F. W. H. M. Merkus

Nasal mucociliary clearance as a factor in nasal drug delivery

The nasal mucociliary clearance system transports the mucus layer that covers the nasal epithelium towards the nasopharynx by ciliary beating. Its function is to protect the respiratory system from damage by inhaled substances. Impairment of nasal mucociliary clearance can result in diseases of the upper airways. Therefore, it is important to study the effects of drugs and drug excipients on nasal mucociliary clearance. A large number of methods are used to assess mucociliary clearance. These methods study the effects of drug and excipients on the mucociliary system in vitro or in vivo in animals and humans. In some cases, the results of different in vitro and in vivo measurements do not correlate well. In vitro methods, especially ciliary beat frequency measurements, have been demonstrated to be valuable tools for toxicity screening. However, in vivo studies are essential to confirm the safety of nasal drug formulations. Nasal mucociliary clearance also has implications for nasal drug absorption. Drugs are cleared rapidly from the nasal cavity after intranasal administration, resulting in fast systemic drug absorption. Several approaches are discussed to increase the residence time of drug formulations in the nasal cavity, resulting in improved nasal drug absorption. However, more experimental evidence is needed to support the conclusion that this improved absorption is caused by a longer residence time of the nasal drug formulation.

Cyclodextrins in nasal drug delivery.

Nasal drug delivery is an attractive approach for the systemic delivery of high potency drugs with a low oral bioavailability due to extensive gastrointestinal breakdown and high hepatic first-pass effect. For lipophilic drugs nasal delivery is possible if they can be dissolved in the dosage form. Peptide and protein drugs often have a low nasal bioavailability because of their large size and hydrophilicity, resulting in poor transport properties across the nasal mucosa. Cyclodextrins are used to improve the nasal absorption of these drugs by increasing their aqueous solubility and/or by enhancing their nasal absorption. With several cyclodextrins very efficient nasal drug absorption has been reported, but also large interspecies differences have been found. Studies concerning the safety of cyclodextrins in nasal drug formulations demonstrate the non-toxicity of the cyclodextrins and also clinical data show no adverse effects. Therefore, some cyclodextrins can be expected to become effective and safe excipients in nasal drug delivery.

The Nasal Mucociliary Clearance: Relevance to Nasal Drug Delivery

Mucociliary clearance is an important physiological defense mechanism of the respiratory tract to protect the body against noxious inhaled materials. This process is responsible for the rapid clearance of nasally administered drugs from the nasal cavity to the nasopharynx, thereby interfering with the absorption of drugs following intranasal application. This review describes the mucociliary system and the methods used for its characterization. Examples are given of the effects of drugs and additives on its functioning. Further, possible approaches are presented for increasing the residence time of drugs in the nasal cavity, thereby improving intranasal drug delivery.

ABSORPTION ENHANCING EFFECT OF CYCLODEXTRINS ON INTRANASALLY ADMINISTERED INSULIN IN RATS

The absorption enhancing effect of α-, β-, and γ-cyclodextrin (CD), dimethyl-β-cyclodextrin (DMβCD), and hydroxypropyl-β-cyclodextrin (HPβCD) on intranasally administered insulin was investigated in rats. Coadministration of 5% (w/v) DMβCD to the insulin solution resulted in a high bioavailability, 108.9 ± 36.4% (mean ± SD, n = 6), compared to i.v. administration, and a strong decrease in blood glucose levels, to 25% of their initial values. Coadministration of 5% α-CD gave rise to an insulin bioavailability of 27.7 ± 11.5% (mean ± SD, n = 6) and a decrease in blood glucose to 50% of its initial value. The rate of insulin absorption and the concomitant hypoglycemic response were delayed for the α-CD-containing solution as compared to the DMβCD preparation. The other CDs, HPβCD (5%), β-CD (1.8%), and γ-CD (5%), did not have significant effects on nasal insulin absorption. DMβCD at a concentration of 5% (w/v) induces ciliostasis as measured on chicken embryo tracheal tissue in vitro, but this effect is reversible. In conclusion, DMβCD is a potent enhancer of nasal insulin absorption in rats.

Absorption enhancers in nasal drug delivery: efficacy and safety

Abstract Efficacy and safety of nasal absorption enhancers depend on many different parameters, such as their influence on nasal epithelial membrane barriers, the enzymatic activities in the nasal cavity, and the mucociliary clearance. Large interspecies differences appear to exist in the nasal absorption of drugs. Nasal absorption enhancers, although very effective in some cases, differ substantially in efficacy and safety. For a number of enhancers like surfactants, bile salts and fusidate derivatives a good relationship (similarity in rank order) can be established between the morphological damage and the influence on the ciliary beat frequency (CBF) of nasal epithelial tissue, making CBF measurements a valuable tool in the search for safe nasal absorption enhancers.

