Innovative Thin Films for Drug Delivery

Considerations for developing a new drug delivery platform include ease of use (self-administration, convenient to swallow), route of administration (oral, transdermal, injectable, etc.), and accurate dosage. An innovative alternative approach to conventional dosage forms is a novel drug delivery tool known as thin films.

Pharmaceutical scientists worldwide are exploring thin films and finding they have many unique characteristics which make them a versatile new option in drug delivery. This article will give an overview of the factors affecting the formulation of thin films and highlight recent trends and perspectives in development by various companies.

What are Thin Films?

They are generally defined as a thin and flexible layer of polymer with or without a plasticizer. Being thin and flexible can make them less obtrusive and more acceptable to a patient. Thin films meet many requirements for being used as effective drug release platforms while making them excellent prospects for targeting sensitive sites not otherwise possible with tablets or liquid formulations.

Ideal thin films have sufficient drug loading capacity, fast dissolution rate or long residence time at the site of administration, and acceptable formulation stability. In addition, they should be biocompatible, biodegradable, and non-toxic.

Some other benefits of thin films when compared with existing traditional drug dosage forms include:

• superiority in terms of enhanced bioavailability
• high patient compliance
• patent extension of active pharmaceutical ingredients
• convenient administration through non-invasive routes
• ease of handling during manufacture and transport
• cost-effectiveness in the development of formulations

Some of the specific efforts in developing thin films are formulations that are administered via buccal, sublingual, ocular, and dermal routes. Of particular interest in recent years are thin films for delivering medicine into the buccal or sublingual mucosa. 

Types of Thin Films

Thin films were first introduced in late 1970 to aid the swallowing of tablets and capsules. Some names of thin films first developed include oral thin film, oral soluble film, wafer, oral strip, orodispersible film (ODF), mucoadhesive film, buccal film, transmucosal film, and ophthalmic film.

Oral Films

Fast-dissolving oral films are ultra-thin (50-150um), about the size of a postage stamp, and dissolve in the oral cavity within one minute after contacting saliva. This ensures rapid absorption and instant bioavailability of the medicine. 

"Wafer" is another term used to refer to paper-thin polymeric films used as carriers for pharmaceutical agents. Taken orally, it does not need water in order to swallow for the absorption of the drug.

Buccal films are designed for staying in contact with the cheek mucosa for a longer period of time. It is, therefore, necessary to differentiate accurately between the film and the correct usage.

Ophthalmic Films

Applied to the anterior segment of the eye, these films are used to treat conditions such as conjunctivitis, glaucoma, and chronic dry eye syndrome. Their advantage over traditional ocular drug delivery systems such as eye drops or solutions lies in their ability to provide high drug bioavailability with a sustained duration of action.

Polymers Used in the Preparation of Thin Films

Used alone or in combination with each other to achieve desired properties, they must be non-toxic, non-irritant, and contain no leachable impurities. Water-soluble polymers are used and produce a thin film with rapid disintegration, good mechanical strength, and good mouthfeel effects. The following polymers are commonly used in manufacturing thin films:

1. Hydroxypropyl methylcellulose (HPMC)
2. Carboxymethyl cellulose (CMC)
3. Hydroxypropyl cellulose (HPC)
4. Poly (vinyl pyrrolidone) (PVP)
5. Poly (vinyl alcohol) (PVA)
6. Poly (ethylene oxide) (PEO)
7. Pullulan
8. Pectin
9. Chitosan
10. Sodium alginate
11. Carrageenan
12. Gelatin

The availability of diverse polymers allows development of thin films with specific properties such as weight, texture, solubility, strength, and stability. 

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The Future of Thin Films

Some of the current research and development is focused on overcoming the limitations of thin films. One major limitation is low drug loading capacity for a less potent drug given at a higher dose. Another is that they are generally hygroscopic in nature, requiring special care and handling for longer preservation.

While it can be done, combining more than one drug is challenging because it is difficult to obtain a high degree of accuracy in dosing. This may lead to therapeutic failure, non-reproducible effects, and sometimes toxicity to the patient.

Conclusion

Despite the challenges of developing and manufacturing thin films, the potential promise of these new, more convenient, more effective drug delivery systems is driving both start-ups and established pharmaceutical companies forward.