Which Pet Medications Fail in a Hot Car: What the Labels Say, What the Studies Measured, and What Nobody Publishes

Heat can degrade some medications, but no one can tell from a temperature alone whether your pet’s medicine survived a hot car. The 59 to 86°F range printed on many labels is a supply-chain storage allowance, not a tested ceiling, and for most of the pet drugs in the table below no heat-stability study of the marketed product is cited. After an exposure, take the specifics (product, lot number, hours, highest temperature) to the pharmacy that dispensed it, the veterinarian who prescribed it, or the manufacturer. They decide whether to keep using it, replace it or substitute.

This page does not tell you to throw anything away, and it does not tell you to keep using anything. FDA’s page on drug safety after a disaster comes closest to a general instruction, and it is about fire: it says high temperatures from a fire can reduce or destroy the effectiveness of medicines, and “Consider replacing medicines that may have been exposed to excessive heat.” That names no product, temperature or duration. What follows separates three things that get collapsed into one sentence online: what your product’s label says, what anyone has measured about that product under heat, and who is entitled to decide. For most pet medications the middle one is mostly empty.

Two topics belong to other pages. Insulin has its own labels and rules: see pet insulin outside the fridge and our pet medication and refrigeration in a power outage guide. Compounded preparations are also outside this page: ask the pharmacy that made the preparation. Neither appears below.

The 59 to 86 Degree Range Is a Shipping Rule

A pet’s prescription bottle often says something like excursions permitted between 15° and 30°C (59° and 86°F). It reads like a tolerance, as if the drug had been tested at 86 degrees. It is a definition borrowed from a pharmacy and supply-chain standard.

USP’s authorized reprint of General Chapter 1079.2, dated October 28, 2024, gives the controlled room temperature framework in four numbers: a storage range of 20° to 25°C, an acceptable excursion range of 15° to 30°C, a maximum temperature of 40°C, and a maximum excursion time of not more than 24 hours, with mean kinetic temperature not more than 25°C over 30 days. The chapter’s scope statement is the sentence that matters most. It applies to “every link in the supply chain from the manufacturer through any entity that transports or stores a finished drug product, with the sole exception of the patient”. The framework is written for manufacturers, warehouses, pharmacies and clinics. It stops at the person holding the bottle, which for this page means your car.

Three more points from the same chapter:

• An excursion is a nonconforming event by default, except where the manufacturer provides otherwise.
• Its Table 1 footnote says exposure beyond the chapter’s ranges “should be evaluated using monographs, product labels, or stability data provided by the manufacturer”. A label’s number is therefore the supply chain’s default, and the manufacturer’s labeling governs a specific product.
• Some products labeled for controlled room temperature may have stability issues at the excursion limits, and they must be evaluated within the stability limits the manufacturer provides. The range does not certify any individual product.

The chapter also rejects the idea that an excursion can be “fixed” by lowering the storage temperature afterward: it says any degradation due to the higher temperature “is not reversible”.

The definitions of controlled room temperature and excessive heat sit in USP General Chapter 659, whose full text is subscriber-only. The warm and excessive-heat figures come from Ondrak, Jones and Fajt (BMC Veterinary Research, 2015), who describe the U.S. Pharmacopeia as defining controlled room temperature as 20 to 25°C, temperatures between 30 and 40°C as warm, and temperatures above 40°C as excessive heat.

What Has Been Measured Inside a Vehicle

Four studies measured different things. Keep them separate, because blending them into one number and attaching it to a drug is the usual mistake.

A passenger cabin, in California, over one hour. McLaren, Null and Quinn (Pediatrics, 2005) parked a dark-blue 2000 Honda Accord with a medium-gray interior in full sun in Fremont, California on 16 cloud-free days between May 16 and August 8, 2002, at ambient temperatures from 72 to 96°F, and logged the interior every five minutes for an hour. The average mean increase was 3.2°F per five-minute interval, with 80% of the rise in the first 30 minutes. Even at the coolest ambient temperature the interior reached 117°F, and the average rise was 41°F (range 28 to 49°F). Cracking the windows did not decrease the rate of rise or the maximum. The sensors sat in the rear passenger section 15 inches above the seat, in the shade. That is cabin air in one car over one hour, measured for risk to children. It is not a trunk, a cargo area or the inside of a closed bag, and it says nothing about a tablet’s potency.

