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Patent rights are crucial value drivers for individuals and technology companies, large or small. This article presents a selection of best practice pointers under the law of the European Patent Office (EPO) on how to get the most out of patent applications, especially the “first filing” that establishes a priority date for and sets the framework for future patent rights.


Of all people involved in the filing, prosecution and enforcement of patent rights, it could be argued that none are as important as the drafters of the initial application. Regardless of the skill and experience of the litigators, certain errors or omissions made by the drafters may be irrecoverable, while stoutly created rights should withstand all slings and arrows, however outrageous.

The fortune of the patent will rest heavily on the combined teamwork of the inventor(s) (the client) and the patent attorney. Thus, the team must work closely together in cooperation. This is especially so as there is often a tension between the needs of the client and the recommendations of the attorney when filing new patent applications as “first filings” (i.e. first applications for an invention, which are to be used subsequently as priority applications).

Often the client requires a speedy filing as they are eager to disclose their invention. For clients who work in competitive fields, the risk of a competitor filing or disclosing the invention before them may be a constant pressure. In addition, for smaller applicants, for example start-ups, funding may be limited and therefore cost is also a factor that the drafting patent attorney must manage.

With premature filings come, however, the danger that the invention may change and therefore a patent granted from the application will no longer cover the commercial product or the application cannot be validly amended to cover the product. Both of these result in a waste of patent prosecution costs. Another consideration is lack of data. If an application is filed without enough data, the application could be refused or the patent once granted could be revoked, long after the invention has been disclosed resulting in a loss of patent protection for the invention.

This article discusses just a few key aspects of patent drafting that, especially from a European perspective, should be considered in order to maximise the value of and reduce the downstream issues that may arise from a first filing.

A selection of pointers for best practice

In later foreign patent applications, priority will be claimed back to the first filing. There is always, however, the very real risk that prior art will emerge in the intervening period – either from the applicant themselves or from a third party. Making the claim to priority stick all the way back to the first filing then becomes life or death for the eventual patents. Our first two tips focus on elements in trying to secure and maintain valid priority rights: avoiding minor changes in wording or definitions that lead to loss of priority and filing only when there is enough support for the subject matter of the invention.

When drafting, it is also important to ask whether this invention is a trailblazer in a field where only the client is operating, or is the client struggling to keep up with (and file before) the Joneses. Do you want to frame the first filing to leave space for later patents covering focussed developments (hopefully by the client), or do you want to establish basis in the first filing, once and for all, to cover future permutations and combinations? That will need to be decided now, and is a decision like many others that may not be reversed.

Lastly, it is crucial to ensure that all the key parameters used in the application to define the invention are clear. Although, they may be clear to the client, the question is whether the notional skilled person would be able to understand and measure them. This can be ensured now, and again it may be now or never.

Loss of Priority by Amendments

Once the hard work of preparing and filing a patent application for a new invention is complete, clients are usually of the belief that they are free to disclose their invention without implications for later foreign applications, which will in time be linked to the first filing by a priority claim. It is very tempting to believe the invention is “safe” from one’s own disclosures once the first application is filed.

In reality, clients should be aware that in order to minimise any negative effect on protecting the invention, nothing should be published until after those later foreign applications are filed (and even more preferably until after the first filing and foreign applications are published), if at all possible. This may not always be practicable for a variety of different reasons, but the effects that an intervening publication could have on the client’s patenting strategy should always be considered before publication by the client outside this framework is permitted.

Entitlement to priority of claimed subject-matter is an issue which is more often dissected in post-grant opposition or litigation, where the options for amendment are more limited, than in pre-grant examination. In both cases, entitlement to priority is vital to the validity of the patent if the invention was disclosed, either by the applicant or by a third party, between the earliest priority date and the filing date of the application. This is particularly the case in competitive fields where several parties are working in the same area.

In order to validly claim priority from an earlier application, current EPO law per G2/98 requires that the claimed subject matter must be directly and unambiguously derived from the earlier application, using common general knowledge alone.

However, given that the first filing is usually filed early on in the development of an invention, it is almost inevitable that there will be some features of the invention that change over the following year. Hence developments may not have even been envisaged, let alone presented in a clear and unambiguous manner, when the first filing was prepared.

In Decision G1/15, the Enlarged Board of Appeal at the EPO clarified its position in the case of “partial priorities” where the definition of a feature is broadened from a first filing in a later priority-claiming application so that the later application no longer validly claims priority and the first filing becomes prior art. The EPO have now decided that in this case, the subject matter disclosed in the first filing is entitled to the earliest priority date and therefore does not become citeable against the later application, whilst the subject matter that was not disclosed in the first filing is entitled only to the priority date of the later application.

This welcome clarification of the law does not, however, protect the applicant in situations where an intervening publication which includes a feature not disclosed in the first filing is made between that first filing and the later foreign application.

It is therefore advisable to monitor developments to the invention that occur after filing the first application. If there are important changes to the invention that are not covered by the first filing, these should be captured in one or more further “follow-up” filings. When the applicant is intending to disclose these improvements, these follow-up filings should, of course, be filed before the disclosure.

Even when no disclosures by the applicant are envisaged, follow-up filings should be filed as soon as practicably possible after identifying the development, to protect against relevant third-party disclosures.

