Zonisamide (a sulfonamide) and low platelets

Ellen's neurologist recently prescribed for her Zonisamide, a sulfonamide anticonvulsant, as a migraine preventative. Because sulfonamides are on the short list* for drug-induced thrombocytopenia, we ran this by the hematologist, who said it is not contraindicated, but I am not so sure. Ellen has been taking Zonisamide for 4 weeks now.

Ellen's platelets had been hovering in the 50-80k range, until Tuesday dropping to 21k from 72k two weeks previous. Her hematologist prescribed dexamethasone pulse and is setting up for her to begin Rituxan.

I am wondering if the drop in platelets might be caused by the Zonisamide (which is not helping her migraines, anyway). My instinct tells me to hold off on the Rituximab, discontinue the Zonisamide, use the dexamethasone pulse to temporarily treat the low platelets, and then wait to see if the platelets recover and hold their previous level minus the Zonisamide.

Counter argument: From 10/2 to 10/16 her platelets INCREASED from 65 to 72k while taking Zonisamide.

The downside to taking Rituxan now is, of course, the medical risk. The upside to doing it now rather than later is a) getting it over before the holidays and b) getting it done on this year's health insurance (out-of-pocket already maxed out, so no co-pay!!!)

So.... What do y'all think? What would you do?

* per Medline: Chemotherapy drugs and a seizure medication called valproic acid may lead to this problem. Other drugs that cause drug-induced thrombocytopenia include:
Furosemid
Gold, used to treat arthritis
Nonsteroidal anti-inflammatory drugs (NSAIDs)
Penicillin
Quinidine
Quinine
Ranitidine
Sulfonamides

my book says hemo side effects: Aplastic anemia, granulocytopenia rare

I would be more worried about the CNS side effect of suicidal Ideation



I think it is like taking anything we all risk having a side effect which one we get we do not know till we take it. If you take a drug for the required time it needs to work and you feel it isn't working and you think it is dropping the platelet count than I would discuss with the doctor stopping the drug.
Ultimately the choice is Ellen's

I agree with Winnie. If you've given the drug enough time to work and it hasn't, stop the drug. She could do the Dex and see what happens from there, then decide on the Rituxan. Any drug can potentially cause thrombocytopenia.

Agree! You don't have a pattern of dropping yet, a single drop so far. Get off the drug that isn't working, then watch for a pattern.
Erica