Rational drug use aims to optimize the use of medications to achieve the best possible therapeutic outcome for the patient.

Polypharmacy, or the use of multiple medications, is generally not considered a principle of rational drug use. It can increase the risk of adverse effects and drug interactions.

Drug selection is the process of choosing the most appropriate medication for a patient based on their individual needs and characteristics.

All of the above factors should be considered when selecting a medication for a patient to ensure the best possible therapeutic outcome.

Patient education is the process of providing information to patients about their medications, including how to take them, potential side effects, and precautions to take.

Patient education can lead to improved adherence to medication regimens, reduced risk of adverse effects, and increased patient satisfaction, but it does not increase the cost of treatment.

Therapeutic drug monitoring is the process of measuring the concentration of a drug in a patient's blood or other body fluid to ensure that it is within the desired therapeutic range.

Therapeutic drug monitoring can lead to optimization of drug therapy, early detection of adverse effects, and prevention of drug interactions, but it does not increase the cost of treatment.

Deprescribing is the process of discontinuing a medication that is no longer needed or is causing harm to the patient.

Cost-effectiveness is not a reason for deprescribing a medication. Deprescribing is typically done when a medication is no longer needed or is causing harm to the patient.

Combination therapy is the process of using a combination of medications to treat a condition. This can be done to improve efficacy, reduce adverse effects, or prevent drug resistance.

Combination therapy can lead to improved efficacy, reduced adverse effects, and prevention of drug resistance, but it does not increase the cost of treatment.

Off-label use is the process of using a medication for a condition that is not approved by the regulatory authorities.

Cost-effectiveness is not a reason for off-label use of a medication. Off-label use is typically done when there is no approved medication for the condition or when approved medications are ineffective.

Long-term use is the process of using a medication for a longer period of time than is typically recommended.