Tylosin phosphate is the phosphoric acid salt of tylosin, a 16-membered macrolide antibiotic obtained by fermentation of Streptomyces fradiae. The API is supplied as a white to off-white powder or granular solid for oral and injectable finished dosage forms, including tablets, capsules, granules, and suspension-type injectables. Grade nomenclature typically distinguishes the milled powder as TP-P and the granulated material as TP-G; these codes are supplier-specific and should be mapped to the registered specification of the lot rather than treated as a universal model number. The Chemical Abstracts Service registry number is 1405-53-4. Pharmacopoeial alignment is established through HPLC assay, related-substance profiling, residual solvent testing, and microbial enumeration, with release values reported in the certificate of analysis. As a low-aqueous-solubility phosphate salt, the product differs from tylosin tartrate and tylosin base in dissolution rate and formulation behavior; the phosphate salt is selected for oral solid matrices and suspension products requiring slower dissolution or reduced water uptake. Target species and indications are established in regional marketing authorizations; the API itself is not a finished product.

The powder grade is typically milled to a particle-size distribution with d90 ≤ 150 µm by laser diffraction (ISO 13320:2020), while the granular grade is sieved to a target interval of 200–800 µm with not less than 85% of the material retained within the designated cut. Bulk density for the powder generally falls between 0.45 g/mL and 0.65 g/mL; granular bulk density is typically 0.55–0.75 g/mL. These ranges are representative of multi-source release data and must be verified against the lot-specific certificate of analysis because particle size and bulk density affect blend uniformity in low-dose tablet formulations. For capsule filling, the granular grade is preferred because improved flow reduces fill-weight variability on dosator and tamping-pin machines; an angle of repose below 35° is generally targeted using USP <1174>.

Specification Framework for Powder and Granular API Release

The following matrix summarizes representative release and formulation-critical parameters for pharmaceutical-grade tylosin phosphate. The values are not a substitute for a registered specification; each supplier applies its own validation data, and injectable grades carry additional requirements for sterility and endotoxin control.

Residual solvent testing is performed by headspace gas chromatography per USP <467>, with limits set by ICH Q3C. Water content is determined by Karl Fischer titration per USP <921>; the loss on drying value is used primarily for process control rather than water-specific assay. Heavy metals are quantified by inductively coupled plasma mass spectrometry per USP <233> when required for the intended market. Batch-to-batch variability in fermentation-derived macrolide APIs is controlled through impurity profiling. Tylosin A is the principal active component; related tylosin components and acid/ketone degradation products are separated by gradient HPLC and quantified using peak normalization. The specification for total related substances is set so that non-active macrolides do not contribute to potency or obscure the main peak. For solid dosage forms, particle-size distribution should be monitored not only at release but after transport because attrition can increase fines and change flow behavior.

How Does Tylosin Phosphate Compare with Tylosin Tartrate and Tylosin Base in Finished-Dose Processing?

Selection among tylosin salts is governed by aqueous solubility, dissolution rate, and the manufacturing route. Tylosin phosphate has low aqueous solubility, whereas tylosin tartrate dissolves rapidly and is used in soluble powders and injectable solutions. Tylosin base has very low aqueous solubility and is mainly employed in non-aqueous or feed-based formulations. The table below summarizes the principal contrasts.

During tablet manufacture, the milled phosphate powder is blended with microcrystalline cellulose, lactose monohydrate, crospovidone, and magnesium stearate. Direct compression is feasible when the phosphate powder has been co-processed or spray-dried; otherwise, the cohesive nature of the milled salt can produce poor flow and weight variation. High-dose strength is usually processed by dry granulation using roller compaction, with ribbon solid fraction controlled between 0.55 and 0.75 to maintain granule porosity and compactibility. If wet granulation is required, non-aqueous binder systems are preferred because the low-solubility phosphate salt can redistribute unevenly during drying if a fully aqueous granulation is used. Uniformity of dosage units is verified by USP <905>; dissolution testing is performed with USP Apparatus II at 50–75 rpm in 900 mL of pH 6.8 phosphate buffer or purified water, with surfactant addition when sink conditions are not achieved.

Granule formation is used to improve flow and reduce dust exposure to the antibiotic powder. Granular material is produced by wet granulation followed by drying and sizing through a 0.8–1.6 mm screen; the resulting granules are filled into hard gelatin or HPMC capsules or compressed into tablets. In capsule filling, fill weight variability on tamping-pin or dosator machines is minimized when the granular material has a bulk density above 0.55 g/mL and a compressibility index below 20% (USP <1174>). Compared with tylosin tartrate, the phosphate salt’s lower solubility frequently reduces the rate of moisture-mediated degradation in solid matrices; however, it also slows dissolution and can require surfactant in dissolution media. The phosphate counterion may influence compactibility; tablets containing phosphate salt can require higher compression force to achieve similar tensile strength compared with an equivalent tartrate granulation, although the effect is formulation-dependent.

Oral granules are also used to prepare reconstituted suspensions; the granular API is blended with sweeteners, buffer, and suspending agent. Reconstitution creates a coarse suspension, not a solution, and the labeled shelf life after reconstitution must be supported by stability data at controlled room temperature. The suspension vehicle is typically thickened with xanthan gum or microcrystalline cellulose/sodium carboxymethylcellulose to minimize settling; viscosity is characterized by Brookfield rotational viscometry at 25°C.

Injectable preparation with tylosin phosphate is suspension-based, not solution-based. The low aqueous solubility of the phosphate salt requires particle-size reduction by wet milling or high-pressure homogenization, with the suspended particle population controlled to d50 below 10 µm and oversize particles above 25 µm limited to avoid syringe needle occlusion. The vehicle composition typically includes a wetting agent such as polysorbate 80 and a suspending agent such as sodium carboxymethylcellulose; the suspension is filled under nitrogen if oxidative degradation is a known risk. Sterility is verified by USP <71>, bacterial endotoxin by USP <85>, and particulate matter by USP <788>. Terminal sterilization may be applied if thermal stability data confirm no loss of potency; otherwise, aseptic processing with sterile API and sterilized vehicle is required.

The dry phosphate salt is hygroscopic; repeated opening of containers under high humidity can increase water content and reduce flow. Storage in tight containers at 15–25°C with desiccant is typical, and the API is protected from light. Pre-drying is required if loss on drying exceeds 4.0% or if storage humidity exceeds 60% RH. Compatibility with strong oxidizing agents, strong acids, and strong alkalis should be assessed because the macrolide lactone ring is susceptible to acid-catalyzed hydrolysis. Forced degradation studies show acid-catalyzed hydrolysis and photodegradation in solution, but published stability data for this specific phosphate salt in alkaline solution are limited. Dust extraction and local exhaust ventilation are used during dispensing, sieving, and granulation to control occupational exposure.