(A) Extrapyramidal side effects:
It is the most important side effects of prochlorperazine. Extrapyramidal system is a neural network in the brain and spinal cord that controls our body posture, muscle tone and the initiation of movement. Prochlorperazine may affect the extrapyramidal system and disturbances its normal functions. Prochlorperazine induced extrapyramidal side effects usually occur with high doses, particularly in children and elderly persons. These are –
1. Parkinsonism – It may occur between 1 to 4 weeks of therapy. Prochlorperazine blocks the dopamine receptors in the substantia nigra in the brain. This leads to reduce dopaminergic output from the substantia nigra and produces the manifestations of Parkinsonism like muscle rigidity, tremor, slowness of body movement, mask like faces and festinating gait. Usually, it disappears after reducing the dose of prochlorperazine.
2. Acute muscular dystonia – It may appear within a few hours of a single dose or at the most in the first week of therapy. Bizarre spasms of the facial, tongue and neck muscles occur in this condition and producing grimacing, torticollis and locked jaw. It is more common in children below ten years, particularly after intramuscular (IM) or intravenous (IV) injection. This effect is treated with central anticholinergic drugs like promethazine.
3. Tardive dyskinesia – It may occur late in therapy or sometimes observed after withdrawal of drug therapy. It is more common in elderly persons on high doses, especially females. The dyskinesia may subside months or years after withdrawal of drug therapy or may be persists lifelong. The symptoms of dyskinesia are rhythmical involuntary movements of the face, mouth, tongue, jaw or limb (e.g. constant chewing, puckering of mouth, protrusion of tongue, puffing of cheeks). There is no satisfactory solution for tardive dyskinesia.
4. Akathisia – It may be seen in some persons between 1 to 8 weeks of therapy. Features of akathisia are restlessness, feeling of discomfort and apparent agitation. A central anticholinergic drug like promethazine may reduce the intensity, but most cases require reduction of doses of prochlorperazine.
(B) Central nervous system side effects:
Lethargy, drowsiness, mental confusion, aggravation of seizures in epilepsy.
(C) Cardiovascular side effects:
1. Postural hypotension – A fall in blood pressure (systolic more than 20 mm Hg or diastolic more than 10 mm Hg) while sudden standing from sitting or lying position is called postural hypotension. Postural hypotension may cause fainting especially in persons who fast stand up after having been flat in bed. If fainting develops, raising the patient’s legs may correct this condition. Prochlorperazine may cause postural hypotension and persons taking prochlorperazine advised to avoid prolonged standing and to stand up slowly.
2. Ventricular tachycardia – Ventricular tachycardia is an abnormal condition that can be diagnosed only in electrocardiography (ECG) in which heart rate more than 100 beats per minute, P waves are absent and QRS complexes are broad. Prochlorperazine may produce ventricular tachycardia. If ventricular tachycardia develops, drug should be stoped and treated with amiodarone, lignocaine or beta-blocker.
3. Atrio-ventricular block – It is a condition in which the conductive tissue of the heart fails to conduct impulses from the atrium to the ventricles. Atrio-ventricular block is detected in electrocardiography (ECG). Prochlorperazine may cause atrio-ventricular block. After stopping the drug, it improves.
4. Prolongation of QT interval
(D) Anticholinergic side effects:
Dry mouth, constipation, urinary hesitancy in elderly males, blurring of vision.
(E) Skin side effects:
1. Mild photosensitivity – Sensitivity to sunlight is called photosensitivity. Prochlorperazine may cause sensitivity to sunlight and producing rash, sunburn or other effects on skin. Persons known to have photosensitivity to prochlorperazine should avoid exposure to sunlight or when in the sun, should use sunscreen or clothing to cover exposed areas of the skin.
2. Skin rash
3. Urticaria – Urticaria is a vascular reaction of skin characterized by a sudden appearance of pale, smooth and slightly elevated wheals that are associated with severe itching. If prochlorperazine causes urticaria, drug should be stopped and use antihistamine. In severe urticaria that does not respond to antihistamine, corticosteroids should be used.
1. Blood dyscrasias – It is a disorder of the blood in which the constituents of blood like red blood cells, white blood cells or platelets are abnormal in structure, function or quality. Prochlorperazine may produce this condition. Therefore, periodic blood cell counts should be monitored during prochlorperazine therapy. If blood dyscrasias develop, discontinuation of drug is required.
2. Cholestatic jaundice – It occurs when the liver cells are unable to transport bilirubin through the bile duct into the duodenum due to bile duct obstruction. Prochlorperazine may cause intra hepatic bile duct obstruction and produce cholestatic jaundice. Therefore, liver function tests should be monitored during prochlorperazine therapy. If the condition develop, discontinuation of drug is required.