Chrysotherapy in Cats

Chrysotherapy, also known as gold therapy, involves the administration of gold salts to the patient by deep intramuscular injection. This is a little-used treatment with sparse data to back up the evidence as to whether it works or not. Chrysotherapy is largely a treatment of last resort for cats that fail to respond to more conventional therapies and where euthanasia may be the only other choice. 

Treatment involves deep intramuscular injection of gold salts once a week, and this can be done in first opinion practice. 

A definitive diagnosis of pemphigus must first be made. This is usually done on biopsy of the affected lesions, to confirm this is immune mediated disease rather than cancer or a severe infection. 

Conventional treatments are attempted first, but if this fails then other options such as chrysotherapy may be considered. This involves weekly intramuscular injections with gold salts. Myochrysine, manufactured by Merck, contains sodium aurothiomalate. The dose is 1 mg/kg/week for 8 to 12 weeks. It can take up to 10 weeks for any improvement to be noted. Therefore, chrysotherapy is usually started in parallel to steroids, to bridge this gap. However, if no improvement is noted by 12 weeks, the dose of golds salts can be doubled. Therapy is continued for around 20 weeks, but if unsuccessful at this point it should be discontinued. 

Where chrysotherapy is effective, the frequency of injections is gradually reduced. The aim is to stabilize the patient with one injection every 2 to 8 weeks. 

Oral gold salts are also available, (Auranofin, SmithKline Beecham) but this seems to be less effective than the injectable form. 

There is limited data about the effectiveness of chrysotherapy. It is most likely to be used as a rescue therapy for cats where euthanasia is the other option, due to non responsiveness to steroids or other immunosuppressive drugs. 

For the cats that do respond, the dose of steroids used during the bridging period is slowly reduced, with the aim of ceasing altogether. Cats that do well often maintain on a once monthly gold salt injection.

Side effects are rare (see: Considerations). The injection is given to the conscious cat, so other than the stress of a journey to the vet clinic, the recovery time is negligible. However, deep intramuscular injections can be painful, so some cats may become less tolerant of the therapy as time goes by. 

A bottle of Myochrysine is around $120 at cost price, and your vet will add markup on top of this. There is also a fee for giving a deep intramuscular injection, which could be around $40. Therefore, the predicted price of each weekly injection is expected to be around $60. 

Added to this is the cost of blood screens ($40 to $120) and urinalysis ($12 to $60 depending on the test involved). Bear in mind this is weekly initially. 

Chrysotherapy is not a 'magic bullet', and even for cats that respond, this can take several weeks or months. An owner considering chrysotherapy for their cat needs to accept that there is no guaranteed outcome and that conventional therapies, such as steroids, may need to be run in parallel during the bridging period.

Whilst side effects are rare, these can be significant. They include suppression of platelet production, kidney failure, sterile abscess formation at the injection site, and toxic epidermal necrolysis (skin dieback). 

The clinician will monitor the cat for side effects by running blood panels and urinalysis every two to three weeks initially, then once the cats is stable running them two to three times a year. 

Pemphigus is triggered by an inappropriate response of the immune system to its own tissue. For some cats this can be because of a genetic predisposition to pemphigus. In others, UV exposure can be a trigger, as can certain drugs. 

Medications linked to triggering pemphigus include methimazole, amoxicillin, itraconazole, sulphonamides, and lime sulfur dips - although it should be noted that such side effects are extremely rare.