A bradykinin cough is a specific type of cough that can develop as a side effect of certain medications. It is characterized by its persistent, dry, and non-productive nature, meaning it does not bring up mucus or phlegm. This cough is distinct from those caused by infections or common respiratory irritants, as it stems from a biochemical imbalance in the body.
Understanding Bradykinin Cough
This chronic, irritating cough often has a persistent, hacking quality. Patients may describe an itchy sensation in their throat that triggers the urge to cough. Unlike coughs associated with colds or allergies, it does not produce phlegm or mucus. This type of cough can significantly impact a person’s quality of life due to its relentless nature.
The onset of this cough can vary, sometimes appearing within the first few weeks to a month of starting a medication. In rare cases, it might be delayed for up to six months or even a year. Predicting who will develop this cough is challenging, as the most significant risk factor is having experienced it previously.
How Bradykinin Triggers a Cough
Bradykinin is a naturally occurring peptide in the body that plays a role in various bodily functions, including inflammation and the regulation of blood pressure. It acts as a local hormone by activating specific receptors, primarily B2 receptors, which mediate many inflammatory and cardiovascular effects. The body typically breaks down bradykinin with the help of an enzyme called angiotensin-converting enzyme (ACE).
When bradykinin accumulates in the airways, it can stimulate sensory nerves, specifically unmyelinated C-afferent fibers, which are involved in triggering the cough reflex. This stimulation leads to reflex bronchoconstriction and an increased sensitivity of the cough reflex.
Common Causes of Bradykinin Cough
The most common cause of a bradykinin cough is the use of angiotensin-converting enzyme (ACE) inhibitors. These medications are widely prescribed for conditions such as high blood pressure, heart failure, and chronic kidney disease. Common ACE inhibitors include lisinopril, enalapril, ramipril, and captopril, often identifiable by their “pril” ending.
ACE inhibitors work by blocking the angiotensin-converting enzyme, which is responsible for converting angiotensin I to angiotensin II, thereby lowering blood pressure. This enzyme also plays a role in breaking down bradykinin.
By inhibiting ACE, these medications prevent the normal breakdown of bradykinin, leading to its accumulation in the respiratory tract. This increased concentration of bradykinin then irritates the airways, triggering the persistent dry cough. The incidence of ACE inhibitor-induced cough can range from 5% to 35% of patients.
Addressing Bradykinin Cough
Managing a bradykinin cough involves confirming the diagnosis with a healthcare professional and discussing potential medication adjustments. Since ACE inhibitors are the primary cause, discontinuing the ACE inhibitor is often the most effective treatment. The cough usually resolves within one to four weeks after stopping the medication, though in some cases, it may take up to three months for complete resolution.
Healthcare providers may suggest switching to an alternative class of medication, such as an angiotensin receptor blocker (ARB). ARBs work on the same physiological pathway to manage blood pressure but do not interfere with the breakdown of bradykinin, thus significantly reducing the risk of a cough. Examples of ARBs include losartan, valsartan, and irbesartan.