Why you need to ask your vet about pet drug interactions & side effects

Discuss potential medication side effects with your vet

In the middle of a busy veterinary practice, many veterinarians may overlook an opportunity to discuss the possibilities of drug interactions and pet medication side effects. For example, many commonly prescribed nonsteroidal anti-inflammatory medications (NSAIDs) can sometimes cause digestive upset and/or liver/kidney problems in some sensitive pets. Corticosteroids like Prednisone can cause similar problems in some pets, as well as predispose pets to diabetes with prolonged use.

While a topic of debate, these risks are increased if Prednisone and nonsteroidal anti-inflammatory drugs are used together.

While potentially lifesaving, antibiotics can also cause allergic reactions from digestive upset to skin irritation. Some pets are sensitive to topical flea and tick medications, and in my practice I always administer topical flea and tick medication on a separate day from heartworm preventative medication or vaccinations, in order to lessen the burden on a pet’s immune system.

Whenever multiple drugs are prescribed it is always important for pet owners to ask questions, because veterinarians not only prescribe pet medication but are also dispensing these medications in private practice.

Do you have a question on potential pet medication interactions or side effects? Leave a comment below. 

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  1. My 108 lb Rottweiler has had skin allergies for the last 4 years which resulted in a lick problem. His front paw had a lick granuloma for almost 2.5 yrs. Endless refills of Baytril finally helped with the lesion but he still has that tendency to lick. He has now scratched an area on the side of his face, near his ear that is red ,bleeding and very sticky. He also is shaking his head, which makes me think it an ear infection? My vet prescribed cephalexin 500mg, 3 pills in the am: 2 pills in the pm. Can I also give him the Benadryl as he is still scratching the area?

    • You can try benadryl at dose of 50 to 75 mg twice daily to see if helps with itch. If not, you may need stronger antihistamine prescription antihistamine and/or low dose prednisone. You can also ask your vet about newer nonsteroid allergy options such as apoquel and cytopoint

  2. I want to know if there are any known contraindications between Trifexis and Zonisamide..my 11lb epileptic Schnauzer was just upped to 50mg of Zonisamide BID..up from 25mg BID..She takes Trifexis monthly..

    • No interaction between zonisamide and trifexis as far as I know specifically but check with local vet who prescribed it for confirmation. I would be aware, though of the rare potential for trifexis to aggravate seizure tendency in very rare dogs on occasion, in my experience and opinion, so make sure she is tolerating that drug ok, as well as check with local vet on their feelings on heartworm/flea meds

  3. Is there any interactions between Clavamox and Clopidogrel for felines….my daughters cat has URI and he has a heart problem so he was given both these meds at the same time…he is either having an allergic reaction to one of the drugs or they are interactions going on between the meds…please let me know ASAP….I am very worried about her cat and suggested she stop giving him the meds…he has a hard time breathing and twitches lying on his side for 5 to 6 hours, then gets up and eats, drinks, etc. but he still has a breathing issue….

    • There is no specific reactions between Clavamox and Clipridogrel as far as I know. However if breathing issues and/or twitching continues, then best to see vet ASAP, and of course stop both meds until the local vet who knows your pet best can revaluate the situation. Might be more related to heart disease itself, rather than either of these drugs.

  4. What are the contradictions in giving a dog with hypothyroidism Chlorpheniramine? I am caring for my sisters husky while she recoopperates from an illness and the dog was in bad shape. She had several bald spots and smelled of yeast. I have gotten her pretty much better but have been treating the severe itching with Chlorpheniramine. I just found an article that says not to give it to a hypothyroid dog. Why not?

  5. I myself am not familiar with chlorphenirimine contraindications in dogs with hypothyroid, however anything is possible. I would check with your local vet. In mean time, I would change to benadryl at dose of 1 mg per pound twice daily as option, as I have used benadryl in many hypothyroid dogs without issue

  6. My cat is on Phenobarbital for seizures. Would I be able to give her a Capstar for fleas? Thank you so much.

    • I would check with your local vet or even veterinary neurologist on whether ok to give the capstar in your pet with tendency to seizures, as occasionally capstar may trigger a seizure in occasional animal. Sometimes prednisone or dexamethasone can help lessen that possibility but best to check with local vet who knows your pet and history best

  7. Patricia DowningMarch 17, 2017 at 2:22 pm · Reply

    My 12 lb poodle Yorkie mix is on 50 mg twice per day of Zonisamide and insulin for diabetes. He showed elevated liver enzymes prior to everything prescribed . Concerned about potential side effects. His seizures did not last more than 5 minutes and com every month to 2 months. Diabetes was just confirmed 2 days ago.

