A nurse is caring for a client who is taking lovastatin and has a new prescription for ezetimibe to lower cholesterol levels.
Which of the following laboratory values should the nurse monitor?

Choice A rationale

Allopurinol is a xanthine oxidase inhibitor. This enzyme is crucial in the purine catabolism pathway, converting xanthine and hypoxanthine into uric acid. By inhibiting xanthine oxidase, allopurinol effectively decreases the de novo synthesis of uric acid, thereby lowering serum uric acid levels. This reduction prevents the formation of uric acid crystals in joints and tissues, which are responsible for the painful manifestations of gout.

Choice B rationale

Tophus formation is a direct consequence of chronic hyperuricemia, where uric acid crystals accumulate in soft tissues, leading to palpable nodules. Allopurinol's primary mechanism of action is to reduce uric acid levels. By achieving this, it prevents further crystal deposition and can even lead to the regression of existing tophi over time. Therefore, it does not increase tophus formation.

Choice C rationale

Allopurinol's mechanism of action is specifically related to uric acid metabolism. It does not directly influence calcium homeostasis in the body. Calcium levels are primarily regulated by parathyroid hormone, calcitonin, and vitamin D, which are distinct physiological pathways unrelated to xanthine oxidase inhibition. Therefore, it does not lower calcium levels.

Choice D rationale

While allopurinol ultimately helps relieve joint inflammation in gout, it does so indirectly. Its primary action is to reduce uric acid production, which then prevents the formation of inflammatory uric acid crystals. The direct reduction of inflammation is typically achieved by anti-inflammatory drugs like NSAIDs or colchicine, which act on inflammatory mediators or pathways, not directly by allopurinol.

Choice A rationale

Cromolyn is a mast cell stabilizer that works by inhibiting the release of inflammatory mediators like histamine from mast cells. This prophylactic action requires consistent, daily use to build up therapeutic levels and prevent the initiation of the asthmatic response, rather than acting as a rescue medication during an acute attack.

Choice B rationale

Using cromolyn as soon as one feels like wheezing is incorrect because cromolyn is not a bronchodilator and does not provide immediate relief for acute bronchospasm. Its mechanism of action involves stabilizing mast cells, which prevents the degranulation and release of inflammatory mediators, thus preventing symptoms from occurring.

Choice C rationale

Expecting to feel better in a week is an inappropriate timeframe for assessing cromolyn's efficacy. The full prophylactic benefits of cromolyn may take several weeks of consistent use to become apparent. Patients should be educated on the preventative nature and delayed onset of action.

Choice D rationale

While cromolyn can be used prophylactically before exercise, using it 2 hours before playing softball is not the recommended timing. For exercise-induced bronchospasm, cromolyn is typically administered 15 to 30 minutes prior to the activity to allow for adequate absorption and mast cell stabilization before exertion.