Disposable Dosators for Pulmonary Insufflation of Therapeutic Agents to Small Animals

Summary

During development of drugs for pulmonary delivery, it is necessary to evaluate pharmacokinetics and efficacy in an animal model. We present a method to build a disposable aerosol dispersion system from of-the-shelf components that can be used to administer intrapulmonary dry powder aerosol to rodents.

Abstract

Development of new therapeutic products requires efficacy testing in an animal model. The pulmonary route of administration can be utilized to deliver drugs locally and systemically. Evaluation of dry powder aerosols necessitates an efficient dispersion mechanism to maintain high concentrations in an exposure chamber or for direct endotracheal administration. While solutions exist to expose animals by passive inhalation to dry powder aerosols, most require masses of powder in large excess of the dose delivered. This precludes conducting early feasibility studies as insufficient drug is available at the research or early development stage to support the dose delivery requirements for conventional aerosol delivery systems. When designing an aerosol drug product, aerodynamic performance can relate directly to delivery efficiency and efficacy. Dispersion of powder into an aerosol requires energy input sufficient to overcome interparticulate forces, and particle engineering approaches can substantially improve aerosol performance. We have developed a dispersion system (dosator) which can aerosolize engineered dry powder aerosols efficiently for the purpose of direct pulmonary insufflation, dispersion into an exposure system or generation for analytical purposes.

Introduction

Development of new therapeutic products requires efficacy testing in an animal model. The pulmonary route of administration can be utilized to deliver drugs locally and systemically ¹. Evaluation of dry powder aerosols necessitates an efficient dispersion mechanism to maintain high concentrations in an exposure chamber or for direct endotracheal administration. While solutions exist to expose animals by passive inhalation to dry powder aerosols, most require masses of powder in large excess of the dose delivered ².

This precludes conducting early feasibility studies as insufficient drug is available at the research or early development stage to support the dose delivery requirements for conventional aerosol delivery systems.

When designing an aerosol drug product, aerodynamic performance can relate directly to delivery efficiency and efficacy ³. Dispersion of powder into an aerosol requires energy input sufficient to overcome interparticulate forces, and particle engineering approaches can substantially improve aerosol performance ^4,5,6. We have developed a dispersion system (dosator) which can aerosolize engineered dry powder aerosols efficiently for the purpose of direct pulmonary insufflation, dispersion into an exposure system or generation for analytical purposes.

Protocol

1. Preparation of Components of the Dosators

1. Perforate the bottom of a 0.5 mL polypropylene microcentrifuge tube by drilling or by simply grinding or cutting off the bottom with a grinding wheel or a sharp pair of scissors. Ensure that the hole is in the center and is no more than 2 mm in diameter and no less than 1 mm in diameter (Figure 1).
2. Perforate the top of the microcentrifuge tube. Using a #22 drill bit (approximately 4 mm in diameter), drill a hole in the center of the cap. This results in a hole that will fit a slip-tip syringe (Figure 1).
3. Prepare the fine screens to be inserted into the microcentrifuge tubes. Make screens from 304 stainless steel wire cloth, 60 x 60 mesh with wire diameter of 0.0045". Cut the screens with tin snips or punch them using a die to an outer diameter of 5 mm (Figure 2).

2. Assembly of the Dosators

1. Using either forceps or the end of a blunt tip needle, insert the screen into the microcentrifuge tube and seat it in the bottom so that it covers the opening. This will serve to support the powder before actuation.
2. Press fit the narrow end of the microcentrifuge tip into the end of a blunt tip needle. Do this by hand or with a bench-top press and a guide. Gently wipe the top of the needle and bottom of the tube with ethanol to clean the parts to ensure a tight, resilient fit.

3. Filling the Dosators

1. Using an analytical microbalance, tare the device and load the desired amount of powder into the dosator. A typical powder mass for dispersion ranges from 1 to 10 mg.
2. Once filled, plug the top of the microcentrifuge tube with an allotment of cotton and a pair of forceps. This will prevent the powder from drawing into the syringe or falling out, while allowing airflow through the dosator to disperse the powder.
3. Close the microcentrifuge tube cap.
4. If not being used immediately, seal the top with a small amount of lab-film to minimize powder exposure to ambient moisture. NOTE: Generally, preloaded dosators should be stored according to storage requirements of the active pharmaceutical ingredient (API). Often aerosol powders are moisture sensitive and should be stored desiccated.

4. Device Actuation

1. Draw back the syringe to the desired volume, which may be application specific. For intrapulmonary administration in guinea pigs, use 2 mL. Dispersion efficiency is related to the volume and velocity of air delivered during actuation, as well as the inherent dispersion properties of the powder ⁷. The top hole of the dosator accommodates a slip-tip syringe. A Luer-lock syringe may be used with an adapter.
2. Insert the syringe into the back end of the dosator.
3. Insert the needle end of the dosator into the dosing port on the exposure chamber. Depress the syringe forcefully, expelling powder out of the device and directly into the animal or into the exposure chamber or analytical instrument (Figure 3).

Results

For easily dispersible powders such as those spray-dried with the intent for pulmonary delivery ^5,8,9, the dosators deliver a bolus dose out of the device. There are many applications for the dosators, including in vitro particle characterization, direct intrapulmonary administration in live animals, and aerosol generation for passive inhalation systems.

Discussion

The dispersion from the dosators was suitable for animals to receive a therapeutic dose via passive nose-only respiration, indicating a large proportion of aerosol dispersed to primary particle size. These dosators can be used for endotracheal administration, in vitro evaluation of powder performance, and general purpose dry powder aerosol dispersion for analytical or efficacious experiments. If used for intrapulmonary delivery, it is important to use an appropriate volume of air for the species chosen, as over-...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.5 mL microcentrifuge tube	VWR	89000-026
High-Volume Particle-Filtering Stainless Steel Wire Cloth, Woven, 304 Stainless Steel, 60 x 60 Mesh, .0045" Wire Diameter	McMaster Carr	9230T44
Stainless Steel Dispensing Needle, Straight, 18 Gauge, 1" Long	McMaster Carr	75165A676	Any luer-fit needle will suffice
Cotton balls	McMaster Carr	54845T16
Parafilm M® Laboratory Film	VWR	100229-550
Black-Oxide High-Speed Steel Jobbers' Drill Bit, Wire Gauge 22, 3-1/8" Overall Length, 1.8" Drill Depth, 135Deg Point	McMaster Carr	2901A195