{"id":3608,"date":"2026-10-09T01:51:36","date_gmt":"2026-10-08T17:51:36","guid":{"rendered":"http:\/\/www.sumbermurah.com\/blog\/?p=3608"},"modified":"2026-10-09T01:51:36","modified_gmt":"2026-10-08T17:51:36","slug":"what-are-the-stability-studies-for-apis-in-different-formulations-4892-8e847b","status":"publish","type":"post","link":"http:\/\/www.sumbermurah.com\/blog\/2026\/10\/09\/what-are-the-stability-studies-for-apis-in-different-formulations-4892-8e847b\/","title":{"rendered":"What are the stability studies for APIs in different formulations?"},"content":{"rendered":"

As an API supplier, I get asked about stability studies for different formulations all the time\u2014usually by formulation scientists pulling together their first market-ready batch, or by quality control teams troubleshooting why a new product just failed a shelf-life test. It\u2019s not a one-size-fits-all process, and cutting corners here isn\u2019t just risky for us as a supplier\u2014it\u2019s risky for patients. Let\u2019s walk through how stability studies work across the most common API formulations, what challenges each brings, and why you can\u2019t treat every tablet, liquid, or topical the same way. API Active Pharmaceutical Ingredient<\/a><\/p>\n

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First, let\u2019s ground this: stability studies aren\u2019t just a regulatory hoop. For APIs, stability means confirming that the active ingredient remains within its approved purity range, doesn\u2019t degrade into dangerous impurities, and the formulation stays effective and safe for its entire intended shelf life. Each formulation type has unique stressors\u2014moisture, light, temperature, chemical reactivity\u2014that test APIs in different ways. That\u2019s why we work closely with every client to tailor stability protocols to their specific API and formulation, not just pull a generic template from a file.<\/p>\n

Let\u2019s start with the most common oral solid dosage form: immediate-release (IR) tablets. This is what most people think of when they say \u201cpill.\u201d For IR tablets, the API is usually mixed with excipients like microcrystalline cellulose, lactose, or stearic acid, compressed into a solid. The biggest stability threats here are moisture and oxidation. Many APIs, especially small-molecule APIs like ibuprofen or paracetamol, can hydrolyze (break down with water) if the tablet isn\u2019t properly sealed. I remember a client came to us last year who had developed a novel IR API for migraine; their initial stability study showed 0.8% total impurities at 6 months, but when we dug into their formulation, we noticed they used a low-melting excipient that absorbed moisture from the environment during manufacturing. We adjusted our packaging guidance to include aluminum blister packs with desiccants, and their impurities dropped to 0.2% at 12 months, well within the ICH Q7A guidelines we all follow. For IR tablets, standard stability testing usually follows ICH Q1A(R2) conditions: long-term storage at 25\u00b0C \/ 60% relative humidity (RH) for 24 months, intermediate at 30\u00b0C \/ 65% RH for 6 months, and accelerated at 40\u00b0C \/ 75% RH for 6 months. We test for assay (API purity), related substances (degradation products), and dissolution to make sure the pill breaks down properly in the body over time. The big catch here is that even small changes to excipients can shift stability\u2014we always flag this early, because changing a single binder can mean redoing 12 months of stability data, which delays a client\u2019s launch.<\/p>\n

Next, modified-release (MR) formulations, which include extended-release (ER), delayed-release (DR), and sustained-release (SR) tablets or capsules. These are trickier than IR, because the API isn\u2019t just released all at once\u2014there\u2019s a coating or matrix that controls how and when the API is released. That means stability isn\u2019t just about the API itself; it\u2019s about the functional performance of that coating or matrix. A client who makes an ER API for hypertension reached out to us with a problem: their 18-month stability test showed the drug was releasing too fast in dissolution studies. Turns out the ethyl cellulose coating they used was slightly hygroscopic, so over time, moisture seeped in and broke down the polymer structure, making it thinner and more permeable. For MR formulations, we don\u2019t just test chemical stability\u2014we test in vitro dissolution at multiple time points, because a coating that degrades over time can turn an ER pill into an IR one, leading to too much API being released at once (which can cause toxicity) or too little (which doesn\u2019t work). ICH guidelines have specific sections for modified-release dosage forms, and we also do stress testing at higher temperatures and humidity to predict when the coating will fail. Another thing we watch for in MR is API-excipient interactions: if the API is basic, it can react with acidic excipients in the matrix, leading to both chemical degradation and coating failure. We do compatibility studies early in our process, usually before the formulation is even scaled up, to catch this before a client invests in large batches.<\/p>\n