    Other dog is 10lbs same breed and he does have elevated liver enzymes, but not diabetic. He’s also currently on an antibiotic after having teeth pulled on March 1.

  8. My 8 pound female Chihuahua who is approximately 7 or 8 years old appears to have an odd reaction when put on doxycycline and prednisone. Years ago, a vet recommended this as a soft kill for heartworm infestation and it worked…however randomly she would just stop doing whatever it was she was doing and yelp out in pain out of nowhere…we stuck it out to eliminate the heartworms, and she is now heartworm free.

    However she has developed a nasty cough for the last few months, and so the vet decided to use this combination again to treat the cough (suspected infection). This is a different vet from the first.

    The second night of the treatment she did the exact same thing…walked up to me sitting in the chair, lifted her leg and yelped out in pain, just like years ago.

    I don’t believe this is a coincidence as it has never occurred in between uses.

    Are there any know rare or uncommon interactions from these two drugs in small dogs? I’m at the point I don’t want to continue her on this particular treatment.

    • HI Brandon. Definitely an odd symptom you describe while on the combo of doxy and pred. As far as I know there is no documented reaction between these two drugs like this that would be responsible for this odd symptom, although you may want to see a veterinary internist or specialist who can review workup thus far and/or see if any other possibilities for causes might be present. From your description, it sounds more like a spinal and/or musculoskelatal reaction i.e disc or sore muscles which can be a problem on occasion as rare reactions to drugs, vaccinations, etc i.e a myosoitis(inflammation of muscle), or neuropathy…. Things to ask the vet specialist

  9. Can a dog that is taking simplicef take medrol at the same time

    • As far as I know there are no problems documented when taking simplicef and medrol at same time, but I would follow your local prescribing veterinarian’s recommendations on this, as well as have appropriate followups depending on what the problem is that is being treated

  10. My Doberman was diagnosed with valley fever and was started on fluconazole 250 mg BID then was found to have hypothyroidism and started with levothyroxine 800mcg, retested and raised to 1000mcg result came back 0.9 lower then last test, third test just came back as 1.0. His levels are not going up myself and our vet is perplexed. My other Doberman has same problem and his levels were normal after only 1 test. (Note the other one doesn’t have valley fever only hypothyroidism) anyway could the fluconazole be making the levothyroxine in effective because I give both meds at same time ?

    • I would first make sure that your vet has done a comprehensive thyroid profile to begin with at the start to make sure your dog actually has low thyroid. This includes not only a T4, but Free T4, TSH and thyroid and thyroglobulin autoantibodies. Many vets try and short cut their thyroid testing. But if your dog is truly hypothyroid, it will be very hard to see the T4 and even the Free T4 climb into the normal range until the Valley fever is brought under control. Unfortunately, other illnesses in the body may artificially lower thyroid levels on their own, in what is known as Euthyroid sick syndrome, so that measuring higher levels may not be possible until the Valley Fever situation is treated and fully addressed.

  11. My 12+ year old beagle mix girl is currently taking gabapentin, phenobarbital, piroxicam, and stasis breaker. She has a lung tumor in her left lung, spleen tumor, mass in her bladder, cyst on her left kidney and enlarged liver. She has not had any seizures in almost a year since she has been taking her medication on a consistent basis. I have not given her the heartworm preventative, Heartgard Plus, in the past 2 months. Will the Heartgard Plus interact with any of the above mentioned medications or harm her in anyway due to her medical conditions? She is a tough little dog. She amazes the veterinarian with how she continues to live pretty normal. She is not in pain, thank God, at this point.

    • Hi Katie. I personally would not give heartguard in pet on all of these drugs and with lung cancer, spleen/bladder tumor, etc. I would not use any chemical heartworm meds or flea/tick meds on pet like this, due to the risks of worsening the other diseases states through pressure on the liver/kidneys, etc. IF you want to use any heartworm and/or flea meds, I would try natural products such as the Bio Vance herbal heartworm protocol from http://www.fiestapetdeli.com

  12. I have a 6 year old female beagle that has cholangiohepatitis and is taking Clavamox, ursodiol, enroflaxcin, and denamarin. Can any or all of these medications make her constipated? Thank you.