Veterinary drug storage compartments, in Texas and Nebraska, over a summer. Ondrak, Jones and Fajt (BMC Veterinary Research, 2015) put temperature loggers in the drug storage units of 24 large-animal practice vehicles in central Texas and south central Nebraska from May 15 to September 16, 2013. This is the study closest to a go-bag.

• The highest temperatures recorded were 54.4°C (about 130°F) in Texas and 47.7°C in Nebraska.
• The mean across all 24 units was 29.1°C: 31.4°C in Texas and 26.9°C in Nebraska.
• In Texas, at least one reading over 25°C occurred on a mean of 123 of 124 days, and 95% of readings were over 25°C. In Nebraska it was 111 of 124 days and 63% of readings.

The authors noted that storage-unit temperatures consistently exceeded environment temperatures, suggesting a greenhouse effect that a lack of shade may have worsened. Comparing their logs with USP’s allowances, they wrote: “Temperatures in study vehicles exceed these allowances both in magnitude and duration.”

Four cars, in the UK, over 7 to 18 months each. Carter, Hall, Connolly, Russell and Mitchell (Open Veterinary Journal, 2020) logged four vehicles at 15-minute intervals, each for between 7 and 18 months. Loggers sat in the boot compartment, shielded from direct sunlight. Internal temperature ranged from -7.4°C to 54.5°C. It exceeded typical drug storage recommendations (above 25°C) in every month, and exceeded the canine thermoneutral zone (above 35°C) from April to September. Peaks came between 14:00 and 17:00. They recommended keeping drugs within the manufacturer’s temperature range year-round, and recorded temperatures below 8°C in every month except June and July, so a vehicle is a cold problem too.

A bag, in different places in a car, in an English spring. Rudland and Jacobs (BMJ, 1994) measured doctors’ visiting bags at different storage sites in a South Devon coastal town in May and June. The bag was coolest in the car boot, but “irrespective of storage site, maximum internal temperature of the bag was always over 25 degrees C and reached up to 80 degrees C”. Coolest is not cool enough. The authors advised storing the bag in the boot while visiting and moving it to a cooler site at other times.

None of these studies logged the inside of a pet owner’s medication pouch in a US passenger-vehicle trunk across a summer. Ondrak’s veterinary storage units are the closest measured compartment.

Labeled Storage Versus Published Stability

The table shows what each product’s own DailyMed label said about storage as of August 2026. DailyMed is the National Library of Medicine’s repository of labeling submitted to FDA, including animal drug labels. The right-hand column is mostly empty. A labeled storage statement is not a failure threshold. A label that says store at 20° to 25°C does not mean the product fails at 26°C. The columns answer two different questions: what the manufacturer instructed, and what anyone has published about measuring it.