Then there are liquid oral formulations\u2014syrups, suspensions, solutions, and elixirs. These are super common for pediatric or geriatric patients, but they\u2019re notoriously unstable because of the high moisture content. For APIs in liquid formulations, the key risks are hydrolysis, microbial growth, and precipitation. Let\u2019s take antibiotics, for example: many penicillin APIs degrade rapidly in water, so liquid formulations often need to be reconstituted from a powder just before use. A client who had a reconstituted amoxicillin API reached out last quarter because their stability data showed the API potency dropping 10% after 7 days of refrigerated storage, which was more than the approved 5% limit. We worked with them to adjust the pH of the reconstitution solution\u2014turns out the original pH was 5.5, right where amoxicillin degrades fastest; shifting it to 6.2 slowed hydrolysis dramatically, bringing potency down to 3% over 10 days. For liquid solutions, we also test for clarity and color over time, because a precipitate means the API isn\u2019t dissolved, so the dose the patient takes is inconsistent. For suspensions, we test for sedimentation and re-dispersibility\u2014if the API settles into a hard lump at the bottom of the bottle, shaking it won\u2019t evenly distribute the dose, which is a safety issue. Stability testing for liquids also includes microbial testing every month, because moisture is a breeding ground for bacteria and mold. We always provide guidance on storage conditions too\u2014many liquid APIs need to be refrigerated, or kept away from sunlight, which is part of our stability package clients get when they work with us.<\/p>\n

Topical formulations\u2014creams, ointments, gels, and transdermal patches\u2014are another category entirely. These are applied to the skin, so stability means the API stays in the formulation, doesn\u2019t irritate, and doesn\u2019t degrade on the skin or in the tube. For ointments, which are oil-based, the biggest threat is oxidation, since oil-based products are more prone to reacting with oxygen. For example, a vitamin D3 API used in a topical psoriasis cream: its stability test at 40\u00b0C \/ 75% RH showed a 2% degradation product after 3 months, which was just over the limit. We recommended adding a low dose of vitamin E as an antioxidant in the formulation, which scavenges the oxygen before it reacts with the vitamin D3, cutting the degradation to 0.5% at 6 months. For transdermal patches, which deliver API through the skin over time, we have to test not just the API, but the adhesion of the patch to the skin and the rate of API release through the membrane. I remember a client who made a transdermal estrogen API had patches that lost adhesion after 9 months of storage at room temperature, so the patch would fall off before delivering the full dose. We adjusted the adhesive excipient ratio in the formulation, and their patch adhesion stayed at 95% (the required minimum) for 24 months, which meets regulatory requirements for shelf life. Topical formulations also have to be tested for pH stability\u2014if a cream is too acidic or too basic, it can irritate the patient\u2019s skin, so we measure pH every 3 months during stability testing.<\/p>\n

Injectable formulations are the most sensitive of all, because they\u2019re administered directly into the bloodstream, so any degradation products can cause serious harm. These are usually solutions or lyophilized (freeze-dried) powders for injection, and the key stability challenges are sterility, pH, and API purity. Lyophilized APIs, for example, are often more stable than liquid injectables because there\u2019s no water to cause hydrolysis, but the freeze-drying process itself can damage the API, leading to degradation products. A client had a lyophilized monoclonal antibody API for cancer treatment that had 3% aggregation (clumping of protein molecules) after 12 months of storage, which was a problem because clumps can cause allergic reactions in patients. We worked with them to adjust the lyophilization cycle\u2014slowing down the freezing step to form smaller ice crystals, which when sublimed left a more uniform powder that didn\u2019t aggregate. Injectables also require rigorous sterility testing every 6 months, and we have to confirm that the pH stays within a narrow range (usually 4 to 8) so that when the powder is reconstituted with sterile water, the solution is safe to inject. Regulatory bodies like the FDA and EMA have very strict requirements for injectable stability, and we make sure our protocols align with ICH Q12, which covers formulation and development stability, to make sure our clients\u2019 products are accepted globally.<\/p>\n

