Ten Questions On Inhalation Drug Delivery To Non-Clinical Species

Management Forum

Management Forum speaker, Simon Moore of Huntingdon Life Sciences answers ten questions on inhalation drug delivery to non-clinical species.

Inhaled, Delivered and Deposited Dose

Question 1

What is the difference between inhaled or delivered dose and deposited dose?

The delivered dose is the amount per unit of body weight that is presented to the animal. The deposited dose is a fraction of the delivered dose depending on the particle size and species.

The FDA assumes 100% deposition in humans, 10% in rats and 25% in dogs or non-human primates irrespective of any information that has been produced by the submitting company. This is based a scientific paper cited by Wolff and Dorato (Wolff and Dorato, Critical Reviews in Toxicology, 23 (4):343-369, 1993). These deposition factors need to be taken into consideration when calculating clinical overages.

Intratracheal Dosing vs Inhalation Dosing

Question 2

What advantages/disadvantages are there of performing efficacy work with dry powder rather than intratracheal dosing if our intended product is intended for DPI administration in the clinic?

Intratracheal dosing is principally only used for very early screening studies. It requires the administrationto be conducted under anaesthesia using a tube that is positioned to the bifurcation of the trachea. Aerosolisation is achieved using a pulsed approach delivering a localised bolus lung dose. The advantages of this methodology are that it is simple; the amount of test article is minimal and dose delivered to the animal is easily quantified.

However, the concern with method is the difficulty extrapolating the data to inhalation as it may produce artefactual toxicological and pharmacological results. Additionally, effective data interpretation is also hindered by the type of aerosolisation device that is used as often the particle size distribution is not representative of pre-clinical administration. Furthermore, direct instillation into the trachea bypasses the upper airways thus reducing the effectiveness of this method of administration as an early screen for lung irritancy during efficacy studies.

Further consideration also needs to be given to the number of exposures due to the practical limitations from repeated administration under anaesthesia. Inhalation dosing delivers compound evenly distributed across the lung tissue penetrating the lung parenchyma. to conscious animals by the clinical route of administration. It removes any doubt from ambiguous data results from the procedure.

However, even though there are a significant number of practical ways to reduce the test article requirement, the test article requirement will be greater irrespective of the method of generation employed. This is mainly due to the indirect method of dose calculation and the continual aerosol delivery that is required. The additional test article that is required will have cost and time implications for the customer.

Irritancy for Inhaled Compounds

Question 3

What study endpoints are used to assess potential irritancy for inhaled compounds? Can you add irritancy endpoints to inhaled efficacy studies prior to toxicology studies?

Typical end points would include airway tissue histopathology, tissue and bronchoalveolar fluid (BALF) cellular infiltration, expression of pro-inflammatory cytokines in the BAL fluid and changes in ventilator parameters (breathing rate, tidal and minute volume) during or after inhalation exposure. Further assessment of lung mechanics ( e.g airway resistance and compliance) during and after exposure and could also be evaluated.

These end points can be measured during efficacy studies but may be limited to evaluation after acute single exposures at efficacious doses. Multiples of the predicted efficacious doses would need to be included in the study protocol to obtain early data on safety margins that could be flags for subsequent toxicology testing. Currently, the safety risk assessment would be using animals that had not received any provocation other than test article or though the discussions regarding the evaluation of toxicology biomarkers in "diseased" animals is ongoing.

Safety Pharmacology Endpoints On Toxicology Studies

Question 4

What are the complications of adding pharmacology endpoints on to toxicology studies?

This requirement is quite rightly becoming increasing popular both from a scientific and 3Rs perspective, however, practical consideration needs to be given for its inclusion into the study design as it could impact on the data quality and hinder subsequent interpretation. There are also several logistical complications that need to be considered as they can influence the results that can be obtained. Consideration needs to be given to the following especially recording respiratory parameters:

  • Noise within the dosing room that is either scheduled on non-scheduled as part of the daily routine can influence the data
  • Movement of staff particularly near the inhalation exposure system can often give elevated respiratory minute volume recordings
  • Any planned data recordings should be preferentially scheduled on days that do not have other ongoing procedures taking place
  • Pre-dose and post dose recordings have to be scheduled around the toxicology regime, which may amend feeding patterns
  • There are practical limitations to the number of animals that can be recorded simultaneously. This is may result in extra test article to cover the additional generation period.

Air or Vehicle Control Group

Question 5

What should the control group be an air control or vehicle control?

The same principles that are used for other routes administration can be applied for inhalation. The decision is based on the contents of the formulation that includes the active test article.

For aerosols that are delivered as powders, the test article is usually blended with a lactose-based excipient and for liquid solutions or suspensions, formulated with surfactants or salts.

The choice of control is of particular important with using novel generation methodology or clinical devices during the pre-clinical evaluation e.g. Metered dose inhalers were the introduction of propellants into the formulation may exude leachable or extractable materials from the internal coating or valve rubbers of the device.

If the test article is being delivered as a neat powder or formulated only in water then an air control would normally suffice.

Surfactants for Liquid Formulations

Question 6

Which surfactants are used for liquid formulations? And what are the toxicological limits of surfactants?

There are a multitude of excipients used in inhalation formulations. The main types of surfactants are anionic, cationic, non-ionic and amphoteric with the toxicological limit dependent on the individual surfactant. The amount included is principally dependent on the physical properties of the active test article.

