product is packaged in multi-wall paper bags lined with polyethylene and stored under dry conditions below 30°C. Sampling and chemical analysis are performed in accordance with ISO 6497:2002 and a validated HPLC method with UV detection.

When Ivermectin Paste Rheology Must Be Adjusted for Equine Oral Syringe Fill

A 1.87% w/w ivermectin oral paste is formulated for equine anthelmintic administration. The paste must exhibit sufficient low-shear viscosity to remain in the graduated syringe during storage, but it must also shear-thin sufficiently to extrude through a 10 mm orifice at 25°C with manual pressure. The vehicle is built from hydrogenated castor oil and corn oil, with titanium dioxide as an opacifier and a hydroxypropyl cellulose thickener. Ivermectin is dispersed under high-shear mixing until a uniform suspension is achieved; agglomerates are removed by passing the paste through a 150 µm screen. Rheological testing is performed on a rotational viscometer with a T-bar spindle at 25°C. The apparent viscosity at 0.5 rpm is typically between 80,000 mPa·s and 120,000 mPa·s, while the viscosity at 10 rpm falls below 20,000 mPa·s, confirming shear thinning. The paste is filled into high-density polyethylene oral syringes calibrated by body weight in 50 kg increments. Each 6.42 g syringe contains 120 mg ivermectin and treats horses up to 600 kg at 200 µg/kg. Syringe fill weight is checked at 15-minute intervals with a target relative standard deviation below 1.0%. Content uniformity is confirmed by sampling the beginning, middle, and end of the filling run and assaying three 1 g aliquots per syringe. Stability under VICH GL3 conditions is evaluated in the commercial container, with particular attention to viscosity drift and API crystal growth. The product is protected from light and stored below 30°C.

Compounded oral capsules for non-standard veterinary species are prepared from the same micronized API when no licensed dosage form or species-specific product is available. The API is first deagglomerated by screening through a 180 µm stainless-steel sieve and then blended with lactose monohydrate NF and magnesium stearate. For low-dose capsule strengths below 1 mg, the trituration protocol is identical to that used for tablets: 1:10 geometric dilution steps reduce the active concentration to approximately 0.05% w/w before encapsulation. The blend is filled into hard gelatin or hydroxypropyl methylcellulose capsules using a semi-automatic capsule filler; weight variation is assessed according to Ph. Eur. 2.9.5 or USP <905>. Content uniformity is the primary release test because the drug load per capsule is often below 1% of the total fill weight. Dissolution testing, where applicable, uses the same USP <711> methodology described for tablets, but acceptance criteria must be justified for the intended species and dosing interval. The compounded capsules are dispensed in amber glass vials with desiccant to limit moisture ingress and photodegradation. Published data for this specific configuration is limited; therefore, stability of compounded capsules is assigned a beyond-use date based on the criteria of the controlling veterinary regulatory authority and the physical and chemical stability data available for the raw API.

Dry oral granules and powders for swine and poultry are prepared by wet granulation of the micronized API with lactose monohydrate, povidone K30, and corn starch. The granulation fluid is purified water or an aqueous isopropanol mixture. The wet mass is extruded through a 0.8 mm screen, spheronized, and dried in a fluid bed dryer at inlet air temperature not exceeding 45°C until loss on drying is below 3.0%. The final granules are sized between 180 µm and 850 µm to minimize segregation during handling. The granules are filled into foil-lined sachets or bulk polyethylene containers. Because ivermectin is light-sensitive and lipophilic, the granules are protected from light and excessive heat. For oral powders, a blend of ivermectin with lactose and silicon dioxide is prepared by geometric dilution; the powder is mixed in a ribbon blender and filled into unit-dose sachets. Content uniformity is verified by USP <905> or Ph. Eur. 2.9.5 depending on the marketed jurisdiction. Granule and powder dosage forms are used where liquid dosing or injection is impractical, but their use in medicated drinking water is constrained by the negligible aqueous solubility of ivermectin; such products generally require solubilizing surfactants and are formulated as dispersible concentrates rather than simple powders. Published data for this specific configuration is limited; therefore, formulation development relies on pilot-scale studies and product-specific stability data.