2-{2-[1-(4-Chlorophenyl)-1-Phenylethoxy]Ethyl}-1-Methylpyrrolidine

Conversion of 2‑{2‑[1‑(4‑chlorophenyl)‑1‑phenylethoxy]ethyl}‑1‑methylpyrrolidine (C₂₁H₂₆ClNO, CAS 15686-51-8) into clemastine fumarate tablets involves an initial salification step in which the free base is dissolved in a 1:1.05 molar ratio with fumaric acid in refluxing 95% ethanol to yield the hydrogen fumarate salt prior to granulation. This in‑situ salt formation mitigates the poor aqueous solubility of the neat base (<0.1 mg/mL), enabling adequate dissolution performance as mandated by USP Clemastine Fumarate Tablets. The resulting dried salt is jet‑milled to a particle size distribution where d90 ≤ 15 µm, as assayed by laser diffraction (ISO 13320), because content uniformity of a 1 mg dose in a 150 mg tablet core — an active loading of merely 0.89% w/w — is acutely sensitive to agglomerate dispersion. Wet granulation is performed in a high‑shear mixer (e.g., Diosna P1/6) using a pre‑gelatinized starch binder and microcrystalline cellulose diluent, with granulation end‑point determined by impeller power consumption and a loss‑on‑drying target of 2.0–3.5% water. After fluid‑bed drying at inlet air temperature 55°C, the granules are lubricated with 0.75% magnesium stearate for 3 minutes in a V‑blender; over‑lubrication beyond 5 minutes has been documented to retard dissolution by forming a hydrophobic film on the friable granule surfaces. Tableting on a rotary press (FETTE 2090i, B‑tooling, 16 stations) at a compression force of 6–10 kN yields tablets with hardness 4–7 kp and friability below 0.5% per USP <1216>. The finished film‑coated tablets — packaged in PVC/PVDC‑aluminium blisters or amber HDPE bottles — comply with USP <905> (AV ≤ 15.0) and USP <711> Apparatus 2 (paddle, 50 rpm, 900 mL 0.1 N HCl, Q = 80% at 30 min). The coating suspension, an aqueous Opadry® system, is applied in a perforated pan coater with exhaust temperature maintained at 45–50°C to prevent moisture uptake by the hygroscopic fumarate salt. Environmental controls are critical: relative humidity in the compression suite must stay below 40% RH to eliminate picking and sticking on the lower punch faces, a behaviour routinely confirmed on production‑scale batches exceeding 200,000 tablets.

What Controls Sedimentation and Crystal Growth Rates in Clemastine Base-Derived Syrup Formulations?

Aqueous oral solutions dosed at 0.5 mg clemastine base equivalent per 5 mL present a distinct set of stability challenges because the active ingredient, added as the pre‑formed fumarate salt, tends to nucleate crystallisation points when dissolved at near‑saturation concentrations in a 60–64% sucrose or sorbitol vehicle. The formulation is buffered to pH 5.2–5.8 with 0.1 M citric acid/sodium citrate to suppress both hydrolytic cleavage of the ether bridge and racemisation at the chiral carbon, which accelerates below pH 4.0 and above pH 6.5. A dual preservative system of sodium benzoate (0.1% w/v) and potassium sorbate (0.1% w/v) is incorporated, and its efficacy must be verified by antimicrobial effectiveness testing per USP <51> against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Aspergillus brasiliensis. Manufacturing is conducted in a 316L stainless‑steel jacketed tank equipped with a bottom‑mounted rotor‑stator mixer; sucrose is dissolved at 60°C in purified water (USP, conductivity <1.3 µS/cm) and cooled to 25°C before adding the fumarate salt pre‑dissolved in a 10% ethanol co‑solvent to avoid thermal degradation. The bulk solution is passed through a 0.45 µm polypropylene depth filter and filled into 100 mL Type III amber glass bottles under nitrogen flushing to limit dissolved oxygen, a known promoter of N‑oxide formation on the pyrrolidine ring. Finished product is tested against USP Clemastine Fumarate Syrup: assay limits 90.0–110.0% of the labeled base content, pH 4.0–6.0, and microbial enumeration with total aerobic microbial count ≤100 CFU/mL and total combined yeasts and molds ≤10 CFU/mL per USP <61>/<62>.

