Final answer:
The principle for dose selection in opioid therapy is 'Start low and go slow', emphasizing gradual dosage increases to achieve the desired effect while minimizing side effects, especially in patients with liver or kidney dysfunction.
Step-by-step explanation:
The principle that guides the dose selection to optimize the effects of opioid therapy is A. Start low and go slow. This approach is important to minimize the risk of side effects while still achieving a clinical cure. The process of determining the optimum dosage and route of administration of a medication is critical and involves various considerations including the patient's age, mass, and specific health conditions such as liver or kidney dysfunction which may affect drug metabolism and clearance.
For children, dosage is often based on the patient's mass, and for adults and children 12 years and over, there is usually a single standard dose. However, due to the variability in adult body mass, some experts suggest that mass should be considered for all patients when determining appropriate dosage. Moreover, to protect patients with liver or kidney issues, careful dosage adjustments are necessary to prevent toxicity due to increased drug levels resulting from reduced clearance from the body.