of the Society of Toxicology
Fall 2001
1 Regulatory and Safety Specialty Section Fall 2001
PRESIDENT’S MESSAGE
Last March at the Annual meeting of S.O.T., I promised you, the members of the Regulatory and Safety Evaluation Specialty Section, that your Council and I would try to make the Section more responsive to your wishes, and I encouraged you to let us know what your wishes are.
Well, the response has not exactly been overwhelming, but certain patterns did emerge, at least to my mind.
You wanted more information about the Section. As a result, we set a goal of sending out four newsletters each year, instead of the one or two that has been the Section’s history. Well, for various reasons, not the least of which is that we are all busy in our jobs trying to do “more with less”, we aren’t going to get out four newsletters; but we will publish three, and that’s lots better than one or two.
You also wanted our reception at the annual meeting of S.O.T. to be more than just a social mixer. So, for this year, we’ve put together a panel discussion topic that we’ll announce in the next newsletter (so we can be sure we have people who’ve agreed to discuss it). I promise it’ll be worth your time. The reception itself will be on Wednesday evening at the annual meeting in Nashville, from 6:00 p.m. to 7:30 p.m. I hope to see you all there.
Finally, you asked for a greater voice in the future of the Section. I encouraged you to run for office or Council, and you responded admirably. We have a full slate of excellent candidates who’ve agreed to run for office or the Section council. Please consider them carefully when the voting forms are sent out for your response.
The officers and council of the Section met last month to discuss these and other issues. It was the first time in a long time that such a meeting, separate from the annual meeting, was held. We all agreed it was extremely worthwhile, and I am encouraging my successors to continue this process. The Section can only become better when there are more opportunities for communication and interaction.
See you in Nashville!
Glenn S. Simon
Society of Toxicology
Congressional
Science Fellowship
Recruiting Qualified Candidates for 2003
Where are you in your career? Are you looking for an exciting opportunity to apply your expertise and talents in the science policy arena? Would you be interested to gain a valuable and unique perspective as well as really make a difference in how science is applied in the legislative process? SOT’s Regulatory Affairs and Legislative Assistance (RALA) Committee has just begun the recruiting process for applications for the 2003 Congressional Science Fellowship (CSF). Applications for consideration must be filed with SOT by August 1, 2002. The 2003 CSF will be the fifth position sponsored by SOT and offers the opportunity to contribute scientific and technical input to the process of developing public policy. Candidates for the one-year fellowship, which begins in January of each year, can come from any sector of the Society. Applicants will be evaluated on the basis of well-rounded scientific training and career history, communication skills and the ability to bring critical thinking and objectivity to the development of science policy. Detailed information and application guidelines can be accessed through the SOT website at You may also contact Michael McCoy at SOT headquarters at 703-438-3115 or for more information.
Articles of Interest to Our Membership
We have endeavored to include an article of interest to our membership in each issue of the newsletter. In the last issue, we had an article about dietary supplement safety. In this issue, we have an article about practical issues concerning infusion toxicity studies. Are these brief articles of interest to our specialty group? If you have any comments on these articles or suggestions for future articles, please feel free to contact any of our officers. Their e-mail addresses are at the end of the newsletter.
Non-Clinical Safety Evaluation by Intravenous Infusion – Technical and Design Considerations
Glenn R. Washer, D.A.B.T.
