What is the effect of terazosin on pulse rate?

Effect of Terazosin on Pulse Rate

Terazosin typically causes a 6-10 beat per minute increase in heart rate during the first few hours after dosing when patients are in the erect position, while measurements taken 24 hours after dosing show no significant change in heart rate. 1

Mechanism of Action and Cardiovascular Effects

• Terazosin is a selective alpha-1 adrenoceptor antagonist that decreases blood pressure by reducing peripheral vascular resistance through vasodilation 1
• The cardiovascular effects of terazosin include:
  • Minimal to no effect on heart rate at 24 hours after dosing (trough effect) 1
  • A transient 6-10 beat per minute increase in heart rate during the first few hours after dosing (peak effect), particularly in the erect position 1
  • The peak hemodynamic response occurs approximately 2-3 hours after dosing and is about twice the magnitude of the trough (24-hour) response 1

Timing of Heart Rate Changes

• Heart rate changes follow a predictable pattern:
  • Initial increase: Within the first few hours after dosing, especially when standing 1
  • Return to baseline: By 24 hours post-dose, heart rate typically returns to pre-treatment levels 1
  • Long-term studies show no significant difference in pulse rate measurements from pre-treatment to post-treatment compared to placebo (-1.0 beat per minute for both terazosin and placebo groups in the supine position) 2

Postural Considerations

• The heart rate effect is position-dependent:
  • More pronounced in the erect position than in the supine position 1
  • Associated with orthostatic changes in blood pressure 1
  • During the first 3 hours after dosing, 12.5% of patients had significant orthostatic hypotension compared to 4% in placebo groups 1

Clinical Implications

• The transient increase in heart rate is a compensatory response to the vasodilation and potential drop in blood pressure caused by terazosin 1
• This effect is more pronounced:
  • With the first dose or first few doses 1
  • When combined with other vasodilators such as calcium channel blockers 3
  • In patients who experience orthostatic hypotension 1

Dosing Considerations

• To minimize heart rate effects and orthostatic hypotension:
  • Start with a low dose (1 mg) and gradually titrate upward 1
  • Consider administering the first dose at bedtime to avoid first-dose syncope 4
  • If blood pressure-related side effects (dizziness, palpitations, orthostatic complaints) occur within a few hours after dosing, consider twice daily dosing instead of once daily 1

Monitoring Recommendations

• Monitor heart rate and blood pressure during initiation of therapy, particularly during the first few hours after the first dose 1
• Be particularly vigilant in patients with:
  • Pre-existing cardiac conditions 5
  • Concomitant use of other medications that affect heart rate 5, 3
  • History of orthostatic hypotension 1

Common Pitfalls and Caveats

• The heart rate increase is transient and not sustained with chronic therapy 2
• Oral dose titration minimizes postural effects on blood pressure and associated symptoms compared to rapid intravenous administration 6
• When combining terazosin with other antihypertensives (especially calcium channel blockers), be aware of potential additive effects on orthostatic hypotension and compensatory heart rate increases 3
• Alpha-1 blockers like terazosin are not recommended as first-line agents for hypertension due to their side effect profile 7