Pharmacokinetics of pentoxifylline and its 5-hydroxyhexyl metabolite after oral and intravenous administration of pentoxifylline to healthy adult horses

Effect of pentoxifylline on the testicular hemodynamic, volume, testosterone, nitric oxide levels and semen quality in Ossimi rams during non breeding-season

During the non-breeding season, Ossimi rams have testicular regression, including reductions in blood flow, size and spermatogenesis. The objective was to determine the effect of pentoxifylline (PTX) on Ossimi rams during the non-breeding season. Fifteen sexually mature Ossimi rams were allotted to three groups: (1) G0 (n = 5) control group (basic diet, no PTX); (2) G1 (n = 5) 10 mg/kg BW PTX; and (3) G2 (n = 5) 20 mg/kg BW PTX. The PTX was given orally once daily for 7 weeks (wk1 to wk7), whereas ultrasonographic assessment of testes, and collection of semen and blood started 1 week before PTX and were done weekly for 8 weeks (wk0 to wk7). In G2, there was a decrease(P < 0.05) in both Doppler indices (resistive index, pulsatility index) in G2 from wk2 to wk4 and an increase(P < 0.05) in ultrasonographic testicular coloration from wk2 to wk7. Moreover, G2 had the highest (P < 0.05) testicular volume (wk5 to wk7), individual motility, sperm viability and acrosome integrity (wk4 to wk7) and sperm cell concentration (wk6 and wk7). Blood concentrations of testosterone and nitric oxide were increased (P < 0.05) concurrent with decreased Doppler indices. In conclusion, PTX enhanced testicular blood flow and volume, semen quality, and concentrations of testosterone and nitric oxide potential in Ossimi rams during the non-breeding season, with potential to ameliorate deleterious effects of heat stress and perhaps enhance ram fertility.

Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology

BACKGROUND

Allergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens.

OBJECTIVES

To review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention.

MATERIALS AND METHODS

The authors reviewed the literature up to November 2022. Results were presented at North America Veterinary Dermatology Forum (2021) and European Veterinary Dermatology Congress (2021). The report was available to member organisations of the World Association for Veterinary Dermatology for feedback.

CONCLUSIONS AND CLINICAL RELEVANCE

Insect bite hypersensitivity (IBH) is the best characterised allergic skin disease. An immunoglobulin (Ig)E response against Culicoides salivary antigens is widely documented. Genetics and environmental factors play important roles. Tests with high sensitivity and specificity are lacking, and diagnosis of IBH is based on clinical signs, seasonality and response to insect control. Eosinophils, interleukin (IL)-5 and IL-31 are explored as therapeutic targets. Presently, the most effective treatment is insect avoidance. Existing evidence does not support allergen-specific immunotherapy (ASIT) using commercially available extracts of Culicoides. Hypersensitivity to environmental allergens (atopic dermatitis) is the next most common allergy. A role for IgE is supported by serological investigation, skin test studies and positive response to ASIT. Prospective, controlled, randomised studies are limited, and treatment relies largely on glucocorticoids, antihistamines and ASIT based on retrospective studies. Foods are known triggers for urticaria, yet their role in pruritic dermatitis is unknown. Recurrent urticaria is common in horses, yet our understanding is limited and focussed on IgE and T-helper 2 cell response. Prospective, controlled studies on treatments for urticaria are lacking. Glucocorticoids and antihistamines are primary reported treatments.

Laminitis Updates: Sepsis/Systemic Inflammatory Response Syndrome-Associated Laminitis

Sepsis or systemic inflammatory response syndrome (SIRS) -associated laminitis is a sequela to primary inflammatory conditions (eg, colitis, ischemic intestinal injury, pneumonia, metritis) and results from a dysregulated systemic inflammatory response that ultimately affects the digital lamellae. Local chemokine production, leukocyte migration, and proinflammatory mediator production occur within the lamellae that can lead to catastrophic lamellar failure. Controlling the primary disease, providing supportive care and anti-inflammatory therapy, applying digital cryotherapy, and providing mechanical support are cornerstones to the prevention of sepsis/SIRS-associated laminitis. Novel therapies targeting specific signaling pathways may provide additional therapeutic options in the future.

Antenatal pentoxifylline therapy to prevent endotoxin-induced fetal injury in the preterm goat model

Objective:

Pentoxifylline (PTX) has immunomodulatory properties and is known to reduce sepsis-associated infant mortality. We aimed to evaluate maternal oral and intra-amniotic administration of PTX for the prevention of fetal inflammation and injury in a caprine model.

