In Vivo Preclinical Studies

In vivo studies, in comparison to in vitro, take place within a living organism. In preclinical trials, this happens within animal subjects. In vivo studies can address the major limitation of in vitro studies, they can demonstrate the impact of a pharmaceutical on the body as a whole, rather than how it impacted isolated cells. However, although in vivo studies solve the disadvantages of in vitro studies, they also have their limitations. Although in vivo studies face major ethical considerations, they are likely to remain an essential part of preclinical research.

The process of drug development begins with the discovery of new drugs, which includes target selection and lead discovery. Fig.1 The process of drug development begins with the discovery of new drugs, which includes target selection and lead discovery. (Brake, 2017)

Animal Models Test

Before a drug candidate is tested in human subjects, it must undergo rigorous animal testing to further evaluate its toxicity, metabolism, and overall efficacy. Vertebrate animal models such as rodents, primates, dogs, and rabbits are commonly used for preclinical in vivo studies. Mice share 95% of their genes with humans, which makes them very attractive models for studying human diseases. These factors contribute to their usefulness when it comes to evaluating the safety and efficacy of drug candidates at the preclinical stage.

Toxicology and Efficacy Study

Researchers must demonstrate not only that a new therapeutic candidate is effective against a target disease but also that it is safe at the dose intended for human treatment. Lack of efficacy and toxicity are considered to be major reasons for drug failures and pharmacokinetics governs them to a large extent. Compound with favorable pharmacokinetics is more likely to be efficacious and safe. Therefore, the preclinical pharmacokinetic evaluation should be comprehensive enough to ensure that compounds do not fail in the clinic. Toxicity study is the foundation of an INDA (Investigational new drug application) and therefore, the final selection of a compound can be performed only after proper toxicological evaluation in animal models.

Bioavailability and Bioequivalence in Drug Development

Bioavailability is referred to as the extent and rate to which the active drug ingredient or active moiety from the drug product is absorbed and becomes available at the site of drug action. When two formulations of the same drug or two drug products are claimed bioequivalent, it is assumed that they will provide the same therapeutic effect or that they are therapeutically equivalent. In this case, most people interpret that they can be used interchangeably.

The Need for In Vivo Research

Drug discovery begins with target selection and leads to discover which can progress into identifying the characteristics of possible medicines ascertained by preclinical trials. The preclinical stage encompasses the use of in vitro and in vivo studies to develop a drug that can safely and effectively be administered for clinical trials. In vivo studies are essential to drug development because they provide the ability to evaluate a drug’s characteristics, including physiological and biochemical processes, such as adverse effects and drug-drug interactions that cannot be observed in vitro. Many challenges surrounding in vivo studies can be overcome by choosing an animal model that best illustrates the human system the drug will affect.

There are limitations for the study of drug dispersion and permeability in vitro and the inability for in vitro studies to accurately mimic a live biological system which produces the need for in vivo studies. The in vitro method of dissolution testing can characterize how an active pharmaceutical ingredient is extracted out of a solid dosage form and can indicate the efficiency of in vivo dissolution, but does not provide any information on drug substance absorption or drug-drug interactions within a system.

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Reference

  1. Brake, K.; et al. In vivo Studies for Drug Development via Oral Delivery: Challenges, Animal Models and Techniques. Pharm Anal Acta. 2017: 2153-2435
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