Contraception implant for cats

Fontaine, C. (2015). Long-term contraception in a small implant A review of Suprelorin (deslorelin) studies in cats. Journal of feline medicine and surgery, 17(9), 766-771.


Rationale: Deslorelin (Suprelorin®; Virbac) is a gonadotropin-releasing hormone (GnRH) agonist licensed in select countries for the long-term suppression of fertility in adult male dogs and male ferrets. This article summarizes studies investigating the use of deslorelin implants for the long-term suppression of fertility in male and female domestic cats.
Evidence base: Slow-release deslorelin implants have been shown to generate effective, safe and reversible long-term contraception in male and female cats. In pubertal cats, a 4.7 mg deslorelin implant suppressed steroid sex hormones for an average of approximately 20 months (range 15–25 months) in males and an average of approximately 24 months (range 16–37 months) in females. Reversibility has been demonstrated by fertile matings approximately 2 years post-treatment in both male and female adult cats. In prepubertal female cats of approximately 4 months of age, puberty was postponed to an average of approximately 10 months of age (range 6–15 months) by a 4.7 mg deslorelin implant.
Challenges: The large variability in the duration of suppression of gonadal activity makes the definition of the optimal time for reimplantation quite challenging. In addition, the temporary stimulation phase occurring in the weeks following deslorelin implantation can induce in adult female cats a fertile estrus that needs to be managed to avoid unwanted pregnancy. Longer duration and larger scale controlled field studies implementing blinding, a negative control group and a carefully controlled randomization to each group are needed. Furthermore, the effects of repeated treatment need to be investigated. Finally, the effect of treatment on growth and bone quality of prepubertal cats needs to be assessed. However, the ease of use, long-lasting effects and reversibility of deslorelin implants are strong positive points supporting their use for controlling feline reproduction.

Progestins to control feline reproduction

Romagnoli, S. (2015). Progestins to control feline reproduction Historical abuse of high doses and potentially safe use of low doses. Journal of feline medicine and surgery, 17(9), 743-752.

Relevance: The high fertility rate of cats means that methods to control feline reproduction are a requirement for cat breeders and pet owners, as well as for those involved in the management of feral cat populations. Progestins continue to be used to prevent queens from cycling, and also as an adjunct or alternative to surgical sterilization within trap–neuter–return (TNR) programs.
Evidence base: A considerable body of information exists on megestrol acetate (MA) and medroxyprogesterone acetate (MPA), thanks to the many studies and case reports published in the scientific literature over the past 50 years documenting their clinical use in cats. Comparatively less is known about the use in cats of more recent progestins such as levonorgestrel, proligestone, delmadinone, chlormadinone and altrenogest.
Dosing, safety and efficacy: Based on a combination of dose, frequency and duration of treatment, MA can be categorized into low (0.625 mg/kg/week for up to 30 weeks), medium (0.625 mg/kg q24h for 1 week or q48h for up to 2 weeks) and high (0.625 mg/kg q24h or q48h for several weeks, or weekly for months or years) dosages. Studies suggest that low dosages can be used relatively safely in cats, while higher dosages increase the risk and severity of adverse reactions. Early work showing that an oral MPA dosage of 0.01 mg/kg administered q24h for 12 months suppresses oestrus in queens effectively and safely has not been considered, and much higher MPA dosages (>6.25 mg/kg q24h) have been used in cats over the past 40 years.
Recommendations: Progestins should always be used with caution. Using the lowest possible dosages, MA and MPA may, however, continue to be used safely in pet queens as well as (in conjunction with TNR programs) for the control of feral cat colonies. More recent progestins appear to be effective and safe, albeit their efficacy and safety need to be further investigated.

No surgery required: the future of feline sterilization

Johnston, S., & Rhodes, L. (2015). No surgery required: the future of feline sterilization. An overview of the Michelson Prize & Grants in Reproductive Biology. Journal of feline medicine and surgery, 17(9), 777-782.