Product, manufacturer, label revision	Labeled storage	Label statement on excursions	Published heat-stability data for this product
APOQUEL (oclacitinib maleate) tablets, Zoetis, revised December 2020	Controlled room temperature, 20° to 25°C (68° to 77°F)	Excursions between 15° and 40°C (59° and 104°F)	None cited.
APOQUEL CHEWABLE (oclacitinib), Zoetis, revised July 2025	Controlled room temperature, 20° to 25°C (68° to 77°F); keep remaining half tablets in the original package for the next dose	Excursions between 15° and 40°C (59° and 104°F)	None cited.
CERENIA (maropitant citrate) Tablets, Zoetis, revised January 2020	Controlled room temperature, 20° to 25°C (68° to 77°F)	Excursions between 15° and 30°C (59° and 86°F)	None cited.
CERENIA Injectable Solution, Zoetis, revised April 2020	At or below 30°C (86°F); after first vial puncture, refrigerate at 2 to 8°C (36 to 46°F) and use within 90 days	Excursions permitted up to 40°C (104°F)	None cited.
VETMEDIN (pimobendan) chewable tablets, Boehringer Ingelheim, revised 11/2025	20° to 25°C (68° to 77°F)	Excursions permitted between 15° and 30°C (59° and 86°F)	None cited.
VETMEDIN Solution, Boehringer Ingelheim, revised 12/2025	At or below 77°F (25°C); use within 8 weeks once the bottle is opened	Excursions permitted up to 86°F (30°C)	None cited.
RIMADYL Caplets (carprofen), Zoetis, revised May 2019	Controlled room temperature, 15° to 30°C (59° to 86°F)	No separate excursion statement	None cited for the marketed caplet under vehicle heat.
GALLIPRANT (grapiprant) tablets, Elanco	At or below 86°F (30°C)	No excursion statement	A laboratory study exists; it is not about tablets in a car (see below).
NEXGARD (afoxolaner) chewables, Boehringer Ingelheim	At or below 30°C (86°F)	Excursions permitted up to 40°C (104°F)	None cited.
HEARTGARD Plus (ivermectin and pyrantel pamoate) chewables, Boehringer Ingelheim	68° to 77°F (20° to 25°C); protect from light	Excursions between 59° and 86°F (15° and 30°C) permitted	None cited.
THYRO-TABS CANINE (levothyroxine sodium) tablets, Lloyd, Inc. of Iowa	Controlled room temperature, 20° to 25°C (68° to 77°F); protect from light and moisture	Excursions allowed between 15° and 30°C (59° and 86°F)	None cited.
CLAVAMOX (amoxicillin and clavulanate potassium) chewable tablets, Zoetis, revised September 2020	Dry, cool place at temperatures not above 25°C (77°F); leave in the foil strip until ready to use	No excursion statement	Classed as equivocal in a published review (see below).
CLAVAMOX DROPS (oral suspension), Zoetis, revised February 2019	The label has no storage-temperature statement for the unreconstituted powder; the mixed suspension must be refrigerated and any unused portion discarded after 10 days; carton says not to use if discolored	None stated	Classed as equivocal in a published review (see below).
Furosemide Tablets, Covetrus North America, ANADA 200-759	Controlled room temperature, 20° to 25°C (68° to 77°F); use half-tablet within 90 days	Excursions permitted to 40°C (104°F)	Classed as equivocal in a published review (see below).
NEURONTIN (gabapentin) tablets and capsules, Viatris, revised 4/2025	25°C (77°F); the oral solution is separate and is stored refrigerated at 2° to 8°C (36° to 46°F)	Excursions permitted between 15° and 30°C (59° and 86°F)	None cited.
Phenobarbital Tablets USP, Sun Pharmaceutical Industries, revised May 2024	The label has no storage-temperature statement	None stated	Listed as stable in a published review (see below).
Phenobarbital tablet, Coupler LLC	20° to 25°C (68° to 77°F), per USP Controlled Room Temperature; protect from light and moisture	Refers to USP Controlled Room Temperature	Listed as stable in a published review (see below).
EpiPen and EpiPen Jr (epinephrine auto-injector), Viatris Specialty, revised 2/2023	20° to 25°C (68° to 77°F); protect from light; patient labeling says not to store in a vehicle’s glove box or trunk	Excursions permitted to 15° to 30°C (59° to 86°F)	Epinephrine is listed as unstable in a published review (see below).

The Same Brand Can Give You Two Different Answers

Read the product, not the drug name.

• Cerenia. The tablet label allows excursions between 15° and 30°C (59° and 86°F). The injectable label allows excursions up to 40°C (104°F), 18 Fahrenheit degrees higher. Applying one number to the other product is a mistake the labels rule out.
• Vetmedin. The chewable tablets are stored at 20° to 25°C with excursions between 15° and 30°C. The solution is stored at or below 77°F (25°C) with excursions up to 86°F (30°C), and it adds an in-use clock: use the contents within 8 weeks of opening.
• Apoquel. The coated tablet and the chewable share the same storage sentence, including excursions up to 40°C. The chewable label adds an instruction to keep remaining half tablets in the original package for the next dose.
• Phenobarbital is not one product. The Sun Pharmaceutical Industries label (revised May 2024) has no storage-temperature statement on DailyMed. Another phenobarbital tablet label, from Coupler LLC, says to store at 20° to 25°C (68° to 77°F), protect from light and moisture.

If your pharmacy hands you a bottle whose label is silent on temperature, the silence is not permission. Ask the pharmacy which manufacturer’s product it dispensed. It can reach that manufacturer’s medical information line.

