Terazosin precautions

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-525-6884

List of precautions

Syncope/"first-dose" effect

• Initiation of treatment
• Study data
• Treatment

Priapism

Prostatic cancer

Orthostatic hypotension

Lab tests

Use with other drugs

Carcinogenesis

Mutagenesis

Impairment of fertility

Pregnancy

• Teratogenic effects
• Nonteratogenic effects

Nursing mothers

Pediatric use

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Syncope/"first-dose" effect

Terazosin hydrochloride capsules, like other alpha-adrenergic blocking agents, can cause marked lowering of blood pressure, especially postural hypotension, and syncope in association with the first dose or first few days of therapy. A similar effect can be anticipated if therapy is interrupted for several days and then restarted. Syncope has also been reported with other alpha-adrenergic blocking agents in association with rapid dosage increases or the introduction of another antihypertensive drug. Syncope is believed to be due to an excessive postural hypotensive effect, although occasionally the syncopal episode has been preceded by a bout of severe supraventricular tachycardia with heart rates of 120 to 160 beats per minute. Additionally, the possibility of the contribution of hemodilution to the symptoms of postural hypotension should be considered. Return to top

Initiation of treatment

To decrease the likelihood of syncope or excessive hypotension, treatment should always be initiated with a 1 mg dose of Terazosin, given at bedtime. The 2 mg, 5 mg and 10 mg capsules are not indicated as initial therapy. Dosage should then be increased slowly, according to recommendations in the Dosage and Administration section and additional antihypertensive agents should be added with caution. The patient should be cautioned to avoid situations, such as driving or hazardous tasks, where injury could result should syncope occur during initiation of therapy. Return to top

Study data

In early investigational studies, where increasing single doses up to 7.5 mg were given at 3 day intervals, tolerance to the first dose phenomenon did not necessarily develop and the "first-dose" effect could be observed at all doses. Syncopal episodes occurred in 3 of the 14 subjects given Terazosin at doses of 2.5, 5 and 7.5 mg, which are higher than the recommended initial dose; in addition, severe orthostatic hypotension (blood pressure falling to 50/0 mmHg) was seen in two others and dizziness, tachycardia, and lightheadedness occurred in most subjects. These adverse effects all occurred within 90 minutes of dosing.
In three placebo-controlled BPH studies 1, 2, and 3 (see CLINICAL PHARMACOLOGY), the incidence of postural hypotension in the Terazosin treated patients was 5.1%, 5.2%, and 3.7% respectively.
In multiple dose clinical trials involving nearly 2000 hypertensive patients treated with Terazosin, syncope was reported in about 1% of patients. Syncope was not necessarily associated only with the first dose. Return to top

Treatment

If syncope occurs, the patient should be placed in a recumbent position and treated supportively as necessary. There is evidence that the orthostatic effect of Terazosin is greater, even in chronic use, shortly after dosing. The risk of the events is greatest during the initial seven days of treatment, but continues at all time intervals. Return to top

Priapism

Rarely, (probably less than once in every several thousand patients) Terazosin and other α1-antagonists have been associated with priapism (painful penile erection, sustained for hours and unrelieved by sexual intercourse or masturbation). Two or three dozen cases have been reported. Because this condition can lead to permanent impotence if not promptly treated, patients must be advised about the seriousness of the condition. Return to top

Prostatic cancer

Carcinoma of the prostate and BPH cause many of the same symptoms. These two diseases frequently co-exist. Therefore, patients thought to have BPH should be examined prior to starting Terazosin hydrochloride therapy to rule out the presence of carcinoma of the prostate. Return to top

Orthostatic hypotension

While syncope is the most severe orthostatic effect of Terazosin, other symptoms of lowered blood pressure, such as dizziness, lightheadedness and palpitations, were more common and occurred in some 28% of patients in clinical trials of hypertension. In BPH clinical trials, 21% of the patients experienced one or more of the following: dizziness, hypotension, postural hypotension, syncope, and vertigo. Patients with occupations in which such events represent potential problems should be treated with particular caution. Return to top

Lab tests

Small but statistically significant decreases in hematocrit, hemoglobin, white blood cells, total protein and albumin were observed in controlled clinical trials. These laboratory findings suggested the possibility of hemodilution. Treatment with Terazosin for up to 24 months had no significant effect on prostate specific antigen (PSA) levels. Return to top

