ICH Climatic Zones IVa and IVb: What "Store at Room Temperature" Actually Means in Africa

"Store at room temperature" is a specification, not a description. In the pharmacopoeias it points at a defined condition: USP General Chapter <659> sets controlled room temperature as a mean kinetic temperature not exceeding 25 °C, with excursions permitted between 15 °C and 30 °C, and transient spikes to 40 °C tolerated only briefly ^[8]. The stability data behind most such statements were generated under harmonised long-term conditions of 25 °C/60% RH or 30 °C/65% RH ^[3]. Neither is a description of an unconditioned storeroom on the Gulf of Guinea in April. If you handle laboratory material anywhere in the hot band of the continent, that label is a target your storage has to be shown to hit — and the only thing that shows it is a temperature record.

The framework that decides which target applies to you is the climatic-zone system. Two of its five bands cover most of tropical Africa: Zone IVa, hot and humid, tested long-term at 30 °C/65% RH; and Zone IVb, hot and very humid, tested at 30 °C/75% RH ^[1]. The difference between them is ten percentage points of relative humidity, and it is the single most consequential number on the page for anyone storing hygroscopic material near a coast, because water taken up by a solid is what feeds the hydrolytic deamidation of asparagine and glutamine residues.

What "room temperature" means as a pharmacopoeial term

The phrase does not mean "whatever the room happens to be". USP <659> defines controlled room temperature as a thermostatically controlled environment whose mean kinetic temperature does not exceed 25 °C; the working band is 20–25 °C, excursions between 15 °C and 30 °C are accepted as the reality of pharmacies, hospitals and warehouses, and short transient spikes to 40 °C are tolerated only where they do not exceed 24 hours ^[8]. USP has a proposal out for comment in Pharmacopeial Forum to lower the band to 15–25 °C, aligning it with the room-temperature definitions used elsewhere; the mean kinetic temperature anchor is unchanged by that proposal. WHO's stability guidance works the other way round, deriving the wording on the label from the data actually generated — statements such as "do not store above 30 °C" or "store below 25 °C" are conclusions from a study, not slogans ^[1].

Two practical consequences follow. First, a storage statement is a claim about a controlled environment, so a room with no control and no record cannot satisfy it, regardless of how cool it feels at eight in the morning. Second, the number in the statement is a mean kinetic temperature, not a maximum — which means the question "did we ever go above 25 °C?" is the wrong question, and "what did this room integrate to over the quarter?" is the right one.

The five climatic zones, and which one you are in

Climatic zones classify markets by the heat and moisture load a product must survive over its shelf life. Zones I and II cover temperate and subtropical regions and carry the familiar 21 °C/45% RH and 25 °C/60% RH conditions. Zone III is hot and dry. Zone IV is hot and humid, and since 2005 it has been split: IVa at 30 °C/65% RH, IVb at 30 °C/75% RH ^[1]. Africa is not one zone. The continent spans III in the arid interiors, IVa across most of the tropical belt, IVb on the equatorial and Indian Ocean coasts, and — by mean kinetic temperature rather than by latitude — something close to II in the high-altitude cities.

Accelerated testing is 40 °C/75% RH almost everywhere, so it is not what distinguishes the zones; the long-term condition is ^[3]. That matters when you read a certificate stating that a material was held under "ICH conditions" without saying which. "ICH conditions" is not a specification. 30 °C/75% RH is.

Why the Zone IV rules did not come from ICH

This is worth knowing because it explains why you will not find a single authoritative global table. The zone framework was extended to hot climates in the late 1990s, with proposed conditions of 30 °C/35% RH for Zone III and 30 °C/70% RH for Zone IV ^[5]. ICH then adopted guideline Q1F in 2003, which set Zone IV long-term testing at 30 °C/65% RH. Several regions judged that too lenient for their conditions and moved to 30 °C/75% RH. In 2006 the ICH Steering Committee withdrew Q1F outright and left the definition of storage conditions for Zones III and IV to the individual regions and to WHO ^[2].

So the authority for your zone is national or regional, with WHO guidance as the default reference — not ICH. Anyone who tells you "the ICH requirement for Africa is X" is quoting a guideline that has been withdrawn for twenty years.

IVa or IVb: your neighbour's answer may not be yours

WHO maintains a country-by-country appendix listing the long-term stability conditions each Member State has notified, organised by region ^[4]. It is the first place to look, and it will sometimes surprise you: adjacent countries with visually similar climates do not always sit in the same row, because the assignment reflects what a national authority decided and notified, not a meteorological calculation someone re-runs each year.

The underlying analysis makes the point sharply. A risk-based study of tropical and subtropical markets built its conditions from mean daily temperatures and dewpoints, deliberately selecting the hottest and most humid locality in each country or region as the worst case ^[6]. A country-level zone is therefore a simplification of a within-country gradient that can be enormous. Consider three storerooms in the same nominal zone:

• A coastal site — Douala, Mombasa, Lagos, Dar es Salaam — where the daily temperature swing is small but relative humidity sits high through most of the year. This is the IVb case: the moisture load, not the heat, is what your container closure has to hold out.
• An interior Sahelian site, where afternoon temperatures far exceed anything on the coast but relative humidity collapses for months at a time. This is the Zone III profile: heat-driven, with wide day-to-night swings that inflate mean kinetic temperature well above the arithmetic mean.
• A highland site — Nairobi at roughly 1,800 m, Addis Ababa above 2,300 m — where ambient conditions can sit near a Zone II profile for most of the year, and where the binding constraint is often the few hours a day when a west-facing room bakes, not the climate at all.

