Doxivetin paste typically consists of:

Active Ingredient: Doxivetin hyclate or monohydrate (1–10% w/w).

Vehicle: Hydrophilic or hydrophobic bases (e.g., polyethylene glycol, petrolatum, or carboxymethyl cellulose) to control drug release and adhesion to mucosal surfaces.

Excipients: Preservatives (e.g., methylparaben), stabilizers, and pH adjusters to enhance shelf life and patient comfort.

Advantages Over Systemic Therapy

Targeted Action: Direct application reduces off-target effects.

Reduced Resistance Risk: Lower systemic exposure delays the emergence of resistant strains.

Improved Patient Compliance: Simplified dosing regimens (e.g., weekly applications for periodontitis).

The active pharmaceutical ingredient doxycycline is produced via a four-step semi-synthetic route starting from oxytetracycline. Step 1: Low-temperature chlorination.Sodium hypochlorite is used to substitute the C11 position of oxytetracycline at 10–15 °C to form the intermediate 11α-chloro-6,12-hemiketal oxytetracycline.

Step 2: Low-temperature dehydration and salt formation.The intermediate reacts with p-toluenesulfonic acid at 0–5 °C to remove hydroxyl groups and form a methylene structure, yielding chloromethylene oxytetracycline sulfonate.

Step 3: Palladium-carbon catalytic hydrogenation and dechlorination. Hydrogen gas is introduced under pressurized conditions to selectively reduce double bonds and eliminate chlorine atoms, stereospecifically generating 6-deoxyoxytetracycline with α configuration.

Step 4: Aminolysis, salt conversion and crystallization. The intermediate reacts with a hydrochloric acid-isopropanol system, followed by recrystallization at a controlled temperature of 35–40 °C. Filtration and drying afford doxycycline hyclate bulk drug with purity ≥99%. HPLC is applied to remove toxic impurities such as epitetracycline so as to guarantee the safety of topical preparations.

A fusion-homogenization compounding process is adopted to prepare sustained-release mucoadhesive paste. The whole process is carried out under light-shielded and temperature-controlled conditions to avoid thermal oxidative degradation of tetracyclines. Auxiliary materials are pretreated by phase separation first.

For the oil phase, paraffin and caprylic/capric triglyceride are heated to 70 °C for melting, followed by addition of antioxidant stabilizers BHT and disodium EDTA. For the aqueous phase, glycerin, purified water and sodium metabisulfite are blended, and the pH value is adjusted to 5.5–6.5 to match the stability range of the bulk drug.

Fine doxycycline hyclate powder is sieved through a 100-mesh sieve and wetted and dispersed with a small amount of propylene glycol to prevent powder agglomeration.

The drug suspension is slowly poured into the molten matrix at constant temperature, followed by vacuum high-shear homogenization for 35 min to achieve uniform dispersion of fine drug particles.

The mixture is cooled to 40 °C, then silicon dioxide (thickener) and sodium saccharin (flavor corrector) are added. Low-speed stirring is performed for defoaming to eliminate bubbles that would impair the paste's mucoadhesion.

After homogenization, the paste is allowed to stand and mature at low temperature for 24 h to stabilize its rheological viscosity and enhance retention and sustained release on wound surfaces.The product is sterile-filtered, filled into containers, and stored hermetically away from light.

The core strengths of this full process lie in the composite antioxidant system that suppresses photodegradation of doxycycline, and the highly mucoadhesive matrix that reduces drug loss, extending local antibacterial duration by 4–6 hours compared with ordinary ointments.

Strict control of synthesis and homogenization temperatures and full protection from intense light drastically cut the generation of epimers. The formulation retains potent antibacterial activity while remaining mild to the skin, suitable for topical administration in periodontal and cutaneous inflammatory lesions.