Clozapine Suspension pH Control and Crystal Inhibition
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Solution Overview
Problem
Clozapine's insolubility in water leads to caking issues in liquid formulations, and its stability is compromised when formed into an aqueous suspension with standard wetting agents, affecting the accuracy of drug dosing.
Innovation Solution
A physicochemically stable aqueous suspension of clozapine is achieved by maintaining the pH between 6 and 11 using a sodium phosphate/sodium hydroxide buffer system, incorporating a wetting agent like propylene glycol or glycerin, and adding polyvinyl pyrrolidone as a crystal growth inhibitor, along with a suspending agent and preservative.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If clozapine is formed into an aqueous suspension with standard wetting agents, then the caking problem is overcome and particles can be readily redistributed, but the suspended active is readily susceptible to hydrolysis causing marked pH change
Solution Approach 1:
The patent changes the pH parameter of the aqueous suspension to a specific range (pH 6-11) using buffer systems, which fundamentally alters the chemical stability of clozapine while maintaining its suspending properties. This parameter change prevents hydrolysis and pH drift that occur at standard pH levels.
Solution Approach 2:
The patent introduces buffer systems (sodium phosphate/sodium hydroxide or potassium phosphate/potassium hydroxide) as intermediary substances that mediate between the wetting agents and clozapine. These buffers maintain pH within the stable range while allowing the wetting agents to function without causing hydrolysis.
2Device complexity
If clozapine is simply added directly to water, then the formulation is simple, but the compound settles rapidly to form a dense cake at the base
Solution Approach 1:
The patent uses wetting agents as intermediary substances that facilitate the interaction between water and clozapine particles. These wetting agents prevent rapid settling by modifying the interfacial properties, allowing the suspension to remain stable without forming dense cakes.
Solution Approach 2:
The patent changes the physical parameters of the suspension by controlling pH and adding suspending agents, which alters the settling behavior of clozapine particles and prevents cake formation while maintaining formulation simplicity.
3Ease of manufacture
If the pH is maintained outside the range of 6 to 11, then standard formulation practices can be used, but hydrolysis occurs and accuracy of drug dose is compromised
Solution Approach 1:
The patent establishes a specific pH range (6-11) as a critical parameter for maintaining drug dose accuracy. By controlling pH within this range using buffer systems, the patent prevents hydrolysis and ensures accurate drug delivery, while still allowing standard formulation practices to be used.
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 formulation maintains stability over a reasonable storage period, ensuring accurate drug delivery and preventing hydrolysis, making it suitable for commercial use.
Implementation Method 1
the pH of the composition is maintained in the range of about 6 to about 11
Implementation Method 2
the pH is maintained within the desired range using a buffer system
Implementation Method 3
a standard formulation technique would be to use a suitable wetting agent, to promote flocculation. Flocculation is a process where suspended particles agglomerate, forming larger particles that settle loosely and can be readily re-dispersed
Implementation Method 4
the composition includes polyvinyl pyrrolidone (PVP) as a crystal growth inhibitor
Implementation Method 5
the composition includes a suspending agent and/or a preservative
Data Source
AI summary
A physicochemically stable aqueous composition including clozapine suspension.