Oral rehydration salts: a simple medicine that saves millions

Oral rehydration salts (ORS) are among the most widely used and medically important interventions in global public health. Consisting of a precise mixture of glucose and electrolytes, ORS is used to prevent and treat dehydration caused by acute diarrhoea, particularly in children. Despite the development of advanced medical technologies, this simple, low-cost medicine remains a foundational therapy. Its efficacy and safety have cemented its place on the World Health Organization (WHO) Essential Medicines List (EML) since the list's inception.

The science of dehydration and rehydration

When a person experiences acute diarrhoea, the gastrointestinal tract loses its ability to absorb fluids normally, leading to the rapid loss of water and essential electrolytes, primarily sodium and potassium. This loss can lead to severe dehydration, a condition that can quickly become life-threatening if fluids are not replaced. Simply drinking plain water is insufficient and can even dilute remaining electrolytes, because the intestines cannot absorb water efficiently without the presence of specific solutes.

The effectiveness of ORS lies in a fundamental physiological mechanism known as sodium-glucose co-transport. In the small intestine, specific proteins actively co-transport sodium and glucose together across the intestinal wall. As these molecules move into the cells lining the gut, they pull water with them through osmosis. This mechanism remains functional even during severe episodes of diarrhoea. By providing both glucose and sodium in the correct proportions, ORS actively facilitates the absorption of water, efficiently rehydrating the body even when the intestines are secreting excess fluid due to infection.

The WHO and UNICEF formulation

The exact composition of ORS has been carefully refined over several decades. The concept of oral rehydration was developed in the 1960s, and the WHO introduced a standard formulation in 1978. Historically, this original formulation had a higher concentration of sodium and glucose. However, after extensive clinical evaluation, the WHO and UNICEF recommended a reduced osmolarity formulation in the early 2000s. "Osmolarity" refers to the concentration of dissolved particles in a solution.

The current reduced osmolarity formulation contains specific quantities of anhydrous glucose, sodium chloride, potassium chloride, and trisodium citrate. Trisodium citrate is generally preferred over sodium bicarbonate, which was used in older formulations, because it is more stable and less prone to breaking down when exposed to heat and humidity. This lower concentration of solutes was adopted because it reduces stool output and the need for intravenous fluids compared to the previous version, without causing an unsafe drop in blood sodium levels.

A cornerstone of child survival strategies

Diarrhoeal diseases have historically been a leading cause of mortality in children under five years old globally. The widespread introduction and use of ORS, alongside improved water and sanitation infrastructure, has been credited as a major factor in the significant reduction of these deaths over the past half-century. It is a highly accessible intervention that can be administered at home by caregivers, often preventing the need for hospital admission.

In standard global health guidelines, ORS is rarely used in isolation for acute diarrhoea. It is commonly combined with zinc supplementation, which is also on the WHO EML for paediatric care. Zinc helps reduce the duration and severity of the current episode and may protect against future infections in the following months. The combination of ORS and zinc is considered a cornerstone of integrated community case management for childhood illnesses, ensuring that dehydration is treated promptly while nutritional status is maintained.

Regulation, pricing, and access

Because ORS is a generic medicine, it is manufactured by numerous pharmaceutical companies worldwide. In South Africa, oral rehydration preparations are regulated by the South African Health Products Regulatory Authority (SAHPRA) and are generally available over the counter without a prescription. While they are inexpensive to manufacture, consistent access can still be influenced by supply chain reliability and local pricing frameworks.

In South Africa, registered medicines are subject to the Single Exit Price (SEP) mechanism, which sets a transparent maximum price at which a specific product can be sold across the country. Patients and healthcare providers can use tools like HealthSA to search for registered ORS products and understand their pricing. Despite its low cost and simplicity, ensuring the consistent quality, registration, and availability of ORS remains a critical regulatory and public health priority globally.