Moderate. These medicines may cause some risk when taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
When these two medicines are taken together, the amount of blood pressure medicine used by your body may be decreased.
What might happen:
The beneficial effects of your blood pressure medicine may be decreased. These decreased effects may be seen for several days after stopping your phenothiazine.
What you should do about this interaction:
You should check your blood pressure regularly. Tell your doctor if there is a change in your blood pressure, since he may need to change the dose of your medicine depending on your blood pressure. You should also tell your doctor if you have any chest pain or shortness of breath, or if you have any dizziness, headache, or blurred vision.Make sure that your doctor knows all of the medicines that you are taking.Your healthcare professionals (e.g., doctor or pharmacist) may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
1.Ober KF, Wang RI. Drug interactions with guanethidine. Clin Pharmacol Ther 1973 Mar-Apr;14(2):190-5.
2.Janowsky DS, el-Yousef MK, Davis JM, Fann WE. Antagonism of guanethidine by chlorpromazine. Am J Psychiatry 1973 Jul;130(7):808-12.
3.Stone CA, Porter CC, Stavroski JM, Ludden CT, Totaro JA. Antagonism of certain effects of catecholamine-depleting agents by antidepressant and related drugs. J Pharmacol Exp Ther 1964;144:196-204.
4.Fann WE, Janowsky DS, Davis JM, Oates JA. Chlorpromazine reversal of the antihypertensive action of guanethidine. Lancet 1971 Aug 21;2(7721):436-7.
5.Tuck D, Hamberger B, Sjokvist F. Drug interactions: effect of chlorpromazine on the uptake of monoamines into adrenergic neurons in man. Lancet 1972 Sep 2;2(7775):492.
6.Gilder DA, Fain W, Simpson LL. A comparison of the abilities of chlorpromazine and molindone to interact adversely with guanethidine. J Pharmacol Exp Ther 1976 Aug;198(2):255-63.
7.Simpson LL. Combined use of molindone and guanethidine in patients with schizophrenia and hypertension. Am J Psychiatry 1979 Nov;136(11):1410-4.
8.Poe TE, Edwards JL, Taylor RB. Hypertensive crisis possibly due to drug interaction. Postgrad Med 1979 Nov;66(5):235-7.
9.Rankin GO, Watkins BE, Sawutz DG. Chlorpromazine interactions with guanethidine and alpha-methyldopa: effects on arterial pressure control and heart rate in renovascular hypertensive rats. Arch Int Pharmacodyn Ther 1982 Nov;260(1):130-40.