From the Guidelines
Yes, clonidine does affect heart rate, typically lowering it as part of its action as a centrally-acting alpha-2 adrenergic agonist. When taken at therapeutic doses (usually 0.1-0.3 mg two to three times daily for adults), it reduces sympathetic outflow from the central nervous system, which decreases heart rate, blood pressure, and peripheral vascular resistance. This heart rate reduction is most noticeable when starting the medication or increasing the dose, and patients may experience a decrease of 5-15 beats per minute. The effect on heart rate is why clonidine should be tapered gradually rather than stopped abruptly, as sudden discontinuation can cause rebound hypertension and reflex tachycardia, as noted in the 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults 1. Patients with existing bradycardia or heart block should use clonidine cautiously, and those taking other medications that slow heart rate (like beta-blockers or certain calcium channel blockers) should be monitored for excessive bradycardia when using clonidine concurrently.
Some key points to consider when prescribing clonidine include:
- Starting with a low dose (0.1 mg) and gradually increasing as needed and tolerated
- Monitoring blood pressure and heart rate regularly
- Avoiding abrupt discontinuation and instead tapering the dose to prevent rebound hypertension
- Being cautious in patients with pre-existing heart conditions or those taking other medications that affect heart rate or blood pressure
- Considering the potential for clonidine to cause significant CNS adverse effects, especially in older adults, as noted in the guidelines 1.
It's also worth noting that clonidine is generally reserved as a last-line treatment due to its significant CNS adverse effects, especially in older adults, as mentioned in the guidelines 1. However, the most recent and highest quality study on this topic, which is the 2019 clinical practice guideline for the diagnosis, evaluation, and treatment of attention-deficit/hyperactivity disorder in children and adolescents 1, provides additional context on the use of clonidine in specific populations.
Overall, clonidine's effect on heart rate is a critical consideration in its use, and careful monitoring and gradual dose adjustments are necessary to minimize the risk of adverse effects, as supported by the evidence from the guidelines 1.
From the FDA Drug Label
CLINICAL PHARMACOLOGY Clonidine stimulates alpha-adrenoreceptors in the brain stem. This action results in reduced sympathetic outflow from the central nervous system and in decreases in peripheral resistance, renal vascular resistance, heart rate, and blood pressure. Slowing of the pulse rate has been observed in most patients given clonidine, but the drug does not alter normal hemodynamic response to exercise.
Clonidine affects heart rate (HR) by decreasing it. This is evident from the decrease in heart rate and slowing of the pulse rate observed in most patients given clonidine 2.
From the Research
Effect of Clonidine on Heart Rate
- Clonidine has been shown to decrease heart rate in various studies 3, 4, 5, 6, 7.
- The reduction in heart rate is thought to be mediated through the drug's effects on the autonomic nervous system, specifically by increasing vagal tone 3, 6.
- Studies have demonstrated that clonidine can reduce the variability of heart rate and blood pressure, leading to a more stable cardiovascular system 4.
- The decrease in heart rate is often accompanied by a reduction in blood pressure, which can be beneficial for patients with hypertension or heart failure 3, 4, 5.
- Clonidine has also been shown to be effective in slowing ventricular rate in patients with rapid atrial fibrillation, with a significant decrease in heart rate observed in patients treated with the drug 7.
- The mechanism by which clonidine reduces heart rate is thought to involve a lengthening of the diastolic period, allowing vagal volleys to arrive at the heart just in time to postpone the next beat 6.