Clinical experience with guanfacine in long-term treatment of hypertension

Systems pharmacology identifies drug targets for Stargardt disease-associated retinal degeneration

A systems pharmacological approach that capitalizes on the characterization of intracellular signaling networks can transform our understanding of human diseases and lead to therapy development. Here, we applied this strategy to identify pharmacological targets for the treatment of Stargardt disease, a severe juvenile form of macular degeneration. Diverse GPCRs have previously been implicated in neuronal cell survival, and crosstalk between GPCR signaling pathways represents an unexplored avenue for pharmacological intervention. We focused on this receptor family for potential therapeutic interventions in macular disease. Complete transcriptomes of mouse and human samples were analyzed to assess the expression of GPCRs in the retina. Focusing on adrenergic (AR) and serotonin (5-HT) receptors, we found that adrenoceptor α 2C (Adra2c) and serotonin receptor 2a (Htr2a) were the most highly expressed. Using a mouse model of Stargardt disease, we found that pharmacological interventions that targeted both GPCR signaling pathways and adenylate cyclases (ACs) improved photoreceptor cell survival, preserved photoreceptor function, and attenuated the accumulation of pathological fluorescent deposits in the retina. These findings demonstrate a strategy for the identification of new drug candidates and FDA-approved drugs for the treatment of monogenic and complex diseases.

Hemodynamic effects of loud noise before and after central sympathetic nervous stimulation

The hemodynamic effects of loud noise after central alpha 2-adrenoceptor stimulation were studied in 13 patients with mild (WHO 1) essential hypertension. The patients were randomized (double-blind) to treatment with either placebo or guanfacine 1-2 mg for four weeks and then crossed over and treated for another four weeks. All patients were exposed to a loud broad-band noise (105 dBA for 30 min) and all were studied both on placebo and guanfacine. Guanfacine significantly reduced the resting blood pressure from 141/92 to 134/88 mmHg (p less than 0.01) as well as heart rate at rest from 63 to 58 beats/min (p less than 0.05). Noise stimulation caused a significant increase in blood pressure and resistance in the placebo-treated group, while cardiac output decreased significantly. Pretreatment for one month with the central alpha 2-adrenoceptor stimulating agent guanfacine did not block the noise-induced pressor response nor the increase in peripheral resistance. A significant decrease in stroke volume was observed and cardiac output also tended to decrease in this group. It could be concluded that loud noise is a potent pressor stimulus which causes vasoconstriction and that the blood pressure response during noise could not be blocked by the centrally acting antihypertensive agent guanfacine. Since noise causes vasoconstriction it also induces an increased tone in the small arteries and, if the noise stimulus is sufficiently strong and repeated for a long time, it might cause structural changes in the resistance vessels and permanent arterial hypertension in humans.

Guanfacine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in the treatment of hypertension

Guanfacine, a phenylacetyl-guanidine derivative, is a centrally acting alpha-adrenoceptor agonist, with a mechanism of antihypertensive action similar to that of clonidine. It reduces blood pressure in patients with essential hypertension at least as effectively as clonidine or methyldopa. Like lower doses of clonidine, guanfacine can be given once daily due to its relatively long elimination half-life. Although dry mouth and sedation occur frequently with higher doses of guanfacine, their incidence is lower than with other centrally acting antihypertensives; in addition, other troublesome side effects such as orthostatic hypotension or sexual dysfunction also occur much less with guanfacine than with other centrally acting antihypertensive agents. While a withdrawal syndrome may occur on abruptly discontinuing guanfacine administration, the symptoms are generally mild, and the incidence of withdrawal symptoms appears lower than occurs with abrupt withdrawal of clonidine. Thus, guanfacine is an effective and well tolerated alternative to other centrally acting antihypertensive drugs. Whether its final place in therapy will be as an alternative 'second-line' drug, or as initial monotherapy in patients with mild to moderate hypertension, remains to be clarified in comparative studies with diuretics, calcium antagonists, and beta-adrenoceptor blocking drugs.