Do not infer your condition from the country. Infer it from the site, then confirm it against whatever your national authority has published ^[4].

Mean kinetic temperature is the number that governs

Mean kinetic temperature is the single virtual temperature at which a material would experience the same integrated rate of change — the same total progress along the routes by which a peptide actually degrades — as it did under a fluctuating profile, derived from the Arrhenius relationship between rate and temperature. It was introduced in 1971 precisely so that stability could be discussed across cities with different temperature patterns ^[7], and it is what pharmacopoeial guidance uses when evaluating whether an excursion during storage or transport matters ^[9].

The practical property to internalise: because the weighting is exponential rather than linear, mean kinetic temperature is always at least as high as the arithmetic mean of the same record, and the gap widens as the swing widens. A room that averages 25 °C but oscillates by eight degrees between night and afternoon is not a 25 °C room in any sense that matters. This is why a wall thermometer read once a day is not evidence, why a maximum-minimum thermometer is only slightly better, and why a continuously logged record is the minimum that can support any storage claim at all ^[9].

What unreliable mains power does to a storage room

Climate is the load; power is what determines whether you can hold against it. The scale of the problem is documented: an interagency assessment found that at least 25,000 health-care facilities in sub-Saharan Africa have no electricity access at all and at least 68,350 lack reliable electricity, with only around half of hospitals in the region reliably supplied ^[10]. Research and teaching laboratories are not systematically better served than the hospitals around them.

An outage does not just pause your cooling; it starts an excursion whose magnitude depends on the physics of the room, and judging afterwards whether one of them mattered is a procedure in its own right. A small partitioned office with a split unit, an uninsulated roof and a west wall will reach ambient within an hour or two. A masonry interior room with thermal mass and no external wall may hold for most of a working day. You cannot know which you have without measuring it, and the measurement has to run through the outages rather than stop with them.

• Put the logger, not only the cooling, on the guaranteed supply. A record with holes in it during exactly the periods that matter is worse than useless, because it looks compliant.
• Site the store on an interior wall, away from the western elevation and away from an uninsulated roof deck. Passive performance during an outage is worth more than a larger compressor.
• Treat relative humidity as a monitored parameter, not an afterthought — in a IVb location it is the parameter that separates your room from the tested condition ^[1].
• Keep material in sealed secondary containment with an appropriate desiccant, and let a container taken from a cold store reach ambient before it is opened, so that humid air does not condense on cold surfaces.
• Log the outages themselves alongside the temperature trace, with times. When you later have to explain an excursion, the power record is what turns an anomaly into an accounted-for event.

Map the room before you trust it

Monitoring tells you what one point did. Mapping tells you where to put that point. WHO's technical supplements on temperature mapping and on monitoring systems for fixed storage areas set out the practice in detail, and they are freely available ^[11][12]. The essentials transfer directly to a small laboratory store:

• Map in the worst season, and ideally in both extremes — a study run in the coolest month of the year certifies nothing about March or October.
• Distribute sensors in three dimensions, deliberately including the suspected hot spots: near the ceiling, beside the door, against the sun-exposed wall, next to heat-emitting equipment and directly in the conditioner's discharge.
• Use instruments with calibration traceable to a recognised standard, and keep the certificates with the mapping report rather than in a drawer.
• Place the permanent monitoring sensors at the worst-case locations the mapping identified, not at the convenient location near the door.
• Set alarm thresholds against the storage specification and define, in writing, who is notified and what they do — an alarm nobody owns is a log entry, not a control.
• Retain the mapping report, the raw traces and the excursion assessments for at least as long as you hold the material they cover.

Who decides the condition in your country

Because ICH withdrew from this question, the answer is your national medicines regulator, with WHO's per-Member-State table as the default reference ^[2][4]. Some authorities publish a stability guideline of their own — Ghana's Food and Drugs Authority, for example, has issued a public guideline on stability testing of active pharmaceutical ingredients and finished products ^[13]. Others are best approached through their registration and dossier requirements, which state the conditions expected in a submission. Regional harmonisation initiatives add another layer: the East African Community's medicines regulatory harmonisation programme maintains a common compendium of guidelines including stability testing, the ZaZiBoNa collaborative operates across several southern African states, and the African Medicines Agency treaty has entered into force with the agency being stood up.

If you cannot confirm a specific requirement for your country from a primary source, do not assume one from a neighbour. Write to the agency, cite the WHO appendix entry you believe applies, and keep the reply. That correspondence is itself a record, and it is the one that will hold up when someone asks why you designed your store to 30 °C/75% RH rather than 30 °C/65% RH — or vice versa.