What the Stability Studies Found

A labeled range says what the manufacturer instructed. It does not say what happens when the instruction is broken. The studies below come mostly from emergency medical services, and the results are neither reassuring nor uniformly alarming.

A veterinary review classified the drugs. Ondrak and colleagues also reviewed published stability data for drugs common on large-animal practice vehicles and sorted them into three groups (their Table 3):

• Demonstrated to be stable outside manufacturers’ storage recommendations included atropine, diazepam, midazolam, morphine sulfate and phenobarbital; amikacin, gentamicin and neomycin; ciprofloxacin, enrofloxacin and marbofloxacin; clindamycin and tylosin; and dexamethasone, diphenhydramine and thiamine.
• Equivocal data included lidocaine and naloxone; erythromycin; amoxicillin with or without clavulanate, ampicillin and penicillin G; doxycycline and tetracycline; and dopamine and furosemide.
• Demonstrated to be unstable included cefazolin and cephalothin, and epinephrine, heparin and oxytocin.

Four cautions travel with that list. The paper excludes extemporaneous solutions, temperature ranges significantly different from those in veterinary practice, and drugs in tissues such as urine or meat. It classifies whether published data exist and what they showed, and attaches no temperature or time to any name. The studies behind the table come from settings such as emergency medical services, hospital pharmacy and the laboratory, so applying a row to a specific dog’s prescription is an extension, not a finding. And “stable” refers to particular tested conditions, not to the drug in your bag. The authors add that more research is needed to determine whether these excursions alter efficacy or produce degradation products that may pose a health risk.

A year in an emergency response vehicle. De Winter and colleagues (Annals of Emergency Medicine, 2013) stored five emergency drugs for one year refrigerated, at room temperature and in an emergency physician transport vehicle, treating a drug as stable if its content stayed above 90%. Adrenaline hydrochloride and methylergonovine maleate stayed stable for a year in the vehicle. Lorazepam became unstable within 4 weeks at room temperature and in the vehicle. Succinylcholine was stable for 1 month in the vehicle, and cisatracurium for 4 months in the vehicle but not at room temperature. A real vehicle did not destroy everything. The shortest sampling interval was one week, so the study says nothing about a single afternoon.

Sixty days of American EMS summer. McMullan and colleagues (Prehospital Emergency Care, 2013) collected benzodiazepine samples before and after 60 days of EMS deployment in spring and summer in 14 metropolitan areas. Midazolam showed no degradation. Lorazepam showed small but statistically significant temperature-dependent degradation. The authors said more study was needed to learn whether clinically significant deterioration occurs after 60 days.

Thermal cycling to vehicle temperatures. Gammon and colleagues (American Journal of Emergency Medicine, 2008) cycled 23 commonly carried EMS medications between -6°C and 54°C every 12 hours for a month. That upper bound is close to the 54.4°C Ondrak logged in Texas and the 54.5°C Carter logged in the UK. Eight of the 23 (35%) ended below 90% of labeled concentration, with a strong correlation to exposure time: lidocaine, diltiazem, dopamine, nitroglycerin, ipratropium, succinylcholine, haloperidol and naloxone. Heat is not harmless to medication, and it does not degrade everything either. Which side a product lands on is a product-specific question you cannot reason out from the drug’s name.

Why 90%. It is the potency floor De Winter and Gammon used. FDA’s Center for Veterinary Medicine, in Guidance for Industry #5 (December 9, 2008), quotes Remington’s Pharmaceutical Sciences (16th edition, page 284, 1985): “Although there are exceptions, 90% of the labeled potency is generally recognized as the minimum acceptable potency level.” The same guidance calls a drug product unstable when the active ingredient loses enough potency to adversely affect safety or efficacy, or falls outside labeled specifications.

Where the Table Is Empty

For oclacitinib, maropitant, pimobendan, afoxolaner, carprofen and ivermectin, no study of the marketed veterinary product held at vehicle temperatures is cited on this page. Levothyroxine and grapiprant each have a nearby study, described next; neither is a hot-car finding.

Okezue and colleagues (Pharmaceuticals, 2023) held three levothyroxine tablet brands at about 23°C, 40°C and 50°C (the last two at 75% relative humidity) for up to 6 months. All three brands met the USP 95.0–105.0% assay requirement at 1.5 months under the 40°C condition, and only one still did at 3 months. The abstract does not name Thyro-Tabs Canine or a vehicle, so it is not a hot-car finding for that product.

