by Aaron Izes PhD candidate
One of the main purposes of our research group is to enrich the lives of all animals through a better understanding of the drugs that we use to treat them. In addition to the pioneering pharmacology research that we do with respect to native Australian animals, we recently have begun to investigate some medications used in cats.
Cats are wonderful and unique creatures in many ways. One such way is how their bodies dispose of certain medicines. The concept of what the body does to a drug is explored by the study of pharmacokinetics. This idea can be contrasted with the concept of pharmacodynamics, which concentrates on the question of what a drug does to the body. Metabolism is one aspect contemplated by pharmacokinetics. It is now known that some medicines previously given to cats develop issues during their metabolism by the feline liver and can result in potentially fatal toxicities in this species. Examples of such medicines include paracetamol (a.k.a acetaminophen), propofol, carprofen and aspirin. With this in mind, it becomes clear that a careful consideration of the metabolism of medicines proposed for the treatment of cats is required to minimise these agents’ potential for harm.
Our project evaluates the drug mefloquine’s suitability as a possible treatment for Feline Infectious Peritonitis (FIP). FIP is a fatal, viral-induced, immune-mediated disease that affects cats globally. It is caused by a virus known as the Feline Infectious Peritonitis virus, although the exact mechanism of how the disease infects cats is still being studied. There is no known cure. Sadly, affected cats have a median survival time of 9 days after diagnosis. Currently, the approach to treatment of FIP relies on the use of immunosuppressive agents to dampen clinical signs temporarily. Yet, there are no viable treatments that address the underlying problem of viral replication.
Recently, we made a fascinating break-through in identifying that a commonly used human anti-malarial drug, mefloquine, substantially reduced the viral load of Feline Infectious Peritonitis virus in infected feline cell cultures without damaging these cells. This finding suggests mefloquine is a strong candidate for further investigation as a potential FIP antiviral agent. However, it is important to note that this finding was the result of pre-clinical laboratory research performed using cell cultures rather than in living cats. Such an experiment is said to have occurred in vitro, literally translated as within the glass. As mefloquine is currently used for human malaria prophylaxis, information on the drug’s pharmacokinetics is available in people. That being said, it is fundamental to recognize that species differences play a large part in their effects on drug pharmacokinetics. As mefloquine is not a commonly used veterinary medication and as the observation that mefloquine inhibits Feline Infectious Peritonitis virus in vitro is very recent, there are no pharmacokinetic studies on mefloquine in the cat. Thus, before we are able to trial mefloquine in FIP affected animals, we first must answer the question of whether the cure is worse than the disease? How we do this is through a thorough exploration of the pharmacokinetics of the drug in cats by way of further in vitro experimentation.
The first step in this process is to develop a protocol that enables us to detect mefloquine. To do this, we have turned to the analytical chemistry technique of High Performance Liquid Chromatography (HPLC). HPLC allows us to separate, identify and quantify the various components of a mixture. As mefloquine does not undergo routine therapeutic monitoring in people or any other species, we have had to develop an HPLC assay from scratch. The HPLC assay that we have developed allows us to detect mefloquine under two different sets of experimental conditions. Under the first set of experimental conditions, the assay allows for the detection of mefloquine within a hepatic microsomal matrix. Hepatic microsomes are components of liver cells that when placed in a system allows us to recreate metabolism in the laboratory as opposed to in a live cat. The concept of microsomes will be discussed in greater detail in later postings. It is anticipated that with further refinement this assay will also identify the presence of metabolites produced when mefloquine is incubated with microsomes. Moreover, under the second set of experimental conditions, the HPLC assay allows for the detection of mefloquine within feline plasma. The ability to detect mefloquine in plasma becomes an important consideration as later plasma protein binding studies will allows us to gauge how therapeutically active mefloquine is and allow us to contemplate starting doses for any would be future clinical trials.
The following chromatograms depict our assay’s ability to detect mefloquine:
Experimental Condition 1 (above): Feline Microsomal Matrix with mefloquine 10uM:
Experimental Condition 2 (above): Feline Plasma with mefloquine 1 ug/mL
As the research progresses, we will continue to update this page to discuss the project further.
We are very grateful for the financial support of this project by the Winn Feline Foundation, Australian Companion Animal Health Foundation and the Feline Health Research Fund.
As always thanks to our colleagues Dr Benjamin Kimble and Dr Kong Li for their technical guidance on this project.