A patent was submitted by Boehringer Ingelheim Pharma Kg entitled "A liquid, propellant-free mixtures for treating asthma or chronic obstructive pulmonary disease; Tiotropium bromide", which provides an extensive list. There is also a Journal of Aerosol Medicine and Pulmonary drug delivery, which can provide further information as well as individual company websites.

Aerosol Generation

Question 7

What governs choosing one powder or liquid generator over another?

The three key factors to determine the most appropriate type of generation is the physical characteristic properties of the test article itself and the resulting formulation, the study design and dose levels. This is because each generator has both advantages and disadvantages; some devices may be best suited for biopharmaceuticals or for delivering a high generation rate or aerosolising powders that are manufactured using novel powder techniques.

An assessment either based on experience or practicality should be completed in advance of any in vivo assessment to ensure study conduct is not compromised with an inappropriate generator selection.

Non-Clinical Dosing Methodology

Question 8

What are the traditional methods of dosing non-clinical species by the inhalation route of administration?

It is not uncommon for very early screening rodent studies to be dosed by intratrachael or intranasal (particularly mice) administration as this method only requires a small amount of test article. This type of dosing is then either replaced by snout-only or whole-body exposure when assessing the efficacy in a pharmacology respiratory model.

Snout-only exposure is then used as default during pre-clinical toxicology testing to mimic the clinical application.

Although more uncommon due to ethical and study cost reasons, the initial technique for dosing non-rodents can start using the same methodology as rodents using intratracheal administration as part of an efficacy model. This methodology is then replaced by face mask exposure or oropharyngeal dosing. Facemask exposure is the principle technique for most clinical applications with oropharyngeal tube dosing used mainly for Metered dose inhalers.

Inhalation Rodent Chambers

 

Rodent Chamber

Question 9

 

In which circumstances would you use a flow past or flow through snout only rodent chamber?

Both have disadvantages and advantages and the decision to use one over the other is dependent on the study design, objective and test article formulation.

The flow through chamber is more robust, easier to clean and better with powders as the simple design
ensures that airway blockage is almost impossible. Their large internal volume allows for better expansion of the propellants using MDIs and conducting a like-for-like comparison have observed a higher generation efficiency using this chamber type. However, they are somewhat dated in concept; they have a basic design, not impressive and have long equilibration time so are not suitable for reactive test articles. Furthermore, if not controlled appropriately, there can be an aerosol concentration gradient within the chamber so the location of the animals would have to be rotated to negate any animal to animal dose variation.

Alternatively, the design of the flow past or direct-flow chamber is more ecstatically pleasing. The geometry of the chamber design provides each animal with fresh aerosol and aids particle size reduction. The latter benefit can be used as an advantage if the input test article is larger than expected. The airflow per animal can be reduced lower than using a flow through chamber. HLS have successfully used an airflow per rat as low as 0.25L/min and considerably lower for mice. However, the chambers are heavy, prone to blockages, complex, difficult to clean and maintain. They have no buffering capacity if there are issues with generation. Generation efficiency tends to be a little lower and some designs do not allow good visibility of the animals during the exposure period, which may impact on animal welfare.

Improved Animal Welfare in Non-Rodent Species

Question 10

What is your view on dosing dogs in slings?

The historic method for dosing dogs is using a sling restraint and is still commonly used amongst certain establishments. The main animal welfare concern with this technique is that it is uncomfortable for the animal and as a result limits the dose duration. The sling also constricts the chest cavity which impairs the breathing, which is obviously detrimental particularly for an inhalation study.

A 3Rs approach was adopted by HLS over 15 years ago radically changing this historical methodology resulting in improved animal welfare and data interpretation due to enhanced animal compliance. The animals are fastened inside a standard dog walking harness. The harness is tethered using a band to a pole at the back of a bench. This method allows the animal extensive freedom of movement. The animals readily accept this methodology to the point where they quite often fall asleep during the dosing phase.


References

 

Data comparison of the respiratory parameters during the acclimatisation phase of rat snout-only and whole-body plethysmography studies
Authors: Moore S, Armstrong R, Jordan S and Mitchell D
Publication: 53rd Annual Meeting, Society of Toxicology, Pheonix, USA, 23-27 March 2014.

 

A refined method of restraint for dogs used in inhalation studies - Refinement in the acclimatisation procedure
Authors: Moore S, Timothy M and Hawes S (2014):
Publication: Animal Technology & Welfare (ATW) publication, April 2014, Vol 3 No. 1 p59-61.

 

Improved animal welfare standards in large animal species allows extended periods of inhalation dosing
Authors: Moore S and Pearse J
Venue: Association of Inhalation Toxicologists, Princeton, NJ, USA 22-24 September 2014

 

An alginate oligomer (OligoG) developed as a dry powder for inhalation for cystic fibrosis demonstrates an excellent safety profile, similar to a nebulised solution used in a phase 2a trial
Authors: Moore S, Myrset A H, Phillips L, Gangadharan B, Dessen A
Venue: Association of Inhalation Toxicologists, Princeton, NJ, USA 22-24 September 2014

 

Comparison of Different Nebulisers to Allow More Effective Decision Making
Authors: Moore S, Richardson J and Gutteridge C
Venue: Association of Inhalation Toxicologists, Princeton, NJ, USA 22-24 September 2014

 

Validation of the Capsule Based Aerosol Generator (CBAG) in an in vivo study for administration of fluticasone propionate in a rat model of LPS-induced non allergic pulmonary inflammation
Authors: Moore S, Jordan S, Armstrong R, Barnes C and Watts C
Venue: Association of Inhalation Toxicologists, Princeton, NJ, USA 22-24 September 2014.

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