Effects of guanfacine on growth hormone, prolactin, renin, lipoproteins and glucose in essential hypertension

The effect of single-dose, short-term (6 weeks) and long-term (7 years) guanfacine therapy on various endocrine and metabolic parameters was evaluated in patients with moderate essential hypertension (WHO phase I and II). A single oral dose (2 mg) of guanfacine did not affect the secretion of growth hormone but produced a prompt decrease in blood pressure (BP) levels. Short-term treatment decreased BP and heart rate, and also produced a marked (p less than 0.001) fall in urinary excretion of norepinephrine and serum prolactin levels. Short-term therapy did not affect growth hormone or renin levels. A mean daily dose of 2.8 mg of guanfacine maintained normal BP levels in 22 patients during the long-term follow-up study. In addition, treatment produced a progressive decrease in prolactin, renin, total cholesterol and triglyceride levels, but did not change growth hormone values or oral glucose tolerance test results. The cumulative incidence of cardiovascular complications was significantly lower (p less than 0.001) in guanfacine-treated patients than in a matched control group. The most significant difference was the absence of fatal complications in the guanfacine-treated patients. The present results support the theory that decreased morbidity and mortality in patients treated with guanfacine may depend not only on its important antihypertensive activity, but also on its beneficial effect on known cardiovascular risk factors.

Comparison of guanfacine versus clonidine for efficacy, safety and occurrence of withdrawal syndrome in step-2 treatment of mild to moderate essential hypertension

Guanfacine, an alpha 2-adrenoceptor agonist, was compared with clonidine as step-2 therapy of mild to moderate essential hypertension in a 24-week, double-blind, randomized, parallel evaluation to determine efficacy, safety and occurrence of withdrawal syndrome. During a 5-week period, patients were weaned from current antihypertensives, if any, and stabilized on step-1 therapy with 25 mg of chlorthalidone once a day. Those with a diastolic blood pressure (BP) from 95 to 114 mm Hg while taking chlorthalidone were randomized to treatment. The 2 agents had equal efficacy; 149 of 270 patients treated with guanfacine (55%) and 164 of 276 treated with clonidine (59%) achieved goal diastolic BP of less than or equal to 90 mm Hg. Terminations because of adverse effects were relatively low. Dry mouth (30% of guanfacine and 37% of clonidine groups) and somnolence (21% of guanfacine and 35% of clonidine groups, p less than 0.05) were reported most frequently. Nonsyncopal dizziness was reported in 11% of guanfacine-treated and 8% of clonidine-treated patients. This difference was not statistically significant. To evaluate the occurrence of a withdrawal syndrome in 316 outpatients and 156 inpatients, vital signs were monitored at least twice a day for up to 7 days after the end of therapy. Segmented 24-hour urine studies were performed on inpatients. Abrupt withdrawal of clonidine produced a rapid increase in diastolic and, especially, systolic BP, whereas guanfacine withdrawal produced more gradual increases. The differences were significant over the first 3 withdrawal days. It is concluded that guanfacine is a safe, effective, second-generation alpha 2-adrenoceptor agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

A multicenter, randomized, double-blind dose-response evaluation of step-2 guanfacine versus placebo in mild to moderate hypertension

Guanfacine, an alpha-adrenoceptor agonist, may exhibit distinct dose-related curves for efficacy and adverse effects in the step-2 therapy of essential hypertension. To determine the lowest clinically effective safe dose, 462 newly or previously diagnosed subjects were admitted to a 5-week prerandomization phase at 8 centers. Patients were weaned from any current antihypertensive drugs and placed on 25-mg chlorthalidone, daily, in the morning. At the end of the 5-week weaning period, 362 patients with seated diastolic blood pressures (BPs) between 95 and 114 mm Hg qualified for the 12-week postrandomization phase. Subjects were randomized to receive either an indistinguishable placebo or 0.5, 1, 2 or 3 mg of guanfacine. Chlorthalidone was changed to bedtime administration and taken with the study medications. Guanfacine was started at the lowest dose in all subjects and increased (if scheduled, according to the randomization code) to the next higher dose at biweekly intervals. Of the 362 randomized patients, 278 completed the study. The 1-mg guanfacine dosage produced a 14/13 mm Hg decrease in BP (p less than 0.0125 compared with placebo). Doses of guanfacine at 2 and 3 mg/day were not more effective than the 1 mg/day dose; 0.5 mg/day was not better than placebo. There was an increase in the frequency of side effects possibly or probably associated with 2 and 3 mg/day guanfacine. Only 3.2% of the patients in the 1 mg/day group dropped out of the study because of side effects. We conclude that when added to a diuretic, 1 mg/day guanfacine at bedtime is the lowest safe and therapeutically effective dose.

