[6] ACTIVITY 6: ALUMINUM-MAGNESIUM HYDROXIDE SUSPENSION

SUSPENSION

definition

“A disperse system in which internal phase is dispersed uniformly as finely divided insoluble particles throughout the external phase”

SUSPENSION

2-phase system:

dispersed phase and dispersing medium

SUSPENSION

Finely divided solid is dispersed in a liquid

EMULSION

Liquid is dispersed in another liquid

2 PHASES: 

solid particles

• Usually greater than 0.5 mcm 

• Can’t be too big → will settle down at the bottom 

• Needs to be finely divided

2 PHASES: 

• Liquid

can be water or oil

PREPARATIONS/DOSAGE FORMS UNDER SUSPENSIONS

• GELOMAMI

  • Gel, Lotion, Magmas, Mixtures

AVAILABILITY

2 FORMS OF SUSPENSIONS:

1. Ready to Use

2. Dry powder/granules for suspension in a liquid vehicle / For Reconstitution

Ready to Use

• Doesn’t need reconstitution 

Dry powder/granules for suspension in a liquid vehicle / For Reconstitution

• Powder/granules for oral dispersion

• Requires reconstitution (Add water & shake them well)

CHARACTERISTICS OF SUSPENSION

• pourable

• settle slowly

• redispersable 

• chemically stable 

• uniform particle size 

• acceptable appearance and taste 

Pourable

• viscosity

  • Use of wide-mouth bottles aids this

Settle slowly

• reduce the particle size to prevent caking

• use viscosity enhancer 

Viscosity enhancer

– suspending agent, thickening agent

Small particle size leads to a slow sedimentation rate. How to achieve this? (settle slowly) 

↓ particle size & ↑ viscosity of solvent (Ex. Sorbitol instead of water)

Redispersable

• Attach a shake well label

Uniform Particle Size

Will behave as a whole because there is no particle-particle interaction

Based on General Classes

• Oral suspension

• Externally Applied suspension

• Parenteral Suspension

Based on Proportion of Solid Particles

• diluted suspension

• Concentrated suspension

Based on Electro Kinetic Nature of Solid Particles

• Flocculated suspension

• Deflocculated suspension

Based on Size of Solid Particles

• Colloidal suspension

• Coarse Suspension

REASONS FOR THE FORMULATION OF A SUSPENSION

• sustaining effect

• stability 

• taste

• basic solubility 

Sustaining effect

• Since finely divided solids are just suspended, it still needs disintegration, causing a longer stay in the body → longer effect/DOA

• Unlike solutions that have immediate effects

Stability

• More stable because the solute is insoluble

• The product may be more stable if stored dry (to be reconstituted) to avoid hydrolysis

• Unlike solutions which are prone to hydrolysis or solvolysis

Taste

less noticeable compared to solutions

Basic solubility

• Internal phase is solid, INSOLUBLE very fine particles, 

• Not all active ingredients are soluble in water

COMPONENTS OF A SUSPENSION

• api

• wetting agents 

• flocculating agents 

• viscosity agents 

• buffer 

• preservative

• colorant

• flavorant 

• vehicle/solvent 

Active Pharmaceutical Ingredient

• Insoluble to vehicle 

• Ex. Aluminum hydroxide gel, Mg Hydroxide, Phenoxymethylpenicillin K

Wetting agents

• Substances that will coat the active agents individually to make them more soluble in their given solvent 

• Added to disperse solid particles in the external phase 

Wetting agents: solvents

Alcohol, Glycerin, Polyhydrate alcohol (Sorbitol)

Wetting agents: surfactants

Sodium lauryl sulfate, Benzalkonium chloride

Surfactants

• Surface acting agents can also be used as wetting agents

• Applied for the oil to be combined with the water component of other drugs 

• To make them miscible/soluble; to mix oil and water

• To become soluble in the given solvent

Flocculating agents

Added to prevent clumping or formation of aggregates / capable of preventing the caking of suspended solid particles

Viscosity agents (thickening agent, suspending agents)

natural 

acacia, tragacanth

Viscosity agents (thickening agent, suspending agents)

synthetic

derivative of methylcellulose

Viscosity agents (thickening agent, suspending agents)

• For internal preparations:

• tragacanth & acacia – 1.25%

• CMC – 2.5%

• Carbopol 934 – 0.3%

Buffer

Resist any change in pH / added to stabilize the suspension to a desired pH range

Preservative

To prevent contamination

Vehicle / Solvent

Water, Glycerin, Sorbitol

Aluminum Magnesium Hydroxide Suspension is an ANTACID 

• Substances which reduce gastric acidity resulting in an increase of pH in the stomach and in the duodenum. Also, antacids are used to neutralize excess gastric hydrochloric acid associated with gastritis and peptic ulcer. 

Peptic ulcer causative agent:

Helicobacter pylori (can also give antibiotic for treatment)

Most antacids raise the gastric pH to

4-5

Antacids are widely used for:

• Uncomfortable feeling from overeating 

• Heartburn 

• Dyspepsia (Indigestion) 

• Duodenal Ulcer 

• Other non-specific GI symptoms

Combination of Aluminum hydroxide and magnesium hydroxide

• To counteract the adverse effects of one another

  • Adverse effect of aluminum hydroxide: constipation

  • Adverse effect of magnesium hydroxide: laxative/cathartic

ALUMINUM HYDROXIDE

• White 

• Viscous suspension (gel) 

• pH 5.5 – 8.0

ALUMINUM HYDROXIDE

disadvantages 

• Al(OH)₃ may interfere with the absorption of other drugs by binding with them (e.g. tetracycline) 

• Can cause constipation

MAGNESIUM HYDROXIDE

• White, fine odorless, amorphous powder

• Insoluble in water and alcohol but soluble in dilute acids 

• Laxatives in high doses or cathartic effect

MAGNESIUM HYDROXIDE

adv

• Fast onset of action 

• No systemic alkalosis 

• High Acid neutralizing capacity

MAGNESIUM HYDROXIDE

disadv

• Short duration of action 

• Laxative/Diarrhea / cathartic effect

• Hypermagnesia 

• Contraindicated to patients with kidney disease