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  IN THIS Article
 ::  Abstract
 ::  Introduction
 ::  Material and Methods
 ::  Results
 ::  Discussion
 ::  Acknowledgements
 ::  References
 ::  Article Tables

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Year : 1977  |  Volume : 23  |  Issue : 4  |  Page : 156-160

Clinical trial with intravenous clonidine in treatment of severe hypertension

Department of Cardiology, K.E.M, Hospital Bombay, and Clinical Pharmacology Unit of Department of Pharmacology, Seth G. S. Medical College and K.E.M. Hospital, Parel, Bombay-400 012., India

Correspondence Address:
U G Gadgil
Department of Cardiology, K.E.M, Hospital Bombay, and Clinical Pharmacology Unit of Department of Pharmacology, Seth G. S. Medical College and K.E.M. Hospital, Parel, Bombay-400 012.
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Source of Support: None, Conflict of Interest: None

PMID: 615261

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 :: Abstract 

Thirty six patients with severe hypertension were treated with intravenous clonidine. In 67% of cases maximum response was obtained within 11 hours of administration of the drug. Aver­age reduction in mean arterial pressure was 29%. Paradoxical rise in blood pressure was observed in some patients, immediately after clonidine administration. This could be prevented with prior administration of phentolamine intravenously. Clonidine (I.V.) sup­plied by two drug firms gave identical results.

How to cite this article:
Gadgil U G, Sunavalla J D, Pinto I J, Sheth U K. Clinical trial with intravenous clonidine in treatment of severe hypertension. J Postgrad Med 1977;23:156-60

How to cite this URL:
Gadgil U G, Sunavalla J D, Pinto I J, Sheth U K. Clinical trial with intravenous clonidine in treatment of severe hypertension. J Postgrad Med [serial online] 1977 [cited 2022 Oct 5];23:156-60. Available from:

 :: Introduction Top

Clonidine is a well established drug for management of hypertension. It is an imidazoline derivative synthesized by Stahle and associates [8] in 1962. Chemical­ly, it is 2- (2, 6-dichlorophenyl amino) -2 imidazoline hydrochloride. This drug is effective when given in microgram doses. The mode of action of clonidine in lower­ing blood pressure is the central stimula­tion of alpha adrenergic receptors at hypothalamic level, which reduces the peripheral sympathetic tone, [2] and a peri­pheral mechanism, characterised by a reduction in the response of vascular smooth muscle to stimuli. [9] Acute intra­venous administration of clonidine pro­duces an initial rise in blood pressure, owing to a direct peripheral alpha adre­nergic action, [10] and this is followed by a prolonged period of hypotension. This paradoxical rise in blood pressure can be prevented by administration of phentola­mine or tolazoline, or use of intravenous sodium nitroprusside.

Effect of clonidine on parenteral admi­nistration (i.v.) and its value in treating severe hypertension are presented in this article.

 :: Material and Methods Top

Thirty six patients with moderate to severe hypertension were selected for this study. All the patients except one, had mean arterial pressure (Diastolic blood pressure + 1/3 pulse pressure) of 130 mm. Hg. or more. Patients were divided into four grades according to the severity of blood pressure.

The patients were admitted to the In­tensive Cardiac Care Unit. The ECG, pulse rate and blood pressure were continuously monitored during the trial. Blood pressure and pulse rate were re­corded in lying down, sitting and stand­ing positions, just before the trial. Pati­ents with either systolic blood pressure of 230 mm. Hg., or diastolic blood pressure of 140 mm. Hg., or more were administer­ed 5 mgm. of phentolamine intravenously 10 minutes before the trial. Then cloni­dine 150 micrograms diluted in 5 ml. of 5% glucose was administered intrave­nously in bolus form.

Blood pressure and pulse rate were recorded in all the three positions at following intervals.

A. Every 1 minute for first 5 minutes.

B. Every 5 minutes upto 15 minutes.

C. Every 15 minutes upto 30 minutes.

D. Every J hour upto 2 hours.

E. Every 1 hour upto 6 hours.

F. Every 6 hours upto 24 hours.

In some cases, where fall in blood pres­sure was not significant, a second dose of clonidine (150 micrograms in 5 ml. of 5% glucose intravenously, in bolus form) was given.

