Wolbachia and its influence on the pathology and immunology of Dirofilaria immitis infection

Since the definitive identification in 1995 of the bacterial endosymbiont Wolbachia that resides in different tissues of the filarial worm Dirofilaria immitis, there has been increasing interest to understand whether and what role it plays in the pathogenesis of and immune response to heartworm infection. The present study evaluated the effects of treatments on lung pathology in 20 beagle dogs experimentally infected with D. immitis. Dogs in Group 1 were treated with doxycycline (10 mg/kg/day) orally from weeks 0-6, 10-12, 16-18, 22-26, and 28-34. Dogs in Group 2 served as infected, non-treated controls. Dogs in Group 3 were given doxycycline as described for Group 1 combined with weekly oral doses of ivermectin (6 mcg/kg) for 34 weeks and intramuscular (IM) melarsomine (2.5 mg/kg) at week 24, followed by two additional melarsomine injections 24h apart 1 month later. Group 4 received only melarsomine as described for Group 3. Lung lesion criteria, scored by two independent blinded pathologists, included perivascular inflammation and endothelial proliferation. Doxycycline treatment alone had no effect on lesion scores, whereas the combination of doxycycline and ivermectin resulted in less severe perivascular inflammation. All lungs were evaluated for positive immunostaining for the Wolbachia surface protein (WSP). Control dogs showed numerous thrombi, intense perivascular and interstitial inflammation and, occasionally, positive staining for WSP. Interestingly, dogs receiving doxycycline/ivermectin/melarsomine showed significantly less severe arterial lesions and the virtual absence of thrombi.     

Heartworm and Wolbachia: therapeutic implications

A safer, more effective adulticidal treatment and a safe method for reducing microfilaremia and breaking transmission of heartworm disease early in the treatment are needed. The present study evaluated efficacy of ivermectin (IVM) and doxycycline (DOXY) alone or together (with or without melarsomine [MEL]) in dogs with induced adult heartworm infection and assessed the ability of microfilariae from DOXY-treated dogs to develop to L3 in Aedes aegypti mosquitoes and subsequently to become reproductive adults in dogs. Thirty beagles were each infected with 16 adult heartworms by intravenous transplantation. Six weeks later, dogs were ranked by microfilarial count and randomly allocated to 6 groups of 5 dogs each. Beginning on Day 0, Group 1 received IVM (6 mcg/kg) weekly for 36 weeks. Group 2 received DOXY (10 mcg/(kgday)) orally Weeks 1-6, 10-11, 16-17, 22-25, and 28-33. Groups 3 and 5 received IVM and DOXY according to doses and schedules used for Groups 1 and 2. At Week 24, Groups 3 and 4 received an intramuscular injection of MEL (2.5 mg/kg), followed 1 month later by two injections 24h apart. Group 6 was not treated. Blood samples were collected for periodic microfilaria counts and antigen (Ag) testing (and later immunologic evaluation and molecular biology procedures). Radiographic and physical examinations, hematology/clinical chemistry testing, and urinalysis were done before infection, before Day 0, and periodically during the treatment period. At 36 weeks, the dogs were euthanized and necropsied for worm recovery, collection of lung, liver, kidney, and spleen samples for examination by immunohistochemistry and conventional histological methods. All dogs treated with IVM + DOXY (with or without MEL) were amicrofilaremic after Week 9. Microfilarial counts gradually decreased in dogs treated with IVM or DOXY, but most had a few microfilariae at necropsy. Microfilarial counts for dogs treated only with MEL were similar to those for controls. Antigen test scores gradually decreased with IVM + DOXY (with or without MEL) and after MEL. Antigen scores for IVM or DOXY alone were similar to controls throughout the study. Reduction of adult worms was 20.3% for IVM, 8.7% for DOXY, 92.8% for IVM + DOXY + MEL, 100% for MEL, and 78.3% for IVM + DOXY. Mosquitoes that fed on blood from DOXY-treated dogs had L3 normal in appearance but were not infective for dogs. Preliminary observations suggest that administration of DOXY+IVM for several months prior to (or without) MEL will eliminate adult HW with less potential for severe thromboembolism than MEL alone.     

