Cover Story | Gastroenterology

No Taper Needed After Medium-Term Use of Omeprazole

By Marie Rosenthal MS

There may not be a need to taper omeprazole when discontinuing the drug if used for a short or medium duration, according to Amy Lovett, BVSc (Hons), DACVIM, FHEA, who provided insights about a study she and her colleagues performed on 14 Thoroughbreds.

Short-term use of proton pump inhibitors (PPIs) like omeprazole are well tolerated in both humans and horses, but there is some concern about the recurrence of gastric disease when PPIs are stopped after long-term use. Some human patients have seen rebound gastric hyperacidity after stopping PPIs, and there are similar concerns in equids, particularly horses that have equine squamous gastric disease, according to Dr. Lovett, who discussed her findings at the 69th Annual AAEP Convention.

“When that PPI treatment is discontinued, rebound gastric hyperacidity has resulted in rapid recurrence of gastric acid related symptoms in 47% to 58% of [human] patients following the discontinuation of PPI treatments across various studies,” she said, and a couple of equine studies suggested a similar result.

Dr. Lovett and her colleagues wanted to know the response after using omeprazole for a medium term of 57 days. They tested 14 retired racing Thoroughbreds, who were used to train jockeys. The horses received 4.4 to 5.3 mg/kg of omeprazole every 24 hours over 61 days and then stopping abruptly rather than tapering to see what it would do to serum gastrin and serum chromogranin A (CGA) in the horses. Gastrin is used by the body to control stomach acid.

“We hypothesized that ome-prazole treatment for this period and its abrupt discontinuation would result in the development of hypergastrinemia and increased ECL [enterochromaffin-like] cell density in horses,” she said.
Enrolled horses received a clinical and lameness examination, and the trainer considered them to be suitable for a conditioning program over a 10-week period. Any horse that had received omeprazole or another acid suppressant within the 2 months prior to enrollment were excluded.

All the horses received a similar exercise training program under the same trainer with the same stable feeding conditions throughout the study. This program was like those used by racehorses in training.

From day 1 to 61 except for withholding periods, horses received 2.28 g of oral omeprazole at 4 AM each morning. The omeprazole was administered 30 minutes before morning feeding on an empty stomach.

The horses received their last dose of omeprazole on either day 59 or 61, but to simulate withholding periods that would be provided to horses that were racing, they also had 2 clear days at the end of week 4 and week 8.

They found a 2.5-fold increase in CGA within 7 days of initiating omeprazole treatment compared with the baseline measurements, and gastrin concentrations remained elevated throughout that entire treatment period until day 56 but did not continue to increase, according to Dr. Lovett, from the Massey University School of Veterinary Medicine, in Manawatu, New Zealand.

“Once elevated serum gastrin concentrations did not change during the omeprazole treatment,” she said.

Following the last dose of omeprazole the SGAs returned to baseline by day 63, she said. “So that’s a return to baseline concentration being observed within 2 to 4 days of administration of the last dose of omeprazole—median serum gastrin concentrations more than halved from days 7 and 56.”

The chance of equine squamous gastric disease (ESGD) recurrence was limited to within just several days of that last dose.

When compared with days 63 to 91 after the discontinuation of omeprazole, the median serum gastrin returned to below baseline from days 70 to 84, she explained.

“And serum gastrin concentrations during the period of ome-prazole treatment in the present study did not continue to increase beyond that initial rise seen by day 7,” she said.

“Our CGA results did not demonstrate a significant change in serum CGA concentrations in response to omeprazole treatment, nor any significant change with omeprazole discontinuation,” Dr. Lovett explained.

“The findings do not support the use of tapering protocols, at least after medium-duration omeprazole treatment in the horse,” she said.

Since there might be rebound after using for more than 8 weeks, a veterinarian might choose to taper in that case. However, she said, a short taper of several days would probably be enough.

“From our study, serum gastrin concentrations increased in response to omeprazole treatment within 7 days, but was not progressive, and hypergastrinemia was very short-lived once omeprazole was discontinued, rapidly returning to baseline within several days after that last dose of omeprazole,” Dr. Lovett said.

“We propose that the findings of the current study don’t support the use of tapering periods following medium-duration omeprazole therapy in the horse, which is any treatment course less than or equal to 8 weeks.”

Because there is a slight risk for ESGD, she said horses should be managed right after the last dose of omeprazole by providing strict rest. Horses should not be exercised or transported and roughage should be maintained by allowing the horse free choice hay.

“And once this immediate period lapses following the last omeprazole dose, normal gastrin protective mechanisms will be restored, and therefore, normal management and workload can be resumed,” she explained. MeV

For more information:
Clark B, Steel C, Vokes J, et al. Evaluation of the effects of medium-term (57 day) omeprazole administration and omeprazole discontinuation on serum gastrin and serum chromogranin A concentrations in the horse. J Vet Intern Med. 2023;37:(94):1537-1543.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10365038/