viernes, 27 de marzo de 2015

USE OF OSELTAMIVIR IN THE TREATMENT OF CANINE PARVOVIRAL ENTERITIS. Part 1. Michelle R. Savigny 2008

RESULTS

A total of 35 dogs were evaluated, with 19 in the treatment group receiving oseltamivir and 16 in the control group receiving a placebo. There were 3 shelter dogs included in the study, all of which were in the control group. Most dogs (30/35) were of the mixed-breed variety, with the purebreds consisting of 2 American pit bull terriers and 1 each of dachshund, beagle, and Labrador retriever. No statistically significant differences were found between groups in the baseline characteristics of age, sex, vaccination status or duration of clinical signs prior to presentation. The median age of dogs in the control group was 14 (8, 36) weeks, while that of the treatment group was 12 (8, 44) weeks (p=0.50). There were 21 (60%) female dogs, with 10 (48%) randomized to the control group and 11 (52%) randomized to the treatment group. Alternatively, there were 14 (40%) male dogs, with 6 (43%) randomized to the control group and 8 (57%) to the treatment group (p=1.0). All dogs were sexually intact. Vaccination status was known for 10/16 (62%) dogs in the control group and 13/19 (68%) dogs in the treatment group. Of these, 5 (50%) dogs in the control group had received at least one vaccination against CPV, whereas 6 (46%) in the treatment group had been vaccinated at least once against CPV (p=1.0). The duration of clinical signs prior to presentation was known for 15/16 (94%) control dogs and 16/19 (84%) treatment dogs. Mean days sick for the control group was 1.4 (+/-0.9) days, while that for the treatment group was 1.8 (+/-1.0) days (p=0.31). There was no significant difference in the degree of estimated dehydration at entry of dogs between groups. The control dogs were estimated to have a mean dehydration deficit of 6.3% (+/-1.54%), while the treatment dogs were estimated at 6.9% (+/-1.7%) (p=0.35). In addition, there was no statistical difference amongst the weights at entry or the weights at discharge between the two groups. Dogs in the control group had a median entry weight of 6.7kg (14.7lb) (1.8, 28.2kg [3.96, 62lb]), and those of the treatment group 4kg (8.8lb) (1.6, 25kg [3.5, 55lb]) (p=0.21). At discharge, the median weight of control dogs was 6.5kg (14.3lb) (1.8, 27.3kg [3.96, 60lb]) and that of the treatment group was 4.4kg (9.7lb) (1.6, 28.6kg [3.5, 63lb]) (p=0.42). However, a significant difference was found in the weight change from entry until discharge.

Dogs in the control group experienced a median change of -0.21kg (-0.46lb) (-2.8, 0.5kg [-6.2, 1.1lb]), while those in the treatment group had a median gain of 0.07kg (0.15lb) (-1, percentage of change in body weight ([discharge weight ñ entry weight / entry weight] * 100%) (Figure 1). Dogs in the control group had a mean change of -4.5% (+/- 6.9%), and those in the treatment group a mean change of +2.6% (+/- 7.1%) (p=0.006). When this analysis was repeated for survivors only, the results were still found to be significant. The control dogs contained all 3 non-survivors, and the new calculation without these dogs resulted in a median percent weight change of -3.9% (-2.8, 0.5), compared to the median percent weight change of 1.3% (-1, 3.6) for the treatment dogs (p=0.012). The percentage of days in the hospital that SIRS criteria were met was calculated for each dog. There was no significant difference between groups, with control dogs meeting SIRS criteria a mean of 52% of days, versus 54% for treatment dogs (p=0.91). No difference was found in the duration of hospitalization between the two groups. Dogs in the control group had a mean stay of 5.9 (+/- 2.6) days, and those of the treatment group 6.0 (+/- 2.3) days (p=1.0). Colloid therapy was not required often, as the median number of days on colloids for the control group was 0 (0, 3) days and also 0 (0, 5) days for the treatment group (p=0.5). None of the 16 dogs in the control group received a blood transfusion, while 2/19 (10%) dogs in the treatment group did (p=0.5). The addition of chlorpromazine was necessary in 10/19 (53%) dogs in the treatment group, and 9/16 (56%) dogs in the control group. Dogs in the treatment group that did receive chlorpromazine did so an average of 21% of their days in the hospital, while the dogs requiring it in the control group were given chlorpromazine an average of 30% of their days in the hospital. The overall survival rate was 91% (32/35). Three dogs died, all from the control group, giving this group a survival rate of 81% (13/16). One animal was euthanized after severe progression of clinical signs despite treatment, and it was deemed that the dog was suffering and would not recover, while the other 2 suffered natural deaths. Survival in the treatment group was 100% (19/19). However, this difference was not found to be significant (p=0.09). Post mortem examinations were performed on all non-surviving dogs. Findings were consistent with a diagnosis of CPV enteritis.

