Age-related differences in pharmacokinetics of phosphonoformate in cats

Prophylactic Efficacy and Bone Toxicity Associated with Phosphonoformate Therapy against Retrovirus Infection

Phosphonoformate (PFA) is a simple pyrophosphate analogue which is a topical and parenteral treatment for human herpes virus infections and is currently undergoing evaluation for treatment of human immunodeficiency virus (HIV) and cytomegalovirus infections associated with (AIDS). In this study, antiretroviral activity of PFA was demonstrated by two separate treatment regimens. In the first, an inoculum of feline leukaemia virus (FeLV) in plasma from viraemic cats was treated with 1024 μM PFA prior to intravenous inoculation into susceptible animals. Three of four cats given the PFA treated inoculum were protected from viraemia by the PFA treatment, while 2 of 2 challenge controls receiving sham treated inoculum and 6 of 6 untreated challenge controls became viraemic. In the second regimen, a long-term continuous intravenous infusion of PFA (1000 mg kg−1 day−1) was administered to 6 young cats beginning 1–2 days prior to and extending 4 weeks following intravenous inoculation with FeLV. Five of the six PFA-treated cats also received heparin intravenously and acetyl salicylic acid (aspirin) orally to reduce risk of thrombosis. Six cats (heparin controls) received only heparin and aspirin and were inoculated with FeLV in an identical manner. Six cats served as untreated challenge controls. Four of 6 PFA-treated cats were protected from FeLV antigenaemia. In contrast, all 6 heparin-control animals and all 6 challenge-control animals became persistently viraemic as evidenced by continuous expression of FeLV p27 antigen. All challenged cats including the 4 protected by PFA treatment developed antibody to FeLV, indicating that PFA did not prevent primary virus infection. Significant toxic effects of PFA treatment were reduced weight-gain and rickets-like bone lesions in the cats receiving the 4 week treatment. Additionally, decreased serum alkaline phosphatase, phosphorus, and calcitriol concentrations, presumably related to the bone lesions, were observed. Results of this study suggest that the antiviral effect of PFA involves an immediate and direct mechanism targeted at cell-free virus and that long-term continuous intravenous infusion of PFA has significant anti-retroviral activity in vivo.

Patient variation in veterinary medicine--part II--influence of physiological variables

In veterinary medicine, the characterization of a drug's pharmacokinetic properties is generally based upon data that are derived from studies that employ small groups of young healthy animals, often of a single breed. In Part I of the series, we focused on the potential influence of disease processes, stress, pregnancy and lactation on drug pharmacokinetics. In this Part II of the series, we consider other covariates, such as gender, heritable traits, age, body composition, and circadian rhythms. The impact of these factors with respect to predicting the relationship between dose and drug exposure characteristics within an animal population is illustrated through the use of Monte Carlo simulations. Ultimately, an appreciation of these potential influences will improve the prediction of situations when dose adjustments may be appropriate.

Prospects for Antiviral Chemotherapy in Veterinary Medicine: 1. Feline Virus Diseases

This paper, which is published in two parts, reviews the literature pertaining to antiviral chemotherapy of viruses of veterinary importance. While early reports in the 1970s referred to the chemotherapy of a number of different RNA and DNA viruses, there was considerable focus in the 1980s, initially on herpesviruses and latterly on retroviruses, particularly in cats. Details are given of the successful treatments of FeLV and FIV, which have been used as animal models for HIV therapy. The high costs of developing and registering a new chemical entity, especially for food species, in which extensive toxicity/residue data are required, is the main reason why specific antiviral compounds are not currently available for veterinary use, although some non-specific immune modulators are now emerging. Concurrent availability of appropriate diagnostic tools is a prerequisite for successful veterinary antiviral chemotherapy, as is a greater understanding of the pathogenesis of virus infections in animals and the development of more sophisticated means of drug delivery, appropriate to both food animal species and companion animals. Additionally, antiviral agents are valuable as research tools per se, as opposed to solely as chemotherapeutic agents.