How can an antibiotic dosage be calculated for a rat? - briefly
Calculate the rat’s body weight in kilograms, multiply by the antibiotic’s recommended dosage expressed in milligrams per kilogram, and then adjust for the preparation’s concentration to obtain the exact volume to administer. Verify the chosen route and dosing interval according to the drug’s pharmacokinetic profile.
How can an antibiotic dosage be calculated for a rat? - in detail
Determining an appropriate antibiotic dose for a laboratory rat requires three basic inputs: the animal’s body weight, the specific drug’s recommended dose expressed as milligrams per kilogram, and the chosen route of administration. The calculation proceeds by multiplying the weight (kg) by the dose (mg / kg) to obtain the absolute amount of drug (mg) to be delivered.
The procedure begins with an accurate measurement of the rat’s mass, preferably to the nearest gram. Next, the selected antibiotic’s label or pharmacological reference provides a standard dosing range for rodents, often expressed as a minimum and maximum value (e.g., 10–20 mg / kg). If the reference supplies a human dose, conversion to a rodent dose may be performed using allometric scaling factors, typically 6–7 × the human mg / kg value for rats.
A step‑by‑step example:
- Weight of rat: 250 g = 0.250 kg.
- Chosen antibiotic: amoxicillin, recommended 15 mg / kg subcutaneously.
- Required drug amount: 0.250 kg × 15 mg / kg = 3.75 mg.
If the drug is supplied as a suspension of 50 mg / mL, the injection volume equals 3.75 mg ÷ 50 mg / mL = 0.075 mL (75 µL). The volume must not exceed the maximum injectable volume for a rat, generally 0.1 mL per 100 g body weight.
Additional considerations include:
- Bioavailability differences between oral, intraperitoneal, and subcutaneous routes; adjust the dose if the chosen route has reduced absorption.
- Dosing interval, derived from the drug’s half‑life in rodents; typical intervals range from 12 to 24 hours.
- Safety margin: select a dose toward the lower end of the recommended range when the therapeutic index is narrow.
- Documentation of weight, dose, concentration, and administration time for reproducibility and regulatory compliance.
«The dosage should be expressed in mg/kg and adjusted for the specific pharmacokinetic profile of the animal». Adhering to this systematic approach ensures accurate, reproducible antibiotic administration in rat studies.