Effects of doxycycline on early infections of Dirofilaria immitis in dogs

The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be highly effective against L(3) and L(4) of Brugia pahangi and Litomosoides sigmodontis in rodent models. Tetracyclines are also now known to have activity against microfilariae and adult Dirofilaria immitis, but assessment of their activity against larval and juvenile heartworms has not been reported previously. This study assessed the effects of doxycycline administered orally at 10mg/kg twice daily for 30-day periods at selected times during the early part of the life cycle of D. immitis in dogs with dual infections of D. immitis and B. pahangi. Twenty beagles were randomly allocated by weight to four groups of five dogs each. On Day 0, each dog was given 50 D. immitis L(3) and 200 B. pahangi L(3) by SC injection. Dogs received doxycycline on Days 0-29 (Group 1); Days 40-69 (Group 2); or Days 65-94 (Group 3). Group 4 served as untreated controls. Blood samples were collected for microfilariae counting and antigen testing. Necropsy for collection of adult heartworms and selected tissues were performed Days 218-222. Heartworms recovered were examined by immunohistology, conventional microscopy/transmission electron microscopy, and molecular biology techniques. No live heartworms were recovered from dogs in Group 1; dogs in Group 2 had 0 to 2 live worms (98.4% efficacy), and dogs in Group 3 had 0-36 live worms (69.6% efficacy). All control dogs had live adult heartworms (25-41). The live worms recovered from dogs in Groups 2 and 3 were less developed and smaller that worms from control dogs. Microfilariae were not detected in any dogs in Groups 1 and 2; one dog in Group 3 had 1 microfilariae/ml at necropsy. All control dogs had microfilariae at necropsy. One dog in Group 1 was antigen positive at one sampling (Day 166). One dog in Group 2 was antigen positive Days 196 and 218-222 and three dogs in Group 3 were antigen positive at one or more samplings All five control dogs were antigen positive at all three sampling times. These findings suggest that doxycycline at 10mg/kg orally twice daily for 30 days has efficacy against migrating tissue-phase larvae and juvenile worms and will delay or restrict microfilarial production.     

Diagnostic, treatment, and prevention protocols for canine heartworm infection in animal sheltering agencies

The high prevalence of heartworm infection in shelter dogs creates a dilemma for shelter managers, who frequently operate with insufficient funding, staffing, and expertise to comply with heartworm guidelines developed for owned pet dogs. The purpose of this study was to survey canine heartworm management protocols used by 504 animal sheltering agencies in the endemic states of Alabama, Florida, Georgia, and Mississippi. Open-admission shelters, which tended to be larger and more likely to perform animal control functions, were less likely (41%) to test all adult dogs than were limited-admission shelters (80%), which tended to be smaller non-profit humane agencies, and foster programs (98%) based out of private residences. Open-admission shelters were more likely to euthanize infected dogs (27%) or to release them without treatment (39%), whereas limited-admission shelters and foster programs were more likely to provide adulticide therapy (82% and 89%, respectively). Of the 319 agencies that treated infections, 44% primarily used a standard two-dose melarsomine protocol, and 35% primarily used a three-dose split-treatment melarsomine protocol. Long-term low-dose ivermectin was the most common treatment used in 22% of agencies. Open-admission shelters were less likely (35%) to provide preventive medications for all dogs than were limited-admission shelters (82%) and foster programs (97%). More agencies used preventives labeled for monthly use in dogs (60%) than ivermectin products labeled for livestock (38%). The most common reason diagnostic testing and preventive medication was not provided was cost. These results indicate a lack of protocol uniformity among agencies and insufficient resources to identify, treat, and prevent infection. Sheltering agencies and companion animal health industries should develop guidelines that are feasible for use in sheltering agencies and provide improved access to preventive and treatment strategies for management of Dirofilaria immitis.     

