DEAR DR. ROACH: Over a 30-day period, my 84-year-old husband went from being mentally sharp, to going into a fog, to not being able to recognize simple objects or name the president. He was admitted to the hospital as a possible stroke victim.

His CT, EEG and MRI were negative. He had been taking gabapentin for four years with a current dosage of 1,800 mg daily. When this was stopped, he immediately began regaining his cognition and was discharged five days later, with the dementia being basically gone.

Have you experienced prescription-drug-induced dementia with any of your patients? Why was he not warned about dementia as a side effect?

• S.C.

ANSWER: Dementia is a longstanding process that gradually changes a person’s ability to think clearly, remember the past, find their way around, and complete many other tasks. A sudden change in mental function is called delirium, which is what your husband had. His doctors appropriately recognized gabapentin as a possible cause and stopped it. Delirium is a major concern as it is very dangerous.

I have often seen acute delirium from prescribed medications, and gabapentin is one of the more common ones to cause it. What is a little confusing is why he suddenly had a bad side effect when he had been apparently doing well with it for four years.

Gabapentin has many drug interactions, and a new drug might have increased the blood level. Gabapentin is also dependent on kidney function. Any change in kidney function from not getting enough fluid or from damage due to a drug like ibuprofen might have prevented the kidneys from getting rid of the gabapentin, which allowed the levels to rise. You also mention that 1,800 mg is his current dose; if it had recently increased, this would explain the delirium.

Although the drug information mandated by the Food and Drug Administration includes warnings about “feeling tired” and “difficulty with speaking,” they don’t warn people about acute delirium. It is wise for physicians to warn their patients about serious potential side effects, even if they are rare. Most patients want this information so that they can look out for these side effects.