Species Considerations with Gastrointestinal Drugs

WIKIDRUGS GASTROINTESTINAL DRUGS

Ruminants

Drugs behave differently in ruminants compared to other species due to the presence of the rumen. The rumen acts like a reservoir, so drugs with low water solubility will remian in suspension in the rumen for days before it slowly enters solution. This can be useful when efficacy of a drug is related to the duration of exposure, for example benzimidazole anthelmintics. The rumenal microflora is held within a very delicate balance and any suppression of these microorganisms by antimicrobials, can lead to life threatening overgrowth of pathogenic microbes. As such few drugs are given orally to ruminants. Drugs can also be altered chemically by the enzymes present in the rumen, this usually leads to a loss of pharmacological activity of the drug. Due to the large volume of the rumen, any drugs present in it will be in high dilution and so it will be difficult to achieve therapeutic doses. Absorption will also be slow thanks to the surface area : volume ratio. If a drug is given systemically, it's plasma concentrations can be reduced by the drug moving into the rumen. This will occur because the volume of the rumen is so big that there will always be a concentration gradient between the blood and the rumen. Any basic drugs will also pass into the rumen, due to the ion trapping, which will occur because of the acidic nature of the rumenal fluid.

Below are some specific drug considerations, when dealing with certain conditions in ruminants:

• Closure of the Oesophageal Groove
  • Sodium bicarbonate or copper sulphate can be given orally to cattle to close the oesphageal groove so that drugs can be delivered directly to the abomasum, for example Anthelmintic Drugs.

• Hypomotility Disorders
  • Disorders such as a non-torsed non-surgical right displaced abomasum can sometimes be resolved with these drugs. Most often used are metoclopramide, bethanechol and buscopan.

• Froathy Bloat
  • Antifoaming agents are usually used, which act as surfactants, examples include; poloxalene and dimethicone.