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Phenoxybenzamine (Dibenzyline)

Phenoxybenzamine, a long-acting, adrenergic, alpha-receptor blocking agent, can increase blood flow to skin, mucosae, and abdominal viscera and lower supine and erect blood pressures. The initial dose is 10 mg of Dibenzyline (phenoxybenzamine hydrochloride) bid with increases once daily, usually up to 20-40 mg 2-3 times/days.

 

Table 19: Phenoxybenzamine (Dibenzyline)

Author Year; Country
Score
Research Design
Sample Size
MethodsOutcome
Lindan et al. 1985;

USA

Pre-post

N=12

Population: 12 subjects with tetraplegia

Treatment: phenoxybenzamine (10 mg bid) and nifedipine (20 mg bid) for 4 days prior cystometry

Outcome Measures: blood pressure during cystometry.

1.     Neither drug effectively prevented AD secondary to bladder filling and a significant number of patients developed troublesome hypotension.

2.     Sublingual dose of nifedipine (10 mg) was effective in managing acute attacks of AD.

McGuire et al. 1976; USA

Case series

N=9

Population: 9 individuals with SCI and severe AD.

Treatment: 6 patients treated daily with phenoxybenzamine (alpha-sympatholytic agent) in doses ranging from 10 to 20 mg.

Outcome Measures: blood, bladder and urethral pressures.

1.     Hypertension, headache and anxiety of AD could no longer be provoked with bladder filling but sweating continued to occur.

2.     Mean resting urethral pressure (based on 30 cc bladder volume) decreased after treatment with phenoxybenzamine from 40.6 to 34.0.

3.     Mean maximum urethral pressure change with filling decreased after the treatment from +20cmH2O to -30cmH2O.

Discussion

McGuire et al. (1976) reported that hypertension, headache and anxiety of AD could no longer be provoked with bladder filling (but sweating continued to occur) in the six subjects who took phenoxybenzamine (dose range from 10 to 20mg) daily. This result is opposite to Lindan et al.’s (1985) findings. They reported that after talking phenoxbenzamine for 4 or more days, blood pressure still rose with bladder distension in ten subjects and remained at the base level in only two subjects.

Conclusion

  • There is level 4 evidence (from one pre-post study and one case series study) for use of Phenoxybenzamine in the management of AD; however, the results are conflicting with no effects seen in one study (Lindan et al. 1985) and positive effects in another (McGuire et al. 1976).
  • It is not known whether Phenoxybenzamine is effective for the management of AD in SCI.