The primary goal of drug therapy is to achieve the intended therapeutic effect with minimal adverse or toxic outcomes. This review discusses the importance of pharmacokinetics in designing dosage regimens that optimize drug therapy for individual patients. Dose calculation must consider the patient’s pathological and physiological conditions, especially in special populations like children, the elderly, and patients with renal or hepatic diseases. Clinicians must ensure precision in dosing to maximize therapeutic efficacy and safety. © 2020 Elsevier B.V., All rights reserved.