Can phenylephrine be given after terbutaline (beta-2 adrenergic agonist) in cases of priapism?

Phenylephrine After Terbutaline in Priapism Management

Yes, phenylephrine can be given after terbutaline in cases of priapism, particularly when terbutaline has failed to resolve the condition. Phenylephrine is the preferred sympathomimetic agent for treating ischemic priapism and has a significantly higher success rate (74%) compared to terbutaline (25%) 1.

Treatment Algorithm for Priapism

1. Initial Assessment

   • Determine type of priapism (ischemic vs. non-ischemic)
   • Perform corporal blood gas analysis (PO2 ≤30 mmHg, PCO2 ≥60 mmHg, pH <7.25 indicates ischemic priapism) 2
   • Assess duration of priapism (critical for treatment decisions)

2. First-Line Treatment

   • Intracavernosal phenylephrine is the recommended first-line treatment for ischemic priapism 3, 2
   • Dilute with normal saline to 100-500 μg/mL
   • Administer 1 mL injections every 3-5 minutes for up to 1 hour 3
   • Success rate: 65-81% 3

3. When Terbutaline Has Been Used First

   • If terbutaline (oral or subcutaneous) has failed to resolve priapism
   • Proceed directly to intracavernosal phenylephrine without delay
   • No contraindication to using phenylephrine after terbutaline 1

Evidence Supporting Phenylephrine After Terbutaline

The American Urological Association (AUA) guidelines strongly recommend phenylephrine as the preferred sympathomimetic agent for ischemic priapism 3. Comparative studies show phenylephrine's superiority:

• Phenylephrine success rate: 74%
• Terbutaline success rate: 25% 1

Phenylephrine is specifically preferred because:

• It is an alpha-1 selective adrenergic agonist
• It has no indirect neurotransmitter-releasing action
• It provides the desired therapeutic action (vasoconstriction) while minimizing other adverse effects 3

Important Considerations When Using Phenylephrine

1. Monitoring Requirements

   • Monitor blood pressure and heart rate during administration
   • Observe for symptoms of hypertension, headache, bradycardia, tachycardia, palpitations, and arrhythmias 3
   • ECG monitoring recommended in patients with cardiovascular risk factors 3

2. Dosage Adjustments

   • For patients with cardiovascular disease: Use lower concentrations
   • For patients with renal failure: Reduce maximum total dose to 500 μg/hour 2
   • For patients on MAOIs: Use gradual dose escalation 2

3. Technique

   • Direct intracavernosal injection without prior aspiration can be effective 4
   • However, aspiration before injection may improve efficacy by lowering intracorporal pressure 3

Common Pitfalls to Avoid

1. Delaying definitive treatment - Each hour of delay increases risk of permanent erectile dysfunction 2

2. Relying solely on oral/systemic medications - Intracavernosal therapy is essential for effective treatment 2

3. Using inadequate phenylephrine doses - Higher doses may be needed in prolonged cases due to acidosis 2

4. Continuing medical therapy when surgical intervention is indicated - For priapism lasting >36 hours, surgical shunting is likely necessary 2

5. Failing to monitor cardiovascular parameters during sympathomimetic administration 2

In conclusion, phenylephrine is the recommended treatment for ischemic priapism and can be safely administered after terbutaline has failed. The evidence strongly supports phenylephrine's superior efficacy compared to terbutaline, with resolution rates of 74% versus 25% respectively 1.