ROBINS' TENEX (GUANFACINE) ANTIHYPERTENSIVE USE WITH DIURETIC

ROBINS' TENEX (GUANFACINE) ANTIHYPERTENSIVE USE WITH DIURETIC is stipulated in FDA approved labeling. The package insert states that since dosing information for Tenex has been established in the presence of a thiazide-type diuretic, "Tenex should, therefore, be used in patients who are already receiving a thiazide-type diuretic." FDA approved the drug Oct. 27 with a 1C designation, indicating a new chemical entity with little or no therapeutic gain over already marketed drugs. Robins plans to launch the product in early 1987.

Robins licensed Tenex from Sandoz and subsequently filed an NDA for the drug in 1983. FDA's Cardio-Renal Drugs Advisory Committee reviewed Tenex in December 1985 and at that time recommended that Robins conduct a dose response study without concomitant diuretic use to demonstrate efficacy. Committee members had trouble distinguishing the anti-hypertensive effect of Tenex from the diuretic.

Tenex is available as a 1 mg tablet, the recommended daily dose, in bottles of 100 and 500 and in unit dose packs of 100. Labeling notes that in clinical trials, "adverse reactions at this dose were not clearly distinguishable from those associated with placebo," while "adverse reactions were clearly present at 2 and 3 mg." Adverse reactions included dry mouth, sedation, weakness, dizziness, constipation, and impotence. "While the reactions are common, most are mild and tend to disappear on continued dosing," the labeling states.

FDA noted at the advisory committee meeting in 1985 that the dose of 1-2 mg guanfacine used in U.S. trials differed markedly from doses found in European titrated trials of up to 20 mg a day where guanfacine was used as monotherapy. Tenex labeling states: "Higher daily doses (rarely up to 40 mg/day, in divided doses) have been used, but adverse reactions increase significantly with doses above 3 mg/day and there is no evidence of increased efficacy. No studies have established an appropriate dose or dosing interval when Tenex . . . is given as the sole antihypertensive agent."

The labeling compares the occurrence of rebound hypertension with guanfacine versus clonidine. "In a double-blind, randomized trial, either guanfacine or clonidine was given at recommended doses with 25 mg chlorthalidone for 24 weeks and then abruptly discontinued. Results showed equal degrees of blood pressure reduction with the two drugs, and there was no tendency for blood pressures to increase despite maintenance of the same daily dose of the two drugs."

The labeling continues: "Signs and symptoms of rebound phenomena were infrequent upon discontinuation of either drug. Abrupt withdrawal of clonidine produced a rapid return of diastolic and, especially, systolic blood pressure to approximately pretreatment levels with occasional values significantly greater than baseline, whereas guanfacine withdrawal produced a more gradual increase to pretreatment levels, but also with occasional values significantly greater than baseline."