    • These medicines usually dont make dogs constipated, however, dogs with liver disease are prone to stagnant blood flow in the liver and subsequent constipation. Ask your vet if ok to add a teaspoon or two of soluble fiber like metatmucil to meals along with a teaspoon of wheat bran as insoluble fiber as well

  13. My vet wants me to give my 4 year old; 15 lbs. alpha lapso 150mg twice a day of rilexine but im afraid to give it to her because of the serious side effects that it can have from vomiting, diaherra, lameness in back legs, even death.. what do you think of this medication?

    • This generic form of the antibiotic cephalexin is usually quite safe in the vast majority of animals. As with any antibiotic, or medicine for that matter, very rare side effects may be seen. The most common one with this drug is self limiting diarrhea and/or vomiting, which usually resolves quickly on stopping the drug, but this side effect is not common and is even less common when the drug is given with food. I would check with your local veterinarian who prescribed the medication if you have any questions and/or concerns.

  14. my dog takes 100 mg of theophylline 3 times a day and has famotidine 20 mg twice a day. are there drug interactions between those for dogs the same as with a person?

  15. i dont see my question so here it is. my dog is on 100 mg theophylline xr 3 times a day and i give him 20 mg of famotidine with breakfast and with lunch. is there a drug interaction between those that i have to be worried about. i see on drugs.com there is a moderate interaction in humans.

    • HI Faith. I have not seen any reactions in my practice on the few rare occasions I recall prescribing these drugs together i.e theophylline and famotidine. Of course, theophylline and/or any other prescription drugs for canine patients should always be monitored by the local veterinarian who prescribed them.

  16. Hi there. My dog is taking 7.5 mg of Piroxicam SID and he is extremely itchy. I’ve had him on Apoquel but it is too expensive to continue although it worked wonders. I’m wondering if it is ok to give him Loratadine to prevent the itching? Any contraindications?

    • While I dont have experience using Loratadine in veterinary practice, I dont see a problem with over the counter antihistamines and piroxicam, although I would check with your local vet who knows your pet best. I have more commonly used meds like Zyrtec or old fashioned benadryl as over the counter antihistamines.

  17. Can pyrantel betaken with methocarbamol?

  18. Can my dog take pyrantel while on robaxin 500 mg

  19. Are there any contraindications with Zyrtec & Atopica. My cats been on atopica for like 8 months & it’s not working. I read that Zyrtec was a good medicine for his itching, biting, over grooming, runny eyes & sneezing. I know the Zyrtec is just to deal with the symptoms, that atopica can help in the long run. I’d like to keep him on both if there are no contraindications. Thank You!!!

    • HI Lisa. As far as I know there are no known contraindications with Atopica and Zyrtec. I would let your local veterinarian know that you are adding the Zyrtec on board. I would also ask your vet about newer prescription allergy meds which are even safer than atopica, at least in short term, in apoquel and Cytopoint injection; both of these latter meds are by prescription as well.

  20. Can I use a seresto tic collar while using amoxicillin?

  21. Jennifer L McmicanApril 19, 2017 at 12:19 am · Reply

    Is it okay for a dog taking prozac to also use dasuquin?

    • Hi Jennifer. I dont see any problem for a dog to be on Prozac and dasuquin at same time. However, check with your local vet on this who is monitoring your pet while on prozac

  22. Can my 7 year old westie take apoquel for itching while taking confortis for flea control?

  23. Hi Michael! My 8lb dog is taking 62.5mg twice per day of metronidazole for diarrhea and is now acting like she has fleas. She has been flinging her head around so as to try to catch something on the back of her head or ears and then also biting near her tail and under her back legs. I don’t see any bites or fleas but I’m assuming that’s the problem. Is it safe to apply her Frontline Plus to her while she is taking the antibiotic? I don’t want to overload her with too many meds at once. Thank you!

