Drugs which increase level of theophylline include:
**Core Concept**
Theophylline is a methylxanthine medication used to treat respiratory diseases such as asthma and COPD. Its plasma concentration is affected by various drugs that either inhibit or induce its metabolism, thereby altering its pharmacokinetics.
**Why the Correct Answer is Right**
Theophylline is primarily metabolized by the cytochrome P450 enzyme CYP1A2 in the liver. Certain drugs can inhibit this enzyme, leading to increased theophylline levels. These include ciprofloxacin, a fluoroquinolone antibiotic, which is known to inhibit CYP1A2 and thus increase theophylline concentrations. Other drugs like cimetidine, a histamine H2-receptor antagonist, and erythromycin, a macrolide antibiotic, also have this effect.
**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect as it does not affect theophylline levels.
**Option B:**
This option is incorrect as it actually decreases theophylline levels by inducing CYP1A2.
**Option C:**
This option is incorrect as it is not known to affect theophylline levels.
**Clinical Pearl / High-Yield Fact**
When prescribing theophylline, it's essential to consider potential drug interactions, especially with other medications that can inhibit or induce its metabolism. This includes antibiotics like ciprofloxacin, which can increase theophylline levels, potentially leading to toxicity.
**Correct Answer: C. Cimetidine. Cimetidine increases theophylline levels by inhibiting CYP1A2.**