Background/Objectives: Fexofenadine hydrochloride is a widely prescribed drug for treating histamine-mediated allergic reactions. This review systematically collates existing research on the clinical pharmacokinetics (PK) of fexofenadine, with a copious emphasis on examining the impact of stereoisomerism, disease states, and drug interactions. Methods: The search engines PubMed, Science Direct, Google Scholar, and Cochrane were scanned systematically for articles concerning the clinical PK of fexofenadine in humans. The extensive literature search yielded 85 articles meeting the inclusion standards. Results: The PK parameters of fexofenadine showed a linear correlation between increasing doses and proportional elevations in PK parameters such as area under the curve from time 0 to infinity (AUC_0–∞) and maximum plasma concentration (C_max). Under fed conditions, its bioavailability was reduced by approximately 50%. Findings from patients with end-stage renal disease (ESRD) displayed a 63% decline in oral clearance (CL/F) of fexofenadine. A drug–food interaction study has displayed that grapefruit juice decreased C_max (201 ng/mL vs. 128 ng/mL), accompanied by a 30% reduction in the bioavailability of fexofenadine. Furthermore, a drug–herb interaction study with St John’s Wort (SJW) has reported a reduction in CL/F by 10% after a single dose, but long-term administration reversed this effect, resulting in elevated CL/F by 17% of fexofenadine. Conclusions: Since no prior systematic review on the PK of this drug exists, this review amalgamates all pertinent PK parameters in humans by pooling up-to-date data from published studies. This detailed literature review can be advantageous for researchers who want to develop and assess PK models.

The physiologically based pharmacokinetic (PBPK) modeling is an in-silico technique that determines drug pharmacokinetics (PK) by considering blood circulation and tissue composition within the body. Fexofenadine is an H₁ receptor antagonist drug recommended for treating seasonal allergic rhinitis and chronic idiopathic urticaria. This study aimed to build a PBPK model of fexofenadine to predict its systemic exposure in healthy, diseased, and pediatric populations. The modeling process commenced with a meticulous literature review to collect pertinent PK data on fexofenadine, which was then consolidated into the PK-Sim simulator to develop a drug-specific model in the healthy population. The model was then extrapolated to patients with chronic kidney disease (CKD) and pediatrics by employing disease and age-related physiological variations. Visual predictive checks were executed to substantiate the model’s accuracy, along with the computation of observed-to-predicted ratios (R_Obs/Pre), average fold error (AFE), and absolute average fold error (AAFE). The developed PBPK model successfully predicted fexofenadine’s PK with AFE values of 0.98, 0.58, and 1.21 for CL/F in healthy, diseased, and pediatric populations, which were confined within a two-fold error range. Furthermore, box-and-whisker plots were generated to critically analyze drug concentration at varying stages of CKD. The presented model offers indispensable insights that may assist clinicians in determining dosing strategies in patients with kidney disease.