All dogs had diffuse, severe, necrotizing enteritis. Bone marrow was examined in 2/3 dogs, both showing sections of moderate hypocellularity. While 2 dogs were noted to have diffuse congestion and edema in their lungs, the third dog was found to have a mild interstitial pneumonia. The white blood cell values that were evaluated (initial counts for WBC, neutrophils and lymphocytes, the nadir values and day of nadir, and significant decreases in counts for WBC, neutrophils and lymphocytes), were compared between groups. No significant differences were found for any of these values between groups. Although it was not found to be significant, it was noted that the treatment dogs had a very slightly lower average WBC (7,500 cells/ul) and neutrophil count (6,220 cells/ul) at presentation than the control dogs (8,540 cells/ul WBC and 6,830 cells/ul neutrophils). Both groups experienced a decline in numbers with an average nadir of WBC at 2,680 and 2,810 cells/ul for the treatment and control groups, respectively, and 1,160 and 1,240 cells/ul for the neutrophils for the treatment and control groups, respectively. While by Day 5 the control dogs had rebounded their WBC (4,580 cells/ul) and neutrophil counts (2,270 cells/ul), the treatment dogs showed a slightly higher value for each at the same time point (6,920 cells/ul WBC and 4,310 cells/ul neutrophils). Seven of the 16 (44%) control dogs had a total WBC nadir occur at less than 100 cells/ul. Two of these 7 (29%) dogs did not survive (1 died, 1 euthanized). In the treatment group, 8/19 (42%) dogs had their total WBC nadir occur at less than 100 cells/ul. None of these dogs died. Comparison of significant decreases in white blood cells, neutrophils and lymphocytes on initial presentation and on Day 4 of hospitalization is shown in Figure 2. Based on the expected timeline of disease progression as previously described,11 Day 4 was chosen for this comparison to represent a period in time that should have encompassed neutrophil and clinical recovery for most dogs. In general, a higher percentage of treatment dogs versus control dogs fulfilled the criteria for significant decreases in initial white blood cells and neutrophil counts. However, by Day 4, more control dogs were significantly affected. When the clinical scores were compared day by day for each category as well as the cumulative total for that day, no significant differences were found between groups (Figures 3) with the exception of Day 6 for the appetite score (p=0.02). There was also a difference for attitude on Day 6, but this was not significant (p=0.086). Looking at the scores for dogs in each group as compared to their white blood cell counts on the same day (Table 2), it can be seen that the treatment dogs did have mildly improved scores across the board on Days 4 and 5 while also having a quicker rebound of WBC and neutrophil counts. Days 4 and 5 were chosen for examination for the same reason as stated above.

 DISCUSSION

Findings While the use of oseltamivir in addition to standard therapy for naturally occurring CPV enteritis did not exhibit a significant effect to help decrease hospitalization time, additional treatments needed or disease morbidity as determined by a clinical scoring system, it was shown to be associated with a significant increase in weight change versus control dogs from entry until discharge. The control dogs tended to lose weight, while the treatment dogs gained. This finding was not affected by the degree of dehydration at presentation, as it was found that there was no significant difference between the two groups in this variable. The importance and implications of this finding are unknown at this time. Other studies have shown that a significant change in weight in study subjects is also associated with an improved outcome. In one study using a mouse model of human influenza infection with secondary bacterial pneumonia, it was found that prophylactic treatment (i.e. dosage begun 4 hours prior to viral infection) with oseltamivir resulted in an average loss of only 5% of body weight in the mice, compared to an average of 25% loss in the placebo mice.18 This study also showed that all mice in the prophylactic oseltamivir group survived the viral and bacterial challenge, versus none of the mice in the placebo group.