Materials and Methods:

Inflammation-mediated fetal injury was induced with maternal granulocyte-colony stimulating factor and intra-amniotic endotoxin at 0.76 of gestation in date-mated pregnant goats. Eight groups were formed (n=4 each): Control, fetal injury, oral 30 mg/kg/day and 60 mg/kg/day PTX for 15 days + fetal injury, intra-amniotic 400 mg/kg and 800 mg/kg estimated fetal weight single-dose PTX with and without fetal injury. Preterm delivery by hysterotomy was performed at 0.80 of gestation to evaluate the fetal and placental effects. Immunochemistry for various markers including interleukins, caspases, cyclooxygenases, vimentin, myelin basic protein, and surfactant proteins were carried out in the fetal lungs, fetal brain, and placenta. Fetal plasma and amniotic fluid interleukins were also evaluated. Kruskal-Wallis H test and Mann-Whitney U test were used for comparisons.

Results:

High-dose (60 mg/kg/day) maternal prophylactic oral treatment attenuated endotoxin-related histological injury and was related to low inflammatory marker expressions comparable to the controls (p>0.05 except cyclooxygenase 2). Following maternal oral administration, fetal plasma and amniotic fluid levels of the studied interleukins were also lower than the untreated endotoxin-exposed animals (p<0.05 for all comparisons). Intra-amniotic PTX was associated with inconsistent results and increased inflammatory markers in some fetuses.

Conclusion:

Oral PTX before preterm birth mitigates intrauterine inflammation with neuroprotective effects in the fetus. PTX can be considered as a candidate drug for fetal brain injury prevention in the preterm period.

Pharmacokinetics of pentoxifylline and its 5-hydroxyhexyl metabolite after intravenous administration of increasing doses to sheep

OBJECTIVE

To determine the pharmacokinetics of pentoxifylline (PTX) and its 5-hydroxyhexyl metabolite (M-I) after IV administration of increasing doses of PTX to sheep.

ANIMALS

6 healthy adult Merino sheep.

PROCEDURES

Each sheep received 10-, 20-, and 40-mg/kg doses of PTX, IV, with a 15-day washout period between doses. Blood samples were collected before and at predetermined times after administration of each dose to determine plasma PTX and M-I concentrations by high-performance liquid chromatography. Pharmacokinetic parameters for PTX and M-I were estimated by noncompartmental analysis.

RESULTS

No adverse effects were observed after administration of the 10- and 20-mg/kg doses. Following administration of the 40-mg/kg dose, all sheep developed tachycardia and hypersalivation and appeared agitated for approximately 4 hours. Plasma PTX concentrations considered therapeutic in other species were achieved in all sheep after administration of all 3 doses. Pharmacokinetic parameters for PTX and M-I varied in a dose-dependent linear manner. For PTX, the mean area under the concentration-time curve (AUC), elimination half-life, and volume of distribution increased with dose and ranged from 15.67 to 94.66 h·μg/mL, 0.68 to 0.91 hours, and 0.55 to 0.66 L/kg, respectively, whereas clearance decreased with dose and ranged from 0.42 to 0.64 L/h/kg. The mean ratio of the AUC for M-I to AUC for PTX ranged from 0.38 to 0.46.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that pharmacokinetic parameters for PTX and M-I varied in a dose-dependent linear manner in healthy sheep. Further studies are warranted to determine the therapeutic threshold and optimal dosage for PTX in sheep.

Diagnosis and Treatment of Undifferentiated and Infectious Acute Diarrhea in the Adult Horse

Acute, infectious, diarrhea in adult horses is a major cause of morbidity and is associated with numerous complications. Common causes include salmonellosis, clostridiosis, Coronavirus, and infection with Neorickettsia risticii (Potomac horse fever). Treatment is empirical and supportive until results of specific diagnostic tests are available. Supportive care is aimed at restoring hydration, correcting electrolyte imbalances, and limiting the systemic inflammatory response. The mainstays of therapy are intravenous fluid therapy, electrolyte supplementation where necessary, nonsteroidal anti-inflammatory agents, and nutritional support. Specific therapies include colloid oncotic support, antibiotics, hyperimmune plasma, polymyxin B, pentoxifylline, probiotics, binding agents, gastroprotectants, laminitis prevention, and coagulation prophylaxis.

Treatment of endotoxaemia and septicaemia in the equine patient

Endotoxins, constituents of the cell wall of gram-positive and gram-negative bacteria, regularly result in severe illness and death in horses. In endotoxaemia, these constituents are present in the systemic circulation; in septicaemia, whole microbes invade normally sterile parts of the body. Interaction of these endotoxins with pathogen recognition receptors leads to an inflammatory response that cannot always be sufficiently contained and hence needs direct treatment. Over the last decennia, our understanding of the pathophysiology of endotoxaemia and septicaemia has significantly increased. Based on improved understanding of the interaction between receptors and endotoxins as well as the subsequent downstream signalling pathways, new therapeutic targets have been identified in laboratory animal species and humans. Important species differences in the recognition of endotoxins and pathogens by their receptors as well as the inflammatory response to receptor activation hamper extrapolation of this information to the horse (and other species). Historically, horses with endotoxaemia and septicaemia have been treated mainly symptomatically and supportively. Based on the identified therapeutic targets, this review describes the current knowledge of the treatment for endotoxaemia and septicaemia in the horse with reference to the findings in other animal species and humans.

Vasodilatory effect of pentoxifylline in isolated equine digital veins

The direct vasodilatory action of pentoxifylline (1-(5-oxohexyl)-3,7-dimethylxanthine) and its signalling pathway was evaluated in equine digital veins. Cumulative concentration-response curves to pentoxifylline (1 nM to 300 μM) were recorded in phenylephrine-precontracted equine digital vein rings under different experimental conditions. Relaxation to pentoxifylline was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (a non-xanthine adenosine receptor antagonist; 3 μM). Nitric oxide synthase (NOS), soluble guanylate cyclase and cyclooxygenase (COX) inhibitors (Nω-nitro-L-arginine methyl ester (100 μM), ODQ (30 μM) and indomethacin (10 μM), respectively) significantly reduced the maximum relaxation induced by pentoxifylline. Moreover, pentoxifylline-induced relaxation was strongly reduced by Rp-8-Br-PET-cyclic guanosine monophosphate-S (a protein kinase G inhibitor; 3 μM), but remained unaffected by H-89 (a protein kinase A inhibitor; 2 μM). Pentoxifylline-induced relaxation was associated with a 3.4-fold increase in tissue cGMP content. To investigate whether pentoxifylline can affect cAMP- and cGMP-mediated relaxations, curves to forskolin, to sodium nitroprusside (SNP) and 8-bromo-cGMP were also recorded in endothelium-denuded equine digital vein rings pretreated with pentoxifylline (10 and 100 μM). Pentoxifylline only potentiated the SNP-mediated relaxation at the highest concentration (100 μM). Thus, pentoxifylline relaxed equine digital veins via endothelium-dependent and endothelium-independent components. The effect was mediated through both the NOS and COX pathways and could also result from inhibition of cGMP specific-phosphodiesterase activity at the highest concentrations used.

Effect of pentoxifylline treatment on testicular perfusion and semen quality in Miniature horse stallions

The objective was to investigate the effects of pentoxifylline (PTX) on testicular perfusion and sperm production in stallions. In a preliminary study, six mature Miniature horse stallions were given 0, 8.5, or 17.0 mg/kg of PTX orally, twice daily, for 3 d. Total Arterial Blood Flow Rate (TABFR) was higher (P < 0.05) in all treated versus control stallions during and after treatment. Two months later (during the fall and winter), the same stallions received either 0 or 17 mg/kg of PTX orally, twice daily for 60 d. Resistance and pulsatility indices (RI and PI, respectively) decreased in PTX-treated stallions between Treatment 1 and Post-treatment periods. Arterial diameter, as well as Total Arterial Blood Flow (TABF), decreased in controls between Baseline and Treatment 1 (P < 0.05). A similar decrease in arterial diameter was delayed in Group TREATED, but reached significance during Post-treatment (P < 0.05), whereas TABF did not change in this group. Furthermore, TABFR had a transient tendency to increase during Treatment 1 (P < 0.1), whereas it steadily decreased in controls and reached significance in the Post-treatment period (P < 0.05). Both RI and PI were negatively correlated with end diastolic velocity (EDV) in both groups (P < 0.0001). There were positive correlations between RI and peak systolic velocity (PSV) in treated stallions during Treatment 1 (RI: r = 0.53, P = 0.021; PI: r = 0.59, P = 0.007). Also, there were negative correlations between Time Averaged Maximum Velocity (TAMAX) and Doppler indexes in treated stallions during Treatment 2 period (RI: r = -0.49, P = 0.006; PI: r = -0.47, P = 0.008), and during Post-treatment periods (RI: r = -0.40, P = 0.049; PI: r = -042, P = 0.039). Transient hydrocele occurred in all treated stallions (a potential complication of high-dose PTX). Semen end points were not significantly affected by PTX treatment. In conclusion, PTX delayed the seasonal decrease of testicular perfusion in stallions. Sperm quality and quantity were not significantly affected; perhaps they would have been enhanced by prolonged treatment.