Testogel is a widely prescribed testosterone replacement therapy in the UK, formulated as a transdermal gel for men with hypogonadism. Understanding how Testogel is made provides insight into the rigorous pharmaceutical processes that ensure its safety, efficacy, and consistency. The manufacturing process involves precise formulation of testosterone within a hydroalcoholic gel base, stringent quality control at every stage, and compliance with UK and European regulatory standards. From raw material sourcing to final batch release, each step is carefully monitored to deliver a product that meets the exacting requirements of the MHRA and pharmacopoeial standards, ensuring patients receive reliable, high-quality treatment.

What Is Testogel and What Does It Contain?

Testogel is a transdermal testosterone replacement therapy (TRT) formulated as a clear, colourless hydroalcoholic gel. It is prescribed for adult men with hypogonadism—a condition characterised by insufficient testosterone production due to testicular, pituitary, or hypothalamic dysfunction. The gel is applied topically to the skin, where testosterone is absorbed directly into the bloodstream, bypassing first-pass hepatic metabolism.

In the UK, Testogel is available in two presentations: Testogel 50 mg/5 g sachets (1% testosterone) and Testogel 16.2 mg/g gel pump. The application sites differ by formulation—sachets may be applied to shoulders, upper arms, or abdomen, while the pump formulation should only be applied to shoulders and upper arms. Each pump actuation delivers approximately 1.25 g of gel (20.25 mg testosterone), with dosing titrated according to clinical response.

The gel base comprises several excipients that facilitate drug delivery and stability. These include ethanol (which acts as a penetration enhancer and evaporates quickly after application), carbomer (a gelling agent that provides the gel's consistency), isopropyl myristate (an emollient that aids skin absorption), and sodium hydroxide (used to adjust pH). Purified water completes the formulation.

Testogel is designed for once-daily application, providing more stable serum testosterone levels than intramuscular injections. The gel should not be applied to the genitals or broken/irritated skin. Patients must be counselled on proper application technique, including allowing the gel to dry completely before dressing (the product is flammable until dry), covering the application site with clothing once dry, and thorough handwashing after application. This prevents inadvertent transfer to others, particularly women and children, in whom testosterone exposure can cause virilisation or other adverse effects. Testogel is authorised for use by the MHRA in the UK, with EU authorisations granted at national level.

Patients should report any suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Quality Control and Regulatory Standards for Testogel

The manufacture of Testogel is subject to stringent regulatory oversight to ensure product safety, efficacy, and consistency. In the UK, the Medicines and Healthcare products Regulatory Agency (MHRA) is responsible for licensing and monitoring pharmaceutical products, including testosterone gels. Manufacturers must comply with Good Manufacturing Practice (GMP) standards as outlined in the MHRA Orange Guide and EudraLex Volume 4, which remain applicable in the UK post-Brexit through retained EU law and domestic regulations.

Quality control (QC) begins with the sourcing of raw materials. The testosterone API must meet pharmacopoeial standards set by the British Pharmacopoeia (BP) or European Pharmacopoeia (Ph. Eur.). Certificates of analysis from API suppliers are scrutinised to verify purity, potency, and the absence of contaminants such as heavy metals, residual solvents, or microbial impurities. Excipients are similarly tested to ensure they meet compendial specifications.

During production, in-process controls monitor critical parameters such as gel viscosity, pH, and homogeneity. Each batch undergoes rigorous testing before release, including:

• Assay testing to confirm testosterone content is within approved specifications

• Uniformity of dosage units to ensure consistent drug delivery across sachets or pump actuations

• Microbial limits testing to confirm appropriate microbiological quality and absence of specified pathogens

• Stability testing under accelerated and long-term conditions to establish shelf life

Manufacturers must also conduct in vitro release/permeation testing as applicable for semisolid topicals to demonstrate that testosterone is released from the gel matrix appropriately upon skin application. Any deviation from specifications triggers investigation and, if necessary, batch rejection. The MHRA conducts periodic inspections of manufacturing sites to verify ongoing GMP compliance, and qualified persons (QPs) must certify batches before release per the Human Medicines Regulations. Additionally, post-marketing surveillance systems, including the Yellow Card Scheme, monitor adverse events and product quality complaints, ensuring continuous safety oversight throughout Testogel's lifecycle.

