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Mary Shomon

Popular Antibiotic Interacts with Thyroid Medication

By February 28, 2008

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The British Medical Journal has reported on a several cases of unexplained hypothyroidism in thyroid patients (on levothyroxine) who were taking the popular antibiotic ciprofloxacin. Ciprofloxacin is the generic name for the fluoroquinolone antibiotic sold under the brand names Cipro, Ciproxin and Ciprobay, Cirpoxine, and Ciflox. The drug is primarily used to treat urinary tract infections, pneumonia, and sexually transmitted diseases. Ciprofloxacin was also in the news during the anthrax scare, given its use in treatment for anthrax exposure.

What the researchers found in these cases were evidence that oral ciprofloxacin interacts with levothyroxine (i.e., Synthroid, Levoxyl, Levothroid) if taken together. It's thought that the ciprofloxacin may somehow decrease the absorption of the levothyroxine.

In one case, a woman taking 125 mcg a day of levothyroxine took ciprofloxacin (750 mg twice a day) and her TSH level rose to 44 after four weeks. Even when her dosage was raised to 200 mcg a day, her TSH didn't respond. Only when the ciprofloxacin was stopped did the TSH return to normal. In another case, a woman who was stabilized on 150 mcg a day of levothyroxine saw her TSH go from 1.6 to 19 after 3 weeks of treatment with ciprofloxacin at 500 mg twice a day.

What Can You Do?

If you're a thyroid patient who is taking ciprofloxacin, what should you do?

The research suggested that thyroid tests were normalized if patients took the levothyroxine and ciprofloxacin at least six hours apart.

So, if you are on levothyroxine, it makes sense to allow at least six hours apart from taking your ciprofloxacin. And if you have to take the antibiotic for a lengthy period, you should discuss the potential impact on your thyroid with your doctor, and possibly request period thyroid testing to ensure that your thyroid treatment is not affected.

Note: Interestingly, there are also anecdotal reports -- including my own -- of bad reactions to other fluoroquinolone antibiotics. Read about my own experience getting what's known as "floxed," in When Drug Side Effects Get Out Of Hand: Side Effects of Quinolone Antibiotics Like Tequin (Gatifloxacin) Can Be Serious.

You may also want to read my discussion of the book Bitter Pills, along with my Q&A with the author Stephen Fried. The book details Fried's wife's debilitating reaction to quinolone antibiotics, and other drug dangers that are not made public.

Source: Cooper, John, "Ciprofloxacin interacts with thyroid replacement therapy," British Medical Journal, 2005;330:1002 (30 April), Online

Photos: istockphoto.com, Pricegrabber.com

February 28, 2008 at 1:03 pm
(1) Betty J says:

I was taking generic Cipro and Levothyroxin and had BAD side effects, like severe migraines. One of them lasted 36 hrs. My head hurt extremely bad, I was dizzy and nauseaus. I had to stop taking the Cipro to get relief.

February 29, 2008 at 4:25 am
(2) Zaynab D'Elia says:

Friends, You won’t believe this, but the first time I was prescribed Cipro was for a thyroid infection! My endo diagnosed a thyroid infection and said that Cipro was the only thing to cure it! I think I better have a talk with him.
Also, our kids are frequently prescribed this for sinus problems, as young as 1 years old. Any news on the effect of this drug on children? Keep bringing these things to our attention, Mary!

February 29, 2008 at 4:27 am
(3) Zaynab D'Elia says:

Friends: I was prescribed Cipro for the first time to treat a thyroid infection! I better have a talk with my endo! He said it was THE drug to take!
Also, our kids are often prescribed this for sinus infections, as young as 1 years old! Anyone have any info on the safety of this family of drugs for children?
Thanks for alerting us to this Mary!

February 29, 2008 at 9:17 am
(4) Nancy says:

I recently had a complete thyroidectomy. I developed a bladder infection after the surgery and was put on cipro. Oddly enough, after 4 weeks and my synthroid being raised to 200 mcg, my thyroid levels instead of being in the “hypo” range – moved into the “hyper” range and was just flagged at .004! I wonder if the cipro had anything to do with that???

February 29, 2008 at 11:05 am
(5) Deborah says:

I developed vitiligo after taking Cipro.

February 29, 2008 at 11:07 am
(6) Linda says:

I don’t know if anyone else has had this problem, but the first time I ever noticed a problem with my thyroid (swelling in the throat) was after taking Cipro. I was later diagnosed with hyperthyroidism (graves disease).

September 29, 2011 at 9:32 pm
(7) Lina says:

So was I. I think cipro caused my graves disease!! How are u feeling now??

February 29, 2008 at 12:58 pm
(8) Diane says:

WOW- I read the article about the bad reaction to Tequin and I too had a reaction (i am on synthroid and cytomel). I have NEVER been allergic to anything in my life and was diagnosed Tequin for a sinus infection. I was so sick for 3 days with vomiting and diarrehea. I felt as if I had been food poisoned. I have taken Cipro and had no problems. How strange. I have never met anyone that has been put on Tequin and even some doctors had to look it up when I mention it. What else must we go thru?!?!?!

