Which of the following drug used against bronchial asthma follows zero order kinetics
**Core Concept**
Asthma is a chronic inflammatory disease of the airways characterized by recurrent episodes of wheezing, shortness of breath, chest tightness, and coughing. Certain medications used to manage asthma, such as theophylline, exhibit unique pharmacokinetic properties.
**Why the Correct Answer is Right**
Theophylline, a methylxanthine derivative, is a bronchodilator used in the treatment of asthma. It follows zero-order kinetics at therapeutic concentrations, meaning that the rate of elimination is independent of the concentration of the drug in the body. This is due to the fact that theophylline is metabolized by the enzyme cytochrome P450 1A2 (CYP1A2), which is saturated at therapeutic concentrations, leading to a constant rate of elimination.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a drug used in asthma treatment that follows zero-order kinetics.
* **Option B:** This option is incorrect because it is not a correct statement about the pharmacokinetics of theophylline.
* **Option D:** This option is incorrect because it is not a correct statement about the pharmacokinetics of theophylline.
**Clinical Pearl / High-Yield Fact**
Theophylline is a narrow therapeutic index medication, and its plasma concentration should be monitored closely to avoid toxicity. A theophylline level of 10-20 μg/mL is considered therapeutic, while levels above 20 μg/mL increase the risk of toxicity.
**Correct Answer:** C. Theophylline.