You are treating a dog with chronic enteropathy (CE) and have identified hypocobalaminaemia. You recommend a course of parenteral cobalamin but the owner is reluctant. They are concerned about the discomfort of injections, the stress of hospital visits and the cost. The client asks if cobalamin tablets, otherwise known as vitamin B12, can be given instead of injections. You decide to explore the literature to give advice on the subject.
Cobalamin is necessary for the methylmalonyl-CoA mutase system. Deficiencies can result in the production of methylmalonic acid (MMA), which in turn may affect the ability to digest particular fats and proteins. Previous studies have shown that over a third of dogs with CE have hypocobalaminaemia, and a quarter of these have elevated levels of MMA.
Dogs with chronic enteropathy display typical gastrointestinal signs such as vomiting, diarrhoea, inappetence and weight loss, as well as subtler signs, including borborygmus, abdominal pain and nausea.
Since hypocobalaminaemia has been shown to be a negative prognostic indicator, it has been recommended that all dogs showing signs of chronic gastrointestinal disease should have their cobalamin levels assessed. Levels below 200ng/L are associated with an increased risk of poor outcome, while normocobalaminaemia has been described as serum levels of 252 to 908ng/L. In the evidence analysed, cobalamin is supplemented once levels are below 285ng/L, as this represents the lowest 5 percent of the reference range.
The common treatment regime is to inject cobalamin once per week for six weeks, with a follow-up injection of hydroxycobalamin four weeks later, at a dosage of 0.25 to 1.25mg/dog, depending on body weight. Some dogs require long-term treatment, such as weekly injections.
However, this protocol and dosage regimen is based on clinical experience and expert opinion, rather than on substantial evidence. Furthermore, it has proved insufficient in certain cases, notably in the report of one dog who remained severely hypocobalaminaemic at day 90, suggesting the recommended parenteral protocol did not adequately supplement cobalamin.
Tablets or injections?
In one study appraised in the Knowledge Summary, dogs were split into two groups by random allocation and either treated with cobalamin orally or parenterally. Though dogs were given a range of doses and sample sizes were small, this study showed promising results that the oral group had similar results to the parenteral group.
While cobalamin levels in dogs treated by injection were higher at day 28, their levels had dropped by day 90. This suggests that monthly injections of cobalamin may not be sufficient at maintaining cobalamin levels in some dogs. Further studies may be needed to determine frequency of injections after the initial course.
By contrast, serum cobalamin levels in those treated with tablets were increased at day 90 compared to the parenteral group, suggesting daily oral supplementation may be preferable long-term to the current parenteral protocols. In addition, serum cobalamin lev-els post-treatment surpassed the reference range for normocobalaminaemia – in one study, the median serum cobalamin level of the oral group at day 90 was 1244ng/L.
Another study demonstrated reduced MMA, indicating that oral and parenteral supplementation are effective at a cellular level. This supports the use of oral cobalamin supplementation in dogs with CE. However, although it has been shown that both cobalamin and MMA concentrations have normalised in dogs with congenital hypocobalaminaemia treated with oral supplementation, there was no significant change in homocysteine levels among the evidence analysed, suggesting the need for further studies in predisposed breeds.
In veterinary patients, tablets are more cost effective and convenient, and cause the dog less discomfort, while parenteral treatment requires frequent visits to veterinary clinics, is costly and can be distressing for dogs and owners.