RECENT ADVANCES OF NASAL DRUG DELIVERY SYSTEMS-A REVIEW
As the field of biotechnology continues to advance, nasal drug delivery is increasingly becoming a more viable alternative to oral and injectable routes of administration. Recently, it has been shown that many drugs have better bioavailability by nasal route than by oral route. This has been attributed to rich vasculature and a highly permeable structure of the nasal mucosa coupled with avoidance of hepatic first-pass elimination, gut wall metabolism and/or destruction in the gastrointestinal tract. The nasal route could be particularly important for drugs used in crisis management such as for pain and for centrally acting drugs where the pathway from the nose to brain might provide a faster and more therapeutic effect.
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Therapy through intranasal administration has been an accepted form of treatment in the Ayurvedic system of Indian Medicine. In recent years many drugs have been shown to achieve better systemic bioavailability through nasal route than by oral administration. Advances in biotechnology have made available a large number of protein and peptide drug for the treatment of a variety of diseases. These drugs are unsuitable for oral administration because they are significantly degraded in the gastrointestinal tract or considerably metabolized by first pass effect in the liver. Even the parenteral route is inconvenient for long term therapy. Of many alternate routes tried, intranasal drug delivery is found much promising for administration of these drugs2. Nasal drug delivery has always been a key development area for both pharmaceutical and device development companies, presenting many opportunities and challenges. The physiology of the nose presents obstacles, but offers a promising route for systemic delivery of numerous therapies and debatably drug deliveryroute to the brain. Leading authorities in nasal drug delivery and associated technologies will cover aspects of physiology, nasal anatomy, nasal delivery to the brain, vaccination via the nose, nasal delivery to the sinuses, the regulation of nasal products and much more. In addition, case histories of existing/in development products/delivery systems will be explored. Intranasal vaccination has gained increased interest in recent years as a deliveryroute for new vaccines as it can provide superior protection at mucosal surfaces. This, in combination with the minimally invasive nature of the nasal vaccination route, makes intranasal delivery an attractive alternative to immunization via injection.
Today's nasal delivery technology - the spray pump - has been the status quo for over 25 years. Despite the fact that up to 90% of the drug ends up in the stomach, somehow spray pumps became accepted as nasal drug delivery devices. Increasing demands for targeted deposition, less peripheral delivery, fewer side effects, compliance monitoring and dose counting, render spray bottle technology ever more inadequate. Nasal administration can be used to deliver drugs for either local or systemic effect. Locally acting drugs are for example decongestants and allergy treatments. Examples of systemically active drugs available as nasal sprays are migraine drugs, nicotine replacement and hormone treatments. The nasal cavity is covered by a thin mucosa which is well vascularised. A drug molecule can therefore quickly be transferred across the single epithelial cell layer directly to the systemic blood circulation without first-pass hepatic and intestinal metabolism. The effect is often reached within 5 min for smaller drug molecules Nasal administration can therefore be used as an alternative to oral administration of for example tablets and capsules if a fast effect is desired or if the drug is extensively degraded in the gut or liver. Nasal administration is primarily suitable for potent drugs since only a limited volume can be sprayed into the nasal cavity. Drugs for continuous and frequent administration may be less suitable because of the risk of harmful long term effects on the nasal epithelium. Nasal administration has also been associated with a high variability in the amount of drug absorbed. Upper airway infections may increase the variability as may the extent of sensory irritation of the nasal mucosa, differences in the amount of liquid spray that is swallowed and not kept in the nasal cavity and differences in the spray actuation process However, the variability in the amount absorbed after nasal administration should be comparable to that after oral administration. Nasal sprays for local effect are quite common. Several antimigraine drugs are also currently administered by nasal administration because a fast effect is desired and oral administration can be prohibited by nausea. Peptide drugs (hormone treatments) are also available as nasal sprays, in this case to avoid drug degradation after oral administration. Nasal delivery has traditionally been restricted to topically acting substances used to treat the common cold and nasal allergies. Recently, however, there has been increased interest in the nose as an alternative to oral delivery and injection for many systemic drugs and vaccines. The highly vascularised and immunogenic nasal mucosa offers potential advantages in terms of quick action, improved bio-availability and patient compliance as well as improved immune response for vaccines If successful, reformulation allied with novel delivery systems provide powerful tools for improving efficiency and differentiating a product from those of competitors. In addition, more efficient and patient-friendly delivery systems and dosage forms can help extend patent life and increase competitiveness. Overall this provides companies with the opportunity to maintain and increase their market share for only a relatively limited investment. It is against this background that interest and investment in novel delivery technologies have increased in recent years. According to a recent report, 13 per cent of the US$337billion global pharmaceutical market was related to sales of products incorporating a drug delivery system, a figure expected to grow to 20 per cent by 2005. Therefore, although oral delivery remains the preferred option of the patient and the pharmaceutical industry, alternatives such as transdermal, pulmonary and nasal delivery systems are gaining increased interest.
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