Injectable medicines contain the active principle suspended or dissolved in a liquid. The label on the bottle indicates the actual amount of medicine usually as mg per ml. Each medicine has a recommended dose level expressed in mg/kg or mg/lb of live weight and instructions as to its administration, frequency and any side effects or contraindications.

Example: Terramycin Q100 injectable solution contains 100 mg/ml of OTC. The therapeutic level is 10mg per kg live weight daily and thus the daily dose level becomes 1ml/10kg of body weight.

In practice, instead of referring to mg /kg, it is normal for the veterinarian to prescribe on the basis of 1ml/kg of live weight, but guidelines are also usually printed on the label.