Cardiovascular patients taking multiple medications for other ailments are at increased risk of drug interactions and adverse reactions. Different drugs have different, specific targets that can adversely affect any heart’s four chambers or coronary arteries with differing end results.
Drugs are extensively researched and tested to ensure that interaction with a specific target molecule achieves the desired therapeutic effect. Research organisations such as Vivonics have been working for many years to assess the effects of new drugs on vital organs, for example, using fully implantable telemetry devices to assess the effects of a drug molecule on the cardiovascular system. In particular, they work to minimise or eradicate what is referred to as off-target activities, which can be harmful to the patient and are commonly known as Adverse Drug Reactions (ADRs).
Common Adverse Drug Reactions
The most common ADRs are nausea, fatigue, headache and diarrhoea, which, while inconvenient and often unpleasant for the patient, are not life-threatening. However, some common drugs can cause more severe ADRs.
ADRs of Major Concern
#1 Arrhythmias
Arrhythmias are altered heart rhythms. Typically, they can be irregular, too fast or too slow and are often described as palpitations. The most common types of arrhythmia are atrial fibrillation (irregular heart rate), supraventricular tachycardia (too fast heart rate) and heart block (abnormal rhythm). Arrhythmias can be caused by the effects of drugs on the heart’s electrical activity and affect individual myocytes’ ion channels.
In the 1990s, several drugs were withdrawn from the market due to the findings of a blockade of a specific potassium channel in myocytes and a QT interval prolongation on ECG with a fatal arrhythmia. Some drugs, such as dofetilide for atrial fibrillation, droperidol for treating nausea and vandetanib for cancer indications, still carry risk warnings for arrhythmia.
#2 Bradycardia and Tachycardia
Bradycardia means a heart rate which is too slow, commonly below 60 beats per minute in the average patient. Whilst not a common ADR, certain cancer drugs such as crizotinib can cause or exacerbate a too-slow heart rate and cause fainting or dizziness.
Tachycardia is a heart rate which is too fast, typically above 100 beats per minute, and can cause the ventricles to fill inadequately, compromising the blood flow to the rest of the body. Palpitations, chest discomfort, fatigue and light-headedness can result. Prolonged tachycardia could lead to the weakening of the heart muscle (cardiomyopathy) and heart failure. Tachycardia is known to be caused or worsened by tricyclic antidepressants or SNRIs such as duloxetine and adrenergic agonists, among others.
#3 Hypertension and Hypotension
Blood pressure of more than 140/90mmHg (150/90mmHg in those over 80) is high or hypertension. Symptomless, it can cause heart attacks, strokes, heart failure, aneurysms, vascular dementia or kidney disease if untreated. Drugs known to cause hypertension include Naproxen, an anti-inflammatory painkiller and ephedrine, a decongestant. Some cancer medications, e.g. VEGF inhibitors, can also cause hypertension.
Hypotension and low blood pressure (less than 90/60mmHg) can be symptomless or cause problems with balance or fainting. Postural hypotension can lead to falls, fractures and ischaemic events. Many drugs can cause hypotension and worsen orthostatic hypotension, e.g. alpha antagonists and SGL2 inhibitors.
#4 Cardiomyopathy and Heart Failure
Cardiomyopathy is a heart muscle disease that compromises the efficient pumping of blood around the ventricles and leads to heart failure when insufficient blood is pumped. Drugs such as beta-blockers and calcium channel antagonists can affect the heart’s ability to pump blood properly.
Drugs such as anthracyclines can cause direct cardiotoxicity at the myocyte level with structural and functional changes to the heart’s ability to pump blood. Some NSAIDs can contribute to heart failure.