Recordings of animal experimentation performed by physicians were found in the 2nd century BCE. Galen, a Roman physician introduced vivisection in the 2nd century. Other notable physicians are Aristotle, Erasistratus, Herophilus, Praxagon and Diocles. Animals have always been used in medical research. In the 19th centuries, the expansion of medical field resulted in an increase in the number of animals used in research (Franco, 2013).

In 1937, a pharmaceutical company in the USA marketed a product called “Elixir Sulfanilamide” made from sulphanilamide, using diethylene glycol (DEG) as a solvent. DEG was poisonous to human but the company was not aware of it. The product was not tested on animals and led to deaths of more than a hundred people.

This incident leads to the passing of 1938 Food, Drug, and Cosmetic Act, which required new drugs to be tested on animals before being marketed by a company. The practice of animal testing in research resulted in a significant advance in the study of diseases and scientists also become more aware of the ethics and social issues aroused. They started to follow the three Rs: Reduction (reduce the use of animals), Replacement (replace the use of animals with alternatives techniques) and Refinement (minimize pain and suffering for the animals used) (Hajar, 2011).There are other alternatives to the use of animals in research such as in vitro test methods, computer models and microdosing. In the in vitro method, cells grow outside of the body in a laboratory environment. The cells and tissues from the liver, kidney, brain, skin etc. are obtained from an animal and grow in a suitable medium for use. In vitro culture of animal/human cells grows as a monolayer over the surface of culture plates and isolates from each other.

Membrane fragments and cellular enzymes are also used. Different cultures are used for a various purposes such as cell culture, tissue culture, callus culture and organ culture. This method is cheap, easy to follow and less time consuming and used for preliminary screening of drug molecules, chemicals and cosmetics molecules to check their toxicity and efficacy. For example, the eye irritancy test requires the test on rabbits, but scientists suggested an alternative method which uses bovine corneal organ culture. Various analytical methods are used in the cultured medium to evaluate the toxicological effect of test chemical irritancy in vitro (Doke & Dhawale, 2015).Computer generated stimulations test a chemical or potential drug of its biological and toxic effect without animal dissection. Specialized computer models and software programs help to design medicines.

Computer Aided Drug Design (CADD) is a software known to predict the receptor binding site for a drug molecule. In vivo experimentation is inevitable to know the receptor binding site for a potential drug molecule. Only promising molecules obtained from primary screening are used in vivo experimentation. CADD is able to identify probable binding sites thus avoiding a tests of chemicals having no biological activity.

This software also helps in the making of new drugs for a specific binding site before animal testing is done to obtain confirmatory results and this helps in lowering the number of experimental animals used (Doke & Dhawale, 2015).Microdosing is a method where humans are given low quantities of a drug to test the effects on the body on the cellular level together with the use of imaging techniques. The original concept of microdosing is the assessment of human pharmacokinetics prior to full Phase I clinical trials. The basic approach is to label a candidate drug using radioisotope 14C, then a therapeutic dose is administered to human volunteers containing about 1-100µg, which is 100x lower than the proposed therapeutic dosage, following with the use of accelerator mass spectrometry (AMS). In human microdose study, sensitive analytical technologies such as AMS are required to measure the ionic species according to mass-to-charge ratio due to the low plasma drug concentrations. The small doses administered has a low toxicological risk therefore it can be tested on humans instead of animals. Microdosing can be used to determine the behaviour of drug reaching its intended target tissues in human subjects. In drug development, microdose studies can be performed before the administration of therapeutic doses and before the therapeutic data are published.

The technique has now further developed to assess the magnitude of drug-drug interactions and the study of polymorphisms and transporters. Before entering of Phase I trial, a microdose study is conducted for the limited safety toxicology, allowing a drug-drug interaction study to be performed in humans. The comparison of pharmacokinetics of the administration of development drug as a microdose before and after pharmacological active doses of a suitable inducer or inhibitor of chosen enzyme or transporter is conducted under the condition that the development drug is a victim of a drug-drug interaction and the marketed drug is the perpetrator. Microdose study has also been used to examine the relationship between polymorphisms and drug transporters. This method reduces cost and time to development decisions as well as does not use animals in the experiment (Lappin et al., 2013).

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