If a decongestant combination product is specified, the 2‑{2‑[1‑(4‑chlorophenyl)‑1‑phenylethoxy]ethyl}‑1‑methylpyrrolidine component is processed into a bilayer tablet containing 60 mg pseudoephedrine hydrochloride in the sustained‑release layer and 0.5 mg clemastine base (as 0.67 mg fumarate) in the immediate‑release layer. The two granulations are prepared separately: the pseudoephedrine portion, which constitutes over 95% of total tablet mass, is wet‑granulated with hydroxypropyl methylcellulose K100M to achieve 8‑hour extended release, while the clemastine granulate is produced by fluid‑bed top‑spray deposition of the fumarate salt solution onto microcrystalline cellulose spheres to guarantee a coefficient of variation below 3.0% in the 0.5 mg fraction. Direct contact between the two layers during bilayer compression on a 55‑station rotary press (Kikusui Libra2) creates a risk of moisture migration from the pseudoephedrine layer (equilibrium moisture content 3.5–4.5%) into the clemastine layer, which catalyzes hydrolysis of the diphenylmethyl ether moiety. This is mitigated by a 2 mm inert barrier of anhydrous dibasic calcium phosphate compressed at the interface. The finished oblong tablet, typically 17 mm in length, has a total weight of 400 mg and a clemastine base loading of 0.125% w/w. Compliance is assessed against the relevant USP monograph for Clemastine Fumarate and Pseudoephedrine Hydrochloride Tablets, with dissolution in 0.1 N HCl requiring ≥75% (Q) clemastine release at 45 minutes and a pseudoephedrine release profile fitting the USP <724> extended‑release acceptance criteria. Terminal packaging in cold‑form aluminium foil blisters provides a moisture vapour transmission rate below 0.005 g/m²/day to protect against the deliquescence of pseudoephedrine HCl.

Veterinary Antipruritic Chewable Matrices for Canine and Feline Administration

Veterinary chewable tablets delivering 1.34 mg clemastine fumarate (1 mg base) per unit are manufactured using a wet massing technique where the active salt is dispersed in a flavoured granulation vehicle containing dried meat solubles, yeast, and microcrystalline cellulose. Palatability studies conducted on mixed‑breed dogs indicate acceptance rates above 85% only when the base‑derived fumarate is pre‑blended with a 1:3 tasting agent comprising desiccated pork liver powder and a non‑volatile maltol‑enhanced sweetener; omitting this step results in rejection due to the inherent bitterness of the free amine, which exhibits a threshold at approximately 5 ppm in saliva. The granulate is prepared in a planetary mixer with 12% water as granulating fluid, extruded through a 1.0 mm screen, and spheronised to achieve a particle size fraction of 0.8–1.2 mm. Drying is carried out at 45°C in a tray dryer to a final moisture content of 2.0–3.0%, critical because residual water above 4.0% fosters hydrolysis of the fumarate salt to clemastine free base and fumaric acid, increasing tablet friability. Compression at 3–5 kN on a D‑tooling press produces tablets with hardness 3–5 kp that disintegrate within 4 minutes in simulated canine gastric fluid (USP buffer pH 1.2 with 0.2% sodium lauryl sulfate). The chewable product conforms to the content uniformity requirements of FDA‑CVM Guidance for Industry #219 and the stability protocols of VICH GL18, with impurity profiling using a validated HPLC method showing no unspecified degradant exceeding 0.2% after 12 months at 25°C/60% RH in high‑density polyethylene jars with child‑resistant caps.

