Nasal delivery of peptides using powder carriers based on starch/poly(acrylic acid)

As peptides are not suitable for oral administration, they are generally administered parenterally. Due to the disadvantages associated with parenteral delivery alternative routes of administration (buccal, nasal, pulmonal, ocular, transdermal, rectal and vaginal route) have been investigated. In the present work, the nasal route was selected as an alternative route for peptide delivery. Despite the advantages related to nasal administration, the bioavailability remains low. In Chapter 1 the barriers to nasal absorption of peptides are described. The strategies which have been described in literature to circumvent the nasal barriers are also mentioned. This research project focused on powder formulations as carriers for the nasal delivery of peptides, aiming to improve the nasal bioavailability by enhancing the residence time of the drug in the nasal cavity by incorporating viscosity-enhancing excipients in the formulation. As carrier for the nasal delivery of insulin and salmon calcitonin (used as model peptides) mixtures of Drum Dried Waxy Maize starch and Carbopol® 974P (ratio: 95/5, w/w) (DDWM/C 974P 95/5) and of spray-dried Amioca® starch and Carbopol® 974P (ratio: 25/75 and 85/15, w/w) (SD 25/75 and SD 85/15) were used. In Chapter 2 the characteristics of the components of the nasal powders were described in detail. In Chapter 3 the influence of powder bulk density on the nasal bioavailability of insulin was investigated in rabbits as in a previous study it was shown that the density of the formulation determined the spray pattern from the device. The powder bulk density of the nasal formulations was modified by changing the solid fraction of the dispersion (prior to freeze-drying) and by changing the freezing rate during the freeze-drying cycle. The bulk density was mainly determined by the solid fraction of the dispersion: the bulk density of the powders increased when the solid fraction of the freeze-dried dispersion was higher. However, no influence of powder bulk density on the nasal bioavailability of insulin in rabbits was seen. In Chapter 4 it was demonstrated that freeze-drying of aqueous dispersions containing spray-dried AmiocaO starch/CarbopolO 974P (ratio: 25/75) and Ca(OH)2 neutralised with NaOH yielded powders containing a mixture of sodium and calcium carboxylate. In Chapter 4.1 the absorption enhancement of those powders was compared with equivalent powders containing only sodium carboxylate. An optimal balance between sodium and calcium carboxylate was required to maximise the absorption of insulin. The highest absorption of insulin was observed at a ratio of 90/10 between SD 25/75 and Ca(OH)2, obtaining a bioavailability of ± 29 % and 19 % for equivalent formulation with and without Ca(OH)2. This increase in nasal delivery was possibly due to the higher water absorbing capacity of the formulation (enhancing the paracellular transport by opening of the tight junctions) and to the higher elasticity after dispersing this formulation in nasal fluid. Furthermore, after nasal delivery of (SD 25/75)/Ca(OH)2 90/10 or (SD 25/75)/CaCO3 90/10 a decrease in tmax was observed, possibly due to a progressive dissociation of Ca2+-ions from the Ca2+-carboxylate after hydration of the powder which resulted in the closing of the tight junctions. Incorporation of salmon calcitonin in the (SD 25/75)/CaCO3 90/10 formulation resulted in a similar trend: a higher Cmax but lower tmax was observed compared to the equivalent formulation without CaCO3. The importance of using a spray-dried mixture of starch and CarbopolO 974P instead of a physical mixture was also highlighted in this chapter. A physical mixture of starch and CarbopolO induced a lower absorption of insulin, possibly due to its lower and slower water absorbing capacity. A similar observation was made after addition of Ca(OH)2 to this mixture: Cmax increased and tmax decreased in comparison with the mixture without Ca(OH)2. As an enhanced bioavailability is frequently associated with a disruption of the integrity of the mucosal epithelium, in Chapter 4.2 it was investigated if the enhanced nasal bioavailability of insulin after administration of the powder formulation containing (SD 25/75)/CaCO3 90/10 was due to mucosal damage. The possible toxicological effects after multiple administration of the powders SD 25/75 and (SD 25/75)/CaCO3 90/10 were evaluated using a non-invasive washing technique in rabbits and using a mucosal irritation assay on slugs. Both powder formulations induced mucosal damage after nasal administration to rabbits as an increased protein, LDH and ALP release from the nasal mucosa after administration was observed. A higher membrane damaging potential was observed for SD 25/75 compared to (SD 25/75)/CaCO3 90/10. For both powders the effects on the epithelium were reversible as the protein and enzyme concentrations decreased within 24 h, returning to their basal levels within 3 days. Using the Slug Mucosal Irritation test, a lower mucosal tolerance was also observed for SD 25/75 as the mucus production and protein and LDH release after repeated administrations were higher in comparison with (SD 25/75)/CaCO3 90/10. However, according to the Slug Mucosal Irritation prediction model both formulations were classified as moderate membrane irritating and mild to moderate membrane damaging. Hence they are not recommended for chronic drug therapies. Two modifications of the Slug Mucosal Irritation test were also described in Chapter 4.2, which were performed in order to optimise the procedure for screening of formulations containing viscosity-enhancing and/or bioadhesive polymers. The results obtained using the modified protocols suggested that the present procedure might underestimate the tissue damaging potential of these formulations, especially for those test formulations at the borderline between a mild and moderate classification. The modified procedure wherein the foot mucosa of the slug was carefully cleaned with paper moistened with PBS after the 30-min contact period with the formulation allowed the best prediction of those test substances. Consequently, this procedure will be further optimised and validated. The stability of the spray-dried Amioca® starch/Carbopol® 974P 25/75 mixture stored during 9 months at different relative humidities (RH) and temperatures (10% RH – 25°C, 60% RH –25°C, 75% RH – 40°C) was investigated in Chapter 5. Storage of a spray-dried mixture of Amioca® starch and Carbopol® 974P 25/75 at 40°C – 75% RH induced structural modifications of the polymers which had an influence on the bioavailability of insulin after nasal delivery to rabbits. In order to maintain the powder characteristics obtained immediately after spray-drying the mixture should be stored at 25°C and 10 % RH. In Chapter 6 the efficacy of oxymetazoline HCl formulated in a starch/Carbopol® powder formulation was compared to a commercial nasal spray (Nesivine®) in healthy human volunteers by measuring the nasal airflow during 8 h after administration and by scoring the nasal side effects (nasal obstruction, itching and sneezing) using a visual analogue scale. Powder formulations based on neutralised Amioca® starch/Carbopol® 974P 25/75 and non-neutralised Amioca® starch/Carbopol® 974P 85/15 were used as carriers for oxymetazoline HCl and two systems (Monopowder and Pfeiffer) were used as delivery devices. Nasal delivery of the neutralised SD 25/75 powder using the Monopowder device hardly improved the nasal airflow, possibly due to an ionic interaction between drug and carrier. In contrast, an increase in nasal airflow was seen for the non-neutralised SD 85/15 powder. The delivery device had an important influence on the pharmacological response. Spraying SD 85/15 with the Pfeiffer device resulted in higher pharmacological effect in healthy volunteers, the response being similar to the effect of the Nesivine® spray. However, the onset of action of oxymetazoline HCl was not as steep when the powder was administered. Longer measurements (> 8 h) are required to verify if a powder formulation based on Amioca® starch and Carbopol® 974P induced a longer nasal decongestion compared to the conventional sprays. Furthermore, the side effects reported following powder administration were possibly related to the nasal delivery system: using the Pfeiffer system the nasal side effects were minimal, whereas with the Monopowder device stinging and watering eyes were reported immediately after administration. Possibly the pressure at which the powder particles are released from the device is too high.