We read with interest the letter of Rizzi et al , which describes a severe hypertensive reaction with tachycardia after injection of 1.5 cm ³ of 1% lidocaine with 1:100 000 U epinephrine into the greater palatine foramen. The patient received 10 mg of midodrine, an antihypotensive agent, on the morning of surgery. We feel a number of issues highlighted in this letter merit further consideration.

Midodrine is used in a number of common chronic conditions that predispose patients to hypotension . It is a short acting agent with a half-life of approximately 4 hours . It has been shown to be effective at relieving hypotensive symptoms . It is commonly administered to patients during the morning and middle of the day, but not at night, to avoid supine hypertension, itself a commonly occurring complication of autonomic dysfunction. Therefore, withholding administration of midodrine on the morning of a surgical procedure is usually sufficient to avoid a hypertensive reaction as described in this case.

Although many patients receiving midodrine develop adverse effects (particularly pruritus and piloerection), hypertension is far less common that the authors state. In the 2 studies quoted , the number of patients who developed supine hypertension secondary to midodrine was in fact less than 10% and not 25% to 75%, quoted by Rizzi et al .

We believe it is also worth noting that a similar hypertensive reaction can occur as a complication of injection of local anesthetic agents containing epinephrine. In individual cases, evaluation of the patient’s heart rate may help determine whether a hypertensive reaction is occurring as a complication to midodrine therapy. Midodrine does not commonly cause tachycardia because its adrenergic effects are mediated principally at α ₁ but not at β adrenergic receptors. Epinephrine exerts an agonist effect at both α and β adrenergic receptors. Therefore, tachycardia is more likely to occur secondary to epinephrine administration than midodrine.

We agree with Rizzi et al that avoiding concomitant use of midodrine and vasoconstrictor containing anesthetic agents is appropriate to minimize the risk of a hypertensive reaction. However, given this agent’s short half-life, we believe that, for most patients, even those for whom use of vasoconstrictor containing anesthetic agent is indicated, withholding administration of midodrine on the morning of surgery is sufficient precaution to avoid a hypertensive reaction.