    • I have not seen any problems with dogs on apoquel to be on comfortis for flea control at same time in my practice

    • Hi Nicole. I would check with your vet on applying front line plus right now, given that she is recovering from diarrhea while on flagyl. Sounds like a bit much on her system as you are asking. Perhaps try some oral benardryl at dose of 1 mg per pound twice daily to try and ease itching. Could be other type of allergies besides flea bite allergy causing itching. Sometimes a leaky gut from a bout of gastroenteritis can lead to systemic allergic reactions elsewhere in the body like the skin so that could be the cause as well which will improve once diarrhea improves. I would not want to overwhelm his body however now with the flea meds

  24. Claudia McDanielApril 21, 2017 at 8:17 pm · Reply

    My 12 year old border collie mixed had had vestibular disease. She was given predisone and is not being weaned off. Prior to this, she took metacam for arthritis. She was taken off of the metacam because of the predisone. She seems to be having trouble walking due to dragging her back legs. Can I give her gabapentin? She is taking 1/2 pill of predisone every other day.

  25. My 4 yr. old American pitbull is on apoquel for her itching issues , she now has diarrhea and I was going to try some liquid Pepto bismol to see if that will help her , along with chicken broth and white rice. Im wanting to know if anyone else has used this combination of medications and if so, did your dog have any kind of bad reaction to the two.

    • HI Stacey. I see no problem with trying pepto for a few days at most. However if diarrhea persists and/or worsens, then best to see your local vet, as may have other cause of diarrhea such as virus, parasite, inflammation of bowels, pancreas, etc

  26. Hello, is it ok to give my cat 10 mg prednisolone (that’s her daily dose), gabapentin for travel (we will be moving on this day, driving in a car for 6 hours), comfortis flea pill 270 mg, mirtazapine 7.5 mg compounded cream in ear flap. My cat has IBD. I would give her the mirtazapine, comfortis, and prednisolone about 4 days before the move. And then on moving day just give her prednisolone and gabapentin. But on moving day she will still be affected by the mirtazapine and comfortis because they both last longer than 4 days. So she will be affected by all 4 meds on moving day even though she will only be taking prednisolone and gabapentin on moving day.

    I’m desperate for this info. Thanks very much.

    • HI Sophie. Excellent questions. Does sound like ALOT of meds to me for cat with IBD and about to undergo a trip. Could be a bit overload on her system. I would perhaps speak to your vet about some other natural alternatives such as L theanine from health food store for anxiety and/or rescue remedy. I would be concerned about these meds overwhelming her already delicate system which is about to undergo travel stress of new home, etc

  27. My 14 year old dog is on rimadyl was wondering if giving him confortis at the same time is a good idea or not thank you for any information you can give

  28. My 19 year old cat takes buprenorphine for arthritis and gabapentin was just added. Since both are given every 8-12 hoyrs, can each medisine be given at the same time, one after the other or shpuld they be given at different times of day?

  29. I gave my small 18 pound shijz poo Heartguard and nexguard at the same time and then only then he changed and became real clingy to my husband afraid to get out of sight. this has been about month ago and he has changed dramtically ? Could that combinatiom together have maybe damaged his nervous system.very concerned! there nothing different in his environment they would make him behave this

    • I have not seen this specific reaction to giving heartguard and nexguard, however I do always try and counsel my clients to give such medications at least a week apart, as well as the same being true for vaccinations, etc. Perhaps the stress on his body did trigger an already underlying predisposing condition to express itself that was already there, or perhaps this is a different problem. Best to see your vet for exam and complete evaluation

  30. I gave my small 18 pound shijz poo Heartguard and nexguard at the same time and then only then he changed and became real clingy to my husband afraid to get out of sight. this has been about month ago and he has changed dramtically ? Could that combinatiom together have maybe damaged his nervous system.very concerned! there nothing different in his environment they would make him behave like this.Need some insight on this

  31. could these meds prescribed for my 10year old pit mix have adverse reactions given together theophylline, clavamox, mirtazapine, baytril, gabapentin.

    • Sounds like ALOT of meds at the same time to me Cathy, so check with your vet if all are completely necessary at this time. For example, baytril and theophylline may have an interaction together, with theophylline toxicity, so these are all best discussed with your vet.

  32. The vet just put my dog on carpaquin. My question is it ok to give her the carpaquin and dasaquin. She has been on cosequin and then dasaquin which seemed to help her arthritis somewhat. I just don’t know if there is any drug interaction between the dasaquin and carpaquin.