Storage and Handling of Testogel

Proper storage and handling of Testogel are essential to maintain its stability, efficacy, and safety. The product should be stored according to the labelled instructions, typically below 25°C, away from direct sunlight and heat sources. Exposure to elevated temperatures can degrade testosterone or alter the gel's physical properties, potentially affecting drug release and absorption. Testogel should not be frozen, and should be kept in its original packaging to protect from light and moisture.

The gel is typically supplied in single-use sachets or multi-dose pump dispensers. Sachets should be kept in their original packaging until use. Once a sachet is opened, the entire contents should be applied immediately; partial use is not recommended due to the risk of dose inaccuracy and contamination. Pump dispensers must be primed before first use according to the manufacturer's instructions, and the cap should be replaced securely after each application to prevent evaporation of the alcohol base.

Patient safety considerations are paramount. Testogel must be stored out of sight and reach of children, as accidental exposure can lead to serious adverse effects, including precocious puberty in boys and virilisation in girls. Patients should be advised to apply the gel to areas of skin that will be covered by clothing, reducing the risk of transfer to others through direct skin-to-skin contact. After application, the gel should be allowed to dry completely before dressing, and patients should avoid showering or swimming for at least 2 hours afterwards. Hands must be washed thoroughly with soap and water after application. If contact with another person is anticipated (e.g., intimate contact, caring for children), the application site should be washed beforehand.

Importantly, Testogel contains ethanol and is highly flammable until dry—patients should avoid open flames, smoking, and heat sources during and immediately after application.

In healthcare settings, Testogel should be stored in a locked cupboard or designated area to prevent unauthorised access. Expired or unused product should be disposed of safely, ideally by returning it to a pharmacy for appropriate pharmaceutical waste disposal. Patients should never dispose of Testogel in household waste or wastewater, as environmental contamination with endocrine-disrupting substances poses ecological risks.

How Is Testogel Manufactured?

The manufacturing process for Testogel involves several carefully controlled stages, each designed to ensure pharmaceutical quality and patient safety. Production typically occurs in specialised facilities equipped with controlled non-sterile manufacturing environments appropriate for semisolid topical products.

Stage 1: Formulation and compounding The process begins with the preparation of the gel base. Carbomer, a synthetic polymer, is dispersed in purified water under controlled mixing conditions to form a viscous gel matrix. The pH is adjusted using sodium hydroxide to achieve target gel characteristics and skin compatibility. Separately, testosterone is dissolved in ethanol along with isopropyl myristate, which enhances solubility and skin penetration. This alcoholic solution is then gradually incorporated into the aqueous gel base under continuous stirring to ensure uniform distribution of the active ingredient. Homogenisation equipment may be employed to achieve a smooth, lump-free consistency.

Stage 2: Quality assurance and in-process testing Throughout compounding, samples are withdrawn for in-process testing. Viscosity is measured using rheometers to ensure the gel will spread easily on skin without running. Testosterone content is assayed using high-performance liquid chromatography (HPLC) to confirm target concentration. pH and appearance are also monitored. Any batch failing to meet specifications is rejected or reprocessed.

Stage 3: Filling and packaging Once the bulk gel passes quality checks, it is transferred to a filling line where it is dispensed into sachets or pump containers under controlled non-sterile conditions. Automated filling equipment ensures precise dosing, critical for therapeutic consistency. Sachets are heat-sealed, and pumps are assembled with actuators calibrated to deliver the correct dose per stroke. Each unit is labelled with batch number, expiry date, and regulatory information.

Stage 4: Final testing and release Finished product samples undergo comprehensive testing, including assay, content uniformity, microbial limits, and packaging integrity. Stability studies confirm the product remains within specification throughout its shelf life. Only after all tests are satisfactory and reviewed by a qualified person (QP) is the batch released for distribution. This rigorous process ensures that every unit of Testogel reaching patients meets the highest standards of pharmaceutical quality.

Frequently Asked Questions