February 29, 2008 at 7:06 pm
(9) Elizabeth says:

A pharmacist has warned me about the dangers of fluoroquinolone antibiotics. My person experience with three of them has been unpleasant.

February 29, 2008 at 9:15 pm
(10) Angela says:

Cipro caused me to have a tendon rupture and severe knee problems ever since. The dr told me I would be susceptible for up to a year to get tendon rupture again so not to do anything to strenuous. Those sorts of things the pharmacy will never tell you about.

March 1, 2008 at 7:14 am
(11) Juliana says:

The TSH effect isn’t the worst one. Flouroquinolones are GABA antagonsists. This means that they can cause seizures in people who have had even unnoticed GABA damage. Benzodiazepines are the usual cause of this GABA insufficiency.

However, anyone who has had a seizure of any magnitude may find that the flourquinolines will precipitate a seizure.

I know that doctors usually ignore this problem and can’t believe that the drug caused these problems when they do occur.

When you are asked if you have any drug allergies, this would be a good time to put into your record any contraindications for flouoquinolones.

March 1, 2008 at 5:45 pm
(12) smiles says:

Cipro should be avoided for people with type B blood.
EAT RIGHT FOR YOUR TYPE, By Dr. Peter J. D’Adamo, page 239.

April 1, 2009 at 5:40 pm
(13) Frank Bryant says:

I don’t understand why doctors today are so oblivious to these problems, I have Hashimoto’s desease and had a possible infection, I went to a urologist and he put me on Cipro (500mg) twice a day for ten days, and I told him in advance that I had a thyroid problem and was on Synthroid, and he still prescribed Cipro, I did not find out about the interaction or nasty things that this drug can do to you after taking it.It just shows how the big drug company’s manipulate todays medical practice.

April 17, 2009 at 4:42 pm
(14) sara says:

Does this medication any collateral damage?
I have seen this drug in a car, my brother, aged 20 years, but he does not complain of any illness!

April 21, 2009 at 2:57 pm
(15) Annabel says:

Itake 150 mcg of Thyroxine daily. I recently had a prolonged kidney infection, taking ciprofloxacin as the third antibiotic to try and cure it. It worked and afterwards (when being treated for stones!) I asked the GP about my thyroid levels and was poo pooed and told there was no connection. On being tested, after insisting, my thyroid levels were at rock bottom and I had to take extra doeses to get it back up again. So this research is worth pursuing.

May 1, 2009 at 10:55 am
(16) PALLINE PLUM says:





July 8, 2010 at 9:41 am
(17) silentk says:

I was just prescribed cipro (500 mg) by the same doctor who first prescribed my levothyroxine for Hashimoto’s 2 years ago. I’m kind of upset I had to find out about this interaction online. It wasn’t even listed in the long page of drug info from the pharmacy, so I’m guessing this isn’t widely known by general practitioners.
I’ll try taking it 6 hours apart from my Synthroid as noted in this article and see how it goes.

July 15, 2010 at 9:36 am
(18) silentk says:

Thought I’d check back with how the 6-hour spacing worked for me. The first day I took Cipro (500 mg) about 2.5 hours after my Synthroid (75 mcg), because I didn’t know about the possible interaction. And I felt awful- tired, dizzy, disoriented. The next day I waited 6 hours and felt much better, but still not 100%. For the rest of the week I mostly felt ok but was definitely more tired and sluggish than usual, and I did have one day near the end when I felt very tired and mentally foggy.
So… while spacing the meds out seemed to help, Cipro still lowered my energy level- although whether this was an interaction between Cipro and Synthroid or just a side effect of the Cipro is hard to say. At least it worked to clear up the infection- but I’d rather not take it again.

September 15, 2010 at 2:06 pm
(19) mamiesilve says:

server thus 2007 activity

October 5, 2010 at 11:32 am
(20) Pam says:

I took Cipro for 3 days twice a day,
I felt like I had pins and needles in my legs and all over my body. Anxiety, dizziness you name it I had it.
I am taking Armour and I felt like it messed up my thyroid.
I slowly recover from this terrible experience still dealing with fatigue and hoping that my thyroid levels will be back to normal soon.

December 21, 2011 at 9:26 am
(21) gretch55 says:

I have Hashimoto’s thyroiditis and have been on synthroid for years. I was recently prescribed a ten day course of cipro for a sinus infection and am half-way through the course. I have already gained five pounds (with no change in diet) and have felt sluggish and terrible as if my thyroid wasn’t working. Suspicious, I checked the internet and low-and-behold I have my answer. I was already taking them about two hours apart. I will try six hours, but I am not confident that will help very much. It is not a good thing to get your antibodies pissed off at your thyroid any more than they already are! I just hope I can lose the weight once the antibiotics are done.

January 16, 2012 at 6:51 am
(22) Patrick says:

This drug will ruin your life look it up on Facebook we have a whole support group for these types of antibiotics. Do your research and tell your friends.

May 8, 2012 at 2:44 pm
(23) Renee says:

I am just on synthroid ( dec. 2011) I think. Took cipro end of march 2012 for uti. After cipro I have 2 huge bald spots in the top of my head. Have to wear a wig to cover it until it grows back. I hope it grows back. Both my md and dermatologist say they don’t think it was cipro. Since it happened immediately after cipro I am convinced it is.

