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The success of drug therapy is highly dependent on the choice of the drug, the drug product, and the design of the dosage regimen. The choice of the drug is generally made by the physician after careful patient diagnosis and physical assessment. The choice of the drug product (eg, immediate release vs modified release) and dosage regimen are based on the patient's individual characteristics and known pharmacokinetics of the drug as discussed in earlier chapters. Ideally, the dosage regimen is designed to achieve a desired drug concentration at a receptor site to produce an optimal therapeutic response with minimum adverse effects. Individual variation in pharmacokinetics and pharmacodynamics makes the design of dosage regimens difficult. Therefore, the application of pharmacokinetics to dosage regimen design must be coordinated with proper clinical evaluation of the patient. For certain critical-dose drugs, monitoring both the patient and drug regimen is important for proper efficacy.

Medication Therapy Management (MTM) was officially recognized by the US Congress in the Medicare Prescription Drug, Improvement, and Modernization Act of 2003.1 The objective of this act is to improve the quality, effectiveness, and efficiency of healthcare delivery including prescription drugs. An MTM program is developed in cooperation with pharmacists and physicians to optimize therapeutic outcomes through improved medication use. MTM provides consultative, educational, and monitoring services to patients to obtain better therapeutic outcomes from medications by the enhanced understanding of medication therapy, improved compliance, control of costs, and prevention of adverse events and drug interactions. MTM programs have been developed for specific practice areas such as elderly care, diabetes, and asthma (Barnett et al, 2009).

Not all drugs require rigid individualization of the dosage regimen. Many drugs have a large margin of safety (ie, exhibit a wide therapeutic window), and strict individualization of the dose is unnecessary. For a number of drugs generally recognized as safe and effective (GRAS), the US Food and Drug Administration (FDA) has approved an over-the-counter (OTC) classification for drugs that the public may buy without prescription. In addition, many prescription drugs, such as ibuprofen, loratidine, omeprazole, naproxen, nicotine patches, and others, that were originally prescription drugs, have been approved by the FDA for OTC status. These OTC drugs and certain prescription drugs, when taken as directed, are generally safe and effective for the labeled indications without medical supervision. For drugs that are relatively safe and have a broad safety-dose range, such as the penicillins, cephalosporins, and tetracyclines, the antibiotic dosage is not dose titrated precisely but is based rather on the clinical judgment of the physician to maintain an effective plasma antibiotic concentration above a minimum inhibitory concentration. Individualization of the dosage regimen is very important for drugs with a narrow therapeutic window (also known as critical dose drugs and narrow therapeutic index, NTI drugs), such as digoxin, aminoglycosides, antiarrhythmics, anticoagulants, anticonvulsants, and some antiasthmatics, such as theophylline. Critical-dose drugs are defined as those drugs where comparatively small ...

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