  33. HI Susan. Do you mean CARPROFEN and Dasaquin. Carprofen is a prescription nonsteroidal anti inflammatory drug that sometimes is necessary for pain/inflammation relief in pets with arthritis. Dasaquin and COSEQUIN would not have side effects if used together, but they are they would never be used together, as Dasaquin is basically Cosequin with an extra ingredient in it, and is a NUTRITIONAL SUPPLEMENT often more effective than cosequin in more advanced stages of arthritis.

  34. Yes I mean carprofen. I am just wondering if it is safe to give the dog carprofen and dasaquin or if there would be any side effects using both on a daily basis.

  35. I took my 13 years old, 56 lbs. Lab mix to the vet because he’s been having weakness in hind legs. That morning they had given out from under him but he eventually got up and went outside. He walked and did his business. That evening I took him to the Vet. Vet gave him overdue Rabies vaccine, took some blood (results not back yet) and physically examined him. Vet mentioned he probably has arthritis, maybe slipped disc. Gave me options and prescribed Carprofen 60mg – 1 daily; Gabapentin 100 mg. 1/2 tablet as needed; Dasuquin 2 x daily. When I got home I gave him one tab of each (instead of 1/2 tablet of Gabapentin). The next morning, yesterday, my dog was lethargic, unable to stand on his own, I am force feeding and forcing water on him – I gave him only 1 Dasuquin all day. Last evening, I had to lift him to go outside and he couldn’t/wouldn’t get up so he urinated & defecated lying down. This morning, he is still lethargic and unwilling or unable to stand. My husband & I lifted him, took him outside, forced him to stand and he urinated. He walked a short distance but unwillingly. He started to collapse so we carried him back in. I’m not giving him any meds today, Sunday. I plan to call the Vet or animal hospital. Is this a reaction to the Rabies vaccine, the meds, and/or both?

    • It is very possible that the rabies vaccination triggered and/or exascerbated the underlying weakness and condition. Given the weakness and signs of neurological or muscular problems with the lower end present, in my opinion, I would not have given him his rabies vaccination, until this issue was sorted out, diagnosed and treated, as rabies vaccinations have been documented to have these potential reactions you describe.

  36. My dog was prescribed Clavamox for a UTI and Previcox for a leg sprain 2 days ago. I forgot to ask if there were any interactions of I give both 3 hours apart.

  37. Are there any contra indications between chlorpheneramine tablets (an otc antihistamine) and glucosamine/chondrointin supplements?

    • Hi Deonna. No contraindications with the chlorphenirimine and joint supplement as far as I know

  38. Michelle CarusoMay 8, 2017 at 4:04 pm · Reply

    I have a 4 year old mixed breed who has valley fever and takes fluconazole. He also has very bad allergies and takes Apoquel. The allergies came first. He has had 2 titer tests and his count has not gone down (1:128). We are waiting results from the third test. Can Apoquel interfere with Fluconazole and keep the titer high? If this test is still high we may switch to Cytopoint for allergies. Wondering why the other vets in the office never mentioned this.

    • Cytopoint just came out and I do think it is a better choice for a dog with Valley Fever. I dont think that the apoquel is keeping the titer high however.

  39. My 12.8 lbs, 14 year, old Jack Russell “Buster” was prescribed medication for pain. He has a long history of pain problems due to his bad warped spine, luxating patella “his knees are at the highest level”, he also has a problem lifting his head up and his shoulder blades appear higher now that he has aged & it hurts sometimes when I pick him up around his rib front leg area. The vet prescribed “Rimadyl” 25 mg 1/2 tab 2/day. On 5/4/2017 I gave it to him right then, before I looked the drug up. After reading all the crazy side effects I freaked and called the vet immediately same day to change the medication. He told me not to give him another dose and bring buster in tomorrow. We got to his appointment 5/5/2017 and had his Rabies vaccination, pre anesthetic profile, fecal exam. The vet said everything was good the BUN was high 33.9 he said probably just dehydrated. On the other small print out vetscan hm5 v2.1 it has the lym circled at .89-10deg./1 & the MPV is 11.6 +fl. (I am not sure what all the things mean he didn’t really go over it) anyways, he changed his medication from to Galliprant 20mg 1/2 tab every 24 hrs. & added Tramadol 50mg 1/2 tab every 8 hrs. To start them immediately. That the Galliprant would be much safer.