June 5, 2012 at 1:28 pm
(24) Lynne says:

Hi renee,

Did your hair ever grow back?

July 12, 2012 at 4:08 pm
(25) Lorian Rivers says:

I was prescribed Cipro to help heal after surgery, and was taking Synthoid after a Thyroidectomy. After a couple of days I started having heart palpitations. Each day it got worse. Finally on the 5th day I was rushed to the ER with major heart fibrilation. It took 6 hours to stabilize my hearty, and was in CCU for 2 days. Later I found out my thyroid surgeon’s wife also took synthoid and cipro and had the exact same reaction.

October 11, 2012 at 6:08 pm
(26) liz says:

I didn’t like the what i read on the papers that came with the Cipro- asked the doc that was giving me my thyroid meds if i could have something else and will it mess with the thyroid meds- he told me it’s fine to take- it’s my second day- but im just starting my thyroid meds tonight- The Cipro is hurting my stomach that I already have problems with and i have tendon issues so I am worried about that too- I have had thyroid issues for a long time but i dont always have insurance- I want into this clinic type place once and they told me my tyroid was fine- I showed her she didnt do any of the right test and I do have a thyroid problem- she told me I needed prozac and threw me out cause I wouldnt take that. It’s been a year and a trip to the ER showed I have a very bad thyroid problem… I also have fybroidmalgia- never spell that right- and thats not being treated- the follow up doctor the ER sent me to does not believe in Fybroidmalgia- When I was even in the office my heart kept racing then they couldnt find my pulse and by bottom number for blood pressure kept coming back bad- they just kept trying to test me to get better numbers cause they didnt want to write down what was happening. Im so sick of doctors- I should mention i wasnt on the Cipro or anything yet at that doctor visit- between under active thyroid- polytheistic ovaries and fribro- i have gained sooo much wait.. yet they tell me i just need to diet- it’s been a while but i use to be 98 pounds… now im 220.. im not eating the best- almost completly bed ridden- my husband has to wash me and dress me- im only 36- but i didnt put on all this weight from eating- oh and for 8 years my red and white blood cells keep coming back high- not one doctor can tell me what that means- I even had a doctor that told me Satan gives you pain and would send me home with bible quotes as treatment-

February 2, 2013 at 7:45 am
(27) Eddie says:

I have been taking CIPRO for 5 days. I take Syntrhorid since I don’t have a thyroid after having it removed because of Cancer. I’m so sleepy all I feel like doing is laying down. Even after a good 8 hous of sleep I feel the same way. This article sure explains it. I’m not sure If I’m going to stop taking CIPRO or just take it 6 hours after my synthroide. I wish I had known about this before.

February 19, 2013 at 12:36 am
(28) MM says:

So basically in order to take synthroid once daily and cipro twice daily with spacing them out 6 hours, I need to be awake 18 hours. 6am synthroid, 12 noon cipro, and midnight cipro! Wow!! I’m going to have to take synthroid later in the day on an empty stomach because I’m not staying awake 18 hours a day for the next week. I will take cipro at 8am, synthroid at 2pm and cipro at 8pm. That sounds a lot better!

September 4, 2013 at 11:38 pm
(29) Irene says:

I take 150mcg of thyroxine every day. I noticed today that have gained 3 kilograms in 2 weeks after taking Ciprofloxacin for 14 days and have felt extremely bloated, sluggish and unable to concetnrate. I think I messed up a job interview yesterday because of it. It’s good at least to know why.

October 19, 2013 at 11:51 pm
(30) Renee says:

I ended up at my urgent care Dr with a horrible bladder infection this week. I thought I had read previously that cipro can interfere with T4 medications, so when I filled my prescriptions at the pharmacy I specifically asked the pharmacist if I need to be concerned about any counter indications or medication interaction issues with my Synthroid or Cytomel. His response, No there’s no problem there at all. Ugh!

October 23, 2013 at 3:36 pm
(31) Deborah says:

I had to say no to Septra, Dr.s first choice (new with her, I get arthralgia, so no.) I’ve responded well to Cipro so far, so she prescribed it, but pharmacist in her clinic waned me to take it six hours apart from my thyroid meds (armour thyroid.)

I have a light UTI, taking a drink that luckily makes it less for me (Naked Juice’s Green Machine, I like it, but your mileage may vary), so only 250 mg 2x daily, only 5 days (I wanted more than 3 days, to protect my kidneys.)

If I’d known, I’d have asked for higher dose for shorter time, but five days isn’t bad. I may eat fish (sushi!) because it helps just a bit.

March 26, 2014 at 9:31 pm
(32) Christi says:

I was curious because I’ve been on Cipro for 3 weeks now for an infection in my arm. I can’t take any other antibiotic because I’m allergic to so many things. Since I’ve been on the Cipro my lips feel like they are so dry they could fall off plus I’m getting that metal taste I had before I was diagnosed with Hyperthyroid. My skin screams at me and I’m cold even when it’s 70* outside. Its good to know I now have a reason!

Thanks guys.

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