Aseptic filling of clemastine base injection solution, typically formulated at 1 mg/mL base (as the fumarate salt, 1.34 mg/mL), commences with dissolution of the pre‑salt in Water for Injection (WFI, USP conductivity ≤1.3 µS/cm) containing 0.9% sodium chloride for isotonicity adjustment and 0.1% anhydrous citric acid/sodium citrate buffer to hold pH at 5.0–6.0. The solution is sparged with pharmaceutical‑grade nitrogen (≤5 ppm O₂) to displace dissolved oxygen, as even trace oxidative environments generate the N‑oxide degradate, which elutes at relative retention time 0.78 relative to clemastine on a C18 column (150 × 4.6 mm, 5 µm). Clarification is achieved by serial filtration through 0.45 µm and 0.22 µm PVDF membrane filters housed in a Grade A isolator; the filters must be integrity‑tested via bubble point with a minimum value of 3.2 bar for the 0.22 µm cartridge. The sterile filtrate is filled into 1 mL amber Type I glass ampoules (USP <660> hydrolytic resistance Type I) under unidirectional airflow at 0.45 m/s ±20% and subsequently subjected to terminal sterilisation in a saturated steam autoclave at 121°C for 15 minutes. A reduction in stereochemical purity of approximately 0.4% of the (R,R) to (S,S) epimer has been observed during this thermal cycle, necessitating a tighter chiral purity specification of ≥99.0% for the base input. The finished ampoules are tested for bacterial endotoxins to meet the limit of <35 EU/mg per USP <85> and for particulate matter per USP <788> Method 1 (Light Obscuration) with counts ≤6000 particles ≥10 µm and ≤600 particles ≥25 µm per container. The terminal product is indicated for intramuscular or slow intravenous administration in acute urticaria and anaphylactoid emergencies.

The (R,R) Stereoisomer Content Is Determined via a Chiralpak IA‑3 Column with the Base as Reference Marker

For quality control laboratories supporting solid and parenteral dosage manufacturing, the unformulated 2‑{2‑[1‑(4‑chlorophenyl)‑1‑phenylethoxy]ethyl}‑1‑methylpyrrolidine is employed as a primary reference standard for both identity and chiral purity assessments, because the pharmacopoeial assay of clemastine fumarate relies on the chromatographic separation of the active (R,R) enantiomer from the stereoisomers (S,S), (R,S), and (S,R). A 10 mg quantity of the base is dissolved in 20 mL of mobile phase (n‑hexane/ethanol/diethylamine 90:10:0.1) and diluted to 100.0 mL to yield a stock standard of 0.1 mg/mL. System suitability is assessed on a Chiralpak IA‑3 column (250 × 4.6 mm, 3 µm) at 25°C with UV detection at 254 nm; the resolution between (R,R)‑clemastine and (S,S)‑clemastine must exceed 2.0, and the tailing factor must remain below 1.5. The base reference material is further used to identify the photolytic degradant 1‑methyl‑2‑[2‑(4‑chlorobenzoyl)ethyl]pyrrolidine formed via oxidative cleavage of the benzhydryl ether under ICH photostability conditions (ICH Q1B, Option 2, 1.2 million lux·h visible and 200 Wh/m² UV). Quantitation of this degradant at a reporting threshold of 0.05% relative to the 1.0 mg/mL test solution anchors the stability‑indicating nature of the HPLC method per ICH Q2(R1) validation parameters for linearity (r² ≥ 0.999 over 0.05–1.5 µg/mL), accuracy (recovery 98.0–102.0%), and intermediate precision (RSD ≤ 2.0%). The certificate of analysis issued with each base batch provides assayed purity by both normal‑phase HPLC area percent and differential scanning calorimetry melting endotherm (mp 128–132°C, DSC endothermic peak purity >99.5%), enabling direct use as a working standard in compendial testing suites without the need for additional correction factor determinations.