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Prazosin (Minipress)

Prazosin, a postsynaptic alpha-1 adrenoceptor blocker, lowers blood pressure by relaxing blood vessels. Prazosin has a minimal effect on cardiac function due to its alpha-1 receptor selectivity. The recommended starting dose in adults is 0.5 or 1 milligram (mg) taken two or three times a day.

 

Table 18: Prazosin (Minipress)

Author Year; Country
Score
Research Design
Sample Size
MethodsOutcome
Phillips et al. 2015

Canada

PEDro = 9

RCT

N= 6

 

Population: N = 6 males with complete, chronic SCI above T6

Mean (SD) age: 36.7 (4.8) years

Mean (SD) time since injury: 139 (47.3) months

ASIA A=3; ASIA B=1; ASIA D=2

Cause of SCI: MVA=3; Athletics=2; Fall=1

 

Treatment: Subjects had 2 penile vibrostimulation (PVS) trials; one with prazosin, other with a placebo (sugar capsule)

 

Outcome Measures:

Cardiovascular parameters (HR and continuous beat-to-beat BP)

1.     All patients experienced AD during PVS regardless of treatment: BP increased in all patients but HR did not change

2.     On average, systolic BP was 44 mm Hg lower when prazosin was administered.

3.     SBP increased an average of 140 +/- 19 mm Hg with placebo, and increased only 96 +/- 14 mm Hg with prazosin

4.     Of the six participants, five had a mitigation of SBP increases when treated with prazosin compared to placebo (the remaining subject had no change in BP response)

5.     Prazosin had no effect on resting BP

 

Effect Sizes: Forest plot of standardized mean differences (SMD ± 95%C.I.) as calculated from pre- and post-intervention data

Krum et al. 1992; Australia

PEDro=9

RCT

N=15

Population: Level of injury: T6 or above, at least 2 episodes of AD in last 7 days.

Treatment: double-blind, randomized to Prazosin 3 mg bid. (n=8) or placebo (n=7) for 2 weeks.

Outcome Measures: frequency and severity of AD, blood pressure.

1.   Prazosin was well tolerated and did not significantly lower resting BP. Compared to baseline, the Prazosin group had fewer severe episodes of AD (reduced rise in BP, shorter symptom duration and less need for acute antihypertensive medication).

2.   The severity of headache during individual AD episodes was also diminished with Prazosin therapy.

Discussion

In a small (n=15) (Krum et al. 1992), but high quality RCT, Prazosin twice daily was well tolerated and did not affect the baseline blood pressure; AD episodes were also less severe and shorter in duration over a 2 week period. Phillips et al. (2015) revealed similar results during penile vibrostimulation trials, where Prazosin lowered systolic blood pressure when administered without affecting resting blood pressure.

Conclusion

  • There is level 1 evidence (from two RCT) (Phillips et al. 2015; Krum et al. 1992), that Prazosin is superior to placebo in the prophylactic management of AD.
  • Prazosin can prophylactically reduce severity and duration of AD episodes in SCI.