A second study was investigating the effect of early enteral nutrition (EEN) on dogs with parvoviral enteritis.10 In this study, it was found that dogs in the EEN group had a significant increase in weight gain from entry on all days of the study, while the conventional group had no significant change in weight. In addition, dogs in the EEN group showed a more rapid clinical improvement, based on normalization of clinical scores, than did the conventional group. While the difference was not significant, it was also found that the 2 dogs that did not survive were both from the conventional group, giving it a survival rate of 87% compared to 100% for the EEN group. These survival statistics are very similar to those found in the present study. These results suggest that the significant change in weight associated with oseltamivir use in this study could imply that more significant beneficial effects on survival and/or disease recovery could also be a plausible effect of the oseltamivir that was not brought out here. The use of oseltamivir did not appear to be associated with any significant adverse effects. The main side effects reported in humans are gastrointestinal effects apparently due to direct local irritation of the gastric mucosa.15 In the experience of the authors, dogs will also often react to the taste of the oseltamivir suspension and nausea and vomiting can be encountered. Dilution with water just prior to administration appears to minimize these effects. This practice was utilized in this study in an effort to not only avoid uncovering group assignment and thereby instituting a bias, but also in an effort to keep the clinical scores an accurate representation of the disease process in the animal and not obscure these scores with drug reaction. Analysis of the clinical scores, specifically vomiting and appetite, did not show any difference between the treatment and control groups. This would tend to support the lack of any significant adverse effects of oseltamivir administration versus placebo in this patient population. The possibility that oseltamivir did have an effect to improve the clinical effects of CPV enteritis in the treatment dogs, but itself caused increased vomiting and nausea as a side effect of the drug and therefore concealed any benefit evident by analysis of the clinical scores does exist. However, subjective observation was that administration of the oral medications (oseltamivir or placebo) was not associated with initiating increased nausea or vomiting directly afterwards. This supports the interpretation of results indicating that side effects of oseltamivir were minimal, as were beneficial effects on decreasing disease morbidity. The intensity of treatment required and the expected cost of treatment were inferred based on additional therapy, such as colloid infusion or blood transfusions, as well as prolonged hospitalization times, which were needed. Colloids were not frequently used, in contrast to a previous report.26 Specifications for the institution of colloid therapy were not elucidated in the previous study.

Protocol in this study required significant decrease in total solids to 3.5g/dl. Much more modest decreases, often around 4.0 to 4.5g/dl, are frequently used in the clinic setting as indication for treatment with colloids. A higher cutoff value as a trigger for colloid infusion likely would have increased the incidence of its use in this study. Whether this increased use would translate into a difference in usage between groups is unknown, but seems unlikely based on the findings of a previous study showing no difference in albumin concentrations between an EEN group and a conventional therapy group.10 Blood transfusions were also rarely indicated. The 2 cases that did require a transfusion received fresh whole blood, rather than packed red blood cells. Packed red blood cell availability was very limited at the time of the first required transfusion. Fresh whole blood was collected from a donor dog and administered in its place. In order to minimize differences in treatment between dogs, when the second transfusion became necessary, although packed red blood cells were available, fresh whole blood from the previous donor was again administered. The total volume of crystalloids as well as colloids administered between the two groups may have been helpful to evaluate. Dogs experiencing greater fluid loss from vomiting and/or diarrhea as well as having less voluntary intake per os would have a greater intravenous fluid need. This would correlate with an increased severity of clinical signs and manifestation of the disease process. Unfortunately, the collection of this data had significant gaps or was outright missing from certain dogs due to recording error or technical difficulties. Therefore this value was not analyzed. The duration of clinical signs prior to presentation was not different between the groups. It has been reported that for human influenza viral infections, oseltamivir is most effective if started within the first 12 hours of clinical signs, with efficacy decreasing up to 48 hours.24 For every 6 hour delay in starting oseltamivir, the duration of illness is predicted to increase by approximately 8%.25 Whether this also holds true for its use in CPV enteritis is unknown. Because replication of CPV does not depend on neuraminidase, administration of oseltamivir in the early stages of infection is unlikely to diminish viral replication and dissemination as with the influenza virus, and thus a timeefficacy response is not expected. Rather, with the proposed mechanism against bacterial translocation, oseltamivir may have a greater impact when administered during the period of leukopenia and severe clinical signs. Further investigation is needed to expand on these speculations.

