Guanfacine (Guanfacine Hydrochloride) - Drug Interactions, Contraindications, Overdosage, etc

DRUG INTERACTIONS

Drug Interactions:

The potential for increased sedation when guanfacine is given with other CNS-depressant drugs should be appreciated.

The administration of guanfacine concomitantly with a known microsomal enzyme inducer (phenobarbital or phenytoin) to two patients with renal impairment reportedly resulted in significant reductions in elimination half-life and plasma concentration. In such cases, therefore, more frequent dosing may be required to achieve or maintain the desired hypotensive response. Further, if guanfacine is to be discontinued in such patients, careful tapering of the dosage may be necessary in order to avoid rebound phenomena (see above). Rebound

OVERDOSAGE

Drowsiness, lethargy, bradycardia, and hypotension have been observed following overdose with guanfacine. Signs and Symptoms:

A 25-year-old female intentionally ingested 60 mg. She presented with severe drowsiness and bradycardia of 45 beats/minute. Gastric lavage was performed and an infusion of isoproterenol (0.8 mg in 12 hours) was administered. She recovered quickly and without sequelae.

A 28-year-old female who ingested 30-40 mg developed only lethargy, was treated with activated charcoal and a cathartic, was monitored for 24 hours, and was discharged in good health.

A 2-year-old male weighing 12 kg, who ingested up to 4 mg of guanfacine, developed lethargy. Gastric lavage (followed by activated charcoal and sorbitol slurry via NG tube) removed some tablet fragments within 2 hours after ingestion, and vital signs were normal.

During 24-hours observation in ICU, systolic pressure was 58 and heart rate 70 at 16 hours post-ingestion. No intervention was required, and child was discharged fully recovered the next day.

Gastric lavage and supportive therapy as appropriate. Guanfacine is not dialyzable in clinically significant amounts (2.4%). Treatment of Overdosage:

CONTRAINDICATIONS

Guanfacine hydrochloride tablets are contraindicated in patients with known hypersensitivity to the drug.

DRUG ABUSE AND DEPENDENCE

No reported abuse or dependence has been associated with the administration of guanfacine.