Validation of chemoprevention of canine monocytic ehrlichiosis with doxycycline

Epidemiological (cohort follow-up) and laboratory techniques studies were done to validate a programme of chemoprevention of canine monocytic ehrlichiosis (CME) with this molecule. 614 dogs returning to France after having spent at least 4 months in a CME-endemic area (Africa, Guyana, Middle-East, etc.) were the object of systematic serological testing by indirect immunofluorescence (IFA). The dogs were given 100 mg of doxycycline per os daily for chemoprevention of CME. In addition, HPLC (high performance liquid chromatography) was used to determine plasma levels of doxycycline in 124 of the dogs. The CEM mortality and morbidity rates for the 614 dogs in the chemoprevention programme were nil. The seroconversion rate was 4% (24/614). Seropositive dogs (low titres) were asymptomatic and generally became seronegative after treatment. A study done on 10 dogs shows that doxycyclinaemia was 1.2 (0.94-1.53) microg/ml 2 h after the drug had been administered. After 24 h, the residual concentration was 0.34 (0.26-0.44) microg/ml. Blind doxycyclinaemia tests done on 110 dogs living in Africa (the results for four dogs were nil and therefore eliminated from the study) showed that the minimum observed concentration was always greater than 0.2 microg/ml. Given that, as concerns infection with Ehrlichia spp., the minimum inhibitory concentration of doxycycline is < or = 0.03 microg/ml, dogs receiving chemoprevention treatment should be protected.     

Influence of the route of administration on efficacy and tissue distribution of ivermectin in goat

The tissue concentration and efficacy of ivermectin after per os and subcutaneous administration were compared in goats experimentally infected with Trichostrongylus colubriformis (ivermectin-susceptible strain, INRA). Infected goats (n = 24) were treated per os (n = 9) or subcutaneously (n = 9) with ivermectin, 0.2 mg/kg, or kept as not treated controls. The faecal egg counts and small intestine worm counts were determined. Ivermectin concentration was measured in the plasma, gastrointestinal tract, lung, skin or hair, liver and adipose tissues at 0, 2, 7 and 17 days post-treatment. The efficacy of ivermectin against T. colubriformis infection in goat was 98.7 and 99.9% for subcutaneous and oral administration, respectively. Ivermectin concentration declined with time and only residual concentration was measured at 17 days post-treatment in plasma and gastrointestinal tract. Ivermectin concentration was higher after subcutaneous compared to per os injection in most of the tissue examined. In skin, hair and subcutaneous adipose tissue ivermectin persisted at significant concentrations 17 days post-treatment for both routes of administration. In our experimental conditions, ivermectin provides similar efficacy against T. colubriformis after subcutaneous or per os administration in goat. However, the lower ivermectin levels in tissues after per os administration suggest that the lasting of efficacy may be shortened after per os compared to subcutaneous administration especially in animals with poor body condition in pasture where re-infection occurs quickly after anthelmintic treatment.     

Pharmacokinetics of doxycycline in dogs.

Six adult dogs were given doxycycline hyclate at a dosage of 5 mg/kg of body weight intravenously so that pharmacokinetic parameters could be evaluated. Serum doxycycline concentrations were determined over a 48 h period using a modified agar well bioassay. Compartmental pharmacokinetic evaluation of the serum concentration time data indicated that doxycycline has a half-life of 10.36 h, a body clearance of 1.68 +/- 0.44 mL/min/kg, and a volume of distribution at steady state of 1.468 +/- 0.237 L/kg. Doxycycline pharmacokinetics are favorable for therapeutic use in the dog.     

Antimicrobial disposition in pulmonary epithelial lining fluid of horses, part II. Doxycycline

Doxycycline concentrations, following two types of oral administration to horses, in pulmonary epithelial lining fluid (PELF) were examined and compared to plasma concentrations. The oral bioavailability was estimated from plasma concentrations achieved after an intravenous study in two horses. Doxycycline (10 mg/kg) was administered either intragastric or as topdressing to nonfasted horses. Blood samples were collected for drug analysis, before and 11 times after administration during 24 h. PELF samples were collected by a tampon device four times after drug administration and analysed for doxycycline concentrations. Another two horses received doxycycline intravenously at a dose of 3 mg/kg and plasma was taken 14 times during a 24- h period. The oral bioavailability of doxycycline was calculated to 17% after intragastric administration and 6% after topdressing administration in nonfasted horses. The degree of penetration of doxycycline into PELF, as described by AUC(PELF) /AUC(plasma) ratios, was 0.87 after intragastric administration. The results indicate that clinically relevant doxycycline concentrations are possible to maintain in PELF after intragastric administration. Furthermore, if bioavailability could be enhanced for per os administration, doxycycline might be a valuable drug for the treatment of lower airway infections in horses.     