    I had buster taking these medications on Friday afternoon 5/5/2017. He started moving around a little more. He wasn’t feeling well for 2 days slept a lot. Then 4 days later 5/9/2017 buster all of a sudden started making sounds like a cat with a hairball. So I took him outside and he made it to the grass and started vomiting and pooping simultaneously. He had his ears down and he just didn’t look good. He walked out further into the yard away to a corner and started diarrhea and stood like so out of it, he didn’t know what was going on his eyes were squinted and closing and then he tried walking a bit further away from me and was almost limp basically collapsed… I thought he was about to pass honestly. He closed his eyes and was just laying not responding at all. So I looked at his gums, they were WHITE. At this point I knew it was an emergency & called the vet to let him know I was on my way in. Then busters legs started to tremble like he was cold so I felt his nose and it was cold his paws cold. I live in Texas it was 88 and sunny. So I swaddles him up in a towel took him in. The vet said he had gastritis without doing any additional blood work. He said the the Galliprant has a side effect of that. Not to give it to him anymore until he speaks with the manufacturer. He gave him a shot of anti nausea medication. Sent me home with Sucralfate 1 go tab give one by mouth 30 minutes prior to feeding, Metronidazole 250 mg 1/2 tab ever 12 hrs, Cerenia 16 mg tabs 1 every 24hrs (4). He said to continue the Tramadol because buster was in a lot of pain. So directions for the night 5/9/2017 were to give sucralfate then 30 mins later give metronidazole, Tramadol-Then feed him & Start cerenia on 5/10/2017.

    I did this then the next day 5/10/2017 after eating he had another episode but only intense diarrhea. Again buster collapsed and was kinda worse. Almost a comatose state, it lasted for 30 minutes. I groomed him told him how much I love him. This time I was just going to love on him and try to get him through it. He is old and I know his days are numbered like our own. I am unsure of what his future is at this point health wise.

    My question is that I wanted to give buster his heart guard, but am unsure if it’s safe to at this point? What is your opinion on this whole ordeal? Do any of these medications interact with each other? When he lays in the grass I noticed worms, fire ants, flies, etc. trying to get on him. Even the birds were flying overhead. Of coarse I was right there for his safety. I just don’t want him getting parasites or something now because of this. Then again I didn’t want to disturb him either. He is indoors mainly. He also needs his flea treatment nexgard. Also another question is what other options do I have for pain management? I am not even sure that it’s really helping that well.

    Can you please give me some advice?

    I appreciate your assistance in this so greatly!


    One loyal loving mother to her puppy son.

    • Unfortunately, I had to put Buster down this morning. He had a ruptured disk that was causing SEVERE PAIN and some paralysis in the back legs. We also found out that buster had a tumor the size of a tennis ball growing on his Liver. It’s been a tough day. Please don’t feel the need to reply to my prior comment.

      • Hi Susan. I am indeed so sorry for your loss. I just wanted to give you some closure on this from my end. While it is truly tragic that Buster had so many severe pathologies present, and you and your vet did everything possible for him within your means and understanding, I just wanted to add that the rabies vaccination given at the time of such severe symptoms and pathologies already present also may have played a significant role in his sudden decline and demise. I have seen rabies vaccination trigger or worsen disc and spinal issues in dogs as well as other neuropathies. You can read more about this research and clinical observations on the education article section at http://www.rabieschallengefund.org Hopefully one day in near future, Texas will consider medical exemptions for rabies vaccinations of elder or sicker animals, since the immunity to rabies vaccinations lasts for years to life of pet. Currently, I dont believe they allow medical exemptions in your state. Likely the combination of all of the drugs AND the rabies vaccination triggered the upset stomach and sudden worsening of the pathologies.

  40. Can u give aspirin to a dog who is taking Apoquel for slight pain? If not can u suggest something I can give him OTC? Or do I have to ask my vet for a prescription?

    • I would check with your vet if ok to give the aspirin to your dog as I dont know the rest of his medical history. I have no problem with giving aspirin for a day or two with food with a “healthy” allergy dog on Apoquel who has no other history of digestive upset or sensitivity and is not on other nonsteroidal anti inflammatory drugs or cortisone

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