Equine tetanus antitoxin for dogs with tetanus

Imagine this clinical scenario: while working in a veterinary hospital, you are presented with a 10-month-old female neutered Golden Retriever that has a two-day history of displaying a “strange” facial expression and generalised muscle stiffness. You diagnose the patient with tetanus, recognising the former symptom as risus sardonicus (a characteristic of the disease), and begin considering treatment options.

You have heard of cases where equine tetanus antitoxin has been used to treat tetanus in dogs but do not know what evidence there is to back this up. You decide to consult the evidence to see if there is any benefit to dogs with tetanus receiving equine tetanus antitoxin versus those that do not.

The evidence

Three studies relevant to the research question were found, all of which were retrospective case-control studies.

Bandt et al. (2007) retrospectively studied 20 dogs diagnosed with, and treated for, tetanus, without evidence of other neuromuscular disease. Sixteen of these received the equine tetanus antitoxin, while the remaining four did not. All 20 dogs were administered penicillin, metronidazole, muscle relaxants and sedatives, methocarbamol, intravenous fluids and nutritional support. Outcomes studied were survival, severity and duration of recovery.

Three studies relevant to the research question were found, all of which were retrospective case-control studies

Burkitt et al. (2007) studied 38 dogs with clinical signs of tetanus, excluding those with incomplete medical records, hypocalcaemia and confirmed neurotoxicoses or myositis. However, the cases in this paper did not have laboratory confirmation of Clostridium tetani and diagnostic testing was not performed to completely rule out other neurotoxicoses or generalised myopathies. Twenty-nine dogs were treated with the tetanus antitoxin, eight dogs were not and information on the use of antitoxin was not available for one dog. Thirty-three dogs were administered antimicrobials, 26 were treated with sedative medicines and 29 were nutritionally supported. Outcomes studied were mortality and progression of clinical signs.

Zitzl et al. (2022) studied 42 dogs with characteristic signs of local or generalised tetanus at presentation. They excluded patients with incomplete medical data, a history or suspicion of neurotoxic substance ingestion, ionised hypocalcaemia of less than 0.8mmol/l on admission and findings consistent with myositis, meningoencephalitis or spinal trauma. Twenty-three dogs received the equine tetanus antitoxin and one dog received a tetanus antiserum of human origin. Eighteen dogs did not receive tetanus antitoxin. Forty dogs were treated with antibiotics, 36 received sedatives and 24 were supported nutritionally. The outcome studied was survival versus non-survival.

Limitations of the evidence

Each study had limitations that weakened the overall strength of evidence. All the papers reviewed had small sample sizes and were retrospective case-control studies, which is a weak study design that could lead to information bias. Each study had variable treatment protocols, which was a confounding factor. This meant that an accurate and reliable association between equine tetanus antitoxin and clinical outcomes in dogs with tetanus could not be established. All three studies also neglected to use a power calculation or use any kind of randomisation.

An accurate and reliable association between equine tetanus antitoxin and clinical outcomes in dogs with tetanus could not be established

Two of the studies, Bandt et al. (2007) and Burkitt et al. (2007), are more than 15 years old. Advances in intensive care management and general nursing care since 2007 could play a part in the mortality rate of dogs affected by tetanus, putting the applicability of these papers’ findings into question.

Summary of findings

There is weak evidence to suggest that there is no effect on the survival of dogs affected by tetanus who were treated with equine tetanus antitoxin. However, this must be considered in conjunction with the limitations outlined above.

Bandt et al. (2007) found that there was no difference in survival to discharge between dogs treated with and without antitoxin. Fifty percent (2/4) of dogs that did not receive antitoxin survived, and 50 percent (8/16) of dogs that received antitoxin survived.

There is weak evidence to suggest that there is no effect on the survival of dogs affected by tetanus who were treated with equine tetanus antitoxin

Burkitt et al. (2007) did not report any association between antitoxin administration and progression of clinical signs or mortality rate. Sixty-four percent (23/36) of dogs developed more severe clinical signs after their initial evaluation. One dog did not have the details of its first evaluation recorded; one had no abnormal findings on its first physical examination and was not initially classified with the canine tetanus severity classification system. Seventy-seven percent (27/35) of dogs survived to day 28. Three dogs were not included in the survival analysis as they either died from causes unrelated to tetanus or were lost to follow-up.

Zitzl et al. (2022) found that there was no significant difference in antitoxin use between survivors and non-survivors. Seventy-five percent (18/24) of dogs that received antitoxin survived, while 75 percent (12/16) of dogs that did not receive antitoxin survived.

Conclusion

Further studies with larger cohorts and robust study design are required to either refute or support the findings of the papers studied

There is weak evidence to suggest that the administration of equine tetanus antitoxin has no effect on clinical outcomes in dogs affected by tetanus. However, the limitations of each paper studied significantly weakened the overall quality of evidence, underlining a need for further studies.

Tetanus in dogs is relatively uncommon, which may explain the small sample sizes in this study. However, further studies with larger cohorts and robust study design are required to either refute or support the findings of the papers studied. Future large randomised prospective studies assessing for optimal timing and dosing of equine tetanus antitoxin administration, complication rates and duration of hospitalisation or time to recovery in survivors would help to improve the overall strength of evidence.

Disclaimer

The application of evidence into practice should take into account multiple factors, not limited to individual clinical expertise, patient’s circumstances, owner’s values, the individual case in front of you, the availability of therapies and resources, and the country, location or clinic where you work.