If a cat's immune system is healthy and mature, the white blood cells should fight off an infection or virus, and allow the cat to build up an immune response, or antibodies.  Cats who develop FIP have an immune defect or deficiency that causes the white blood cells to replicate, rather than fight, the virus. Essentially, the cats immune system is spreading the virus throughout the cat's body rather than trying to eliminate it.  Cats who have no immune response develop wet FIP, while cats who have a partial immune response develop dry FIP. The nucleoside analog GS-441524 is a molecular precursor to a pharmacologically active nucleoside triphosphate molecule. These analogs act as an alternative substrate and RNA-chain terminator of viral RNA dependent RNA polymerase.  In layman's terms, GS441 interjects itself into the chain reaction and stops the replication of the virus.  
Dr Pedersen's case study determined that a successful course of treatment with GS441 is 12 weeks, administered daily.  Some owners have stopped treating once blood work and diagnostics returned to normal; however, the few cats who did relapse were among those who stopped prior to the 12 week protocol.  Because the course of treatment is both emotionally and financially taxing, most owners currently using GS opt to pursue the full 12 weeks, to ensure the highest probability of success.  Cats who undergo the full 12 weeks and remain symptom-free for 90 days following conclusion of treatment are officially cured of FIP.  
GS441 comes in both injectable form, and as of June 2019, a pill form.  Both are administered daily and the dose is based on the weight of the cat. For wet & dry FIP without neurological or ocular symptoms, the recommended dosage is 5mg (GS) x weight (kg) / GS concentration per 1mL = dose per 24 hr.   Neurological and Ocular FIP cats require 7mg/kg MINIMUM, and can go as high as 10mg/kg for extreme ocular or neurological cases.A dosing calculator can be found here.It is important to note that the dosage should not be reduced during the course of treatment, regardless of how well the cat is responding.  Conversely, if the cat is not responding to the starting dosage, it is safe to increase. It is also crucial to check the cat's weight often, and adjust the daily dose accordingly. The only known side effect of GS441 is skin lesions or burns, due to the acidity of the solution (injectable form). For this reason, it is recommended to always clean the cat's skin after giving an injection.  Many owners also opt to give oral CBD oil or Hemp oil 30-60 minutes before injecting, to help minimize the stress.  Should you opt to do this, it is critical that the product be veterinary grade and the proper dose should be determined by a veterinarian. CBD and/or hemp oil can be fatal to a cat if not administered properly.  More commonly, Gabapentin, a mild pain medication can be given orally 60-90 minutes prior to the injection. The vast majority of cats using GS tolerate the injections just fine without the need for any pain medication or sedative. 

If a cat's immune system is healthy and mature, the white blood cells should fight off an infection or virus, and allow the cat to build up an immune response, or antibodies.  Cats who develop FIP have an immune defect or deficiency that causes the white blood cells to replicate, rather than fight, the virus. Essentially, the cats immune system is spreading the virus throughout the cat's body rather than trying to eliminate it.  Cats who have no immune response develop wet FIP, while cats who have a partial immune response develop dry FIP. The nucleoside analog GS-441524 is a molecular precursor to a pharmacologically active nucleoside triphosphate molecule. These analogs act as an alternative substrate and RNA-chain terminator of viral RNA dependent RNA polymerase.  In layman's terms, GS441 interjects itself into the chain reaction and stops the replication of the virus.  
Dr Pedersen's case study determined that a successful course of treatment with GS441 is 12 weeks, administered daily.  Some owners have stopped treating once blood work and diagnostics returned to normal; however, the few cats who did relapse were among those who stopped prior to the 12 week protocol.  Because the course of treatment is both emotionally and financially taxing, most owners currently using GS opt to pursue the full 12 weeks, to ensure the highest probability of success.  Cats who undergo the full 12 weeks and remain symptom-free for 90 days following conclusion of treatment are officially cured of FIP.  
GS441 comes in both injectable form, and as of June 2019, a pill form.  Both are administered daily and the dose is based on the weight of the cat. For wet & dry FIP without neurological or ocular symptoms, the recommended dosage is 5mg (GS) x weight (kg) / GS concentration per 1mL = dose per 24 hr.   Neurological and Ocular FIP cats require 7mg/kg MINIMUM, and can go as high as 10mg/kg for extreme ocular or neurological cases.A dosing calculator can be found here.It is important to note that the dosage should not be reduced during the course of treatment, regardless of how well the cat is responding.  Conversely, if the cat is not responding to the starting dosage, it is safe to increase. It is also crucial to check the cat's weight often, and adjust the daily dose accordingly. The only known side effect of GS441 is skin lesions or burns, due to the acidity of the solution (injectable form). For this reason, it is recommended to always clean the cat's skin after giving an injection.  Many owners also opt to give oral CBD oil or Hemp oil 30-60 minutes before injecting, to help minimize the stress.  Should you opt to do this, it is critical that the product be veterinary grade and the proper dose should be determined by a veterinarian. CBD and/or hemp oil can be fatal to a cat if not administered properly.  More commonly, Gabapentin, a mild pain medication can be given orally 60-90 minutes prior to the injection. The vast majority of cats using GS tolerate the injections just fine without the need for any pain medication or sedative.