Prospective comparative study of 3 treatment protocols using doxycycline or imidocarb dipropionate in dogs with naturally occurring ehrlichiosis

This paper reports the clinicopathologic responses of 93 dogs with spontaneously occurring ehrlichiosis to 3 different treatment protocols. Thirty-two dogs were treated with doxycycline (10 mg/kg/day for 28 days), 31 were treated with imidocarb dipropionate (5 mg/kg given 15 days apart in 2 separate injections), and 30 were treated with both drugs simultaneously, at the doses as specified. The dogs underwent clinicopathologic evaluation before and after treatment, and were examined periodically during the 24-month period after the treatment. No differences were found in the clinical responses among the dogs in the 3 treatment groups. As for the clinicopathologic response, in spite of the fact that at the end of the study the results obtained with the 3 protocols were similar, the platelet count and serum protein electrophoresis results returned to normal more slowly in dogs that received imidocarb dipropionate as compared to those given the other 2 treatments.     

Assessment of toxicosis induced by high-dose administration of milbemycin oxime in collies

Fifteen Collies, previously having mild reactions to ivermectin challenge (120 micrograms/kg of body weight; 20 times the recommended dosage level), were studied to evaluate the effects of milbemycin oxime administration at 5 and 10 mg/kg (10 and 20 times the manufacturer's recommended dosage). Five replicates, comprising 3 dogs each, were formed on the basis of body weight. Within replicates, each dog was randomly allocated to treatment with 5 or 10 mg of milbemycin/kg or served as a untreated control. Dogs were examined repeatedly for signs of toxicosis for 4 days after treatment and daily thereafter. Two of 5 dogs treated at 5 mg/kg (10x) developed signs of mild depression on the day of treatment, but were normal 24 hours after treatment. All 5 dogs treated at 10 mg/kg (20x) developed signs of mild depression and ataxia by 6 hours. Signs persisted for 24 hours in 3 dogs. Two of these dogs also had mydriasis, whereas 3 salivated excessively. All dogs recovered completely by day 2 after treatment. The results of this study demonstrated that Collies sensitive to the effects of 120 micrograms of ivermectin (20x)/kg show similar sensitivity to the effects of milbemycin oxine administered at 10 mg/kg (20x). We conclude that ivermectin and milbemycin commercial formulations have similar margins of safety and that milbemycin toxicosis appears to be dose-dependent in Collies with a demonstrated sensitivity to ivermectin.     

Efficacy of an adulticide used alone or in combination with an insect growth regulator for flea infestations of dogs housed in simulated home environments.

OBJECTIVE: To determine the effect of an adulticide on flea populations of dogs and to evaluate efficacy of combined use of the adulticide and an insect growth regulator (IGR) in dogs with experimentally induced flea infestations. ANIMALS: 40 adult Beagles. PROCEDURE: Each group of 5 dogs was housed in a separate room. Each dog was infested 3 times with 50 fleas, and fleas were counted beginning on day -21. Groups of dogs and treatments (initiated on day 0) were as follows: 1, adulticide once; 2, adulticide on days 0 and 7; 3, adulticide on days 0, 3, and 7; 4, sham treatment; 5, IGR monthly; 6, IGR monthly plus adulticide once weekly for 6 weeks; 7, IGR monthly plus adulticide twice weekly for 6 weeks; 8, sham treatment. Flea counts were compared between treated and control dogs. RESULTS: By 24 hours after initial treatment, all adult fleas but 1 were dead in treated dogs. In groups 1 and 3, populations increased to 15 to 20 fleas/dog 2 months after treatment, compared with 48 fleas/dog in group 4. After treatment, mean flea counts were significantly lower for groups 1, 2, and 3, relative to group 4. Efficacy of treatment for group 5, relative to group 8, was > 94% after day 84. Efficacy of treatment for groups 6 and 7 was 99% after day 28. CONCLUSIONS AND CLINICAL RELEVANCE: Treatment with adulticide alone or in combination with an IGR had better efficacy, compared with sham treatment or IGR alone. Administration of adulticide twice weekly was not more efficacious than treatment once weekly.     