The treatment group may have been further along in their course of disease, despite the lack of difference in reported duration of clinical signs. This would be supported by the fact that this group, on average, had a slightly lower white blood cell and neutrophil counts at entry, as well as a somewhat quicker rebound after these numbers dropped. The clinical scores also showed the trend of quicker improvements in the treatment group. With the inherent inaccuracies of estimation of duration of clinical signs by the owner or caretaker, it is plausible that the times reported at entry were not correct, and that the treatment group did include dogs at a more advanced stage of disease. Conversely, if the reported duration of signs was accurate, the seemingly quicker recovery of the treatment dogs could be attributed to a beneficial effect of oseltamivir. A clinical scoring system was utilized in order to evaluate the subjective criteria of attitude and appetite, as well as to quantify the severity of vomiting and characterize the feces to allow for comparison across dogs. One investigator (MRS) had the responsibility of assigning scores to all dogs to minimize inter-observer variability. This investigator was also blinded to group assignment in order to minimize bias. Values for each category and cumulative scores were compared between the 2 groups for each day, and although mild trends could be seen for lower scores in the treatment group, there were no significant differences. This could be attributed to the small sample size in this study, as well as the variability in the timeline of illness among dogs. Since dogs presented in all stages of their disease (i.e. clinical symptoms for less than 12 hours to up to 4 days), a straight out comparison of scores per day may not illustrate true differences and a larger group would be needed to further examine this effect. In addition, the clinical scoring system utilized is a very simple system, and as such, was relatively insensitive in its ability to differentiate between various stages of aberrancy in each of the clinical attributes. There was not much room to allow for representation of subtle yet clinically significant differences. A scoring system with a greater degree of stratification between assigned values may allow for a greater sensitivity and a more accurate representation of the clinical status of the patient. CPV is not reliant on neuraminidase for replication. However, anecdotal reports of the use of oseltamivir in dogs with CPV enteritis have claimed decreased morbidity and shortened recovery time in the treated dogs. It is speculated that the drug may inhibit bacterial translocation that subsequently leads to endotoxemia, sepsis, SIRS and death. Bacterial adherence and colonization of respiratory epithelial cells is potentiated in the presence of viral NA, and inhibited with NA blocking agents.17-19 It is believed that the bacteria that commonly invade the lower respiratory tract express their own NA, thus enabling them to penetrate the protective mucin layer and infect the epithelial cells.17

Although unproven, a similar mechanism may exist in the gastrointestinal tract. Oseltamivir may exert a beneficial effect by inhibiting NA on enteric bacteria, preventing their translocation across the gastrointestinal mucosal barrier. In CPV enteritis, the mucosal barrier is already impaired, allowing easier passage of bacteria. If bacterial NA plays a role similar to that in the lungs, the NA would cleave sialic acid residues on the gut epithelium, exposing receptor sites for bacterial adherence and further encouraging translocation. In addition, CPV suppresses the dogís immune system, both humoral and cell-mediated factors, allowing for systemic spread of bacteria and the resultant deleterious effects. Further studies are needed to accurately define the actual mechanism behind the observed anecdotal benefits of the use of oseltamivir to treat CPV enteritis. Limitations Limitations of this study do involve the concern of administration of an oral medication to a vomiting patient, and its variable systemic absorption in the face of a diseased gastrointestinal tract. Gastric emptying times are quicker for liquid substances as compared to solids, with gastric emptying starting as soon as 10-30 minutes after administration. The oseltamivir suspension thus has the probability of starting to move through the gastrointestinal system and being absorbed before an episode of vomiting occurs. In addition, the act of vomiting is reported to only empty 40-50% of stomach contents. This would suggest that even with the presence of vomiting, it is reasonable to expect that at least a portion of the drug will remain in the system. Early safety studies of oseltamivir show that it has a bioavailability of 73% in healthy dogs, with detectable levels of the drug in plasma within approximately 30 minutes after oral administration.27