Overview: For many years, researchers have been studying reproduction of cats and dogs, including approaches to non-surgical sterilization, but scant funding has been available for this work. Recognizing the need to fund research and to attract researchers from the biomedical community to apply their expertise to this area, the Michelson Prize & Grants (MPG) in Reproductive Biology program was founded. Since 2009, it has funded 34 research projects in seven countries toward discovery of a safe single-administration lifetime non-surgical sterilant in male and female cats and dogs.
Goal: The goal of the MPG program is the reduction or elimination of the approximately 2.7 million deaths of healthy shelter cats and dogs in the US every year. The successful product is expected to be a single-dose injectable product approved by the US Food and Drug Administration as a veterinary prescription item. The most optimistic prediction is that such a product will reach the hands of practicing veterinarians within the next decade.
Areas of research: Active research is in progress using approaches such as immunocontraception with a single-administration vaccine against gonadotropin releasing hormone (GnRH). Long-term therapy with GnRH agonists such as deslorelin administered in controlled-release devices is also being studied. Other scientists are targeting cells in the brain or gonads with cytotoxins, such as are used in cancer chemotherapy. Gene therapy expressing proteins that suppress reproduction and gene silencing of peptides essential to reproduction are further avenues of research. Findings are available at www.michelsonprizeandgrants.org/michelson-grants/research-findings

Review of sterilization injections for male cats

Kutzler, M. A. (2015). Intratesticular and intraepididymal injections to sterilize male cats: From calcium chloride to zinc gluconate and beyond. Journal of feline medicine and surgery, 17(9), 772-776.
Aim and rationale: The aim of intratesticular and intraepididymal injections is to provide an inexpensive non-surgical method for sterilizing tom cats. Intratesticular and intraepididymal injections have been studied for decades and warrant continued investigation. While both methods result in azoospermia, intratesticular injection of sclerosing agents induces orchitis, resulting in decreased spermatogenesis, whereas intraepididymal injection blocks sperm transport but does not alter spermatogenesis.
Evidence base: Sclerosing agents that have been used effectively for intratesticular injections in cats include calcium chloride dihydrate and zinc gluconate. For sclerosis by intraepididymal injections, chlorhexidine digluconate has been used successfully in cats. The volume, formulation and concentration of sclerosing agents for intratesticular and intraepididymal injections in cats have not been standardized.
Challenges: Neither intratesticular nor intraepididymal injections entirely eliminate gonadal testosterone production, which may be undesirable for pet cats and therefore may restrict the application of this method of sterilization to feral cats with limited human contact. In addition, both methods may require sedation or general anesthesia, leading some to support routine castration over these non-surgical methods. Lastly, even if the technique is successful in inducing permanent sterility, normal fertility may persist in treated males for 1–2 months after treatment because of sperm present within the epididymis and vas deferens.

Non-surgical contraceptives for use in cats and dogs

Rhodes, L. 2015. Getting non-surgical contraceptives approved for use in cats and dogs. Journal of Feline Medicine and Surgery, 17 (9): 783-789

Relevance: Non-surgical contraceptives or sterilants need regulatory approval to be sold for that use. This approval process gives veterinarians the information required to assess the benefits and risks of each product, and to provide comprehensive information on the required dose, method and duration of use, safety and effectiveness.
Aim: This article reviews the information that must be developed and provided to regulatory agencies worldwide, with a focus on the European Union and the United States, in order to achieve regulatory approval.
Processes: The main components of developing a drug include developing extensive information on the safety and effectiveness of the product, and also the safety to the environment and to humans handling and administering the drug. Most importantly, a robust method of manufacturing both the drug itself and the formulated drug product (pill, liquid implant or injection) must be developed to assure quality and consistency in each batch. This information is then compiled and submitted to regulatory agencies; in the United States, this includes the Food and Drug Administration, the United States Department of Agriculture and the Environmental Protection Agency, and, in Europe, the European Medicines Agency.
Challenges: Because of the unique nature of non-surgical contraceptives for use in cats and dogs, particularly the desire to have these products last over multiple years, there are special challenges to their regulatory approval that are discussed in this review.

Non surgical vs. surgical sterilization in feral cat populations

Budke, C. M., & Slater, M. R. (2009). Utilization of matrix population models to assess a 3-year single treatment nonsurgical contraception program versus surgical sterilization in feral cat populations. Journal of Applied Animal Welfare Science, 12(4), 277-292.

This study constructed matrix population models to explore feral cat population growth for a hypothetical population (a) in the absence of intervention; (b) with a traditional surgical sterilization-based trap, neuter, and return program; and (c) with a single treatment 3-year nonsurgical contraception program. Model outcomes indicated that cessation of population growth would require surgical sterilization for greater than 51% of adult and 51% of juvenile (<1 year) intact female cats annually, assuming an approximate 3-year mean life span. After the population stabilizes, this would equate to sterilizing approximately 14% of the total female population per year or having approximately 71% of the total female and 81% of the adult female population sterilized at all times. In the absence of juvenile sterilization, 91% of adult intact females would need to be sterilized annually to halt population growth. In comparison, with a 3-year nonsurgical contraception program, an annual contraception rate of 60% of female juvenile and adult intact cats would be required to halt population growth, assuming that treatedcats were retrapped at the same rate after 3 years.