Background <p>Limited research has explored the genetic variability of CYP3A4 and CYP3A5 in the Saudi population, particularly concerning tacrolimus (Tac) therapy among Saudi kidney transplant patients (SKTP).</p> Objectives <p>To investigate specific CYP3A4 and CYP3A5 polymorphisms in SKTP and evaluate their influence on Tac dose requirements and trough levels.</p> Methods <p>A total of 251 Saudi participants were recruited, comprising 129 kidney transplant patients and 122 healthy volunteers. Genomic DNA was extracted, and polymorphisms in CYP3A4 (*1B, *6, *18, *22) and CYP3A5 (*2, *3, *4) were analyzed using real-time PCR and allele-specific sequencing. Genotype frequencies and minor allele frequencies (MAF) were calculated, and the impact of CYP3A variants on Tac dosing and trough levels (C0) was assessed in SKTP.</p> Results <p>The CYP3A41B polymorphism was absent, with all participants being homozygous wild type (G/G). For CYP3A5*3, 98.4% of participants carried the mutant genotype (*3/*3), while 1.6% carried the wild-type genotype (*1/*1). Patients with the wild-type allele (*1/*1) required significantly higher Tac doses and exhibited lower trough concentrations (C0) compared to those with the mutant genotype (*3/3). Other polymorphisms, such as CYP3A4*22, were rare, with approximately 90% of participants carrying the wild-type allele.</p> Conclusion <p>This study highlights the high prevalence of the CYP3A5*3/*3 genotype and wild-type CYP3A4 alleles in the Saudi population. The genetic variability significantly affects Tac trough levels and dosing requirements necessary to achieve therapeutic targets. These findings underscore the importance of pharmacogeneticguided Tac dosing to optimize therapeutic outcomes in SKTP</p>