CTBR
Senneville (Montreal), Quebec
Canada
Non-clinical safety evaluation by the intravenous (IV) infusion route is typically employed to mimic the intended clinical regimen and route. There can, however, be other reasons to conduct IV infusion studies, even in cases where the intended clinical route is other than IV infusion; these include poor oral bioavailability and/or poor solubility. Although virtually every procedure and parameter included in a more routine toxicology study can likewise be included in an infusion study employing an indwelling catheter, there are technical issues which need to be considered (e.g. longer acclimation for post surgical recovery, drug-catheter compatibility, possible test article-antibiotic interaction). The choice of infusion method (jacket & tether vs. ambulatory pump for large animals; jacket & tether vs. tail-cuff for rodents) should be made with due consideration to the relative merits of each method, as they pertain to the particular study’s objectives and any anticipated test article effects. Utmost attention should be given to the choice of vehicle and to the pH and osmolality of the infused formulation as local, and possibly systemic, vehicle/test article-related irritation can significantly influence the outcome of an infusion study. Related to this latter issue are the rate and volume of administration since very high rates/volumes can likewise result in dose-limiting irritation and other systemic concerns, while very low rates can lead to catheter occlusion. Even with highly experienced technicians, the presence of indwelling catheters and the infusion procedures themselves do result in a normal level of “baseline” histopathology. Therefore it is critical that the histopathological evaluation be conducted with prior experience of material-related and vehicle-related histopathology, since this will allow apparent test article-related findings to be put into context. Inexperience in such
evaluations can result in misinterpretation of “normal” findings. In the following article, we will go on to explore these issues in more detail.
Intravenous infusion toxicology studies are typically conducted in rodents and non-rodents in order to mimic the clinical route and regimen. Other instances where IV infusion may be necessary include compounds intended for oral clinical administration, but for which there is poor oral bioavailability in animals. In such cases, the use of IV infusion permits higher systemic multiples of the clinical dose to be achieved, while controlling the Cmax (which may not be feasible by IV injection). In instances where the intended clinical route is IV injection but where solubility is limited, the use of infusion can permit larger volumes and hence greater multiples of the clinical dose than by simple injection. Additionally, the IV infusion route is sometimes employed to investigate the toxicological significance of apparent changes seen by the intended clinical route (e.g. are lesions in the nasal turbinates in rats related to gavage reflux or to true systemic toxicity following GI uptake?) or to overcome a particular toxic effect which may be exclusively related to a given route of administration (e.g. gastric irritation of an oral compound).
The difficulty of maintaining animals on long term IV infusion (i.e., 6 months and longer) is obvious; however, there is no formal regulatory exception afforded to limit the duration of animal infusion studies. When studies extend to 6 months and longer, the frequency of catheter patency problems can lead to exclusion of animals from the study; furthermore, degradation of the indwelling catheter may implicate toxicity issues completely unrelated to the test article.
In spite of the technically demanding nature of continuous IV infusion studies, regulators have come to expect that such studies be comparable to more routine routes in terms of numbers of animals, parameters and end-points. Infusion studies in rats and dogs have become common place as have, to a much lesser extent, studies in primates and rabbits. The use of mice and mini-pigs continues to be very limited due to the unique issues these 2 species
present (particularly their extremes of size).
As compounds progress from Phase I through Phase II and III clinical trials, the need for developmental and reproductive toxicology studies employing the infusion route become necessary. Such studies are definitely feasible but introduce the additional concerns for the potential effects of surgery, anesthesia and infusion-related stress on successful mating, pre/post implantation loss and fetal development. Clearly, to be considered a valid study, the control group’s values for these and other reproductive parameters should fall within the laboratory’s range of historical control data for non-infusion studies; otherwise it may be that inadequate surgery/infusion procedures are the source of the abnormal control values.
Although the basic design of acute, subchronic and chronic infusion studies should be comparable to designs for more traditional routes, there are additional assessments and considerations which should be made either prior to the conduct of a study or within the study itself. These include: a longer prestudy acclimation to afford adequate post-surgical recovery; the possibility of test article interaction with the presurgical antibiotic regimen; the relative technical competence may warrant inclusion of more spare animals; the need for analysis of compatibility (adsorption or leeching) of test article formulations with components of the infusion apparatus; the means of accurately quantifying test article delivery over each daily interval.