Usefulness of low dose guanfacine, once a day, for 24-hour control of essential hypertension

The 24-hour duration of the antihypertensive effect of guanfacine, a centrally acting alpha 2-adrenoceptor agonist administered once a day, was demonstrated in a 12-week, multicenter, double-blind, placebo-controlled study. Two hundred and forty-nine patients who remained mildly to moderately hypertensive following a 5-week period, during which they had been weaned from previous antihypertensive medications and stabilized on 25-mg chlorthalidone taken once a day, were involved. Of the 249 patients, 126 received guanfacine as a step-2 agent and 123 received placebo. Both groups were further subdivided so that blood pressure (BP) measurements were determined either 12 or 24 hours after dosing. The initial dose of guanfacine was 1 mg/day, which could be raised 1 mg at 2-week intervals to a maximum daily dose of 3 mg/day at the discretion of each investigator. The daily dose could also be lowered by 1 mg at 2-week intervals, depending on patient response. The mean 24-hour reductions with guanfacine in sitting diastolic BP (-11 mm Hg), systolic BP (-14 mm Hg) and mean arterial pressure (-12 mm Hg) were statistically significant (p less than 0.01) compared with the reductions in BP with placebo. Heart rate also decreased with guanfacine, but no clinically relevant bradycardia (less than 60 beats/min) was observed. Dry mouth (47%), constipation (16%), fatigue (12%) and drowsiness (4%) were the most frequently reported side effects. The highly acceptable side-effects profile of guanfacine was also indicated by the small percentage of patients (7%) who prematurely left the study because of adverse reactions.

Improvement of glucose tolerance in hypertensive diabetic patients treated with guanfacine one year

In the present study the effect of 1 year of antihypertensive treatment with guanfacine (g) has been evaluated in 18 hypertensive patients with adult-onset, non-insulin-dependent diabetes mellitus (WHO Type II). The treatment produced a marked improvement in the oral glucose tolerance test; guanfacine significantly decreased serum glucose levels, and affected only slightly the insulin secretion. It is suggested that the effect of g may be mediated via a reduction in catecholamine and/or growth hormone and ACTH secretion. The present results also suggest that treatment with guanfacine may improve individual coronary risk in hypertensive diabetic patients.

Content of reports on clinical trials: a critical review

A 10% sample of English language papers, published in 1980, listed in Index Medicus, and classified under the heading, Clinical Trials, was used to assess the state of trials and reports from them. Tabulations are presented concerning the design of the trials represented by the papers in the sample. The manuscript concludes with a discussion of reporting responsibilities for investigators involved in trials and of methods for meeting those responsibilities.

Identification of vascular postsynaptic alpha 1- and alpha 2-adrenoceptors in man

We studied postsynaptic alpha-adrenoceptors in human blood vessels by measuring the influence on forearm blood flow induced by intra-arterial infusions of selective alpha 1- and alpha 2-adrenoceptor agonists (methoxamine, B-HT 933, clonidine and guanfacine) and antagonists (doxazosin and yohimbine). The studies were done in healthy volunteers, and forearm blood flow was measured by plethysmography. All agonists produced a significant and dose-dependent vasoconstriction. The effect of B-HT 933 was completely abolished by the concomitant infusion of yohimbine, whereas it was hardly influenced by doxazosin. The effect of methoxamine was prevented by doxazosin and little influenced by yohimbine. The vasoconstriction by clonidine and guanfacine was partially prevented by both doxazosin and yohimbine. The single intra-arterial infusion of yohimbine, as well as doxazosin, resulted in vasodilation. These findings provide strong evidence for the existence of postsynaptic alpha 1- as well as alpha 2-adrenoceptors, both mediating vasoconstriction and contributing to basal vascular tone. The (patho-)physiological significance of this subdivision of alpha-adrenoceptors remains to be elucidated.

