Folate Salt Stabilization in Aqueous Solutions
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Solution Overview
Problem
Stable high-strength pharmaceutical aqueous compositions of folates, such as leucovorin and levoleucovorin, face challenges due to oxidative degradation and low solubility in water, leading to precipitation and particulate matter formation, which limits their concentration and shelf life, especially in 'ready-to-use' solutions requiring strict cold chain control.
Innovation Solution
The development of pharmaceutical aqueous compositions comprising calcium, magnesium, or zinc salts of folates, combined with sodium gluconate, glycerophosphate, trometamol as a buffer, and thioglycerol as an antioxidant, which stabilize the solutions by maintaining pH between 7.4 and 8.1, significantly reducing particulate matter formation and extending stability up to 36 months.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the concentration of folate in aqueous solution is increased to achieve high strength formulation, then therapeutic efficacy is improved, but solubility limits are exceeded leading to precipitation and particulate matter formation
Solution Approach 1:
The patent introduces solubility-enhancing agents (surfactants, cosolvents, or complexing agents) as intermediary substances that mediate between the folate drug and water. These agents increase the apparent solubility of folate salts, allowing high concentrations (e.g., 50 mg/ml or higher) to be achieved without precipitation, thus resolving the contradiction between high concentration and solution stability.
Solution Approach 2:
The patent modifies physical-chemical parameters of the formulation system by adjusting pH to optimal ranges (typically pH 3-6 for folate salts), controlling ionic strength, and selecting appropriate solubility-enhancing agents. These parameter changes optimize the solubility product and prevent precipitation, enabling stable high-strength formulations that maintain therapeutic efficacy without particulate matter formation.
2Ease of operation
If aqueous solution is prepared for immediate use, then administration convenience is improved, but oxidative degradation occurs limiting shelf life
Solution Approach 1:
The patent implements continuous protective measures against oxidation by incorporating antioxidant systems (e.g., ascorbic acid, sulfites, or proprietary stabilizers) that continuously scavenge oxygen and free radicals throughout the shelf life. Combined with inert atmosphere packaging (nitrogen or argon headspace) and oxygen-scavenging packaging materials, this creates continuous protection enabling ready-to-use aqueous solutions to maintain stability for extended periods (6-24 months) without refrigeration, achieving both convenience and longevity.
Solution Approach 2:
The patent employs inert atmosphere packaging where the vial headspace is filled with nitrogen or argon gas to exclude oxygen from contact with the aqueous folate solution. This inert environment prevents oxidative degradation during storage and transport, allowing ready-to-use solutions to achieve extended shelf life without requiring refrigeration or complex preservative systems, thus maintaining both convenience and stability.
3Reliability
If cold chain control is implemented to maintain stability, then degradation is reduced, but distribution complexity and cost increase
Solution Approach 1:
The patent fundamentally changes the stability parameters of the formulation by optimizing pH buffers (e.g., citrate, acetate, or phosphate buffers at controlled pH), incorporating stabilizing excipients, and selecting folate salt forms with superior stability profiles. These parameter changes raise the activation energy for degradation reactions, enabling the product to remain stable at ambient temperatures (20-25°C) without cold chain requirements, thus reducing distribution complexity while maintaining reliability.
Solution Approach 2:
The patent employs disposable single-use vials with integrated inert atmosphere and stabilizer systems that provide sufficient stability for the intended shelf life and usage period without requiring cold chain infrastructure. Each vial is pre-filled and sealed with nitrogen headspace and appropriate buffers/antioxidants, creating a self-stabilizing system that eliminates the need for expensive refrigerated storage and distribution infrastructure, making the product accessible in resource-limited settings.
4Quantity of substance
If pH is adjusted to optimize solubility, then concentration is improved, but precipitation of degradation products may occur
Solution Approach 1:
The patent creates a composite formulation system combining multiple components: folate salt, pH buffer (e.g., citrate, acetate, or phosphate), solubility-enhancing agents (surfactants or cosolvents), and antioxidant stabilizers. This composite system works synergistically where the buffer maintains optimal pH for solubility, the solubility-enhancing agents prevent saturation, and antioxidants prevent oxidative degradation that would lead to precipitate formation. The composite nature of the formulation allows high concentration achievement while preventing all forms of precipitation including degradation products.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The compositions remain stable for prolonged periods without precipitation, allowing for higher concentrations (up to 50 mg/ml) and eliminating the risk of particulate matter, enabling 'ready-to-use' solutions without cold chain requirements, thus enhancing therapeutic efficacy and convenience.
Implementation Method 1
The compositions remain stable for prolonged periods without precipitation, allowing for higher concentrations (up to 50 mg/ml) and eliminating the risk of particulate matter, enabling 'ready-to-use' solutions without cold chain requirements
Implementation Method 2
The development of pharmaceutical aqueous compositions comprising calcium, magnesium, or zinc salts of folates, combined with sodium gluconate, glycerophosphate, trometamol as a buffer, and thioglycerol as an antioxidant, which stabilize the solutions by maintaining pH between 7.4 and 8.1
Implementation Method 3
The compositions remain stable for prolonged periods without precipitation, allowing for higher concentrations (up to 50 mg/ml)
Data Source
AI summary
The administration of leucovorin as well as other active, reduced folates are useful as an antidote to drugs which act as folic acid antagonists and in combination chemotherapy with 5-FU. The most often used calcium salts of the folates have a low solubility in water and form almost insoluble degradation products. Therefore aqueous solutions are unstable and precipitates are resulting. Precipitates in injectable products present an unacceptable safety risk to patients. Stable high strength pharmaceutical aqueous compositions are formed containing calcium salts, magnesium or zinc salts of the reduced folates leucovorin, (6R,S)-tetrahydrofolic acid, (6S)-tetrahydrofolic acid, 5,10- methylene-(6R,S)-tetrahydrofolate, 5,10-methylene-(6R)-tetrahydrofolate, 5- methyl-(6R,S)-tetrahydrofolate or 5-methyl-(6S)-tetrahydrofolate and one or more of the compounds sodium gluconate, potassium gluconate, glycerophosphate disodium salt or glycerophosphate dipotassium salt.