A Guide to Oral Suspensions for Formulation Scientists

Posted by Nicholas DiFranco on 04/17/2024

Oral suspensions are pharmaceutical formulations in which solid particles of active ingredients are dispersed in a liquid vehicle. These suspensions are commonly used for administering medications to patients who have difficulty swallowing solid dosage forms, such as tablets or capsules, or for those who require customized dosages. Here's a comprehensive guide to understanding and formulating oral suspensions:

Understanding Oral Suspensions

Key Components

Active Ingredient: The therapeutic substance intended to produce the desired pharmacological effect.

Vehicle: The liquid component that suspends the active ingredient. It typically includes water, along with additives such as suspending agents, preservatives, flavoring agents, and sweeteners.

Suspension Agents: These agents prevent the settling of solid particles and ensure uniform distribution throughout the liquid vehicle.

Flavoring Agents and Sweeteners: Added to improve taste and palatability, especially for pediatric formulations.

Core Advantages

Ease of Administration: Particularly beneficial for patients who have difficulty swallowing solid dosage forms.

Flexible Dosage: Allows for precise dosing adjustments, making it suitable for patients with specific dosage requirements.

Enhanced Bioavailability: Some formulations may improve drug absorption and bioavailability compared to solid dosage forms.

Customization: Can be tailored to meet the needs of specific patient populations, such as pediatric or geriatric patients.

Formulation Considerations

Selection of Active Pharmaceutical Ingredients (APIs)

Consider the solubility and stability of the active ingredient in the chosen vehicle.

Evaluate the pharmacokinetic properties and dosage requirements of the medication.

Choice of Vehicle:

  • Water is commonly used as the primary vehicle due to its compatibility with most medications.
  • Other vehicles such as syrups, suspending agents, or oils may be used based on the characteristics of the active ingredient and patient preferences.

Suspension Agents

Select appropriate suspending agents to prevent sedimentation and ensure uniform distribution of particles. “Smooth” formulations that minimize grittiness are preferred by patients in all age groups.

Common suspending agents include polymers (e.g., Carbopol®), clays (e.g., bentonite), cellulose derivatives (e.g., sodium carboxymethylcellulose), and natural gums (e.g., xanthan gum).

While “natural” thickeners have a long history of use in oral suspensions, they have suffered from recent supply chain issues related to crop shortages and global import/export restrictions. In these cases, high-quality synthetic options (such as carbomers) may provide better supply chain reliability with equivalent or improved technical performance.

Flavoring and Sweetening

Choose flavors and sweeteners that mask the taste of the active ingredient and enhance palatability.

Consider the preferences and sensitivities of the target patient population. For example, it is known that children in the United States of America tend to prefer bubble gum and grape flavors, whereas European children gravitate towards citrus and red berry flavors.

Look for opportunities to replace sucrose with sugar-free sweeteners, especially in long-term therapies where sugar intake could lead to health or dental issues.

Preservatives and Stability

Incorporate preservatives to prevent microbial growth, especially when using natural thickeners, which may act as a food source for microorganisms. Ensure the formulation is compatible with the selected preservatives.

Conduct stability studies to assess the shelf-life and storage conditions of the oral suspension.

Formulation Process

Weighing and Mixing

Accurately weigh and measure the active ingredient and excipients according to the formulation recipe.

Mix the ingredients thoroughly to ensure uniform distribution and dissolution.

Particle Size Reduction

If necessary, perform particle size reduction techniques such as milling or micronization to achieve the desired particle size distribution and/or enhance solubility/bioavailability of the API.

Suspension Preparation

Disperse the active ingredient and suspending agents in the liquid vehicle using appropriate mixing techniques.

Ensure the suspension is homogenous and free from lumps or aggregates.

Quality Control

Conduct quality control tests to assess the uniformity, viscosity, pH, and microbial content of the oral suspension.

Adjust the formulation as needed based on quality control results.

Packaging and Labeling

Fill the oral suspension into suitable containers, ensuring proper sealing to maintain product integrity.

Label the containers with essential information including dosage instructions, expiration date, and storage conditions.

Using Carbopol® Polymers for Oral Suspensions

Carbopol® polymers provided by Lubrizol Life Science are valuable tools for formulating oral suspensions. Designed to enhance patient experience and streamline manufacturing processes, Carbopol® polymers provide numerous benefits for both patients and formulators alike.

Patient-Centric Features

Carbopol® polymers are tailored to meet the needs of patients across various age groups, particularly pediatric and geriatric populations. Here are some patient-centric advantages:

Convenience: Enables stable liquids with pourable, smooth rheology, making oral suspensions easy and pleasant to swallow.

Customizability: Broad compatibility with a range of flavors, sweeteners, and preservatives, ensuring suspensions can be customized to meet palatability and patient preferences without compromising performance.

Uniqueness: Additional benefits such as soothing tissue protection for cough/cold medicines or "no-spill" liquids that enhance pediatric dosing, enhancing the overall patient experience.

Reliability: Patients can trust the safety and quality of Carbopol® suspensions, as they are manufactured to IPEC-GMP standards and have a long history of use in pharmaceutical products.

Formulator Friendly Characteristics

Formulators benefit from Carbopol® polymers due to their ease of use and consistent performance. Here's why Carbopol® is a preferred choice:

Permanent Suspension: Carbopol® polymers are extremely effective suspending agents, even at low inclusion levels. Thanks to their high yield value, Carbopol polymers can permanently prevent settling across a wide range of viscosities, improving shelf life and eliminating the need for frequent re-suspension.

Simplified Manufacturing: Cold processing and low thixotropy of Carbopol® polymers simplify the mixing process, reducing energy usage and complexity in manufacturing.

Consistent Performance: Carbopol® suspensions exhibit low bioburden and minimal lot-to-lot variation, ensuring reliable product performance over time.

Bioavailability Enhancement: The excellent mucoadhesive properties of Carbopol® polymers can enhance bioavailability, allowing for differentiated products with improved drug delivery.

Case Study: Shelf Stable Paracetamol Oral Suspension Using Carbopol® Polymers

  • Objective: Demonstrate the superior suspending ability of Carbopol® polymers
  • Description: A stable, palatable, and non-sedimenting oral suspension formulation.
  • Polymer Used: Carbopol® 974P NF polymer.

This suspension has undergone extensive study for sedimentation using Turbiscan analysis, demonstrating its stability over time. Similar approaches can be applied to develop suspensions with other active pharmaceutical ingredients (APIs) and dose strengths. 


Oral suspensions offer a versatile and patient-friendly dosage form for administering medications. By understanding the key components, formulation considerations, and processing techniques outlined in this guide, pharmaceutical professionals can develop high-quality oral suspensions that meet the therapeutic needs and preferences of patients. Always adhere to regulatory guidelines and conduct thorough quality assurance measures to ensure the safety and efficacy of oral suspension formulations.

If you are struggling to achieve a stable oral suspension with patient-friendly properties, then Carbopol® polymers may be the solution.

Start your project today to leverage the advantages of Carbopol® polymers for enhanced patient experience and improved formulation efficiency. 


Nicholas DiFranco


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