Due to its unique physiology and ready accessibility, the nasal cavity is an attractive delivery site for the systemic administration of therapeutics. The nasal membrane or mucosa lines the nasal cavity and is located posterior to the external nares. The surface area of the nasal mucosa is relatively large (180 cm2) and has a rich blood supply (40ml/min/100g). Molecules absorbed across the mucosal membranes are transported directly to the blood stream and therefore avoid clearance due to first pass metabolism. Also, the protease activity in the nasal cavity is greatly diminished relative to the small intestine making enzymatic degradation in the nasal cavity less likely. Relative to chronic parenteral administration, intranasal delivery offers increased patient compliance and in some cases, increased pharmacokinetic control.
Intranasal formulation is a remarkable and easy mode of drug delivery. It is a needle-free, patient-friendly route that does not contribute to biohazardous waste (Wermeling, Miller, & Rudy, N.D.). Pharmacokinetically, the absorption rate is so rapid that it results in a faster onset of action compared with oral and intramuscular administration. In addition, hepatic first-pass metabolism is avoided (Wermeling et al.,). (The metabolism of an administered dose of a drug by the liver before it reaches systemic circulation is referred to as the first-pass metabolism.) For many oral drugs, a clinically significant portion of the drug taken is destroyed during first-pass metabolism, requiring a higher oral dose for a given effect (Wynne, Woo, & Olyaei, 2007).
Intranasal drugs can be delivered in a variety of formulations that include powders, drops, topical gels, and sprays. Consideration must be given to normal physiologic processes when using the intranasal route, as the nose is an important defense system for environmental hazards. Any disruption of its normal physiology may leave the patient vulnerable to a variety of complications (Wermeling et al.). The delivery devices for intranasal medications can be costly, as illustrated by intranasal insulin, and can be a deterrent to patient use. Initially thought to be a desired route compared with subcutaneous insulin, patients found intranasal insulin to be burdensome and costly (R. Talbert, personal communication, February 21, 2008).
Until recently, vitamin B 12 has been available only by intramuscular injection. Calomist (cyanocobalarain) Nasal Spray is now available in a 25-mg/spray form that is used daily in lieu of the monthly injections. This can now be included in the daily routine with less impact of a missed dose.
Medication adherence can be problematic with older adults. One of the most basic forms of medication delivery, the pillbox, is continually being updated. An interactive pillbox can be a useful tool in reminding this population about their medication times. Pillboxes are available that can hold as much as a 1-month supply of medications, with separate compartments for as many as four drugs. After programming, the box will beep at the time a medication is due to be taken, indicate the appropriate compartment, and display the number of pills to take. When the compartment lid is lifted, an audio message instructs the patient on the number of pills to take, along with specific information about how that medication should be taken. The data are gathered and can be transmitted via phone lines to the caregiver to confirm the time at which the medication was taken. Even patients thought to be compliant accidentally skip doses of medication, a silent problem improved by these devices. Pillboxes with multiple compartments are particularly helpful for older patients when dealing with multiple pill regimens.
The intranasal administration of small organic compound is a well-established mode of delivery. The majority of these drugs however, are intended for local administration to the nasal mucosa rather than systemic administration.
Factors affecting nasal absorption-
1. Drug effect- molecular size, lipophilic balance and ezymatic degradation in nasal cavity.
2. Nasal effect- membrane permeability (interspecies differences), environmental pH, mucociliary clearance, colds, rhinitis etc.
3. Delivery effect- formulation (concentration, pH, Osmolality), delivery systems (sprays, drops, gels), deposition, formulation effects in mucociliary clearances, toxic effects on ciliary functions and epithelial membranes.
Pharmacology & Toxicological considerations-
The safety of any delivery technology must be rigorously evaluated before it can be considered as a viable delivery alternative. The assessment should occur individually with both the delivery system and in combination with the active component. This is especially for trans-nasal delivery systems, which will be used systemically. For a nasal product which contains an excipient, that affects nasal permeability, the systemic topical effects of the excipients as well as individual peptide be evaluated. Mucociliary transport rate, patho/histo morphology and ciliary beat frequency tests are the commonly prescribed test for formulations delivered by nasal route.