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Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Complications of hypertension are by far the greatese preventable public health problem in many of the developed countries of the world. Pharmacologic interventions which primarily involve drug interactions are the generally available and effective means of preventing or delaying these hypertensive complications. Mechanisms of beneficial antihypertensive drug interactions involve simultaneous reduction or control of blood volume (diuretic agents) and decrease of peripheral resistance. Reduction of peripheral resistance without producing intolerable side effects has recetnly been achieved by a complex drug interaction. This interaction involves simultaneous vasodilation and inhibition by beta-adrenergic blocking agents of reflex activation of the renin-angiotensin axis. Clonidine, by effects similar to propranolol, can substitute for propranolol in some patients, or add to the beneficial effects of this important drug interaction.
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PMID:Additive effect of beta-adrenergic blockers in combination with vasodilators in lowering blood pressure. 1 26

The influence of the dosage or duration of treatment on the incidence and severity of clonidine withdrawal responses was examined in normotensive rats. Clonidine (0.01 or 0.1 mg/kg i.m.) was administered either in single doses, or twice daily for 3 days or 3 weeks. Rats were then anesthetized and arterial catheters were inserted. Significant overshoots in blood pressure and heart rate, reaching peak values 16 to 26 hr after the last injection, occurred in all clonidine-treated rats, but in no control rats. The overshoots after single injections of clonidine were as great as those after suspension of sustained treatment. Moreover, withdrawal responses were as great after the low dose as they were after the 10-fold greater dose. Only plasma renin activity showed a significantly greater elevation during withdrawal of the high dose of clonidine. Since ganglionic blockade reduced blood pressures and heart rates to the same levels in rats with clonidine withdrawal hypertension as in control rats, the withdrawal overshoots appear to be nervously mediated. Neither the dosage nor the duration of treatment could be shown to determine the magnitude of the response to withdrawal of clonidine.
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PMID:Withdrawal of clonidine: effects of varying dosage or duration of treatment on subsequent blood pressure and heart rate responses. 2 15

Intra-cisternal clonidine (3 microgram/kg) reduced hypertension and cardiac acceleration after defrenation in dogs, but did not act in intra-venous infusion (10 microgram/kg). The renin activity was not modified. Clonidine was always inactive on hypertension after stimulation of visceral afferences or after injection of potassium cyanidine. These results show that a central mechanism was implied in the anti-hypertensive action of clonidine.
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PMID:[Effect of clonidine on three types of experimental hypertension and on plasma renin activity in dogs]. 15 Aug 95

1. Clonidine (6 mg of base/l of water) was given as drinking fluid to normotensive rats or rats with established or early hypertension. 2. Spontaneous hypertensive rats (6 months old: average dose of clonidine, 0.6 mg 24 h-1 kg-1) showed a sustained fall in blood pressure over 3 weeks. 3. The same clonidine solution given for 6 weeks to two-kidney Goldblatt rats with early-stage hypertension (average dose of clonidine: 1 mg 24 h-1 kg-1) or spontaneously hypertensive rats (clonidine dose: 1 mg) induced a fall in mean blood pressure, but no change in normotensive rats. 4. Replacement of clonidine by water induced hypertension and lability which led to death in hypertensive but not in normotensive rats.
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PMID:Effect of chronic clonidine treatment and its abrupt cessation on mean blood pressure of rats with a normal or an elevated blood pressure. 15 30

In various kinds of hypertension clonidine induced a decrease in urinary catecholamines, plasma renin activity and urinary aldosterone, concommitant with a fall in blood pressure and pulse rate in both short term and chronic studies. Furthermore, clonidine lowered the plasma levels of noradrenaline and adrenaline but a postural increase in upright position still occurred. The capacity to increase renin during salt restriction seemed mainatined. When clonidine was withdrawn all parameters returned to pretreatment levels but in some cases a marked rebound increase in catecholamine production was seen. --During clonidine the increase in catecholamines and renin after insulin induced hypoglycemia was largely abolished. Under basal conditions oral penbutolol induced a decrease of pule rate and blood pressure but no change in plasma or urinary catecholamines. During treatment plasma renin was suppressed at rest and after exercise. A work load, which led to only minor changes in blood catecholamines before treatment, was associated with a marked increase during penbutolol. Medication with penbutolol reduced the response in plasma catecholamines after hypoglycemia and renin activity remained low. Clonidine seems to act mainly by central inhibtion of symapthetic tone. Penbutolol probably acts mainly peripherally but may also have a central effect.
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PMID:The effect of clonidine and penbutolol, respectively on catecholamines in blood and urine, plasma renin activity and urinary aldosterone in hypertensive patients. 23 81

