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Table 1 Phases of R&D and Technology Readiness Levels (TRLs) in drug development

From: Insights into early stage of antibiotic development in small- and medium-sized enterprises: a survey of targets, costs, and durations

R&D Phase Description TRL
Research - Discovery activities, hit generation and testing Generation of chemical starting points (hits) from screens or other drug discovery strategies 2
Research - Lead compound identification Hits are evaluated and undergo limited optimization to identify promising lead compounds with meaningful activity against the target pathogens and possess the properties needed to make an effective and safe drug 3
Research - Lead compound optimization Modifying and testing lead compound series to improve compound properties; selecting a candidate drug for further preclinical studies 4
Development - Preclinical testing Conducting required toxicity and efficacy in vitro and vivo studies under good laboratory practice (GLP) protocols, and chemistry, manufacturing and control (CMC) studies 5
Development - Phase I clinical trials Testing the candidate drug in healthy volunteers to determine pharmacokinetics, safe dose ranges and identify common toxicity; pharmacokinetic data feed into pharmacokinetic/ pharmacodynamic (PK/PD) models to determine the most appropriate doses for the next phase 6
Development - Phase II clinical trials Testing the candidate drug in a small number of patients to obtain preliminary efficacy data and more short term safety information; refining PK/PD models 7
Development - Phase III clinical trials Testing on a larger number of patients to document efficacy, determine non-inferiority activity (or rarely superiority) and safety compared to other indicated drugs 8