Oseltamivir does require transformation to its active metabolite by esterases located within the liver, and to a certain degree, within the intestinal system. 27, 28 The importance of the intestinal system esterases is unknown. Due to this need for transformation, it is believed that oseltamivir effects are not due to a purely local action, but do require systemic distribution. The effect of a diseased gastrointestinal system such as that seen in CPV enteritis on the absorption, systemic distribution and transformation is unknown at this time and future pharmacokinetic studies, in this situation especially, are needed. The reasoning behind any beneficial effect of oseltamivir in the treatment of CPV enteritis suggests that it helps decrease bacterial translocation and therefore the ensuing endotoxemia, SIRS and MODS that can develop. In this study, although certain physical and clinic pathologic parameters were monitored, there was no direct test for the presence of bacterial translocation or sepsis. SIRS criteria were evaluated, but this is a fairly crude assessment, especially considering the confounding factors. As the dogs were starting to  feel better, they would oftentimes become very excitable when being handled. This frequently resulted in an elevation of their heart rate to over 140 bpm, or their respiratory rate to greater than 40/min. The presence of these two variables would classify these healthy, excitable puppies as being positive for SIRS. In addition, the effect of the virus itself on the white blood cell count confounds the definition slightly. A WBC of less than 6,000 cells/ul can simply reflect destruction of progenitor cells in the bone marrow and is not necessarily associated with systemic inflammation. Other methods to evaluate for the presence of bacterial translocation, endotoxemia or SIRS would be more fruitful. Culture of mesenteric lymph nodes is considered the gold standard in human medicine and animal models for evaluation of bacterial translocation.29 The feasibility of this procedure in this patient population (client-owned, live animals) and setting is questionable. Other methods, such as blood cultures or measurement of serum endotoxin levels or other inflammatory mediators may provide a more accessible method for differentiating animals in which bacterial translocation is present from those in which it is not. Further investigation would be needed before any true conclusions can be made.

 CONCLUSIONS

CPV enteritis can be a devastating disease process. The financial constraints often encountered with treatment can be very frustrating given the treatable nature of this disease. Despite the anecdotal reports touting the success of oseltamivir to decrease the disease morbidity and mortality of CPV enteritis, scientific evidence of this was not found in this study. However, a significant difference in the change in body weight during hospitalization stay was established, as was the apparent safety of the drug in this 31 patient population. It is believed that, given the paucity of adverse side effeccts and the findings presented in this study, further investigation is warranted not only for its effects in CPV enteritis, but possibly any disease state in which bacterial translocation is a concern.

REFERENCES:

1. Hoskins JD. Canine viral enteritis, in Greene CE, 2nd Ed (ed): Infectious disease of the dog and cat. Philadelphia, WB Saunders, 1998, pp40-44. 2. Otto CM, Jackson CB, Rogell EJ, et al. Recombinant bactericidal/permeabilityincreasing protein for treatment of parvovirus enteritis: a randomized, doubleblinded, placebo-controlled trial. J Vet Intern Med 2001; 15:355-360. 3. Kariuki Njenga M, Nyaga PN, Buoro IBJ, Gathumbi PK. Effectiveness of fluids and antibiotics as supportive therapy of canine parvovirus-2 enteritis in puppies. Bull Anim Health Pod Afr 1990; 38:379-389. 4. Glickman LT, Domanski LM, Patronek GJ, et al. Breed-related risk factors for canine parvovirus enteritis. J Am Vet Med Assoc 1985; 187:589-594. 5. Macintire DK, Smith-Carr S. Canine parvovirus part II. Clinical signs, diagnosis, and treatment. Comp Cont Ed Pract Vet 1997; 19(3):291-302. 6. Otto CM, Drobatz KJ, Soter C. Endotoxemia and tumor necrosis factor activity in dogs with naturally occurring parvoviral enteritis. J Vet Intern Med 1997; 11:65- 70. 7. Mann FA, Boon GD, Wagner-Mann CC, et al. Ionized and total magnesium concentrations in blood from dogs with naturally acquired parvoviral enteritis. J Am Vet Med Assoc 1998; 212:1398-1401. 8. Rewerts JM, McCaw DL, Cohn LA, et al. Recombinant human granulocyte colony-stimulating factor for treatment of puppies with neutropenia secondary to canine parvovirus infection. J Am Vet Med Assoc 1998; 213:991-992. 9. Mischke R, Barth T, Wohlsein P, et al. Effect of recombinant human granulocyte colony-stimulating factor on leukocyte count and survival rate of dogs with parvoviral enteritis. Res Vet Sci 2001; 70:221-225. 10. Mohr AJ, Leisewitz AL, Jacobson LS, et al. Effect of early enteral nutrition on intestinal permeability, intestinal protein loss, and outcome in dogs with severe parvoviral enteritis. J Vet Intern Med 2003; 17:791-798. 11. Cohn LA, Rewerts JM, McCaw D, et al. Plasma granulocyte colony stimulating factor concentrations in neutropenic, parvoviral enteritis-infected puppies. J Vet Intern Med 1999; 13:581-586. 12. Dimmitt R. Clinical experience with cross-protective antiendotoxin antiserum in dogs with parvoviral enteritis. Canine Pract 1991; 16:23-26. 13. De Mari K, Maynard L, Eun HM, et al. Treatment of canine parvoviral enteritis with interferon-omega in a placebo-controlled field trial. Vet Rec 2003; 152:105- 108. 14. Martin V, Najbar W, Gueguen S, et al. Treatment of canine parvoviral enteritis with interferon-omega in a placebo-controlled challenge trial. Vet Micro 2002; 89:115-127. 15. Gubareva LV, Kaiser L, Hayden FG. Influenza virus neuraminidase inhibitors. Lancet 2000; 335:827-835. 16. Kaiser L, Wat C, Mills T, Mahoney R, Ward P, Hayden F. Impact of oseltamivir treatment on influenza-related lower respiratory tract complications and hospitalizations. Arch Intern Med 2003; 163:1667-1672. 17. McCuller JA, Bartmess KC. Role of neuraminidase in lethal synergism between influenza virus and Streptococcus pneumoniae. J Infect Dis 2003; 187:1000- 1009. 18. McCullers JA. Effect of antiviral treatment on the outcome of secondary bacterial pneumonia after influenza. J Infect Dis 2004; 190:519-526. 19. Peltola VT, Murti KG, McCullers JA. Influenza virus neuraminidase contributes to secondary bacterial pneumonia. J Infect Dis 2005; 192:249-257. 20. Bhatia A, Kast RE. How influenzaís neuraminidase promotes virulence and creates localized lung mucosa immunodeficiency. Cell & Mole Bio Letters 2007; 12:111-119. 21. Matheson NJ, Harden AR, Perera R, Sheikh A, Symmonds-Abrahams M. Neuraminidase inhibitors for preventing and treating influenza in children (review). Cochrane Lib 2007; 1:1-40. 22. Turk J, Miller M, Brown T, er al. Coliform septicemia and pulmonary disease associated with canine parvoviral enteritis: 88 cases (1987-1988). J Am Vet Med Assoc 1990; 196:771-773. 23. Smith-Carr S, Macintire DK, Swango LJ. Canine parvovirus part I. Pathogenesis and vaccination. Comp Cont Ed Pract Vet 1997; 19(2):125-132. 36 24. Houston DM, Ribble CS, Head LL. Risk factors associated wiith parvovirus enteritis in dogs: 283 cases (1982-1991). J Am Vet Med Assoc 1996; 208:542- 546. 25. Gillissen A, Hoffken G. Early therapy with the neuraminidase inhibitor oseltamivir maximizes its efficacy in influenza treatment. Med Microbiol Immunol 2002; 191:165-168. 26. Mantione NL, Otto CM. Characterization of the use of antiemetic agents in dogs with parvoviral enteritis treated at a veterinary teaching hospital: 77 cases (1997- 2000). J Am Vet Med Assoc 2005; 227:1787-1793. 27. Li W, Escarpe PA, Eisenberg EJ, Cundy KC, Sweet C, et al. Identification of GS 4104 as an orally bioabailable prodrug of the influenza virus neuraminidase inhibitor GS 4071. Antimicrob Agents Chemother 1998; 42:647-653. 28. He G, Massarella J, Ward P. Clinical pharmacokinetics of the prodrug oseltamivir and its active metabolite Ro 64-0802. Clin Pharmacokinet 1999; 37:471-484. 29. Gatt M, Reddy BS, Macfie J. Review article: bacterial translocation in the critically ill ñ evidence and methods of prevention. Aliment Pharmacol Ther 2007; 25:741-757.

No hay comentarios:

Publicar un comentario en la entrada