Bone marrow, blood, and clinical findings in dogs treated with phenobarbital

ACVIM consensus statement on the diagnosis of immune thrombocytopenia in dogs and cats

Immune thrombocytopenia (ITP) is the most common acquired primary hemostatic disorder in dogs. Immune thrombocytopenia less commonly affects cats but is an important cause of mortality and treatment-associated morbidity in both species. Immune thrombocytopenia remains a diagnosis of exclusion for which diagnostic guidelines are lacking. Primary, or non-associative, ITP refers to autoimmune platelet destruction. Secondary, or associative, ITP arises in response to an underlying disease trigger. However, evidence for which comorbidities serve as ITP triggers has not been systematically evaluated. To identify key diagnostic steps for ITP and important comorbidities associated with secondary ITP, we developed 12 Population Evaluation/Exposure Comparison Outcome (PECO) format questions. These questions were addressed by evidence evaluators utilizing a literature pool of 287 articles identified by the panelists using a structured search strategy. Evidence evaluators, using panel-designed templates and data extraction tools, summarized evidence and created guideline recommendations that then were integrated by diagnosis and comorbidity domain chairs. The revised PECO responses underwent a Delphi survey process to reach consensus on final guidelines. A combination of panel expertise and PECO responses were employed to develop algorithms for diagnosis of ITP in dogs and cats, which also underwent 4 iterations of Delphi review. Comorbidity evidence evaluators employed an integrated measure of evidence (IME) tool to determine evidence quality for each comorbidity; IME values combined with evidence summaries for each comorbidity were integrated to develop ITP screening recommendations, which also were subjected to Delphi review. Commentary was solicited from multiple relevant professional organizations before finalizing the consensus. The final consensus statement provides clinical guidelines for the diagnosis of, and underlying disease screening for, ITP in dogs and cats. The systematic consensus process identified numerous knowledge gaps that should guide future studies. This statement is a companion manuscript to the ACVIM Consensus Statement on the Treatment of Immune Thrombocytopenia.

Pharmacokinetics and tolerability of a veterinary phenobarbital product in healthy dogs

Introduction

Phenobarbital has been used for many decades in both human and veterinary epileptic patients. Many formulations for a particular drug exist, most of which are marketed for humans. Recently a veterinary specific phenobarbital product has been introduced to the market in the United States. Utilizing a specific formulation to treat patients may help decrease the issue of bioequivalence between one pharmaceutical product to another. Therefore, the goal of this study was to determine single and multiple dosing pharmacokinetics and tolerability of a veterinary specific phenobarbital product over a 4-week time period.

Materials and methods

8 Healthy dogs from a canine research colony were used in the study.

Results

Overall, this phenobarbital formulation was well tolerated in the dogs in this study. Cmax, Tmax, half-life, and AUC after single 12 mg/kg oral dose were 23.5 μg/mL, 4.2 h, 94 h, and 2,758 h*μg/mL. Following chronic dosing, these parameters were 29.1 μg/mL, 3.4 h, 70 h, and 2,971 h*μg/mL, respectively.

Discussion

This formulation demonstrated a mean absolute bioavailability of 100%, with similar pharmacokinetic properties to previously published data.

A retrospective evaluation of phenobarbital-induced hematologic changes in 69 cats

BACKGROUND

Phenobarbital (PB) is used as a first-line treatment for recurrent epileptic seizures in cats. While hematologic abnormalities are well-known side effects of antiepileptic therapy with PB in humans and dogs, little is known about such alterations in cats.

OBJECTIVES

The aim of this retrospective study was to investigate the prevalence and clinical relevance of cytopenia during PB treatment in cats.

METHODS

In this single-center, retrospective clinical study, 69 cats-with suspected idiopathic epilepsy admitted to the Small Animal Clinic of the University of Veterinary Medicine in Vienna (VMU)-were included. A complete blood count for each patient was performed, and changes in hematocrit, leukocytes, neutrophils, and thrombocytes were documented and graded.

RESULTS

Fifty-three out of 69 cats (76.8%) showed cytopenias with a reduction of at least one cell fraction during PB treatment. The most frequent change was neutropenia (60%), followed by leukopenia (49.3%), thrombocytopenia (24.1%), and anemia (20.3%). Most of the changes were mild or moderate; only one patient (1.5%) showed severe leukopenia and neutropenia, and one was a life-threatening neutropenia (1.5%) with a serum PB concentration within or even below the therapeutic range. These patients did not present with clinical symptoms other than those related to epileptic episodes. Cats who received combination therapy showed lower hematocrits than those who received monotherapy. A tendency for leukocytes and neutrophils to decrease during PB treatment was also seen.

CONCLUSIONS

Blood cytopenias may frequently occur in cats on chronic PB therapy, even when serum drug levels are within the therapeutic range. However, clinical signs are typically mild to moderate and rarely severe.

Presumptive phenobarbital-induced systemic lupus erythematosus in a domestic dog

CASE DESCRIPTION

We describe a case of presumptive acquired systemic lupus erythematosus secondary to phenobarbital administration in a dog, which resolved with withdrawal of the drug.

CLINICAL FINDINGS

A 3.5 year-old poodle presented to a veterinary teaching hospital for Tier 1 idiopathic epilepsy and was treated with phenobarbital. The dog experienced fever, multiple cytopenias, and proteinuria in conjunction with a positive antinuclear antibody (ANA) titer.

DIAGNOSTICS

Serial CBCs, urine protein : creatinine ratios, and sternal bone marrow aspirates were performed to evaluate improvement.

TREATMENT AND OUTCOME

Phenobarbital was withdrawn and levetiracetam initiated. All abnormalities resolved with supportive care, without initiation of immunosuppressive drugs. All cytopenias and proteinuria resolved and ANA test results became negative within 3 months. The patient recovered and did well clinically.

CLINICAL RELEVANCE

Systemic lupus erythematosus is a disease of multiple autoimmune syndromes occurring concurrently or sequentially in conjunction with the presence of circulating ANA. It has been well described in dogs as an idiopathic condition, but in human medicine may occur secondary to drug reactions (drug-associated lupus) including as a reaction to phenobarbital. The findings in our case are consistent with the criteria for drug-induced lupus in humans and we suggest it as the first report of phenobarbital-induced lupus in a dog.