Antihypertensive effects and plasma levels of guanfacine in man

The antihypertensive effect and the plasma levels of guanfacine were studied for two months in 25 patients with sustained essential hypertension. In three patients, blood pressure was unchanged. In ten patients, blood pressure returned to the normal range within 15 days, at a daily dose of 2 mg. In 12 patients, increasing doses were necessary to normalize the blood pressure within two months. In these cases, the decrease in systolic pressure was negatively correlated with the daily dose of guanfacine (r = -0.40) and the steady-state plasma level (r = -0.62; P less than 0.01); analysis of the curves showed that the normalization of blood pressure coincided with a plasma drug level of 8 ng/ml, i.e., a 4-mg daily dose. This study demonstrated the efficacy of guanfacine monotherapy in hypertension and suggests that the normalization rate of blood pressure levels does not further increase with daily doses higher than 4 mg.

Guanfacine and other centrally acting drugs in antihypertensive therapy; pharmacological and clinical aspects

Centrally acting antihypertensive agents exert an agonist action on alpha-adrenoceptors in certain areas of the brain, thereby reducing sympathetic outflow and lowering blood pressure without paralysing peripheral homeostatic control mechanisms. Some also stimulate peripheral alpha-adrenoceptors, both postsynaptic and presynaptic. Guanfacine, a representative member of this class of drugs, resembles clonidine in most of its basic pharmacological properties. In some respects, however, clear differences exist and may account for an improved therapeutic usefulness. In cats the two drugs have a different site of action within the CNS. Unlike clonidine, guanfacine does not inhibit dopamine turnover in the corpus striatum of the rat and its hypotensive effect is not inhibited by central H2-receptor blockade. In rat EEG studies guanfacine is much less sedative than clonidine. The newer drug shows a higher selectivity for (peripheral) presynaptic alpha-adrenoceptors than clonidine. On a weight basis guanfacine is about 10 times less potent in lowering blood pressure, but at equipotent doses its antihypertensive effect lasts longer. With an elimination half-life of approximately 18 to 21 h in man guanfacine is suitable for once-a-day treatment. The long duration of action is likely to explain the lack of rebound hypertension in chronically treated spontaneously hypertensive rats as well as the very low incidence and the remarkably mild nature of withdrawal symptomatology in man.

Clinical experience with guanfacine in long-term treatment of hypertension. Part II: adverse reactions to guanfacine

1 In 580 hypertensive patients treated with guanfacine for one year and 169 patients who continued the treatment for a second year, laboratory measurements were made before, during and after the end of treatment. Side-effects were registered every month. On completion of the one and two-year studies respectively, therapy was discontinued and blood pressure, heart rate and side-effects were recorded in order to assess the frequency of a withdrawal syndrome.

2 No impairment of laboratory values was seen during long-term treatment. There was no retention of sodium, chloride and water, and no potassium depletion. Guanfacine did not interfere with carbohydrate metabolism during the long-term treatment, and there was no deterioration of clinical diabetes.

3 The overall frequencies of dryness of the mouth and sedation were 60 and 33%, respectively. At the end of one year of treatment these figures dropped to 15 and 5.7%. Further untoward reactions in the first and second year, respectively, were orthostatic disturbances (15 and 6.5%), constipation (14 and 4.1%), male sexual dysfunction (4.6 and 0.6%), insomnia (5.5 and 2.2%), and sweating (5.3 and 1.7%).

4 The frequency and severity of side-effects were dose dependent and related to increases in dosage. Doses of 2 mg and lower caused practically no dryness of the mouth.

5 A withdrawal syndrome occurred in about 3% of patients after discontinuation of prolonged treatment. It was seen in patients with a history of very high blood pressure readings, who showed a tendency to tachycardia and who had been treated with divided doses of guanfacine exceeding 4 mg daily.

6 Only patients with clinical symptoms of increased sympathetic activity were considered to have a withdrawal syndrome (or `phenomenon').

7 No signs of tachyphylaxis or habituation (tolerance) were seen during the long-term treatment with guanfacine.