Bile salts and intranasal drug absorption

Abstract The nasal route has been proven to be very effective for drug absorption. Bioavailability of intranasally administered drugs depends on the structure of the drug and can be as high as 100%. The absorption of drugs with a lower bioavailability can be improved with the aid of absorption promotors such as some surfactants, e.g. bile salts. The intranasal absorption of gentamicin, as a model drug, was studied in rabbits with six different bile salts as absorption promotors (cholate, taurocholate, glycocholate, deoxycholate, taurodeoxycholate and glycodeoxycholate). Without a surfactant, gentamicin is not absorbed by the nasal mucosa. The serum concentrations of gentamicin after intranasal administration were compared with those obtained after an intravenous injection. Concentrations were measured with EMIT. The bioavailability of the intranasal gentamicin in rabbits was related to the hydrophobicity and the pK a s of the bile salts. Furthermore the effects on ciliated epithelium of the six bile salts, used in the absorption experiment, were studied in an in vitro model. Ciliary activity was studied with a photo-electric method. Bioavailability increased with the increase of the hydrophobicity of the trihydroxy bile salts (cholate, taurocholate and glycocholate). Sodium cholate and sodium taurodeoxycholate were the most active absorption promotors (F = 41 ± 16%, respectively, 34 ± 13%). The dihydroxy bile salts (deoxycholate, taurodeoxycholate and glycodeoxycholate) showed a decreasing activity in the promotion of gentamicin absorption as the hydrophobicity increases. Depending on the pH/pK a relation, increasing hydrophobicity results in lower solubility and therefore decreasing activity. Ciliotoxicity of the bile salts increased with increasing hydrophobicity. Dihydroxy bile salts are more toxic than trihydroxy bile salts. At the used concentrations ciliary beat arrested within 30 min. Deoxycholate is extremely ciliotoxic, ciliary arrest occurred within 1 min at a concentration of 5 mmol/l.

Efficacy, safety and mechanism of cyclodextrins as absorption enhancers in nasal delivery of peptide and protein drugs.

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins. Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated beta-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-alpha-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed. The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.

Effects of N-trimethyl chitosan chloride, a novel absorption enhancer, on caco-2 intestinal epithelia and the ciliary beat frequency of chicken embryo trachea.

N-trimethyl chitosan (TMC) polymers are quaternized chitosans in different degrees of trimethylation. These polymers enhance the absorption of macromolecules through mucosal epithelia by triggering the reversible opening of tight junctions and only allow for paracellular transport. To investigate the safety of these novel absorption enhancers cytotoxicity and ciliotoxicity studies have been performed. Intestinal Caco-2 cell monolayers were chosen to study possible membrane damaging effects of these polymers, using confocal laser scanning microscopy visualization of nuclear staining by a membrane impermeable fluorescent probe during transport of the paracellular marker Texas red dextran (MW 10 000). Ciliated chicken embryo trachea tissue was used to study the effect of the polymers on the ciliary beat frequency (CBF) in vitro. In both studies the TMC polymers of different degrees of substitution (20, 40 and 60%) were tested at a concentration of 1.0% (w/v). No substantial cell membrane damage could be detected on the Caco-2 cells treated with TMCs, while the effect on the CBF in vitro was found to be marginal. TMC60 and TMC40 enhance paracellular transport of Texas red dextran in Caco-2 cell monolayers, whereas TMC20 is ineffective. In conclusion, TMCs of high degrees of substitution may be effective and safe absorption enhancers for peptide and protein drug delivery.

Nasal Insulin Delivery with Dimethyl-β-Cyclodextrin as an Absorption Enhancer in Rabbits: Powder More Effective than Liquid Formulations

The nasal absorption of insulin using dimethyl-β-cyclodextrin (DMβCD) as an absorption enhancer in rabbits was studied. The nasal administration of insulin/DMβCD liquid formulations did not result in significant changes in serum insulin and blood glucose concentrations. In contrast, previous experiments in rats showed that the addition of DMβCD to the liquid nasal formulation resulted in an almost-complete insulin absorption, with a concomitant strong hy-poglycaemic response. Apparently, the effect of the cyclodextrin derivative on insulin absorption differs between animal species following nasal delivery of insulin/DMβCD solutions. On the other hand, nasal administration of the lyophilized insulin/DMβCD powder dosage form in rabbits resulted in increased serum insulin concentrations, and a maximum decrease in blood glucose of about 50%. The absolute bioavailability of the nasally administered insulin/DMβCD powder was 13 ± 4%, compared to 1 ± 1% for both an insulin/ DMβCD liquid and an insulin/lactose powder formulation. It is concluded that insulin powder formulations with DMβCD as an absorption enhancer are much more effective than liquid formulations.

Effects of absorption enhancers on rat nasal epithelium in vivo: release of marker compounds in the nasal cavity.

AbstractPurpose. The assessment of the effects of nasal absorption enhancers on the rat nasal epithelium and membrane permeability in vivo after a single nasal dose of the enhancers. Methods. The release of marker compounds (protein, cholesterol and acid phosphatase) from the nasal epithelium was measured using a lavage technique. The nasal membrane permeability was determined after intravenous administration of a systemic tracer (FITC-albumin). Results. The effects of the absorption enhancers could be classified into four categories. The first consisted of HPβCD (5%), DMβCD (2%) and RAMEB (2%) and was not different from the control (physiological saline). For the second category, DMβCD (5%), effects were significantly higher than for the control. The third category, SGC (1%), was more active than DMβCD (5%) but less active than the last group. The fourth, most membrane damaging, category consisted of STDHF (1%), laureth-9 (1%) and LPC (1%). Administration of these three enhancers also resulted in release of acid phosphatase, indicating that severe membrane damage occurred. The release of cholesterol from nasal epithelium was largely dependent on the cholesterol solubilisation of the absorption enhancers. The amount of cholesterol released by laureth-9 and LPC was the largest. Conclusions. The results of this in vivo study are in agreement (i.e. similarity in rank order) with morphological and ciliotoxicity studies of nasal absorption enhancers, demonstrating that this invivo model is a valuable tool to classify nasal absorption enhancers according to their effects on the rat nasal epithelium.