Guidelines on dosage calculation and stock solution preparation in experimental animals' studies

Dosage calculation and stock solution preparation in preclinical studies, involving the use of experimental animals is important in screening and development of new drugs. The present literature provides the basic principles and guidelines on dosage calculations and preparation of stock solution (with reference to crude plant extracts, sylimarin tablets, alloxan monohydrate, gentamicin injection as well as chemiron blood tonic) for experimental animal studies. Experimental animals have been of very important tools in the history of non-human research models for scientific purposes in almost every aspect of biomedical, behavioral researches and testing conducted in Universities, Medical schools, Pharmaceutical companies, research institutes, farms and commercial facilities that provide animal-testing services to industry (Festing, 1979). Experiments on animals are necessary in drugs discovery and development as well as to advance medical and biological knowledge (Baker, et al, 1979). Dosage calculation and stock solution preparation based on dosage rationale formula are prerequisites to drug administration in experimental animals. However, drugs dosage calculations and stock solution preparations are not clearly explained in most scientific literatures involving the use of experimental animals, and this is a major challenge to some undergraduate students, post-graduate students and other researchers. Since over 90% of animals used in in vivo experiments in medical, physiological, pharmacological, chemical, toxicological, biological, biochemical and genetic studies are rats and mice, this work is aimed to simplify calculation of doses, preparation of stock solution in experimental animal for the benefits of all researchers. 2. Vehicle of choice, drugs dissolution and volume selection rationale A vehicle is any substance that acts as a medium in which a drug is administered. Vehicle, which is an essential consideration in all animal research should be biologically inert, have no toxic effects on the animals and not also influence the results obtained for the compound under investigation. Example of suitable vehicles for animal research include; water, normal saline (0.9% sodium chloride), 50% polyethylene glycol, 5 to 10% Tween 80, 0.25% methylcellulose or carboxymethylcellulose (Karl-Heinz, et al., 2001; Nebendahl,2000). In most researches involving experimental animals, dosages are usually calculated from stock solution of the test drugs dissolved in appropriate volume of solvent (vehicle). According to the OECD's (organization of economic corporation and development's) guidelines, dosage of drug (mg) should be constituted in an appropriate volume not usually exceeding 10 ml/kg (1 ml/100g) body weight of experimental animals (mice and rats) for non-aqueous solvent in oral route of administration. However in the case of aqueous solvents, 20 ml/kg (2 ml/100g) body weight can be considered (OECD, 2000). Large dose volumes (40 ml/kg body weight) can cause unnecessary stress to animals and can also overload the stomach capacity and pass immediately into the small bowel or can result in passive reflux in the stomach, aspiration pneumonia, pharyngeal, esophageal, and gastric irritation or injury with stricture formation, esophageal and gastric rupture and stress (Germann & Ockert, 1994; Hejgaard, et al., 1999; Bonnichsen, et al., 2005). Lower volume (5 ml/kg) can be considered to dissolve highly soluble solute drugs. Such low volume would ease the administration of drug in solution. However, highly viscous drug solution should be diluted, whenever possible, for ease of administration. However, final dilution volume should not exceed 20 ml/kg. Based on 10 ml/kg volume selection, required dose volume for a 100 g rat can be calculated as follows; × 10 ml = 1 ml