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Oral Drug delivery system challenges

There are many ways to deliver drugs into the body, via oral (through swallowing), through buccal and sublingual mucosa, injection, skin, inhalation, etc. Among these deliveries oral delivery is widely accepted. In oral drug delivery, many scientific challenges and breakthrough technologies are required to generate novel dosage forms raising drug delivery to higher level. This article reviews recent technologies and products with their importance, and novel approaches implemented till date to overcome the challenges in oral drug delivery systems.

Oral drug delivery formulation and technologies are mainly focused on the following areas of gastro intestinal tract:

  • Oral
  • Stomach
  • Small Intestine
  • Colon

Various challenges associated with oral route include:

  • Pill-swallowing difficulty
  • Irritant and unpalatable drugs are not given by this route
  • Gastrointestinal (GI) destruction of labile molecules
  • Low levels of macromolecular absorption; absorption of drugs may be affected by food in the stomach
  • Slow onset of action
  • Very little control over release of the drug; non-specific delivery site & side effects

1. Oral Delivery

The most facing challenges in oral delivery are to overcome problems like pill-swallowing difficulty, delivery of unpalatable drugs, and reducing dosing frequency. Pill swallowing difficulty primarily affects the patients having dysphagia, geriatric and pediatric populations.

To eliminate these problems associated with swallowing difficulties, a new dosage form, known as fast dissolving tablets (FDT), has been developed. The fast dissolving tablets are also called fast-melt or fast disintegrating or orally disintegrating tablets (ODT). The orally disintegrating tablets disintegrate within 60 seconds in the oral cavity. ODT are gaining popularity over conventional tablets due to their convenience in administration and suitability for patients having dysphagia. Moreover no water is required for swallowing the tablets and hence suitable for geriatric, pediatric and traveling patients.

2. Stomach

Another challenge in oral drug delivery is to develop gastric retention platforms for long-term (ranging from 6 to 24 h) delivery of drugs. A controlled drug delivery system with prolonged residence time in the stomach is of particular interest for drugs which are locally active in the stomach.

Various attempts have been made to develop gastro-retentive delivery systems. There are 3 ways by which this can be achieved

  • Altering the density of drug particles
  • Use of mucoadhesive polymers
  • Altering the size of dosage form

3. Small Intestine

Challenges related to delivery to small intestine include development of formulations of poorly soluble and high molecular weight drugs. The first step in drug absorption is dissolution of a drug in an aqueous environment. Drugs with low solubility are those requiring more than 250 mL of water to dissolve the highest dose. Volume of 250 mL is not easy to find in the intestine. Only a limited number of commercial formulations are available for poorly water soluble drug. Self-Emulsifying Systems, a novel self-emulsifying drug delivery system (SEDDS) is useful for the adminis-tration of a water-insoluble drug. The SEDDS comprises a hydrophilic surfactant with hydrophilic-lipophilic balance (HLB) value greater than 10.

4. Colon

Drugs with high solubility may prematurely release before reaching the colon. Preventing premature release would require a very thick coating which may result in incomplete drug release in the colon. Drugs with poor solubility may not dissolve in the colon where there is not as much fluid as in the upper portion of the GI tract. The current technologies are mainly focused on delayed release, i.e. no release until the dosage form reaches the colon. The time-delay approach relies on drug release following a predetermined lag time and would therefore be less dependable. Combinations of time-delay and enzymedegradable systems would seem more reliable.

Current and Future Developments

Although oral delivery meets the need for self-administered drugs but targeted, sustained release and increased bioavailability present the areas of difficulty in meeting the emerging value proposition. To address this difficulty, companies are developing micro-fabricated drug delivery systems. In future more research work can be carried out for further developments in oral drug delivery systems.

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