The world of medicine is vast. Not only in the type of medications, but also the form of medicines we see around us. You might have used painkillers in the form of tablets, but also as a topical spray. And sometimes even an injection.
So, what are these different types of drug formulations and what are their advantages and disadvantages?
Well, this blog has the answer to all those questions and more. Let us understand the characteristics and making of different types of drug formulations like tablets, emulsions, etc., in this guide.
What is A Drug Formulation?
When a chemical molecule is tested to be used against a disease, it generally starts as a simple molecule. However, a chemical as it is cannot be ingested or applied topically, due to many reasons:
- Poor solubility and absorption.
- Degradation through enzymes.
- Unpleasant odour or taste.
- Very short duration of action.
To overcome this problem, a dosage form is designed. A dosage form, simply put, is the active drug along with excipients like bulking agents, sweeteners, solvents, preservatives, and more.
- Dosage forms are designed to deliver the
- Right amount of API
- To the right place in the body
- At the right rate, and
- In a way, the patient can use it safely
Common categories include
- Solid
- Tablets
- Capsules
- Liquid
- Solutions
- Syrups
- Semisolids
- Creams
- Gels
- Dispersions
- Emulsions
- Suspensions
These are all categorized as conventional drug delivery systems. There is also a novel drug delivery system, or NDDS, but that is a discussion for another time.
Let us break down these conventional drug formulations in detail.
1) Tablets
These are the most familiar solid forms and are the most widely used. Tablets are compressed solid units that contain the API with excipients. They may be:
- Immediate-release
- Chewable
- Effervescent
- Extended or modified release
Key components
- Active drug
- Fillers and diluents
- Lactose
- Microcrystalline cellulose
- Binders that help particles stick
- Starch paste
- PVP
- Disintegrants that help the tablet break apart to release the API
- Sodium starch glycolate
- Lubricants help reduce sticking during manufacturing
- Magnesium stearate
- Coatings that protect taste, control release, and improve swallowing
- HPMC
- Permitted colours
How they work:
- When a tablet is swallowed, it disintegrates and the drug dissolves.
- Dissolution influences how much drug reaches the bloodstream or the bioavailability.
- Regulatory agencies use dissolution testing to ensure consistent performance between batches.
Pros
- High dose accuracy
- Good chemical stability
- Lower manufacturing cost
- Suitable for modified release design
Cons
- Not suitable for patients who cannot swallow
- Some drugs have poor solubility; tablets may need a special formulation
- Stability issues with moisture or heat if not coated or packaged properly
2) Capsules
- Capsules use a shell, either hard or soft, to contain
- Powders
- Pellets, or
- Liquids
- Hard capsules hold powders or multiparticulates.
- Soft capsules usually hold liquid or semi-solid fills.
Advantages
- Excellent for poorly compressible powders
- Easier to swallow than some tablets
- Suitable for taste-masking and protecting sensitive APIs
- Can deliver multiparticulate systems
- Flexible and can deliver different drug forms, like liquid or powder
Limitations
- Shell can be sensitive to moisture
- Softgels require specialized machinery
- Gelatin is animal-derived and can have limited use due to cultural sensitivity
3) Liquids
In liquid formulations, the drugs are carried through a fluid vehicle. They can be indifferent forms as well:
- A solution has the drug fully dissolved.
- A suspension has fine solid particles dispersed in a liquid.
- Syrups and elixirs are commonly used for oral liquids.
When liquids are preferred
- Pediatric and geriatric populations for easy dosing and swallowing.
- Drugs that need rapid absorption.
Formulation challenges
- Chemical stability
- Microbial growth risk
- Requires preservatives and aseptic manufacturing or single-use packaging
- Uniformity of dose in suspensions
- Shorter shelf life
Advantages
- Fast onset of action
- Easy administration
4) Emulsions
Emulsions are dispersions of tiny droplets of one liquid within another immiscible liquid. It can either be oil dispersed in water or water droplets dispersed in oil. They are common in
- Topical products
- Parenteral nutrition, and
- Some oral or injectable medicines
Emulsions require emulsifiers or stabilizers to remain stable.
Key points
- Types: oil-in-water (O/W) and water-in-oil (W/O)
- Stability depends on
- Droplet size
- Emulsifier used
- pH
- Storage conditions
- Advanced emulsion technologies like micro- and nano-emulsions can improve solubility and targeted delivery
Why use an emulsion?
- Improve solubility of oil-soluble APIs
- Modify absorption profiles
- Produce pleasant topical textures
- Controlled-release formulations
Challenges
- Prone to creaming, cracking, and coalescence
- Temperature-sensitive
- Require controlled droplet size
Quick Comparison Table
| Feature | Tablets | Capsules | Liquids | Emulsions |
| Best for dose precision | Excellent | Excellent | Good (depends on dosing device) | Good |
| Ease of swallowing | Moderate | High | Highest | Varies |
| Stability and shelf life | High | High | Lower | Moderate (requires stabilization) |
| Manufacturing complexity | Moderate to high | Moderate to high | Low to moderate | Moderate to high |
| Rapid absorption | Variable | Variable | Often rapid | Can be engineered |
Quality and Regulatory Highlights
Dissolution and bioavailability:
- For oral solids, regulators require validated dissolution testing to ensure in-vivo performance and batch-to-batch consistency.
- This is a pillar of product quality evaluation.
Excipients and safety:
- Excipients must be chosen for safety, stability, and performance.
- Some co-processed excipients carry extra scrutiny.
Stability and microbial control:
Liquids and emulsions need
- Preservatives
- Maintained sterility for injectables
- Specific packaging
To prevent degradation and contamination.
Preparation Tips
Drug formulations and their properties are an important part of exams like GPAT and OPRA. Here are a few tips that can make your preparation journey easier.
- Understand the main tests required for quality control of these formulations:
- Tablets: disintegration test
- Capsules: disintegration and dissolution
- Liquids: stability and microbial limits
- Emulsions: droplet size and emulsion stability tests
2. Memorize common excipient functions like binders, lubricants, and surfactants.
3. Understand BCS classification because it affects formulation strategy.
4. Always connect dosage form to bioavailability concepts.
5. Modified-release systems often rely on:
- Polymers
- Coatings, or
- Multiparticulates
This is a very commonly asked question in theory.
Closing note
Formulation science balances chemistry, engineering and patient needs. The goal of each formulation is the same:
- Deliver the right drug
- Safely and reliably
- To the right place in the body
The study of different drug formulations forms the basis of pharmaceutical science. The changes and development in these formulations in response to the needs of the patients drive drug discovery and development.
These topics are also highly scoring in exams like OPRA. So make sure you brush on them before the exam. And if you need full notes on more such topics, reach out to us at Academically.
Happy Learning!
