Background: Tamoxifen is useful in managing breast cancer and it is reported to have significant variability in its pharmacokinetics. This review aimed to summarize reported population pharmacokinetics studies of tamoxifen and to identify the factors affecting the pharmacokinetics of tamoxifen in adult breast cancer patients. Method: A systematic search was undertaken in Scopus, Web of Science, and PubMed for papers published in the English language from inception to 20 August 2022. Studies were included in the review if the population pharmacokinetic modeling was based on non-linear mixed-effects modeling with a parametric approach for tamoxifen in breast cancer patients. Results: After initial selection, 671 records were taken for screening. A total of five studies were selected from Scopus, Web of Science, PubMed, and by manual searching. The majority of the studies were two-compartment models with first-order absorption and elimination to describe tamoxifen and its metabolites’ disposition. The CYP2D6 phenotype and CYP3A4 genotype were the main covariates that affected the metabolism of tamoxifen and its metabolites. Other factors influencing the drug’s pharmacokinetics included age, co-medication, BMI, medication adherence, CYP2B6, and CYP2C19 genotype. Conclusion: The disposition of tamoxifen and its metabolites varies primarily due to the CYP2D6 phenotype and CYP3A4 genotype. However, other factors, such as anthropometric characteristics and menopausal status, should also be addressed when accounting for this variability. All these studies should be externally evaluated to assess their applicability in different populations and to use model-informed dosing in the clinical setting.

<p class="abstract">Medical device means any instrument, apparatus, machine, appliance, implant, reagent for in vitro use, software, material or other similar or related article, intended by the manufacturer to be used, alone or in combination, for human beings, for one or more of the specific medical purpose. Medical devices are generally classified based on risks; the actual risk-based classification of the medical device depends upon its intended use and purpose.<strong> </strong>Development of an entirely new device typically begins with a concept by a physician or bioengineer for a solution to a medical problem. If the idea is determined to be workable and practical (proof of concept) an early design of the device, known as a prototype, will be built. A prototype device will undergo a cycle of preclinical testing, redesigning, preclinical testing of the redesign and so forth, until the design has been refined and tested to a point that it is ready for production and testing in humans. Preclinical animal tastings are conducted to provide reasonable evidence that novel technologies and therapies are safe and effective. When studying medical devices, clinical trials are not always required, and whether or not one will be conducted depends on a risk assessment. Post marketing surveillance is the practice of monitoring the safety of a medical device after it has been released on the market.</p>