Storing Veterinary Medicines When the Yard Hits 45 °C

"Store below 25 °C" appears on almost every veterinary product sold. In a yard where the shaded ambient temperature sits above 40 °C for four months of the year, that instruction requires actual engineering rather than good intentions.

What heat does

Degradation follows chemistry, not opinion. As a working rule, reaction rates roughly double for every 10 °C rise. A product stored at 45 °C is degrading at roughly four times the rate it would at 25 °C.

The failure modes differ by product type:

Suspensions — such as procaine penicillin — can cake irreversibly. Once it will not resuspend evenly, the dose in each millilitre is unknown.

Emulsions — oily vitamin preparations, astaxanthin — separate, and separation is not always reversible by shaking.

Biologicals — vaccines, hormones, hyaluronic acid — lose potency without any visible change at all. This is the dangerous category, because nothing looks wrong.

Oral pastes — become runny and separate in the syringe, so the dose delivered is not the dose intended.

Tablets — take up moisture, soften and crumble.

Heat and light together are worse than either alone. Products labelled "protect from light" are usually the ones where photodegradation compounds the thermal problem — B12 is the obvious example.

The tack room is not storage

A metal-roofed tack room in the Gulf routinely exceeds 55 °C in the afternoon. A truck cab parked in the sun exceeds 70 °C. The vet box in the back of a pickup is the worst storage location on most yards, and it is where most yards keep their medicines.

What actually works

A dedicated pharmacy fridge for anything requiring 2–8 °C. Not the staff fridge — a lockable unit with a thermometer, in a room that is itself air-conditioned so the compressor is not fighting ambient heat.

A min/max thermometer in the fridge and another in the medicine cupboard, read and logged daily. The log matters: it turns "I think it has been fine" into evidence.

An air-conditioned medicine room, or, failing that, an insulated cabinet in the coolest interior room. Not against an external wall.

A cool box with gel packs for anything that leaves the building, including the trip from the delivery vehicle to the fridge. Products get cooked in the twenty minutes they sit on the yard waiting for someone to put them away.

A first-in-first-out system. Date everything as it arrives and use the oldest stock first. Write the broaching date on multi-dose vials — most are discarded 28 days after first entry regardless of the printed expiry.

Judging a product that has been too hot

There is no reliable field test, which is the honest answer.

Discard without hesitation if you see:

• Precipitate, crystals or particulate matter in a solution that should be clear
• A suspension that will not resuspend evenly after thirty seconds of shaking
• A colour change beyond what the label describes as normal
• A separated emulsion that does not recombine
• Any bulging, leaking or compromised container

Assume loss of potency, even with no visible change, for any biological product that has been outside its temperature range for more than a few hours. Potency loss in a vaccine or a hormone is invisible and total.

The cost of discarding a suspect vial is one vial. The cost of administering a degraded antibiotic is a treatment failure you will not recognise until the infection has advanced.

Receiving deliveries

Have someone available to receive shipments. Check the cold chain products first, get them into the fridge before anything else is unpacked, and record the arrival temperature if the shipment includes an indicator.

If a temperature-controlled shipment arrives warm, photograph the packaging and the indicator and contact the supplier before you put it away. That conversation is much easier on the day than three weeks later.