Oral route still remains the favourite route of drug administration in many diseases and up today it is the first way investigated in the development of new dosage forms.
The major problem in oral drug formulations is low and erratic bioavailability, which mainly results from poor aqueous solubility. This may lead to high inter- and intra subject variability, lack of dose proportionality and therapeutic failure. It is estimated that 40% of active substances are poorly soluble in water. The improvement of bioavailability of drugs with such properties presents one of the greatest challenges in drug formulations.
Various technological strategies are reported in the literature including micronization, solid dispersions or cyclodextrines complex formation and different technologies of drug delivery systems. Oral drug delivery systems are also primary topics in pharmaceutical industry.
There are two categories of oral drug delivery systems: controlled-release preparations and targeting preparations. Recently, many novel oral drug delivery systems have been invented which are prepared in traditional dosage forms such as tablets or capsules. The controlled release may be achieved by changing the physical and chemical properties of drugs and excipients as well as those of dosage forms. Numerous new concepts of the technologies are proposed.
Various technological solutions are connected with modified push-pull osmotic systems and capsules containing different multicompartmental systems. To deliver slightly water-soluble drugs, two-layered push-pull oral osmotic pumps were developed and marketed. They can deliver drug in a controlled manner over a long period of time. A several new options are available in this field, including modified system for simultaneous delivery of two drugs to reduce the problems with multidrug therapy (1).
To achieve desired results after oral administration, micro- and nanotechnologies are also developed. Insoluble drugs, which may require large doses to promote absorption can be administered as a micro- or nanoparticles with a lower frequency and smaller quantity (2) Biodegradable and biocompatible polymer nanoparticles can be used as drug carriers. Their advantage lies in the fact that they can be absorbed in an intact form in the gastrointestinal tract after administration. As a drug delivery systems they can be widely applied in different diseases where continous and controlled drug administration is important (3).
Another approach is the incorporation of the drug into inert lipid vehicles. Recently much attention has been focused on self-emulsifying drug delivery systems, mixtures of oil and surfactant and cosurfactant that have the ability to form fine o/w emulsions when exposed to aqueous media upon mild agitation. The incorporation of self-emulsifying systems in pellets is a promising proposal for delivery of a nonaqueos system in novel solid dosage forms.
In situ-gelling pectin formulations are the next technological solutions of oral sustained delivery. Gels are formed after oral administration of aqueous solution of drugs. It is essential for drugs that they should be absorbed primarily in the stomach.
References:
1. Prabakaran D. et al .Int. J. Pharm. 284, (2004),95-108
2. Freiberg S. et al. Int .J. Pharm. 282, (2004), 1-18
3. Yan Wu et al. In . J. Pharm. 295, (2005), 235-245. |