Each trial lasted for 24 hours at the end of which the results were analysed.

 :: Results Top

Analysis of results was done under following headings.

A. Maximum response as regards fall in blood pressure and grading of the response.

B. Time taken to obtain maximum response after clonidine adminis­tration.

C. Relationship of pulse rate and fall in blood pressure following admi­nistration of the drug.

D. Paradoxical rise of blood pressure.

E. Time taken to return to pre-trial blood pressure level.

F. Presence of side effects.

Maximum response was graded accord­ing to fall in mean arterial pressure (MAP) after administration of the drug. Since this drug is used parenterally and is likely to be used during acute hyper­tensive emergencies in clinical practice, supine blood pressure was considered in evaluating the response.

Criteria for grading the response

A. Poor response:
(i) Mean arterial pressure does not fall by any of the above mentioned grades [Table 1].

(ii) If mean arterial pressure falls by less than 10 mm. Hg. inspite of a fall in grade.

(iii) Presence of severe side effects or severe postural hypotension.

B. Fair Response:

If mean arterial pressure falls by one grade only.

C. Good Response:

If mean arterial pressure falls by two grades.

D. Excellent Response:

If mean arterial pressure falls by three grades or comes to normal.


The average age was 45.3 years. The youngest patient was a 10 year old girl while the eldest one was a 74 year old male.


There were 29 males and 7 females taken for the trial.

Hypotensive Effect of Clonidine

Average reduction in mean arterial pressure for all 36 patients was 29% [Table 2].

According to our criteria, out of 36 patients 4 showed excellent response, 11 good, 12 fair and 9 showed poor response.

Fall in Systolic and Diastolic Blood Pressure

Average systolic pressure before trial was 210.5 mm. Hg. which came down to 155.2 mm. Hg., at which time maximum fall in blood pressure was obtained, show­ing a 26.3% fall [Table 2].

Average diastolic blood pressure was 136.7 mm. Hg. before trial which fell to an average of 106.7 mm. Hg, with cloni­dine administration showing a fall of 21.9%.

Time taken for obtaining Maximum Response

When an antihypertensive agent is ad­ministered parenterally, time taken to obtain its maximum effect is very impor­tant. Analysing our cases, we found that, in 670 of patients, maximum response was obtained within 12 hours of adminis­tering the drug [Table 3].

Paradoxical Rise in Blood Pressure after Intravenous Administration of Clonidine

In 11 out of first 24 cases, blood pres­sure increased instead of decreasing after administration of Clonidine, in the first few minutes. This rise was especially frequent in grade IV cases. Therefore, 5mg. of phentolamine was administered intravenously, 10 minutes before Cloni­dine administration, to all cases with sys­tolic blood pressure of 230 mm. Hg., or more and/or with diastolic pressure of 140 mm. Hg., or more. After that, only 2 cases showed paradoxical rise in blood pressure.

None of the patients went into left ven­tricular failure in spite of this sudden rise in blood pressure immediately after Clonidine administration.

Return of Blood Pressure to Pre-trial Level

Except in 5 cases, blood pressure did not return to pre-trial level within 24 hours after drug administration. Out of 5 cases, 1 took 24 hours, 1 took 5 hours, two took 4 hours and one came to pre­trial level in 2 hours time.

Fall in pulse Rate

There was an average fall of 9 beats/ min. when maximum fall in blood pres­sure was obtained. No severe bradycardia was observed in any of these cases.

Comparison of Two Brands of Clonidine

Clonidine supplied by M/s. C. H. Boehringer, Ingelham was used for first 18 cases and that supplied by M/s. Uni­chem Laboratories was used for next 18 cases. On comparing the results by stu­dents t-test, no statistically significant difference was found between these two brands of I.V. Clonidine, both in patient response and side effects.

Side Effects

Almost half the patients (17) suffered from side effects, which might be attri­buted to the therapy. Drowsiness was the commonest side effect followed by giddiness and headache. One patient developed a syncopal attack and one got rigors following administration of the drug [Table 4].

 :: Discussion Top

The hypotension following intravenous Clonidine is due to reduction in cardiac output and heart rate without a corres­ponding rise in peripheral resistance. [5],[7] These facts are also observed in haemo-dynamic studies in normotensive and in uncomplicated hypertensive patients after intravenous Clonidine administra­tion. [1],[3] Onesti et al [7] have noted that greatest decrease in blood pressure is within 1-2 hours after drug administra­tion.