Grapiprant has the other nearby study, and it is a narrow one. Gumulka, Tarsa, Dabrowska and Starek (Biomedicines, 2022) tested a Galliprant tablet and found 20.29 mg of active substance against the 20 mg declared. But the stability work was on grapiprant solutions at varying pH, held at room temperature and at 70°C. Degradation was much faster at 70°C and in acidic media. That is a laboratory forced-degradation study of the substance in solution. It is not a measurement of a tablet in a glove box and supplies no threshold for one.

USP’s own framework points to “stability data provided by the manufacturer” for exposure beyond its ranges, which is why the answer below is a phone call rather than a number.

The Go-Bag Problem Differs From the Errand Problem

An hour of errands and a summer in a trunk are two different exposures, and only one has been measured well.

The errand case is what the Pediatrics study describes: a fast rise, 80% of it in the first 30 minutes, to a cabin temperature of 117°F on the coolest day. USP’s framework caps a permitted excursion at not more than 24 hours.

A kit packed in April and left in a vehicle through hurricane season is not having an excursion. It is being stored. In Ondrak’s data, Texas storage units averaged 31.4°C and Nebraska units 26.9°C, and Carter’s UK cars exceeded 25°C in every month. Rudland and Jacobs found the boot coolest of the sites tested, and the bag still went over 25°C. If the medication compartment lives in a vehicle year-round, these studies suggest it will spend a great deal of time above the 25°C storage figure that many labels print. That is our reading of the studies, not a measurement of your kit, and you can plan for it in advance. FDA’s pet-disaster page lists medications among the items to take when you evacuate, so the pouch has to go with you either way.

That makes this a placement decision rather than a discard decision. Our rotation checklist handles the calendar half of kit maintenance. The temperature half is deciding which parts of the kit ride in the car and which stay indoors. One option, which is our suggestion and not a sourced rule: the bag lives in the car, the medication pouch lives inside the house by the door, and a note in the bag says what is missing and where it is. Our go-bag checklist covers the rest of the packing decision, and the pet emergency binder is where the note belongs.

Can You See Heat Damage?

Only where the label says so, and only for that product.

The EpiPen and EpiPen Jr patient labeling says epinephrine exposed to air or light changes quickly to a pinkish or brown color and should not be used. It tells patients to replace the device if the solution appears discolored, cloudy or contains particles. The CLAVAMOX Drops carton says “Do Not Use if Product is Discolored.” Heartgard Plus and Thyro-Tabs Canine carry protect-from-light instructions, and Thyro-Tabs adds moisture.

No source on this page supports the idea that a normal-looking tablet is undamaged. Labels that say nothing about appearance say nothing in either direction. FDA’s disaster guidance says to check all medicines for possible damage or improper storage. For a medicine needed to treat a life-threatening condition after fire or unsafe water, when no replacement is readily available, it says the medicine may be used if it appears unchanged and should be replaced as soon as possible. It adds that a medicine that is wet or otherwise altered should not be used and should be discarded. That guidance is about people’s own medicines after fire and flood, for the case where the alternative is going without a lifesaving drug. No stability finding in it transfers to a veterinary product.

Who to Call, and What to Have Ready

Most of the veterinary labels above print a manufacturer contact line under a contact heading, and several offer technical assistance. The APOQUEL label lists Zoetis Inc. at 1-888-963-8471 or www.zoetis.com for adverse events, technical assistance or a Safety Data Sheet. The VETMEDIN label lists Boehringer Ingelheim Animal Health USA Inc. at 1-888-637-4251 for the same purposes. Both also point to FDA at 1-888-FDA-VETS for adverse event reporting. Use the number on your own label, since contact lines change.

For a human-labeled generic dispensed for your pet, call the pharmacy first. It knows which manufacturer’s product it handed you. FDA’s disaster page tells people whose refrigerated medicine was not kept at the recommended temperature during a power outage to check the storage instructions or contact a pharmacist, health care provider or the manufacturer to find out if it can still be used. No FDA page we found gives that instruction for a hot car, so applying it here is our recommendation.

