Pharmaceutical Suspensions

Pharmaceutical Suspensions

Objectives

• Understand what suspensions are.
• Recognize the advantages and disadvantages of suspensions.
• Define and differentiate between solutions and suspensions.
• Understand the importance of suspending agents in pharmaceutical dosage forms.
• Discuss the different methods of formation of suspensions.
• Learn how to evaluate the stability of a suspension.
• Understand what structured vehicles are and how they help in increasing the stability of a suspension.
• Describe the formulation of a suspension.

Definition of Suspension

• A suspension is a two-phase system.
• It consists of a solid material dispersed in a liquid.
• The liquid can be oily or aqueous, but most pharmaceutical suspensions are aqueous.

Advantages of Suspensions

1. Stability: Some drugs are not stable in solution form and must be administered as a suspension.
   • Example: Procaine Penicillin G is more stable as a suspension.
2. Choice of Solvent: Suspensions are suitable when a drug is not soluble in water and other solvents are not acceptable.
   • Example: Parenteral corticosteroids.
3. Taste Masking: Drugs can be made insoluble and dispensed as a suspension to mask objectionable tastes.
   • Example: Chloramphenicol base is bitter, so the insoluble chloramphenicol palmitate is used.
4. Prolonged Action: Suspensions can have a sustained effect because the solid particles must dissolve before absorption, which takes time.
   • Example: Protamine Zinc Insulin and procaine penicillin G.
5. Bioavailability: Drugs in suspension exhibit higher bioavailability compared to other dosage forms (except solutions) due to a large surface area and higher dissolution rate.
   • Example: Antacid suspensions provide immediate relief from hyperacidity compared to chewable tablets.

Types of Suspensions

• Pharmaceutical suspension preparations are differentiated into suspensions, mixtures, magmas, gels, and lotions.

Suspensions

• Simple suspension: An insoluble solid dispersed in a liquid.
• Drugs are often manufactured in dry form to be reconstituted as suspensions using a suitable vehicle before administration to improve stability.
  • Examples:
    • Dispersible tablets of antibiotic, amoxycillin (e.g., PRESSMOX).
    • Procaine penicillin G powder (e.g., PENIDURE).

Gels

• Gels are semisolid systems.
• They consist of small, inorganic particles suspended in a liquid medium, forming a network of discrete particles.
• Gels are two-phase systems.
  • Example: Aluminum hydroxide gel.

Lotions

• Lotions are suspensions intended for application to unbroken skin without friction.
  • Example: Calamine lotion, hydrocortisone lotion.

Magmas and Milks

• Magmas and milks are aqueous suspensions of insoluble, inorganic drugs.
• They differ from gels mainly in that the suspended particles are larger.
• They are thick and viscous when prepared, so there is no need to add a suspending agent.
  • Examples: Bentonite magma, milk of magnesia.

Mixtures

• Mixtures are oral liquids containing one or more active ingredients dissolved, suspended, or dispersed in a suitable vehicle.
• Suspended solids may separate slowly on standing but are easily re-dispersed on shaking.
  • Example: Kaolin mixture with pectin.

Types of Suspension (Examples)

1. Antacid oral suspension.
2. Antibacterial oral suspension.
   • Example: Ciprofloxacin suspension.
3. Dry powder for oral suspension.
   • Example: Zithromax powder for oral suspension (azithromycin).
4. Analgesic oral suspension.
   • Example: Ibuprofen suspension.
5. Anthelmentic suspension.
   • Example: Mintezol oral suspension.
6. Anticonvulsant oral suspension.
   • Example: Phenytoin suspension.
7. Antifungal oral suspension.
   • Example: Nystatin suspension ($100,000$ units per mL).
8. Antidiarrheal oral suspensions.
   • Example: Bismuth subsalicylate suspension.
     • Used for controlling simple diarrhea in animals.
     • Dosage varies for dogs, cats, calves, foals, horses, and cattle.
     • Warning: Consult a veterinarian if diarrhea persists.
     • Composition: Bismuth Subsalicylate $1.75 \%$ in a palatable aqueous suspension.
     • Storage: Store at room temperature not above $37^\circ C$ ($98.6^\circ F$).
9. Parenteral suspensions.
   • Examples: Procaine penicillin G, Insulin Zinc Suspension.
10. Ophthalmic suspensions.
    • Example: Betoptic S (betaxolol hydrochloride ophthalmic suspension).
11. Suspension for external use.
    • Example: Calamine lotion.
12. Vaccines.
    • Example: Cholera vaccine.
13. X-ray contrast agent.
    • Example: Barium sulfate for examination of the alimentary tract.
      • E-Z-HD Barium Sulfate for Suspension ($98 \% w/w$).