56 Section 1/ General Principles of PharmacologyDrug affected Drug interacting Effect
Infections
Aminoglycosides e.g. Ethacrynic acid, furosemide, skeletal Increased ototoxicity, increased
gentamycin etc. muscle relaxants neuromuscular blockade.
Cephalosporins Ethacrynic acid, furosemide, gentamycin Increased nephrotoxicity.
Chloramphenicol Phenobarbitone Reduced plasma concentration
of chloramphenicol & increased
levels of phenobarbitone.
Dapsone Probenecid Reduced excretion: Increased
side effects.
Griseofulvin Phenobarbitone Impairs absorption.
Ketoconazole Antacids, anticholinergic drugs, Decreased absorption.
cimetidine, ranitidine
Metronidazole Alcohol ‘Antabuse’ reaction.
Tetracycline Antacids, dairy products, oral Reduced absorption.
iron, sucralfate, zinc sulphate
Malignant disease & immunosuppression
Azathioprine Allopurinol Potentiation: Increased toxicity.
mercaptopurine
Cyclosporin Ketoconazole Increased plasma concentration of
cyclosporin.
Methotrexate Aspirin, phenylbutazone, probenecid Delayed excretion: Increased
toxicity.
Antiepileptics, cotrimoxazole, pyrime- Increased anti-folate effect.
thamine
Central nervous system
A. Analgesics
Aspirin Metoclopramide Potentiation.
Ketoprofen, naproxen Probenecid Increased plasma concentration.
Paracetamol Cholestyramine, metoclopramide Reduced absorption.
B. Antiepileptics
General Tricyclic antidepressants, oral contra- Increased seizure activity.
ceptives
Carbamazepine Cimetidine, dextropropoxyphene, eryth- Potentiation.
romycin, isoniazid
Ethosuximide Carbamazepine Reduced plasma concentration of
ethosuximide.
Phenobarbitone, Phenytoin, sodium valproate Increased sedation, increased
primidone blood levels of phenobarbitone.
Contd.....