Have this ready before you call (the list is our suggestion, not a sourced rule):

• The product name, strength and dosage form exactly as printed (tablet, chewable, solution or injectable).
• The manufacturer’s name, lot number and expiry date from the label.
• Roughly how long the product was in the vehicle: one afternoon or a season.
• The highest temperature you can document, and how you know it. A minimum and maximum recording thermometer left in the compartment turns a guess into a number.
• Where in the vehicle it sat, and whether the vehicle was shaded.
• Whether the product changed visibly, and whether its label says anything about appearance.

Then let them decide. Keeping a product, replacing it or substituting it is up to the veterinarian who prescribed it, the pharmacist who dispensed it, or the manufacturer who set the label. If the answer is replace and your animal cannot go without the drug, refill timing becomes its own problem. Our medication refill calculator works the dates, and the hurricane season prep calendar is where a pre-season refill belongs.

Coolers and Insulated Cases

We do not claim that any cooler, insulated case or phase-change product holds a temperature. Manufacturers publish performance claims for their own products, and restating one as fact turns a marketing number into a safety statement. If you shop, read the claim on the manufacturer’s page, note the conditions it was measured under, and treat it as a claim.

Two low-cost items change what you know rather than what you assume:

• A minimum and maximum recording thermometer. It converts the most important input to the phone call, the highest temperature reached, from a guess into a reading. Put it in the compartment with the medication, not in the cabin.
• An opaque, closed container inside the bag. Several labels above carry protect-from-light instructions, including Heartgard Plus and Thyro-Tabs Canine, and Clavamox Chewable says to keep it in a dry, cool place and in its foil strip until use. Following those label instructions is free. It is not the same as claiming a container fixes a temperature problem.

For medication that must be refrigerated, see our insulin cooler travel case guide and the medication refrigeration in an outage guide, which report what manufacturers say and separate a cooling wallet from a refrigerator.

Your Hot-Car Medication Checklist

• Read the storage sentence on every medication in your pet’s kit, one product at a time, and write it on the outside of the pouch. Two products from the same brand can carry different numbers.
• If a label has no storage-temperature statement, note that too. Silence is a reason to ask the pharmacy which manufacturer’s product you were dispensed, not a reason to assume the product is unbothered.
• Stop reading the excursion range as a tolerance. USP treats an excursion as a nonconforming event by default, caps a default excursion at not more than 24 hours, and excludes the patient from its framework.
• Decide which parts of the kit live in the vehicle and which live indoors. A season in a car is a storage condition, not an excursion.
• Put a minimum and maximum recording thermometer in the medication compartment now, so a future phone call has a number in it.
• Follow the label’s other instructions: protect from light, protect from moisture, keep it in the original foil. FDA’s pet medication storage page asks you to “Keep pet medications in their original containers with intact labels.”
• If an exposure has already happened, gather the six items above and call the prescriber, the pharmacy or the manufacturer.
• Do not apply this page to insulin or to a compounded preparation. Pet insulin outside the fridge covers insulin labels product by product. Ask the compounding pharmacy about a compounded preparation.
• Remember the cold half. The UK vehicle study recorded internal temperatures below 8°C in every month except June and July, and at least one label above rules out extreme cold by name alongside extreme heat.
• Keep the medication list somewhere the heat cannot reach and where you can produce it if the bottles are gone: see paper versus digital pet medical records and reconstructing pet records when the clinic is gone.

Where to Go Next

This page is the temperature spoke of our pet evacuation kits hub.

• If the medication needs a refrigerator: pet insulin outside the fridge, the medication refrigeration in a power outage guide and the insulin cooler travel case guide.
• If the problem is the calendar: the pet emergency kit rotation checklist and the medication refill calculator.
• If the animal is the one in the hot car: that is a different emergency with a different clock. See our heat and hot cars page for pets and leaving a pet in the car at an evacuation stop.
• If a missed dose actually threatens your animal: the seizure dog emergency kit and the senior dog emergency kit.

Then do the one thing this page asks, on a quiet afternoon rather than in an evacuation. Take every medication out of the bag, read its storage sentence off the label, and write those sentences down in one place. That list, in your handwriting, turns a panicked search for a number into a two-minute phone call with the people who can answer.