Since not all infused test articles are intended for 24-hour/day administration, there can be instances where short daily infusions may permit the use of temporary peripheral vein catheters as opposed to surgically implanted catheters. Depending on factors such as: study duration, daily administration frequency, vehicle irritancy, accessible vessels (species dependant), number of animals, and cost, it may still be appropriate to employ indwelling catheters even in instances of short daily infusions (e.g. 30 minutes/day). In such cases the use of indwelling catheters permits all animals on a study to be dosed approximately concurrently (thus
avoiding differences in circadian rhythms) and within their home cages (thus avoiding stress due to restraint and handling). Furthermore, with vehicles/test articles prone to induce irritation, the small diameter of peripheral vessels (as compared to the abdominal vena cava – the ideal site for an indwelling catheter) makes them more susceptible to occlusion related to vascular irritancy.
The two most commonly employed blood vessels for implantation of central catheters in laboratory animals are the jugular vein (catheter tip resides in jugular vein or superior vena cava near the right atrium) and the femoral vein (catheter tip resides in abdominal vena cava at the level of the kidneys). In general, femorally implanted catheters are better tolerated by animals than are jugular catheters and, due to the larger diameter of the abdominal vena cava, lead to fewer complications (reduced risk of occlusion and larger volume of blood in which test article can dilute prior to delivery to the heart). Additionally, the risk of accidental introduction of the catheter into the heart is avoided with a femoral catheter. Regardless of the vessel employed, indwelling catheters are typically tunneled subcutaneously to exit in the interscapular region and connect to an external pump (the latter either outside the cage and connected via a jacket and lightweight tether, or secured to the animal within a jacket). Alternatively the catheter may terminate at a subcutaneous access port into which a needle must be inserted to permit infusion. For rodents, some researchers choose to exteriorize the catheter at the base of the tail, via a “tail-cuff”, as opposed to the scapular region. There are varying degrees of risks (e.g. infection potential, tissue damage, stress, technical limitations, disruption of mating) associated with each of these various options (requiring too much text within the space permitted), and these should be carefully reviewed prior to deciding on the method to be used.
Whenever possible, the components of the infusion system coming directly into contact with the test article formulations (e.g. catheter, tubing, syringes, filters) should be standard commercially available, clinical-grade materials, since these are typically inert and intended for use with a majority of
formulations. The preferred catheter material for implantation is surgical-grade silicone-based tubing, since this is the most commonly used catheter material used in humans. It is superior to most alternative materials since it combines strength and flexibility, is easily steam sterilized and causes minimal tissue reaction. Even when clinical-grade materials are employed, the conduct of compatibility tests of the test article formulations with the assembled components of the infusion system should be performed. This will help to demonstrate whether the formulation concentrations are reduced due to adsorption to the components and may indicate whether any of the chemical constituents of the components are leached into the formulations. Typically a range of concentrations are infused through mock-up infusion sets over a range of infusion rates and at environmental conditions representative of their intended eventual use in animals. Samples are collected periodically over the course of a representative infusion period and the concentrations compared to the original formulation. Should there be evidence of leaching or adsorption, components made from alternative materials (e.g. polyurethane or polyethylene catheters) may be substituted. Alternatively, when adsorption is minor, infusion lines may be “primed” to saturate “binding-sites” prior to infusion into the animals.
Whenever possible, the vehicle employed should be one with minimal potential for vascular irritancy and the pH and osmolality of the final test article formulations should be assessed. Ideally formulations with pH 5.5 to 7.0 and approximately 300 mOsm/L should be employed, however extremes of pH and osmolality may be employed depending on the intended volume and rate of administration. As pH moves outside of the 5.5 to 7.0 range in either direction, the risk of vascular irritation increases (potentially leading to catheter occlusion). Likewise, the lower the osmolality, the greater the risk of hemolysis and resulting adverse effects. Higher osmolalities (e.g. 700 mOsm/L as employed with total parenteral nutrition products) are manageable, but are not without complications. The relative concern for extremes of pH and osmolality will depend on the volume and the rate of infusion. That is, administration of a small volume
of very low pH and low osmolar solution will likely be well tolerated but increasing volumes of the same formulation, particularly when infused over a shorter time, will be less well tolerated.