Use with other drugs

In a study (n=24) where Terazosin and verapamil were administered concomitantly, Terazosin's mean AUC0–24 increased 11% after the first verapamil dose and after 3 weeks of verapamil treatment it increased by 24% with associated increases in Cmax (25%) and Cmin (32%) means. Terazosin mean Tmax decreased from 1.3 hours to 0.8 hours after 3 weeks of verapamil treatment. Statistically significant differences were not found in the verapamil level with and without Terazosin. In a study (n=6) where Terazosin and captopril were administered concomitantly, plasma disposition of captopril was not influenced by concomitant administration of Terazosin and Terazosin maximum plasma concentrations increased linearly with dose at steady-state after administration of Terazosin plus captopril. Return to top

Carcinogenesis

Terazosin, administered in the feed to rats at doses of 8, 40, and 250 mg/kg/day (70, 350, and 2100 mg/M2/day), for two years, was associated with a statistically significant increase in benign adrenal medullary tumors of male rats exposed to the 250 mg/kg dose. This dose is 175 times the maximum recommended human dose of 20 mg (12 mg/M2). Female rats were unaffected. Terazosin was not oncogenic in mice when administered in feed for 2 years at a maximum tolerated dose of 32 mg/kg/day (110 mg/M2; 9 times the maximum recommended human dose). The absence of mutagenicity in a battery of tests, of tumorigenicity of any cell type in the mouse carcinogenicity assay, of increased total tumor incidence in either species, and of proliferative adrenal lesions in female rats, suggests a male rat species-specific event. Numerous other diverse pharmaceutical and chemical compounds have also been associated with benign adrenal medullary tumors in male rats without supporting evidence for carcinogenicity in man. Return to top

Mutagenesis

Terazosin was devoid of mutagenic potential when evaluated in vivo and in vitro (the Ames test, in vivo cytogenetics, the dominant lethal test in mice, in vivo Chinese hamster chromosome aberration test and V79 forward mutation assay). Return to top

Impairment of fertility

The effect of Terazosin on fertility was assessed in a standard fertility/reproductive performance study in which male and female rats were administered oral doses of 8, 30 and 120 mg/kg/day. Four of 20 male rats given 30 mg/kg (240 mg/M2; 20 times the maximum recommended human dose) and five of 19 male rats given 120 mg/kg (960 mg/M2; 80 times the maximum recommended human dose) failed to sire a litter. Testicular weights and morphology were unaffected by treatment. Vaginal smears at 30 and 120 mg/kg/day, however, appeared to contain less sperm than smears from control matings and good correlation was reported between sperm count and subsequent pregnancy.
Oral administration of Terazosin for one or two years elicited a statistically significant increase in the incidence of testicular atrophy in rats exposed to 40 and 250 mg/kg/day (29 and 175 times the maximum recommended human dose), but not in rats exposed to 8 mg/kg/day (> 6 times the maximum recommended human dose). Testicular atrophy was also observed in dogs dosed with 300 mg/kg/day (> 500 times the maximum recommended human dose) for three months but not after one year when dosed with 20 mg/kg/day (38 times the maximum recommended human dose). This lesion has also been seen with prazosin, another selective alpha-1 blocking agent. Return to top

Pregnancy

Pregnancy Category C

Teratogenic effects

Terazosin was not teratogenic in either rats or rabbits when administered at oral doses up to 280 and 60 times, respectively, the maximum recommended human dose. Fetal resorptions occurred in rats dosed with 480 mg/kg/day, approximately 280 times the maximum recommended human dose. Increased fetal resorptions, decreased fetal weight and an increased number of supernumerary ribs were observed in offspring of rabbits dosed with 60 times the maximum recommended human dose. These findings (in both species) were most likely secondary to maternal toxicity. There are no adequate and well-controlled studies in pregnant women and the safety of Terazosin in pregnancy has not been established. Terazosin hydrochloride is not recommended during pregnancy unless the potential benefit justifies the potential risk to the mother and fetus. Return to top

Nonteratogenic effects

In a peri- and post-natal development study in rats, significantly more pups died in the group dosed with 120 mg/kg/day (> 75 times the maximum recommended human dose) than in the control group during the three-week postpartum period. Return to top

Nursing mothers

It is not known whether Terazosin is excreted in breast milk. Because many drugs are excreted in breast milk, caution should be exercised when Terazosin is administered to a nursing woman. Return to top

Pediatric use

Safety and effectiveness in pediatric patients have not been determined. Return to top

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The content of this page is taken from the FDA package insert for this drug and should not be edited.