Insulin and GLP-1 cold chain in Belize's heat: what the evidence says

Peptide drugs are fragile molecules sold into a hot country. Belize's National Meteorological Service describes a heat season that runs roughly from April to October¹. In May 2023 the station at Libertad, in the Corozal District, set new daily highs on five days, reaching 38.7 °C on 24 May, and Central Farm near Belmopan reached 38.5 °C on 30 May¹. In April 2024 the service issued a heat alert for inland areas with temperatures "projected to reach and possibly exceed 97 degrees Fahrenheit (37 degrees Celsius)"², and Chief Meteorologist Ronald Gordon later recalled of 2024: "We had temperatures exceeding 100°F for several days"³. With one in six Belizeans living with diabetes¹⁴, how insulin and GLP-1 drugs such as semaglutide and tirzepatide are stored is a clinical question, not a logistics footnote.

What the labels say: semaglutide and tirzepatide storage

The manufacturer's guidance for the Ozempic pen (semaglutide) is that it "should be refrigerated at 36 °F to 46 °F (2 °C to 8 °C)" until first use; after first use it may be kept for up to 56 days at 15–30 °C or in a refrigerator, should be "protected from excessive heat and sunlight" and must not be used if frozen⁴. For the Mounjaro pen (tirzepatide), the guidance is refrigeration at 2–8 °C, and "If needed, each single-dose pen can be stored unrefrigerated at temperatures not to exceed 30°C (86°F) for up to 21 days"; the pen should be protected from heat and light and not used if frozen⁵. Both limits sit well below the outdoor maxima Belize records in its heat season¹³. A car, a mailbox or a market stall can exceed them.

Insulin: more heat-tolerant than its label suggests

Insulin is the best-studied peptide in tropical conditions. Researchers from the University of Geneva and Médecins Sans Frontières logged temperatures in a refugee camp in northern Kenya, found daily swings between 25 and 37 °C, and reproduced them in the laboratory⁶. Several commercial insulin formulations stored under those swings for four weeks showed "perfect conformity to pharmacopeia guidelines" by high-performance liquid chromatography, unchanged structure by circular dichroism, and the same activity on the insulin receptor as refrigerated samples⁶. The authors concluded that insulin can be kept at such oscillating ambient temperatures for the usual four-week period of use⁶. A 2002 report from the Liverpool School of Tropical Medicine looked at traditional clay pots as storage containers for insulin in hot climates¹⁰. Others have argued for thermochromic heat indicators, like the vial monitors used on vaccines, on insulin and other biologics, because heat exposure anywhere in the chain can reduce potency invisibly⁹.

Semaglutide: temperature, pH and degradation

The data for semaglutide are laboratory data, not field data. In a preformulation study, semaglutide remained stable for three hours at 80 °C, but degradation was greatest between pH 4.5 and 5.5, near its isoelectric point of 5.4⁷. In solid state, the molecule kept its native α-helical conformation up to 60 °C, but α-helical content fell from 49.07 % to 43.75 % at 60 °C and to 0.2 % at 80 °C, with temperature-dependent degradation and impurity formation; the authors call temperature "a critical factor" for semaglutide stability⁸. Neither study tested a commercial pen left in a hot car, and neither supports storing products outside their labelled conditions. They show why the labelled limits exist⁴⁵⁷⁸.

Belize's cold chain and the law

WHO's model guidance on time- and temperature-sensitive pharmaceutical products sets out the "principal requirements for the safe storage and distribution" of such products for regulators and supply-chain and pharmaceutical professionals¹¹. Belize's Food and Drugs (Registration, Licensing and Inspection) Regulations, 2017 give inspectors power to "monitor the sale of drugs, and oversee the management, storage, distribution, disposal and record keeping" wherever drugs are made, stored or distributed, and to seize drugs that contravene the Act¹². Public cold-chain capacity has grown: in 2023 US funding implemented by PAHO/WHO bought Belize 20 refrigerators with ice liners, four refrigerated trucks, 200 cooler boxes, 500 temperature-tracking devices and 35 remote temperature monitors, mainly for vaccines¹³. Products bought outside licensed channels have no such chain. In one study, semaglutide sold online without a prescription arrived as lyophilized powder with purity of 7.7 % to 14.37 % and endotoxin in every sample¹⁵.

What it means for Belizean physicians

When a patient's glucose control or weight response changes without explanation, storage history is part of the differential. The relevant facts are on the label: refrigeration before first use, a 30 °C ceiling and a limited number of days at room temperature⁴⁵. For insulin, field-condition evidence is reassuring within the four-week use period⁶; for semaglutide and tirzepatide, only the labelled conditions are backed by the manufacturer⁴⁵. Suspected loss of effect is a reportable event: Belize's adverse-event reports now reach the WHO global database¹⁶.