Theophylline ventricular arrhythmias caused

A. To control excessive sinus tachycardia or ventricular arrhythmias caused by catecholamine excess (eg, theophylline or caffeine), sympathomimetic drug intoxication (eg, amphetamines, pseudoephedrine, or cocaine), or excessive myocardial sensitivity (eg, chloral hydrate, freons, or chlorinated and other hydrocarbons). 

The mercury ion is capable of causing local or systemic toxicity. For local irritation, they are combined with theophylline in an attempt to diminish the irritative toxicity at the site of injection. IV administration may lead to ventricular arrhythmias. They cause hepatocellular damage and even precipitate hepatic failure. They can also lead to low salt syndrome, hypochloraemic alkalosis and potassium depletion. 

Interactions. Several types of drug interfere with lithium excretion by the renal tubules, causing the plasma concentration to rise. These include diuretics (thiazides more than loop type), ACE inhibitors and angiotensin-11 antagonists, and nonsteroidal anti-inflammatory analgesics. Theophylline and sodium-containing antacids reduce plasma lithium concentration. The effects can be important because lithium has such a low therapeutic ratio. Diltiazem, verapamil, carbamazepine and pheny-toin may cause neurotoxicity without affecting the plasma lithium. Concomitant use of thioridazine should be avoided as ventricular arrhythmias may result. 

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