The curative and antioxidative efficiency of ivermectin and ivermectin + vitamin E-selenium treatment on canine <Emphasis Type="Italic">Sarcoptes scabiei</Emphasis> infestation

The objective of the present study was to investigate the curative and antioxidative efficacy of ivermectin and ivermectin + vitamin E-selenium, and the influence of these agents on oxidative stress parameters in canines infested by Sarcoptes scabiei. Twenty two sarcoptic mites infested dogs and nine healthy dogs of 6 months to 2 years of age were divided into three groups. Group I comprised of healthy dogs (n = 9) whereas animals in group II (n = 11) and III (n = 11) were positive for scabies. Group II animals were treated with only 1% ivermectin @ 0.2 mg/kg SC whereas group III were additionally treated with Vitamin E and selenium (tocopherol 50 mg + Se 1.5 mg/ml) @0.5 ml/20 kg IM at weekly intervals for three times. Blood samples were collected on day 0 and 28 post therapy. The values for hemato-biochemical parameters and activities of antioxidant enzymes were significantly decreased (P < 0.05) whereas level of lipid peroxidation was significantly increased in all the infested dogs in comparison to the healthy dogs on day 0 which approached normalcy by day 28 post therapy. The dogs of group III showed better clinical recovery in comparison to group II at the end of therapy. Thus, administration of vitamin E and selenium in addition to standard therapy can alleviate these alterations hastening the clinical recovery of diseased dogs and can be recommended as an adjunct therapy with miticides for canine sarcoptic mange.     

Comparison of anthelmintic control programs for sheep in Virginia.

Haemonchus contortus is the most serious parasitic problem encountered by sheep producers in southwestern Virginia. Four anthelmintic control programs for grazing lambs were tested. Group TR received monthly SC injections of ivermectin (200 micrograms/kg of body weight). Group SI received the same dose of ivermectin at 0, 3, 6, 9, and 12 weeks after the start of the grazing season. Group SL was given levamisole (8 mg/kg, PO) 0, 3, 6, 9, and 12 weeks after the start of the grazing season, and group TA received ivermectin (200 micrograms/kg) 0, 8, 16, 20, and 24 weeks after the beginning of grazing. None of the 4 programs provided satisfactory control of parasites as indicated by fecal egg counts and serum pepsinogen concentrations, although group-TR lambs gained significantly more weight than lambs in groups SI and TA. Group-TA lambs developed clinical haemonchosis in early August and required additional treatment at that time. These findings suggest that reliance on anthelmintics alone may not provide the most effective and economic control of parasitic infection.     

Suspected side effects of doxycycline use in dogs - a retrospective study of 386 cases

This study investigated doxycycline-related side effects in a large population of dogs. Data from 386 dogs that had received doxycycline for the treatment of various infectious diseases were analysed retrospectively. Potential side effects that developed during treatment were documented, and correlations with signalment, dose, duration of treatment, frequency of application, doxycycline preparation and use of additional drugs were investigated. Vomiting was reported in 18.3 per cent of dogs, 7.0 per cent developed diarrhoea and 2.5 per cent developed anorexia. While being treated with doxycycline, 39.4 per cent of dogs showed an increase in alanine aminotransferase (ALT) activity and 36.4 per cent showed an increase in alkaline phosphatase (ALP) activity. There was a dose-related risk of an increase in ALP activity (P=0.011, odds ratio [OR]=1.27, 95 per cent confidence interval [CI] 1.06 to 1.53), and older dogs treated with doxycycline were more likely to develop an increase in ALT activity (P=0.038, OR=1.23, 95 per cent CI 1.01 to 1.50) and vomiting (P=0.017, OR=1.11, 95 per cent CI 1.02 to 1.21).     

