Salicylates increase the effects of oral anticoagulants. Caution is necessary when salicylates and anticoagulants are prescribed concurrently. Also salicylates may depress the concentration of prothrombin in the plasma. Salicylates may potentiate sulfonylurea hypoglycemic agents. Large doses of salicylates may have a hypoglycemic action, and thus affect the insulin requirements of diabetics.
Salicylates can produce changes in thyroid function tests.
Sodium excretion produced by spironolactone may be decreased in the presence of salicylates. Although salicylates in large doses are uricosuric agents, smaller amounts may depress uric acid clearance and thus decrease the uricosuric effects of probenecid, sulfinpyrazone and phenylbutazone. Caffeine may cause nausea, nervousness, insomnia, headache, vomiting, palpitation, vertigo, muscle tremor, sensory disturbances, excessive diuresis in sensitive patients. Large doses may cause gastric ulceration. In addition to these characteristics typical of narcotic poisoning, focal and generalized convulsions constitute a prominent feature in most cases of severe propoxyphene poisoning.