Now, let\u2019s talk about common mistakes we see clients make with stability studies, especially when working with API suppliers. One big one is not starting stability testing early enough in formulation development. We\u2019ve had clients scale up a 100kg batch of a new formulation only to find that the API degrades faster than expected, and they have to go back to the drawing board, wasting months and thousands of dollars. That\u2019s why we recommend doing pre-formulation stability compatibility studies with our API as soon as a client has a rough formulation outline\u2014this lets us flag potential stability issues before they invest in large batches. Another mistake is not accounting for packaging in stability testing. The packaging itself can interact with the formulation: plastic containers can leach chemicals, or glass can adsorb (stick to) the API, leading to lower potency over time. For example, a client who used plastic bottles for a liquid API found that 5% of the API was sticking to the plastic after 6 months, so we switched them to amber glass bottles, which eliminated that adsorption. We always provide packaging recommendations as part of our stability support, because it\u2019s a critical part of the overall stability profile.<\/p>\n

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At the end of the day, our job as an API supplier isn\u2019t just to provide a high-quality active ingredient\u2014it\u2019s to make sure that ingredient stays stable no matter what formulation our clients develop. Stability studies are the backbone of every approved drug, and cutting corners here puts patients at risk and undermines all the hard work that goes into bringing a new drug to market. If you\u2019re working on a new API formulation and need support with stability testing, or you have questions about how different formulation types affect API stability, we\u2019re here to help. We collaborate closely with formulation scientists, quality teams, and regulatory experts to tailor stability protocols that meet your specific needs and global regulatory requirements. For a consultation to discuss your API formulation stability needs, reach out to our team.<\/p>\n

API Active Pharmaceutical Ingredient<\/a> References:<\/p>\n

    \n
  1. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). ICH Q1A(R2): Stability Testing of New Drug Substances and Products. 2003.<\/li>\n
  2. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). ICH Q7A: Good Manufacturing Practice for Active Pharmaceutical Ingredients. 2000.<\/li>\n
  3. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). ICH Q12: Pharmaceutical Development. 2019.<\/li>\n
  4. Aulton ME, Taylor KMG. Aulton\u2019s Pharmaceutics: The Design and Manufacture of Medicines. 5th ed. Churchill Livingstone; 2013.<\/li>\n
  5. Bruno G, et al. Stability of Active Pharmaceutical Ingredients in Pharmaceutical Dosage Forms: A Review. Journal of Pharmaceutical Sciences. 2018;107(10):2579-2596.<\/li>\n<\/ol>\n
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    Kintai Healthtech Inc.<\/a>
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    Address:
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    WebSite:     https:\/\/www.healthkintai.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    As an API supplier, I get asked about stability studies for different formulations all the time\u2014usually … What are the stability studies for APIs in different formulations?<\/span>Read more<\/a><\/p>\n","protected":false},"author":49,"featured_media":3608,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3571],"class_list":["post-3608","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-api-active-pharmaceutical-ingredient-42ab-8ebc12"],"_links":{"self":[{"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/posts\/3608","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/users\/49"}],"replies":[{"embeddable":true,"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/comments?post=3608"}],"version-history":[{"count":0,"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/posts\/3608\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/posts\/3608"}],"wp:attachment":[{"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/media?parent=3608"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/categories?post=3608"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.sumbermurah.com\/blog\/wp-json\/wp\/v2\/tags?post=3608"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}