How do you calculate an antibiotic dose for a rat? - briefly
Determine the animal’s weight in kilograms and multiply by the drug’s recommended dosage expressed in milligrams per kilogram (for example, 10 mg kg⁻¹ for many antibiotics); the product yields the required dose in milligrams. Adjust the calculation for the specific antibiotic’s potency, formulation, and route of administration as indicated on the label.
How do you calculate an antibiotic dose for a rat? - in detail
To determine the appropriate antibiotic dosage for a laboratory rat, follow a systematic calculation based on body weight, species‑specific dosing guidelines, and the concentration of the prepared solution.
First, obtain the exact body mass of the animal. Weigh the rat on a calibrated scale and record the value in kilograms (kg) or grams (g); conversion to kilograms is required for the dosing formula.
Second, locate the recommended dose for the chosen antimicrobial. Sources such as the Veterinary Handbook of Antimicrobial Therapy or peer‑reviewed articles provide dosage ranges expressed as milligrams of active drug per kilogram of body weight (mg · kg⁻¹). Note the route of administration (intraperitoneal, subcutaneous, oral) because the dose may differ.
Third, apply the basic formula:
dose (mg) = body weight (kg) × recommended dose (mg · kg⁻¹)
If the drug is supplied as a stock solution, calculate the volume to inject using the solution’s concentration:
volume (mL) = dose (mg) / concentration (mg · mL⁻¹)
Example calculation:
- Rat weight: 250 g = 0.250 kg
- Recommended dose of enrofloxacin: 10 mg · kg⁻¹ (subcutaneous)
- Required drug amount: 0.250 kg × 10 mg · kg⁻¹ = 2.5 mg
- Stock concentration: 5 mg · mL⁻¹
- Injection volume: 2.5 mg / 5 mg · mL⁻¹ = 0.50 mL
Fourth, adjust the dose if the animal exhibits renal or hepatic impairment. Reduce the calculated amount by 25–50 % according to the severity of organ dysfunction, referencing pharmacokinetic studies for the specific antibiotic.
Fifth, verify the final volume does not exceed the maximum injectable volume for the chosen route. For subcutaneous administration, the limit is typically 0.1 mL per gram of body weight; in the example, the maximum would be 25 mL, well above the calculated 0.50 mL, confirming safety.
Finally, document the calculation, the source of the dosing recommendation, and any adjustments made. Record the administered volume, time, and route to ensure reproducibility and compliance with ethical standards.