Drug Interactions: Know the Ingredients (cont.)

Several months later, I called the transplant director to thank him and the transplant team on behalf of John. The transplant director told me that they were still uncertain of the cause for the liver failure, but examination of John's liver under the microscope suggested drug toxicity-most likely acetaminophen.

Acetaminophen is the pain-reliever in Tylenol. Acetaminophen also is in many prescription and OTC pain relievers and cold/flu remedies. For example, each tablespoon of the common nighttime cold remedy, NyQuil, contains acetaminophen. Similarly, each tablet of hydrocodone/acetaminophen (Vicodin), a popular narcotic painkiller also contains acetaminophen in some of its formulations.

For the average healthy adult, the maximum recommended dose of acetaminophen over a 24 hour period is four grams (4000 mg) or eight extra-strength pills. (Each extra-strength pill contains 500 mg and each regular strength pill contains 325 mg of acetaminophen.). In recommended doses, acetaminophen is quite safe to use for minor headaches, fever, aches and pains. Acetaminophen usually is toxic to the liver only in high doses; a single dose of 7 to 10 grams of acetaminophen (14 to 20 extra-strength tablets) can cause liver damage in the average healthy adult. The most common cause of acetaminophen induced liver damage is suicidal overdose.

Can acetaminophen cause liver damage in lower doses?

The answer is yes. It seems that certain individuals are more prone than others to develop acetaminophen-induced liver damage; doses as low as 3 to 4 grams in a single dose or 4 to 6 grams over 24 hours have been reported to cause severe liver injury, sometimes even resulting in death. People who drink alcohol regularly appear to be especially susceptible to acetaminophen-induced liver damage. Therefore, a person who drinks more than two alcoholic beverages per day should not take more than two grams of acetaminophen (equivalent to four extra strength tablets) over 24 hours.

John's illness illustrates the potential danger of interactions of food or drugs with other drugs. (Alcohol can be considered both a food and a drug). I believe that John's alcohol consumption during the holiday party rendered him susceptible to acetaminophen liver damage. He then unknowingly took too many acetaminophen-containing tablets the next day. The amount of acetaminophen he took that day would not have damaged his liver if he had not been drinking alcohol. In other words, the alcohol-acetaminophen interaction was the problem. Always read the labels of all prescription and over-the-counter medications and understand the active ingredients and their strengths.

Another adverse drug interaction I encounter periodically involves warfarin (Coumadin), the active ingredient in Coumadin. Warfarin is an anti-coagulant (blood thinner) that prevents the liver from making factors that are necessary for the formation of blood clots. It is useful in preventing blood clots in patients who are prone to develop blood clots in the veins of their legs (deep vein thrombosis). Blood clots in the veins of the leg can break loose and travel to the lungs (pulmonary embolism) to cause chest pain, shortness of breath, and even life-threatening shock. Warfarin also is used sometimes to prevent blood clots in patients with an irregularity in the rhythm of their hearts called atrial fibrillation and in patients with artificial heart valves. Patients with atrial fibrillation are prone to form clots in the chambers of their hearts. Patients with artificial heart valves are prone to form blood clots on the artificial valves. Blood clots that break loose from the heart can travel to the arteries in the brain, disrupt the blood supply to the brain, and cause strokes.

Medically Reviewed by a Doctor on 12/9/2014