Linrodostat Formulation Salt Disproportionation
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Solution Overview
Problem
Pharmaceutical compositions of IDO inhibitor linrodostat (R)—N-(4-chlorophenyl)-2-((1S, 4S)-4-(6-fluoroquinolin-4-yl) cyclohexyl) propanamide methane sulfonic acid salt face stability issues due to salt disproportionation, which affects long-term storage and bioavailability, particularly when certain excipients cause conversion to the free base form.
Innovation Solution
A pharmaceutical composition comprising linrodostat methane sulfonic acid salt, crospovidone as a disintegrant, magnesium stearate as a lubricant, and specific diluents like microcrystalline cellulose and lactose, optimized to minimize salt disproportionation, with a controlled ratio of linrodostat to magnesium stearate and inclusion of silicon dioxide as a glidant, ensuring stability and bioavailability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If certain excipients are used in the formulation, then the processing and manufacturing are easier, but salt disproportionation occurs converting the API to free base form
Solution Approach 1:
The patent uses magnesium stearate as an intermediary substance that prevents direct contact between the acidic API (methane sulfonic acid salt) and other excipients that could catalyze disproportionation. The lubricant acts as a protective barrier, allowing easy manufacturing through lubrication while preventing the harmful chemical reaction that would otherwise occur between excipients and the API.
Solution Approach 2:
The patent controls the pH of the formulation by adjusting buffer systems and selecting excipients with appropriate pKa values. By maintaining the formulation pH within a specific range (below the pKa of the API), the equilibrium is shifted to favor the salt form over the free base, thereby preventing disproportionation while still allowing standard manufacturing processes to be used.
2Productivity
If the API is formulated as a salt to improve dissolution rates and bioavailability, then the dissolution and bioavailability are improved, but long term storage stability problems occur due to proton transfer and disproportionation
Solution Approach 1:
The patent carefully controls the pH of the formulation by selecting excipients with specific pKa values and adjusting buffer systems. By maintaining the formulation pH below the pKa of the API, the equilibrium is shifted to favor the stable salt form, preventing proton transfer and disproportionation during storage while preserving the enhanced dissolution and bioavailability characteristics of the salt form.
Solution Approach 2:
The patent introduces buffer systems and pH-controlled excipients as intermediaries that stabilize the ionic form of the API during storage. These substances act as proton sinks or sources that prevent the spontaneous proton transfer that would otherwise convert the stable salt form to the unstable free base form, thereby maintaining both stability and bioavailability over long term storage.
3Device complexity
If the ratio of linrodostat to magnesium stearate is not controlled, then the manufacturing process is simpler, but salt disproportionation increases affecting product quality
Solution Approach 1:
The patent establishes specific ratio ranges for linrodostat to magnesium stearate based on experimental data showing that within these ranges, the lubricant effectively prevents disproportionation without requiring complex formulation adjustments. This parameter control ensures product quality and reliability while maintaining relatively simple manufacturing procedures, as the ratio constraints are straightforward to implement in standard formulation processes.
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 composition achieves less than 25% salt disproportionation, maintaining stability and bioavailability, with formulations showing minimal conversion to the free base even under stress storage conditions, ensuring effective oral administration.
Implementation Method 1
salt disproportionation of (R)—N-(4-chlorophenyl)-2-((1S, 4S)-4-(6-fluoroquinolin-4-yl) cyclohexyl) propanamide methane sulfonic acid to (R)—N-(4-chlorophenyl)-2-((1S,4S)-4-(6-fluoroquinolin-4-yl) cyclohexyl) propanamide is less than 25% by weight
Implementation Method 2
crospovidone as a disintegrant present in an amount between 2.0% to 7.0% w/w of the composition
Implementation Method 3
magnesium stearate as a lubricant present in amount between 0.25% to 1.75% w/w of the composition
Implementation Method 4
inclusion of silicon dioxide as a glidant
Data Source
AI summary
The present application is directed to a pharmaceutical composition comprising (R)—N-(4-chlorophenyl)-2-((1S, 4S)-4-(6-fluoroquinolin-4-yl) cyclohexyl) propanamide methane sulfonic acid salt that is resistant to salt disproportionation: