Drug Interactions 55
Contd.....Drug affected Drug interacting Effect
Lignocaine, mexiletine, Diuretics: Bumetanide, ethacrynic acid, Antagonised by hypokalaemia.
tocainide. frusemide, thiazides
Lignocaine Cimetidine, propranolol Increased risk of lignocaine toxicity.
Verapamil Beta-adrenoceptor blocking drugs Asystole, hypotension.
Digoxin & other cardiac Diuretics: Bumetanide, ethacrynic acid, Increased toxicity.
glycosides furosemide, thiazides
Cholestyramine, colestipol Reduced absorption.
Phenobarbitone, rifampicin Inhibition (Digitoxin only)
Digoxin Amiodarone, quinidine, quinine Potentiation may occur.
Nifedipine, verapamil Potentiation may occur.
Diuretics Indomethacin Antagonism.
Carbenoxolone, corticosteroids, corti- Hypokalaemia.
cotrophin, estrogens
Aldosterone antagonists: Captopril, potassium supplements, Hyperkalaemia.
Amiloride, triamterene trilostane
Heparin Aspirin, dipyridamole. Potentiation.
Adrenaline, noradrenaline Beta-adrenoceptor blocking drugs Potentiation of hypertensive effect.
Respiratory system
Theophylline Cimetidine, erythromycin, influenza Potentiation.
vaccine, oral contraceptives
Carbamazepine, phenytoin, rifampicin, Plasma concentration of theophylline
sulphinpyrazone may be reduced.
Antihypertensive drugs
Captopril Antiinflammatory analgesics such Reduced effects.
as indomethacin, phenylbutazone,
corticotrophin, estrogens, oral con-
traceptives
Alcohol, antidepressants, hypnotics, Potentiation.
sedatives, tranquillizers, fenfluramine,
levodopa, vasodilators such as nitrates,
nifedipine, verapamil
Potassium supplements, potassium Hyperkalaemia.
sparing diuretics.
Clonidine Beta-adrenoceptor blocking drugs Increased risk of clonidine with-
drawal hypertension.
Tricyclic antidepressant Antagonism.
Beta-adrenoceptor Indomethacin Antagonism of antihypertensive
blocking drugs effect.
Nifedipine Severe hypotension and heart
failure occasionally.
Sympathomimetic amines such as Severe hypertension reported.
adrenaline, amphetamines, phenyl-
ephrine
Labetalol Cimetidine Potentiation possible because of
reduced metabolism.