Food Effects, Pharmacokinetic Drug–Drug Interactions, and Clinical Optimization of Oral Anticancer Agents

Oral targeted therapies now constitute a substantial and growing share of the anticancer armamentarium, shifting drug administration from the controlled intravenous setting to the patient’s home, where systemic exposure becomes contingent on factors that parenteral therapy largely bypasses. Absorption variability, food effects, gastric pH, first-pass metabolism, transporter activity, organ function, concomitant medications, and adherence each contribute to interpatient and intrapatient variability in exposure, and many oral anticancer agents possess narrow therapeutic indices in which modest exposure changes carry clinical consequence. This review synthesizes the pharmacokinetic determinants of oral anticancer drug exposure across twenty-seven exemplar agents spanning the major mechanistic classes—tyrosine kinase, cyclin-dependent kinase 4/6, poly(ADP-ribose) polymerase, Bruton tyrosine kinase, B-cell lymphoma 2, BRAF/MEK, ALK, mTOR, and androgen-axis inhibitors—and translates them into actionable pharmacy practice. We examine the physicochemical and physiological basis of food effects, distinguishing agents that require fasting administration from those that should be taken with food and those with flexible dosing. We address the often underappreciated interaction between acid-suppressive therapy and pH-dependent agents, the dominant role of cytochrome P450 3A4 and the efflux transporters P-glycoprotein and breast cancer resistance protein in mediating drug–drug interactions, and the exposure–response and exposure–toxicity relationships that motivate emerging therapeutic drug monitoring. We highlight several agents whose pharmacokinetic profile diverges sharply from class expectations—including the contrasting acid-suppression sensitivity of acalabrutinib versus ibrutinib, and the perpetrator role of enzalutamide and apalutamide as strong CYP3A4 inducers—and we consider special populations in whom altered pharmacokinetics necessitate individualized management. Synthesizing this evidence, we propose a structured framework through which oncology pharmacists can operationalize pharmacokinetic principles—encompassing interaction screening, meal-timing counseling, acid-suppression review, organ-function assessment, and toxicity monitoring—to optimize the safety and effectiveness of oral anticancer therapy within a precision medicine paradigm.