Clonidine (Catapres) administered intramuscularly in a dose of 150 microng produced a satisfactory reduction in blood pressure in 13 of 16 hypertensive patients. Its effect occurred within five minutes, was maximal at 75 minutes and persisted for five hours. In six patients who received two doses (150 microng and 300 microng), the response was shown to be dose-related. No serious side effects were noted. Intramuscular administration of clonidine thus appears to be safe and effective. It has a place in the management of uncontrolled hypertension when a rapid reduction in blood pressure is undesirable and in the maintenance of blood pressure control when oral therapy cannot be tolerated.
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PMID:The use of clonidine by intramuscular injection in the treatment of hypertension. 26 67

The morbidity and mortality due to cardiovascular complications of chronic arterial hypertension are distinctly reduced by persistent and successful antihypertensive therapy. The principal emphasis is on drug therapy. Diet and psychotherapy should be used as supportive measures. Examples of antihypertensive drugs available for general practice: saluretics, beta-receptor blockers, dihydralazine (Nepresol), alpha-methyldopa, clonidine (Catapresan), reserpine and guanethidine (Ismelin). With mild hypertension (diastolic blood pressure up to 105 mm Hq), monotherapy with a beta-receptor blocker or a saluretic is indicated first. Contrary to the medical rule never to use a combination preparation if it can possibly be avoided fixed combinations have proved valuable in hypertensive therapy and facilitate therapy for the hypertensive patient and for the doctor.
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PMID:[Therapy of hypertension in general practice. Comments on the recommendations of the German Antihypertension League (author's transl)]. 30 37

1 A double-blind cross over trial between clonidine, propranolol and a placebo in patients with moderate hypertension has been performed. 2 Thirty-two patients completed the study which consisted of three treatment periods in random order of 3 months each. Patients had their blood pressure recorded by an unbiased observer using a random-zero machine. 3 Both clonidine and propranolol produced a significant reduction in blood pressure (P less than 0.01), which was apparent by the second week of therapy. Propranolol gave a greater reduction in pulse rate than clonidine (P less than 0.01) but clonidine also reduced the pulse rate significantly (P less than 0.05). There was no evidence of postural hypotension on either drug. Side-effects were more common with clonidine but these tended to wear off after several weeks of therapy. 4 Clonidine and propranolol were equipotent in reducing blood pressure, but clonidine has more initial side-effects than propranolol.
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PMID:A comparative trial of clonidine, propranolol and placebo in the treatment of moderate hypertension. 33 18

Clonidine, propranolol, bethanidine and debrisoquine effectively decrease blood pressure by suppressing renin secretion or interfering with function of the sympathetic nervous system. In man these compounds exert an antihypertensive effect within several hours or days and their duration of action is sufficient to permit administration twice or thrice daily. Clonidine and propranolol are especially useful if sexual dysfunction or postural hypotension is undesirable. Although bethanidine and debrisoquine may produce these adverse effects, they are beneficial in severe hypertension and produce fewer side effects than guanethidine. Clonidine frequently causes sedation, and rebound hypertension may occur with sudden cessation of therapy. Injudicious use of propranolol may provoke heart failure or asthma in susceptible individuals. The combination of a thiazide diuretic with propranolol and one of hydralazine, bethanidine and debrisoquine may be used to treat severe or complicated hypertension.
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PMID:New drugs in hypertension. 34 94

Among the newer antihypertensive agents are the beta-blocking drugs, such as propranolol. These agents are useful as second-step drugs to be used if diuretic therapy alone is not effective. In mild to moderately severe hypertension, propranolol, in does of up to 480 mg/day in combination with a thiazide diuretic, has been found to be effective in over 80% of patients on long-term therapy. This degree of response is essentially similar to that noted with a combination of reserpine and a diuretic agent. Although some observers believe that propranolol produces many fewer side effects than the other step 2 drugs (reserpine and alpha-methyldopa), there are some patients who do experience restlessness, insomnia, and depression. Clonidine may be substituted for another step 2 drug, is of moderate potency, but may not be tolerated by a large number of patients because of the severe dry mouth and drowsiness that it produces. Prazosin appears to be a suitable substitute for hydralazine as an effective vasodialator if thiazides plus propranolol or thiazides plus reserpine or alpha-methyldopa are not effective. In some instances, it many be an acceptable second-step drug because of its alpha-adrenoreceptor-blocking properties. The angiotensin II competitive inhibitors or converting enzyme inhibitors may in the future have some place in the management of hypertension.
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PMID:Propranolol and newer antihypertensive drugs in the management of hypertension. 42 60


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