Analytical Services

Consultancy Services

In addition to running standardised assays, Sirius has a highly experienced team of consultants in the UK and the US, with over 65 years of combined experience.

Our consultants are ready and able to understand the challenges you are facing, and if we are able to help then we will work with you to develop a specified work package that we will commit to deliver on time and to a budget agreed in advance.

We have successfully completed dozens of these projects, and the anonymised examples below are a small selection of real-world examples of some of the diverse projects we have recently completed, by kind permission of the customers who engaged us to perform them.

Case Study 1: Selecting excipients to stabilise a high-solubility solid-state form

A New England Biotechnology company submitted a sample initially just for standard, fixed price assays: Gold Standard pKa, log P and solubility. Data from SiriusT3 showed it was an acidic drug with pKa between 7 and 8, and log P between 2 and 3.  A CheqSol experiment to measure aqueous solubility found that the sample precipitated when the pH was lowered below 8.4. Because of the way CheqSol works, we were able to observe that It initially precipitated as a metastable form that was 9 times more soluble than the crystalline form, and the metastable form persisted for an hour before crystallizing.

As a value-add, we informed the client of this interesting behaviour and pointed out that if the more soluble form could be stabilized for a longer time, it could be useful for making a formulation with higher solubility. They immediately asked us to extend the study by running Controlled Supersaturation experiments on the Sirius inForm. In these experiments, supersaturated solutions are created by solvent quench or by pH-shift, and the concentration of dissolved sample is monitored spectroscopically or pH-metrically. Tests were run with the drug in aqueous solution and also in the presence of various solubility-enhancing excipients that we have available.

The goal was to identify those excipients which could best keep the drug at the supersaturated concentration. The most successful were HPMC AS and PVP S-630; when these excipients were used there was no evidence of crystallization during the entire experiments. Encouraged by these studies the client now has a new formulation under development based around an amorphous solid dispersion.


Case Study 2: Effect of excipient and formulation on dissolution of a poorly soluble drug in simulated gastric fluid

This study, commissioned by a multinational chemical company based in Germany, featured a poorly soluble basic drug with one pKa around 3.8. The crystalline form is extremely insoluble but there is an amorphous form that is some 16 times more soluble.  The customer asked us if we could use one of our biorelevant dissolution assays to measure dissolution rates over two hours at 37°C in simulated gastric fluid at pH 2. The samples studied included the crystalline form of the drug, and a formulation in which the amorphous form and excipient were bound by hot melt extrusion. Samples were introduced as powders, and concentrations in solution were determined by in-situ UV.   The following dissolution profiles were measured:

As is clear from the graph above, significantly more drug was released into solution from the formulation than from the drug alone, and the customer used this information to make a ‘go’ decision.

Case Study 3: Effect of salt form on dissolution rate

A basic sample with one pKa was submitted to us for standard Gold Standard pKa and log P measurement by an emerging pharma company of the Eastern Seaboard.

As the compound seemed interesting, we also measured solubility by CheqSol, and observed that the precipitated neutral form was amorphous. The client then prepared salts with various acidic counter-ions, and we used the Sirius inForm to investigate their dissolution rates under simulated gastrointestinal conditions. We ran GI Dissolution experiments in which the samples were introduced in powder form. Experiments ran for 30 minutes at pH 2.5 to simulate gastric pH, after which FaSSIF was added and the pH was increased linearly to 6.5 over 30 minutes to simulate gastric emptying. This was followed by 30 minutes at pH 6.5. All the salts dissolved at low pH but some salts dissolved much faster than others:

Unsurprisingly, precipitation occurred during all dissolution experiments as the pH approached the pKa – interestingly, further analysis showed that all the precipitates were amorphous.

The client used the knowledge obtained during these experiments when selecting a salt for what is now the commercial formulation.

Case Study 4: Dissolution data to support bioequivalence study

An Italian generics company wanted to change suppliers for an API. They purchased several batches from a proposed new supplier and asked us to compare their dissolution performance with API manufactured by the existing supplier. To determine the Intrinsic Dissolution Rate we ran each batch in triplicate experiments for 30 minutes at pH 1.2. Samples were prepared as compressed tablets with a 3 mm diameter of which only one face was exposed to the dissolution medium. The tablets were prepared by compressing approximately 10 mg of API for 6 minutes under a constant pressure. The dissolution medium (55 mL) was stirred at 300 rpm throughout the experiment. The following profiles were observed:

As can be observed from the graph above, the data generated in this study indicated that there was no significant difference in the dissolution behaviour of the various batches of API. Such information helped the generics manufacturer to demonstrate that the new API exhibits bioequivalence to the original version.

The customer got a “Double Whammy”!  They were able to both remove risk from their supply chain, and simultaneously achieve very significant cost savings as a result of this project.


Case Study 5: In vitro dissolution experiments to replace tests done with animals?

Toxicity and bioavailability of new drugs and formulations are often investigated in experiments using animals, but industry-wide there is an strong desire to replace these with in vitro tests where practical.

One of the world’s most successful generics companies, headquartered in Germany, asked us to use the Sirius inForm to investigate the dissolution of a weakly acidic drug that was poorly soluble below its pKa of 8. Their intention was to compare our results with animal data from their lab in order to assess the scope for replacing animal tests with an in vitro method.

We ran three-sector GI Dissolution experiments for the free acid, two HCl salts, a choline salt and an amorphous solid dispersion stabilised with a cellulose polymer. In each experiment, the equivalent of 10 mg of API was added in powder form to the dissolution media in the first sector after the pH adjust, and a quaternary surfactant (HTAB, hexadecyltrimethylammonium bromide) was added at the start of the gastric emptying stage. Ionised surfactants are often used in crude formulations, and can improve the stability of suspensions and also solubilise neutral molecules by surrounding them with a charged layer.

For the free acid and salts, the amount dissolving at pH 2 increased slightly after the addition of HTAB, and increased again after pH 7, close to the pKa. However, the solid dispersion dissolved much faster than the salts after introduction of HTAB and reached a far higher concentration at pH 7 (although it precipitated slightly after one hour at this pH):

Thus the amorphous solid dispersion greatly increases the solubility of the compound over the physiological pH range and, consequently, the ability of the API to be absorbed. This was reflected in animal trial data.

The customer was extremely satisfied with the report we prepared for them, and they generously allowed us to write this story up as an Application Note.