Chlorpromazine Antihypertensives

Should it occur, treatment is largely symptomatic chlorpromazine 50-100 mg may control the central excitatory symptoms, and contribute to control of others, while more specific antihypertensive therapy may be required labetalol, a combined a- and p-adrenoceptor antagonist, has been used successfully. Arrhythmias may require 3 blockade. 

Phenothiazine neuroleptics (e.g. chlorpromazine, thioridazine) + vasodilators and antihypertensive drugs —> increased hypotensive effects due to increased peripheral vasodilation. 

VASODILATOR ANTIHYPERTENSIVES ANTIPSYCHOTICS Risk of hyperglycaemia when diazoxide is co-administered with chlorpromazine Additive effect both drugs have a hyperglycaemic effect Monitor blood glucose closely, particularly with diabetes... 

May increase the effects of antihypertensive drugs except for guanethidine, whose antihypertensive actions chlorpromazine may antagonize... 

Acute poisoning is manifested by excitement and peripheral sympathomimetic effects convulsiorrs may occur also, in acute or chronic overuse, a state resembling hyperactive paranoid schizophrenia with hallucinations develops. Hyperthermia occurs with cardiac arrhythmias, vascular collapse and death. Treatment is chlorpromazine with added antihypertensive, e.g. labetalol, if necessary these provide sedation and a- and P-adrenoceptor blockade (not a P-blocker alone), rendering unnecessary the enhancement of elimination by urinary acidification. 

Accidental overdose with adrenaline occurs occasionally. It is rationally treated by propranolol to block the cardiac p effects (cardiac arrhythmia) and phentolamine or chlorpromazine to control the a effects on the peripheral circulation that will be prominent when the P effects are abolished. Labetalol (a + p block) would be an alternative. P-adrenoceptor block alone is hazardous as the then unopposed a-receptor vasoconstriction causes (severe) hypertension (see Phaeochromocytoma, p. 494). Use of antihypertensives of most other kinds is irrational and some may also potentiate the adrenaline. 

A patient taking chlorpromazine who was given nifedipine [dosage not stated] for 2 days before snidery, developed marked hypotension during surgery, which was eventually controlled with noradrenaline (norepinephrine). Other phenothiazines and calcium-channel blockers may interact similarly, see Antihypertensives + Other drugs that affect blood pressure , p.880. 

Large doses of chlorpromazine may reduce or even abolish the antihypertensive effects of guanethidine, although in some patients the inherent hypotensive effects of the chlorpromazine may possibly predominate. Case reports surest that haloperidol and tiotixene may interact similarly. Molindone is reported not to interact with guanethidine, and a single-dose of prochlorperazine also did not interact with guanethidine. 

Farm WE, Janow DS, Davis JM, Oates JA Chlorpromazine reversal of the antihypertensive action of guanethidine. Lancet (1971) ii, 436-7. 

The hypotensive adverse effects of chlorpromazine and other phenothiazines may be additive with the antihypertensive effects of methyldopa. Patients may feel faint and dizzy if they stand up quickly. An isolated report describes paradoxical hypertension in a patient given methyldopa and trifluoperazine. 

The increased hypotension and orthostasis that can occur if chlorpromazine or other phenothiazines are used with antihypertensive drugs such as methyldopa is established. Note that, of the phenothiazines, levome-promazine is particularly associated with postural hypotension. Warn patients that they may feel faint and dizzy particularly during the initial stages of concurrent use, and that if this occurs they should lie down, and that they should remain lying down until symptoms abate completely. Dosage adjustments may be necessary. 

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