Q1. A 67 year old lady comes to you with generalized body aches, headache, chills and fever. She says that her appetite has decreased since yesterday. It all started on the day after she attended a party - day before yesterday for Christmas eve. She ate some lobster and rice. One other person who got sick after the party did not eat those foods. Her PMH is significant for COPD. She is febrile, has a heart rate of 70 and her physical exam is normal otherwise. Complete blood count is normal. Chest X ray is normal, as is her urinalysis. Serum chemistry is also normal. You make a preliminary diagnosis of Influenza. You do not have a test for differentiating Influenza A from B. Which of the following drugs is best to use in this case empirically?
The answer is coice 2. I would accept choice 1 too as the right choice for this question. The prime reason of this is Cost/benefit ratio. On calling a local pharmacy, The cost of Amantadine today was $7.69 for the course. Rimantadine was ~ $22 and both Oseltamivir and Zanamivir were over $40. Most doctors got this question right. The CDC reports on February 26, 2000 "Since October 3, WHO and NREVSS laboratories have tested a total of 73,576 respiratory specimens for influenza viruses, and 12,651 (17%) were positive. Of the positive results, 12,622 (99.8%) were influenza type A and 29 (0.2%) were influenza type B. Of the 12,622 influenza A viruses, 3,310 (26%) have been subtyped and 3,266 (99%) were A(H3N2) and 44 (1%) were A(H1N1)."
This means that out of every 1000 patients who tested positive for Influenza, only 2 had Influenza B. 998 were influenza A. Although Rimantadine is better tolerated, it is almost 3 times as expensive as Amantadine. If someone suffers side efects from Amantadine, I would consider Rimantadine in the future. As far as Choices 3 & 4 are concerned, we should avoid their use because the advantage is negligible but cost is substantially higher.
Theoretically speaking, Choices 3 & 4 are god empiric choices because they have activity against Influenza A AND B but practically speaking, Amantadine takes the prize.
Q 2. You start her on appropriate therapy. A day after she starts on it, she feels much better. What should you do?
The correct answer is choice 3. Refer to the CDC recommendations . This is done to prevent emergence of drug resistance.