Study of ehrlichiosis in kennel dogs under treatment and prevention during seven months in Dakar (Senegal)

In Dakar kennels where morbidity and mortality attributed to diseases transmitted by ticks were high, we conducted a field study to assess the prevalence of Ehrlichia canis, Anaplasma platys and Babesia spp. infections in two kennels (n = 34 dogs) and to study the impact of tick protection. The first day of the study, the E. canis PCR were positive in 18 dogs (53%). A. platys was found in one dog and all dogs were negative for Babesia spp. After one month of doxycycline treatment, the number of PCR positive dogs decreased significantly to 2 (5.9%). During seven months, all dogs were treated monthly topically with a novel combination (Certifect^®, Merial) delivering at least 6.7 mg fipronil/kg body weight, 8.0 mg amitraz/kg and 6 mg (S)-methoprene/kg. The number of PCR positive dogs remained stable all over the seven months, with 4 dogs being positive at Day 90 and 2 at Day 210. The combination of treatment and monthly prevention had a significant effect in the two kennels. All dogs remained healthy, which was not the case in previous years.     

Study of intragastric administration of doxycycline: pharmacokinetics including body fluid, endometrial and minimum inhibitory concentrations

The objectives of this study were to determine the pharmacokinetics and tissue concentrations of doxycycline after repeated intragastric administration, and to determine the minimum inhibitory concentrations (MIC) for equine pathogenic bacteria. In experiment 1, 2 mares received a single intragastric dose of doxycycline hyclate (3 mg/kg bwt). Mean peak serum concentration was 0.22 microg/ml 1 h postadministration. In experiment 2, 5 doses of doxycycline hyclate (10 mg/kg bwt), dissolved in water, were administered to each of 6 mares via nasogastric tube at 12 h intervals. The mean +/- s.e. peak serum doxycycline concentration was 0.32+/-0.16 microg/ml 1 h after the first dose and 0.42+/-0.05 microg/ml 2 h after the fifth dose. The mean trough serum concentrations were > 0.16 microg/ml. Highest mean synovial concentration was 0.46+/-0.13 microg/ml and highest mean peritoneal concentration was 0.43+/-0.07 microg/ml, both 2 h after the fifth dose. Highest urine concentration was mean +/- s.e. 145+/-25.4 microg/ml 2 h after the last dose. Highest endometrial concentration was mean +/- s.e. 1.30+/-0.36 microg/ml 3 h after the fifth dose. Doxycycline was not detected in any of the CSF samples. Mean +/- s.e. Vd(area) was 25.3+/-5.0 l/kg and mean t1/2 was 8.7+/-1.6 h. In experiment 3, minimum inhibitory concentrations of doxycycline were determined for 168 equine bacterial culture specimens. The MIC90 was < or = 1.0 microg/ml for Streptococcus zooepidemicus and 0.25 microg/ml for Staphylococcus aureus. Based on drug concentrations achieved in the serum, synovial and peritoneal fluids and endometrial tissues and MIC values determined in the present study, doxycycline at a dose of 10 mg/kg bwt per os every 12 h may be appropriate for the treatment of infections caused by susceptible (MIC < 0.25 microg/ml) gram-positive organisms in horses.     

Efficacy of thiabendazole, mebendazole, levamisole and ivermectin against gullet worm, Gongylonema pulchrum: in vitro and in vivo studies

In vitro and in vivo studies were conducted to evaluate the effects of thiabendazole, mebendazole, levamisole and ivermectin against Gongylonema pulchrum. For in vitro assays, third-stage larvae (L3) incubated with the drugs were administered orally to mice and the ability of larvae to invade the gastric mucosa of the animals was examined. After incubation, only those larvae treated with high concentrations of levamisole (1 and 10 microg/ml) were tightly coiled with intestines exhibiting morphological abnormalities. Good dose-response data for the drugs tested was observed at the time of worm recovery from mice, with no worms recovered at the two highest concentrations of levamisole. In vivo efficacy of the drugs against adult worms was evaluated in six groups of three rabbits, each of which was infected with 30 L3 of G. pulchrum and treated with thiabendazole at 100 mg/kg for 3 days, mebendazole at 70 mg/kg for 3 days, levamisole as a single dose of 8 mg/kg, and subcutaneously injected ivermectin as a single dose of 0.2 mg/kg or vehicles of the drugs (control) at 4 months post-infection. Necropsy 14 days after treatment revealed that levamisole, mebendazole and ivermectin reduced worm burdens by 63.2%, 22.8% and 25.8%, respectively, with no reductions in worms observed with thiabendazole. The surviving worms were principally found in the esophagus with the remainder distributed among the buccal mucosa, the tongue, and/or pharyngeal mucosa in all groups. A number of morphologically abnormal eggs were observed within the uterus and ovijector in female worms recovered from the thiabendazole-treated group. These findings suggest that levamisole exhibits in vivo efficacy against G. pulchrum infection and that the larval invasion tests using mice could be used to screen for anthelmintic susceptibility of nematodes.     

