Hydralazine is a direct-acting vasodilator used to treat high blood pressure (hypertension) and heart failure, often combined with other drugs. It works by relaxing the smooth muscles in the walls of the arteries, which lowers systemic vascular resistance and blood pressure. Using hydralazine in older adults requires special consideration due to age-related physiological changes that can alter the drug’s effects and increase the risk of adverse reactions. These changes make the elderly population susceptible to side effects, necessitating careful dosing and monitoring.
Common Cardiovascular Reactions
Hydralazine’s function of lowering blood pressure causes its most common cardiovascular side effects. Orthostatic hypotension, a sudden drop in blood pressure upon standing, is concerning in older patients. This can lead to dizziness, lightheadedness, and syncope, increasing the risk of falls and injuries.
The body attempts to compensate for the rapid decrease in blood pressure by increasing the heart rate, known as reflex tachycardia. This can manifest as palpitations. In older adults, especially those with underlying coronary artery disease, this increased cardiac stimulation can lead to chest pain, anginal attacks, or myocardial ischemia.
Other common reactions include headache and flushing. Patients may also experience peripheral edema (fluid retention), usually in the legs and ankles. This often requires a diuretic medication to manage the sodium and water retention induced by the blood pressure drop.
Unique Vulnerabilities in Older Patients
Older patients face unique challenges with hydralazine due to age-related shifts in how the body processes and responds to medications. A significant factor is the decline in renal function that often accompanies aging, leading to slower drug clearance. Although hydralazine is largely metabolized by the liver, its metabolites are excreted through the urine; reduced kidney function can cause these compounds to build up in the bloodstream.
Metabolism of hydralazine involves acetylation, which varies widely among individuals. Older adults who are “slow acetylators” metabolize the drug less efficiently, resulting in higher blood concentrations and a prolonged effect. This increases the risk of adverse reactions, necessitating lower starting doses for this population.
Changes in body composition also contribute to vulnerability, as older individuals generally have a higher fat-to-lean muscle ratio. Since hydralazine is relatively fat-soluble, this altered distribution can affect how the drug is stored and released over time. These physiological changes necessitate a cautious approach, involving starting at a low dose and gradually increasing it while closely monitoring the patient’s response.
Monitoring for Severe or Delayed Reactions
Hydralazine carries a risk of severe, delayed adverse reactions that require long-term vigilance. The most notable is Drug-Induced Lupus Erythematosus (DILE), a syndrome resembling systemic lupus erythematosus. The risk of DILE depends on both the dose and the duration of therapy, with the highest risk associated with doses greater than 200 mg per day.
Symptoms of DILE can include arthralgia, arthritis, fever, and fatigue, and may develop months or even years after starting the medication. More severe manifestations can involve the lungs or kidneys. If a patient develops these symptoms, the medication should be discontinued, as the condition typically resolves after the offending drug is stopped.
Regular blood tests are important for long-term monitoring, particularly in patients on higher doses. An Antinuclear Antibody (ANA) titer test may be used to screen for autoimmunity, though a positive ANA alone does not confirm DILE. Monitoring baseline and ongoing kidney function through tests like creatinine clearance is necessary to detect potential drug accumulation or kidney involvement.