20% Lidocaine Gel-Cream Formulation (HCl and Base Forms)

Question

Dear Sir,

I need a 20% Lidocaine cream formula for both the HCl and Base forms.

Texture: Gel-cream
Type: Oil-in-water (O/W)

Answer 1

To formulate a 20% Lidocaine Gel-Cream (Oil-in-Water), it is important to distinguish between the HCl (Salt) and Base forms, as they require different stabilization strategies due to their solubility and electrolyte behavior.

At a 20% concentration, both formulas face significant stability challenges: the HCl form creates a high electrolyte load that can break standard gels, while the Base form is prone to crystallization.

1. Lidocaine HCl Formula (Water-Soluble)

Lidocaine HCl is highly soluble in water but acts as a strong electrolyte. You must use an electrolyte-resistant thickener like Pudding Gel Maker™ to maintain the gel-cream structure.

Phase	Ingredient	% Weight	Function
Water	Purified Water	61.2%	Solvent
Water	Lidocaine HCl	20.0%	Active Ingredient
Water	Propylene Glycol (USP)	7.0%	Humectant / Solvent
Water	Ethoxydiglycol	3.0%	Penetration Enhancer
Water	Pudding Gel Maker™	0.8%	Electrolyte-Resistant Thickener
Oil	Satin Cream Maker™	3.0%	O/W Emulsifier
Oil	Light Oil (e.g., Mineral Oil or Ester)	4.0%	Emollient
Preservative	Phenoxyethanol SA	1.0%	Preservative

Procedure:

Dissolve Lidocaine HCl in water, Propylene Glycol, and Ethoxydiglycol.
Sprinkle Pudding Gel Maker™ into the water phase and mix with high shear until a uniform gel forms.
Mix the Oil phase (Satin Cream Maker™ and Oil) separately.
Slowly add the Oil phase into the Water phase while stirring at high speed to emulsify.
Add the preservative and mix until uniform.

2. Lidocaine Base Formula (Oil/Solvent-Soluble)

Lidocaine Base is practically insoluble in water. To keep 20% in solution and prevent crystallization, a high concentration of Ethoxydiglycol is required.

Phase	Ingredient	% Weight	Function
Water	Purified Water	49.2%	Solvent
Solvent	Ethoxydiglycol	13.0%	Primary Solvent for Base
Solvent	Propylene Glycol (USP)	7.0%	Co-solvent
Active	Lidocaine Base	20.0%	Active Ingredient
Thickener	Pudding Gel Maker™	0.8%	Gel-Cream Stabilizer
Oil	Satin Cream Maker™	3.0%	O/W Emulsifier
Oil	Light Oil (e.g., Mineral Oil)	6.0%	Emollient
Preservative	Phenoxyethanol SA	1.0%	Preservative

Procedure:

Drug Concentrate: Dissolve Lidocaine Base completely in Ethoxydiglycol and Propylene Glycol. You may need gentle heat (40-50°C) to ensure it is fully clear.
Prepare the water phase by hydrating Pudding Gel Maker™ in water.
Mix the Oil phase (Satin Cream Maker™ and Oil).
Emulsify the Oil phase into the Water phase.
Slowly blend the Drug Concentrate into the emulsion while stirring.
Add the preservative and cool to room temperature.

Important Technical Notes:

Electrolyte Resistance: Lidocaine HCl will "kill" the viscosity of standard carbomers. Pudding Gel Maker™ (Polyacrylate Crosspolymer-6) is essential because it is specifically designed to remain stable in high-salt environments.
Crystallization Risk: In the Base version, if the solvent (Ethoxydiglycol) evaporates or the temperature drops, the Lidocaine may crystallize. Ensure the container is airtight.
pH Control: The HCl version is naturally acidic. The Base version may require pH adjustment to around 5.5–7.0 for skin compatibility and stability.