At present no ideal drug for treatment of hypertensive crisis exists. Therefore many workers have compared antihyper­tensive effect after intravenous Clonidine administration with effectiveness of other currently available antihypertensive agents. Considering the potency, speed of action, contra-indications, and side effects of currently available antihypertensive drugs, Clonidine appeared to be superior to reserpine, methyl dopa, hydralazine and guanethidine. When compared with trimetaphan, sodium nitroprusside and diazoxide, clonidine appeared to be in­ferior in speed of action and potency, but has less serious side effects. [6]

In our patients, clonidine was very effective in reducing both systolic and diastolic blood pressure in cases of severe hypertension and hypertensive emergen­cies. Most of the patients showed their response in first 90 minutes. Except drowsiness, a few minor side effects were observed in a small number of cases. Our results are comparable to those of Niar­ chos et al [6] and Mroczek et al [4].

Parenteral Clonidine is a safe and effective alternative drug for the treatment of severe hypertension and hypertensive emergencies. Clonidine I.V. as supplied by both the firms showed identical results.

 :: Acknowledgements Top

Our thanks are due to the Dean, Seth G. S. Medical College and K. E. M. Hospital, Parel, Bombay-40-0012, for his kind permission to publish this article.

Joint financial support for this study from, C. H. Boehringer and Unichem Laboratories through Research Society, Seth G. S. Medical College and K. E. M. Hospital, Bombay, is gratefully acknow­ledged.

Thanks are also due to C. H. Boehrin­ger and Unichem Laboratories for the generous supply of clonidine IN. as Cata­press and Arkamine respectively.

 :: References Top

1.Finnerty, F. A. Jr.: Evaluation of the anti-hypertensive effect of catapress in man. In "Catapress in hypertension", a symposium held at the Royal College of Surgeons of England, March 1969, Butter­ worths, London, 155-166. 1970.  Back to cited text no. 1    
2.Kobinger, W. and Pichler, L.: Evidence for direct alpha-adrenoreceptor stimula­tion of effector neurons in cardiovascular centers by clonidine. European J. Phar­macol., 27: 151-154, 1974.  Back to cited text no. 2    
3.McRaven, D. R . , Kroetz, F. W . , Kios­chos, J. M. and Kirkendall, W. M.: The effect of clonidine on haemodynamics in hypertensive patients. Amer. Heart J. 81: 482-489, 1971.  Back to cited text no. 3    
4.Mroczek, W. J., Davidov, M. and Fin­nerty, F. A. Jr.: Intravenous Clonidine in hypertensive patients. Clin. Pharmacol. & Therap., 14: 847-851, 1973.  Back to cited text no. 4    
5.Muir, A. L . , Burton, J. L. and Lawrie, D. M.: Circulatory effects at rest and exercise cf clonidine, an imidazoline deri­vative with hypotensive properties. Lancet, ii: 181-185, 1969.  Back to cited text no. 5    
6.Niarchos, A. P, and Baksi, A. K.: Treat­ment of severe hypertension and hyper­tensive emergencies with intravenous clonidine hydrochloride. Postgrad. Med. J., 49: 908-913, 1973.  Back to cited text no. 6    
7.Onesti. G., Bock, K. D., Heimsoth, V., Kim, K. E. and Merguet, P.: Clonidine, a new antihypertensive agent. Amer. J. Cardiol., 28: 74-83, 1971.  Back to cited text no. 7    
8.Stahle, H., Hauptmann, K. H. and Zeile, K.: First report from the laboratories of C. H. Boehringer, Sohn, Ingelheim, Rhein, 1962.  Back to cited text no. 8    
9.Zaimis, E. and Hannington, E. A.: Pos­sible pharmacological approach to mig­raine. Lancet, ii: 293-300, 1969.  Back to cited text no. 9    
10.Zaimis, E.: On the pharmacology of cata­press (st. 155) in "Catapress in hyper­tension." A symposium held at the Royal College of Surgeons of England, March 1969, Butterworth, London, 9-22, 1970.  Back to cited text no. 10    


  [Table 1], [Table 2], [Table 3], [Table 4]


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