How should a capsule be given to a rat? - briefly
Administer the capsule orally, either by gently inserting it with a calibrated gavage needle or by embedding it in a small, palatable food morsel that the rat will readily ingest and swallow whole.
How should a capsule be given to a rat? - in detail
Administering a solid oral dosage form to a laboratory rat requires careful preparation, precise technique, and post‑administration monitoring to ensure accurate dosing and animal welfare.
First, select a capsule size appropriate for the rat’s body weight. For adult rats (250–300 g), a size 0 or 00 gelatin capsule typically holds 0.1–0.3 ml of powdered or finely ground material. Verify that the capsule material is compatible with the test compound and does not contain substances that could affect the experiment.
Prepare the capsule by opening it, loading the exact amount of drug or test material, and resealing it. Use a calibrated analytical balance to weigh the dose, then gently tap the capsule to settle the contents and avoid air pockets. If the compound is hygroscopic, work in a low‑humidity environment and seal the capsule promptly.
Equipment needed includes:
- Small‑animal restrainer or a padded hand‑hold technique
- Oral gavage needle or blunt‑ended feeding tube (1–2 mm outer diameter, length appropriate for rat’s esophagus)
- Sterile water or saline for capsule lubrication, if needed
- Disposable gloves and aseptic wipes
The administration procedure:
- Restrain the rat: Place the animal in a supine position on a soft surface. Gently secure the forelimbs against the body using a thumb and forefinger, while supporting the head with the other hand. Avoid excessive pressure that could cause stress or injury.
- Open the mouth: With the thumb of the restraining hand, apply gentle pressure to the lips and cheek to expose the oral cavity. Ensure the tongue is retracted to prevent the capsule from being swallowed prematurely.
- Insert the gavage needle: Align the needle with the midline of the mouth, directing it toward the back of the pharynx. Advance the needle slowly until resistance is felt at the entrance of the esophagus (approximately 2–3 cm for an adult rat). Do not force the needle; misplacement can cause trauma or aspiration.
- Deposit the capsule: Using a fine forceps or a sterile spatula, place the sealed capsule into the distal end of the needle. Release the capsule by gently pushing the plunger or retracting the needle while maintaining a steady hand.
- Verify delivery: Observe the rat for signs of capsule passage, such as a brief swallow reflex and return of normal breathing. Inspect the oral cavity and needle for any residual material.
- Release the animal: Return the rat to its cage, monitor for at least 10 minutes, and record any immediate adverse reactions (e.g., coughing, choking, lethargy).
Alternative methods include mixing the powdered content with a palatable vehicle (e.g., flavored gel or soft food) and allowing voluntary ingestion, or using a miniature gelatin capsule that can be placed directly into the mouth without a gavage needle for very small doses. Each approach must be validated for dose accuracy and bioavailability.
Post‑administration, document the exact dose, capsule size, administration time, and any observations. Maintain a log of animal health status for the duration of the study to detect delayed effects.
Adhering to these steps ensures reliable delivery of a solid oral formulation to a rat while minimizing stress and procedural complications.