Theophylline does not potentiate the effects of a low dose of dexamethasone in horses with recurrent airway obstruction

REASONS FOR PERFORMING STUDY: Theophylline has been shown to have corticosteroid-sparing effects for the treatment of human asthma. A similar effect, if present in horses, would allow diminishing the dose of corticosteroids administered to equine patients with inflammatory airway diseases. OBJECTIVES: To evaluate whether theophylline potentiates the effects of a low dose of dexamethasone when treating horses with recurrent airway obstruction (RAO). HYPOTHESIS: Theophylline has steroid-sparing effects in horses with RAO. METHODS: Ten mature mixed breed horses in clinical exacerbation of RAO were studied. Using an incomplete crossover design and 3 experimental periods of 7 days duration, horses were distributed randomly in 5 treatment groups; and administered dexamethasone s.i.d., at either 0.05 mg/kg bwt i.v. or per os, or 0.02 mg/kg bwt alone or combined with theophylline at 5 mg/kg bwt per os b.i.d. A fifth group was treated with theophylline alone at the above dosage. Lung function was evaluated prior to drug administration and then 3 and 7 days later. RESULTS: Oral administration of dexamethasone alone or combined with theophylline failed to improve lung function significantly in RAO affected horses. Theophylline alone also failed to improve lung function in all treated horses. Conversely, dexamethasone administration at 0.05 mg/kg bwt i.v. resulted in a significant improvement in lung function starting on Day 3. CONCLUSIONS AND POTENTIAL RELEVANCE: Oral theophylline for 7 days did not improve the effects of a low dose of dexamethasone for the treatment of horses with RAO.     

Cyclophosphamide exerts no beneficial effect over prednisone alone in the initial treatment of acute immune-mediated hemolytic anemia in dogs: a randomized controlled clinical trial

Cyclophosphamide is commonly used with prednisone in the initial treatment of severe idiopathic immune-mediated hemolytic anemia (IMHA) in dogs because retrospective reports suggest its benefit. This randomized controlled prospective clinicaltrial evaluated whether combined cyclophosphamide and prednisone therapy is more efficacious than prednisone therapy alone in the initial treatment of IMHA. Eighteen dogs with acute, severe idiopathic IMHA were randomly assigned to 1 of 2 treatment groups. The P group received prednisone therapy alone (1-2 mg/kg PO q12h), and the PC group received prednisone (1-2 mg/kg PO q12h) and cyclophosphamide (50 mg/m2 PO q24h for 4 consecutive days a week) for 4 weeks. The mortality rate in the P group was 20% (2 of 10), and in the PC group, the mortality rate was 38% (3 of 8). There was no difference in sequential CBC evaluations between the 2 groups. However, whereas dogs in the P group showed increases in reticulocyte count, reticulocytosis was suppressed in dogs in the PC group during the 1st week of therapy. Spherocytosis resolved more quickly in the P group (day 21) than in the PC group (day 28), but the time taken to achieve a negative Coombs' test result was comparable between groups. No difference was observed in the volume of packed red blood cells (pRBCs) given per transfusion between treatment groups, but more dogs in the PC group required a 2nd transfusion. The results of this limited study suggest that cyclophosphamide plus prednisone has no benefit over prednisone alone in the initial treatment of acute, severe idiopathic IMHA indogs.