Detailed Explanation of the Differences Between Controlled-Release and Extended-Release Tablets, and Case Analysis of Aspirin Contraindications

What's the difference between controlled-release and sustained-release tablets? Many patients are often confused by different dosage forms of the same drug when buying medication. For example, the antihypertensive drug nifedipine is available in two forms at pharmacies: controlled-release and sustained-release. What are the differences between them? Which one is better? Dr. Zhou will focus on this topic in this lecture.

Controlled-release tablets: Also known as controlled-release formulations, these are preparations that release the drug slowly and at a constant rate within a specified medium. Controlled-release tablets make drug release more predictable and are not affected by gastrointestinal motility, pH, patient age, or whether the drug is taken with food.

A controlled-release tablet consists of an expansion chamber, a movable diaphragm, the drug, and a semi-permeable membrane with laser perforations. After entering the stomach, the expansion chamber acts like a sponge, absorbing water and expanding at a uniform rate. The drug is then slowly and at a constant rate pushed out through the diaphragm from the release orifice.

Controlled-release tablets: Release drug at a constant rate, resulting in stable efficacy. However, they should not be chewed or broken, as this will disrupt the tablet's overall structure, causing the entire drug to be released rapidly and leading to adverse effects.

Sustained-release tablets: Also known as sustained-release formulations, these are preparations that release drug slowly and at a non-constant rate within a specified medium. Generally, the drug release concentration is higher initially and then decreases, and pharmacokinetics are easily affected by the gastrointestinal environment, such as gastrointestinal motility and emptying rate, gastrointestinal pH, whether it is taken with food, and the patient's age. Blood drug concentration is less predictable.

Sustained-release tablets: Release drug at a higher initial rate and then decreases, not at a constant rate. Some sustained-release tablets can be broken and taken.

Case Study: Taking aspirin without understanding its benefits is extremely dangerous: Ms. Zhang, a 60-year-old woman, presented to our outpatient clinic with symptoms of palpitations and fatigue. Initial examination revealed a haggard appearance, pale lips, and an increased heart rate. An electrocardiogram (ECG) indicated sinus tachycardia. A blood test showed a hemoglobin level of 68 g/L, lower than the normal range of 110 g/L. A fecal occult blood test was positive. Based on this, the diagnosis was that her palpitations and fatigue were caused by anemia resulting from gastrointestinal bleeding.

Further questioning revealed that she was generally healthy and had no history of cardiovascular disease, hypertension, or diabetes. Six months prior, a friend had advised her to take aspirin to prevent cardiovascular disease, so she began taking 100 mg of aspirin after meals daily. Due to a lack of indication for aspirin and incorrect administration, she experienced adverse reactions—gastrointestinal ulceration and gastrointestinal bleeding.

Aspirin is a double-edged sword. While it is a cornerstone drug for treating cardiovascular diseases and can reduce the incidence and mortality of diseases, it also carries the risk of bleeding. Therefore, whether or not one can take aspirin should be determined by a doctor after evaluation.