As a rule of thumb, physiologic saline (pH 5.5), administered as a vehicle by continuous intravenous infusion at 2.5 to 3.0 mL/kg/hour for 24 hours per day (i.e. circa 1 to 1.5 blood volumes/day), is very well tolerated. Although much higher rates and volumes (e.g. 65 mL/kg/hour as a 1-hour infusion of a blood substitute) can be tolerated, repeated daily administration at such volumes can quickly result in local tissue reaction at the site of infusion, possibly leading to severe thrombus and eventual lung emboli. Physiologic saline being the preferred vehicle, recommended alternatives include: 5% dextrose, 5% mannitol and cyclodextrins. Whenever possible, more exotic vehicles (e.g. PEG, ethanol, and water combinations) are to be avoided due to irritancy and hemolysis concerns.
When properly performed, intravenous infusion of physiologic saline at 2.5 to 3.0 mL/kg/hour, via an indwelling catheter will result in only minor tissue reactions, restricted to the site of infusion (catheter tip) and should not result in deposition of emboli within the vasculature of the lung. Typical, normal reactions consist of a low incidence and severity of thrombi and intimal proliferation (phlebitis). Combinations of more irritant vehicles, extremes of pH, low osmolality, high infusion rates and/or volumes, or poor technique will increase the severity and incidence of the local infusion site changes and can eventually lead to break down of the vascular wall, periphlebitis, lung emboli and opportunistic infection.
ABOUT THE AUTHOR
Glenn R. Washer, B.S., D.A.B.T., is the Scientific Director of Infusion, Pharmacology & Neurotoxicology at CTBR, 87 Senneville Road, in Senneville (Montreal), Quebec, Canada. Glenn has more than 10 years of experience in conducting infusion studies. Glenn will be among the presenters at an RSESS co-sponsored SOT Continuing Education course on this topic in March 2002.
Glenn can be reached at: .
REFERENCES
Copeman, C., Robinson, K. (2000). Femoral Cannulation for Reproductive Toxicity Studies, Handbook of Pre-Clinical Continuous Intravenous Infusion, Eds. Healing & Smith, Taylor & Francis, London. 95-109.
FDA (1999). Guidance for Industry – Catheter-Related Bloodstream Infections – Developing Antimicrobial Drugs for Treatment. Rockville, MD.
Fort, F., et al. (1983). Hemolysis Study of Aqueous Polyethylene Glycol 400, Propylene Glycol and Ethanol Combinations In Vivo and In Vitro. Journal of Parenteral Science and Technology. 38:82-85.
Kuwahara, T., et al. (1998). Effects of pH and Osmolality on Phlebitic Potential of Infusion Solutions for Peripheral Parenteral Nutrition. Journal of Toxicological Sciences. 23:77-85.
Perkin, C., Stejskal, R. (1994). Intravenous Infusion in Dogs and Primates. Journal of the American College of Toxicology. 13:40-47.
Sherer, A., Kinter L. (1995). A Guide to Manufacture, Surgical Implantation, Maintenance and Use of Micro-Renathane Vascular Catheters in Laboratory Animals. Braintree Scientific Inc., Braintree, MA.
van Wijk, H. (2000). Continuous Intravenous Infusion in Athymic (nude) Rats: An Animal Model for Evaluating the Efficacy of Anti-Cancer Agents. Laboratory Animals. 34:63-69.
Washer, G. (2000). Guide to Non-Clinical Infusion Studies. CTBR Ltd., Montreal, Canada.
STUDENT AWARDS 2002
The SOT is looking for nominations for student awards for excellence in toxicology research. We encourage faculty advisors to look at the SOT Website for information about specialty section requirements, deadlines, and areas of research, contacts, forms (the Student Award Sheet), etc. The Website is: