Pharmacokinetics and Relative Bioavailability of d -Penicillamine in Fasted and Nonfasted Dogs

Chelation therapy in liver diseases of childhood: Current status and response

Chelation is the mainstay of therapy in certain pediatric liver diseases. Copper and iron related disorders require chelation. Wilson’s disease (WD), one of the common causes of cirrhosis in children is treated primarily with copper chelating agents like D-penicillamine and trientine. D-Penicillamine though widely used due its high efficacy in hepatic WD is fraught with frequent adverse effects resulting discontinuation. Trientine, an alternative drug has comparable efficacy in hepatic WD but has lower frequency of adverse effects. The role of ammonium tetra-thiomolybdate is presently experimental in hepatic WD. Indian childhood cirrhosis is related to excessive copper ingestion, rarely seen in present era. D-Penicillamine is effective in the early part of this disease with reversal of clinical status. Iron chelators are commonly used in secondary hemochromatosis of liver in hemolytic anemias. There are strict chelation protocols during bone marrow transplant. The role of iron chelation in neonatal hemochromatosis is presently not in vogue due to its poor efficacy and availability of other modalities of therapy. Hereditary hemochromatosis is rare in children and the use of iron chelators in this condition is limited.

Cystinuria in Dogs and Cats: What Do We Know after Almost 200 Years?

The purpose of this review is to summarize current knowledge on canine and feline cystinuria from available scientific reports. Cystinuria is an inherited metabolic defect characterized by abnormal intestinal and renal amino acid transport in which cystine and the dibasic amino acids ornithine, lysine, and arginine are involved (COLA). At a normal urine pH, ornithine, lysine, and arginine are soluble, but cysteine forms a dimer, cystine, which is relatively insoluble, resulting in crystal precipitation. Mutations in genes coding COLA transporter and the mode of inheritance were identified only in some canine breeds. Cystinuric dogs may form uroliths (mostly in lower urinary tract) which are associated with typical clinical symptoms. The prevalence of cystine urolithiasis is much higher in European countries (up to 14% according to the recent reports) when compared to North America (United States and Canada) where it is approximately 1-3%. Cystinuria may be diagnosed by the detection of cystine urolithiasis, cystine crystalluria, assessment of amino aciduria, or using genetic tests. The management of cystinuria is aimed at urolith removal or dissolution which may be reached by dietary changes or medical treatment. In dogs with androgen-dependent cystinuria, castration will help. In cats, cystinuria occurs less frequently in comparison with dogs.

D-Penicillamine: The State of the Art in Humans and in Dogs from a Pharmacological and Regulatory Perspective

Chelant agents are the mainstay of treatment in copper-associated hepatitis in humans, where D-penicillamine is the chelant agent of first choice. In veterinary medicine, the use of D-penicillamine has increased with the recent recognition of copper-associated hepatopathies that occur in several breeds of dogs. Although the different regulatory authorities in the world (United States Food and Drugs Administration-U.S. FDA, European Medicines Agency-EMEA, etc.) do not approve D-penicillamine for use in dogs, it has been used to treat copper-associated hepatitis in dogs since the 1970s, and is prescribed legally by veterinarians as an extra-label drug to treat this disease and alleviate suffering. The present study aims to: (a) address the pharmacological features; (b) outline the clinical scenario underlying the increased interest in D-penicillamine by overviewing the evolution of its main therapeutic goals in humans and dogs; and finally, (c) provide a discussion on its use and prescription in veterinary medicine from a regulatory perspective.

Liquid chromatography/tandem mass spectrometric analysis of penicillamine for its pharmacokinetic evaluation in dogs

Copper storage disease occurs in multiple dog breeds and is one of the most common causes of chronic hepatitis in this species. The disease is caused by hereditary defects in copper metabolism in conjunction with high dietary copper levels. The progressive copper accumulation leads to hepatitis, cirrhosis, and eventually death if left untreated. Copper chelators are critical in modulating the effects of this disease. It is therefore of significant practicality to understand the pharmacokinetic (PK) parameters of chelating agents, particularly since they are oftentimes quite expensive. A liquid chromatography-tandem mass spectrometric (LC/MS/MS) method was developed to measure plasma levels of one of the most common chelators, d-penicillamine. The compound was discovered to exist in two forms, monomeric and dimeric, and various chemical derivatizations were tried to force the compound into one form or the other. Eventually, the simplest approach was individual determination of penicillamine and its dimer, with summation of the two quantities. This enabled determination of canine PK parameters for penicillamine based on comparison of oral and intravenous administration of the drug, including time to maximum drug level (Tmax), concentration at maximum (Cmax), clearance (Cls) and volume of distribution (Vdss). The drug was found to exist predominantly in the dimeric form in plasma, which is incapable of chelating copper owing to lack of free sulfhydryl groups and must therefore provide a storage form of the drug in equilibrium with its monomeric form in vivo. Mechanisms are discussed for the electrospray-induced fragmentation of penicillamine as well as of its dimer.

ACVIM consensus statement on the diagnosis and treatment of chronic hepatitis in dogs

This consensus statement on chronic hepatitis (CH) in dogs is based on the expert opinion of 7 specialists with extensive experience in diagnosing, treating, and conducting clinical research in hepatology in dogs. It was generated from expert opinion and information gathered from searching of PubMed for manuscripts on CH, the Veterinary Information Network for abstracts and conference proceeding from annual meetings of the American College of Veterinary Medicine and the European College of Veterinary Medicine, and selected manuscripts from the human literature on CH. The panel recognizes that the diagnosis and treatment of CH in the dog is a complex process that requires integration of clinical presentation with clinical pathology, diagnostic imaging, and hepatic biopsy. Essential to this process is an index of suspicion for CH, knowledge of how to best collect tissue samples, access to a pathologist with experience in assessing hepatic histopathology, knowledge of reasonable medical interventions, and a strategy for monitoring treatment response and complications.

Ammonium tetrathiomolybdate treatment of copper-associated hepatopathy in dogs

Background

Copper‐associated hepatopathy (CAH) is a common cause of liver disease in dogs. Although d‐penicillamine can be an effective treatment, some dogs fail treatment or develop adverse effects. Ammonium tetrathiomolybdate (TTM) has been used to treat pathologic copper accumulation in other species, but its therapeutic potential for CAH is unknown.

Objectives

To investigate short‐term safety and efficacy of TTM for treatment of CAH.

Animals

Ten dogs with CAH.

Methods

Prospective study. All dogs were treated with TTM PO for 6 weeks, and hepatic biopsies were performed after the treatment course. Dog experiencing initial decreases in hepatic copper concentrations ([Cu]_H) received 6 additional weeks of TTM treatment and underwent 1 additional biopsy. Physical and laboratory examinations were performed every 2 weeks for study duration.

Results

Eight of 10 dogs had decreases in [Cu]_H. Compared to baseline (median, 1606 μg/g; range, 572‐5158 μg/g), [Cu]_H were decreased at 6 weeks (1033 μg/g, 450‐2975 μg/g; P = .04) and 12 weeks (931 μg/g, 218‐1677 μg/g; P = .02). Hepatic molybdenum concentrations increased >50‐fold (P < 0.001). Changes in histologic scores and hematologic and biochemical test results were variable and not significantly different from baseline. One dog developed presumed immune‐mediated anemia and thrombocytopenia, but it was unclear if this was related to TTM administration.

Conclusions and Clinical Importance

Results suggest that TTM can effectively decrease [Cu]_H in some dogs with CAH. Larger studies are needed to determine the overall safety and efficacy of TTM for treating CAH and how it compares with current treatments.

Canine Copper-Associated Hepatitis

Copper-associated hepatitis is recognized with increasing frequency in dogs. The disease is characterized by centrolobular hepatic copper accumulation, leading to hepatitis and eventually cirrhosis. The only way to establish the diagnosis is by histologic assessment of copper distribution and copper quantification in a liver biopsy. Treatment with the copper chelator d-penicillamine is the most commonly used treatment. In addition, a low-copper/high-zinc diet can help prevent accumulation or reaccumulation of hepatic copper. Mutations in the copper metabolism genes COMMD1 or ATP7A and ATP7B have been associated with hepatic copper concentrations in Bedlington terriers and Labrador retrievers respectively. In the Labrador retriever, dietary copper intake contributes strongly to the disease phenotype.

Pharmacologic evaluation of ammonium tetrathiomolybdate after intravenous and oral administration to healthy dogs

OBJECTIVE

To evaluate pharmacokinetics of ammonium tetrathiomolybdate (TTM) after IV and oral administration to dogs and effects of TTM administration on trace mineral concentrations.

ANIMALS

8 adult Beagles and Beagle crossbreds (4 sexually intact males and 4 sexually intact females).

PROCEDURES

Dogs received TTM (1 mg/kg) IV and orally in a randomized crossover study. Serum molybdenum and copper concentrations were measured via inductively coupled plasma mass spectrometry in samples obtained 0 to 72 hours after administration. Pharmacokinetics was determined via noncompartmental analysis.

RESULTS

For IV administration, mean ± SD terminal elimination rate constant, maximum concentration, area under the curve, and half-life were 0.03 ± 0.01 hours(-1), 4.9 ± 0.6 μg/mL, 30.7 ± 5.4 μg/mL•h, and 27.7 ± 6.8 hours, respectively. For oral administration, mean ± SD terminal elimination rate constant, time to maximum concentration, maximum concentration, area under the curve, and half-life were 0.03 ± 0.01 hours(-1), 3.0 ± 3.5 hours, 0.2 ± 0.4 μg/mL, 6.5 ± 8.0 μg/mL•h, and 26.8 ± 8.0 hours, respectively. Oral bioavailability was 21 ± 22%. Serum copper concentrations increased significantly after IV and oral administration. Emesis occurred after IV (2 dogs) and oral administration (3 dogs).

CONCLUSIONS AND CLINICAL RELEVANCE

Pharmacokinetics for TTM after a single IV and oral administration was determined for clinically normal dogs. Absorption of TTM after oral administration was variable. Increased serum copper concentrations suggested that TTM mobilized tissue copper. Further studies will be needed to evaluate the potential therapeutic use of TTM in copper-associated chronic hepatitis of dogs.