At 4 to 5 half lives the concentration of drug in blood is

Correct Answer: A

Rationale: The concentration of a drug in the blood decreases by half with each half-life. Thus, after 4 to 5 half-lives, the amount of drug remaining in the blood would be approximately 6.25% to 3.125% of the original concentration. This translates to the concentration being around 50% or less, making the correct answer A. 50%.

Correct Answer: C

Rationale: Lithium is commonly used as a mood stabilizer in the treatment of bipolar disorder. It helps reduce the intensity of manic episodes, thereby stabilizing the patient's mood and preventing extreme mood swings. While lithium is primarily known for its mood-stabilizing effects, it is not used to lower blood glucose, slow the heart, or heal ulcers.

Correct Answer: C

Rationale: Iron is classified as an Antianemic agent. Anemia is a condition characterized by a lack of healthy red blood cells, which are responsible for carrying oxygen to the body's tissues. Iron is essential for the production of hemoglobin, the protein in red blood cells that binds oxygen. Therefore, iron supplements are commonly used to treat iron-deficiency anemia by replenishing the body's iron stores and supporting the production of healthy red blood cells.

Correct Answer: A

Rationale: Dopamine has a short half-life due to rapid metabolism by monoamine oxidases and catechol-O-methyltransferase, while others have longer half-lives.

Correct Answer: C

Rationale: A P450 enzyme inducer (e.g., rifampin) speeds metabolism of itself and other drugs, reducing its own effect over time as levels drop faster, requiring dose adjustments. No effect on others is extreme-some drugs' metabolism increases, lowering their effect. Increased effects suggest inhibition, not induction. Self-induction lowers efficacy, a pharmacokinetic principle affecting long-term use.