Which of the following transdermal products is used once weekly?

Transdermal therapeutic systems (TTS) are designed to deliver a steady state of medication across the skin into the systemic circulation. These patches use either a reservoir or matrix design to control the rate of drug release over a specific duration. The wear time is determined by the drug's half-life and the patch's diffusion capacity. Proper patient education regarding the frequency of patch changes is critical to avoid sub-therapeutic levels or drug accumulation. Rationale: A. Daytrana is a methylphenidate patch used for ADHD and is applied daily. It is specifically designed to be worn for only 9 hours and then removed to avoid insomnia and mimic the pharmacokinetic profile of oral stimulants. It does not have the drug reservoir capacity to maintain therapeutic levels for an entire week. Daily application is required for symptom management. B. Catapres-TTS-3 contains clonidine and is specifically engineered for once-weekly application. The patch utilizes a programmed delivery system that maintains a constant plasma concentration of the antihypertensive agent for 7 days. This long duration improves patient adherence by reducing the frequency of dosing. It is one of the most common examples of a long-acting transdermal system. C. NicoDerm CQ is a nicotine replacement patch used for smoking cessation that must be replaced every 24 hours. Continuous nicotine delivery is required to manage withdrawal symptoms, but the patch does not contain enough active ingredient to last beyond one day. A fresh patch is needed daily to maintain consistent serum nicotine levels. Using it weekly would lead to treatment failure. D. Nitro-Dur contains nitroglycerin and is typically worn for only 12 to 14 hours a day. It requires a "patch-free" interval of 10 to 12 hours to prevent the development of nitrate tolerance. Because the body quickly desensitizes to continuous nitroglycerin, a weekly patch would be clinically ineffective. Daily application and removal are the standard therapeutic protocol. E. Vivelle-Dot is an estradiol patch used for hormone replacement therapy and is applied twice weekly. The patch is changed every 3 to 4 days (e.g., on Monday and Thursday) to maintain stable estrogen levels. While it lasts longer than a daily patch, it does not reach the seven-day duration of a clonidine patch. It is a multi-day but not weekly system.