Whilst larger R&D departments may be more used to identifying and acting upon such developments, smaller applicants with less patent experience may be not be as well attuned to spotting these subtle changes, especially when the “overall invention”, through the eyes of the inventor(s), appears to be the same. Patent attorneys should therefore emphasise to clients the importance of informing them of developments, and preferably arrange regular meetings to go over any developments, paying attention in particular to all details even if at first sight minor ones, that have changed since the first filing.

When filing later applications, for example International applications which claim priority back to the first filing, it is important not to change the wording or vocabulary used to describe the invention without good reason. A simple change of wording can lead to a loss in priority for a certain feature where the meaning of the wording is not identical. If a change of wording is required, it is recommended to retain the original wording (with the new wording added) to ensure that you leave open the option of relying on the earliest claimed priority date for the original wording.

The later-filed application should therefore contain both the original wording used, which should have a valid priority claim in case of any relevant intervening prior art, and the new wording which may reflect more recent developments in the invention, but of course may not be entitled to the earlier filing date. In that way, two options are left open regarding the scope of protection which can be decided upon during prosecution or litigation once relevant prior art documents have been identified.

In summary, when preparing later applications, e.g. foreign or International patent applications with amendments compared to the first filing, information should only be added and nothing should be deleted compared with the first filing. It is also highly advisable to keep a “tracked-changes” copy of any amended specifications that have been filed, so that the priority date of each feature of the invention can be easily identified during prosecution of those later applications.


Although not a strict requirement under the EPC, the question of plausibility is applied to European patent applications in various ways. The first is in asking whether the invention is sufficiently disclosed (is it plausible that the invention can be worked based on the teachings in the patent/application?). Another is when asking whether the invention involves an inventive step (has the objective technical problem been plausibly solved?)

When considering these questions, assessing the amount of data or supporting evidence in the application is imperative.

Whilst applicants may often not wish to disclose all their experimental data to their competitors in the form of a patent application, enough evidence must be provided to show that the invention to be claimed is plausible. Therefore, when drafting an important consideration is how much data or evidence relating to the invention should be included.

According to established EPO case law, in order to validly establish priority for subject matter in a first filing, the subject matter must be sufficiently disclosed in that filing. Therefore, even though further data can be included in later priority claiming applications, it is important to ensure that the first filing, i.e. the priority application, itself is sufficient and thus meets the requirements of Art. 83 EPC.

At the EPO, sufficiency objections and inventive step objections are often interrelated. An objection of lack of inventive step may result from insufficient evidence that the objective technical problem has been solved.

In the case where an application contains no or an inadequate amount of data, applicants can find themselves in an “inventive step / sufficiency squeeze”. Although the applicant can argue that the skilled person would readily understand that the subject matter is sufficient based on knowledge from the prior art, this may then attract an objection that it would have been obvious to the skilled person to reach the invention based on those very teachings in the prior art. Whilst this is a developing area of case law, it is one that is best avoided, where possible, by ensuring that applications contain adequate levels of data.

Even though sufficiency of disclosure must, in principle, be established at the priority date, post-published documents can be used as evidence that the claimed concept can be put in practice (EPO Case Law II, C-5.8). So, post-published documents can successfully be used as evidence for supporting sufficiency, but the application as filed must at least be credible (T1264/04). Post-published documents cannot “cure” alleged insufficiency in the application as filed, but can be used to confirm the teachings in the application as filed (T1205/07).

Two important areas of insufficiency in the pharmaceutical field include insufficiency over the breadth of the claims (“Agrevo”-type objections) and sufficiency of second medical use claims.

In the case where the claims are considered broad compared to the exemplified compounds, an objection that the technical problem has not plausibly been solved across the entire scope of the claims may be raised. This type of objection was first made in AGREVO (T 939/92) and hence is commonly referred to as an “Agrevo”-type objection).

The best solution is data. If your first filing is a bit thin then ensure that your first filing contains at least some general definitions or formulae which tightly cover the invention, e.g. the compounds, exemplified in the application and would clearly be supported by these examples. As further data becomes available, “follow-up” applications can be filed successively with enhanced support for your claims, without waiting for the end of the priority year. At this stage, the additional general formulae can also be added with enhanced scope having assessed the relevance of the new results.

For second medical use claims, T443/05 provides guidance on the level of evidence required to support these claims:

For the acceptance of sufficient disclosure of a therapeutic application, it is not always necessary for results of clinical trials to be provided at the relevant date, but the patent/patent application must provide some information showing that the claimed compound has a direct effect on a metabolic mechanism specifically involved in the disease. Once this evidence is available from the patent/patent application, post-published evidence may be taken into account to support the disclosure in the patent application (T 433/05).

Speculation in this area, albeit ultimately correct, will most likely not yield valid patent rights. Data is needed linking the activity of the compound to the disease mechanism. So don’t file on a hunch, file when you have the (barest) data.

This is also relevant to compound per se claims; whilst passing one element of the test for sufficiency is often easily achieved (it is only necessary to provide the skilled person with enough information to synthesise the compounds), the question of plausibility is often raised in relation to inventive step. Even if the claims are apparently sufficient in simple terms of making the compounds, the Examiner may object to the lack of evidence supporting use of the compounds in a disease state on the grounds that the objective technical problem has not been plausibly solved. Put another way, absent data how does one know whether these new compounds are useful for anything?

It is sometimes difficult to persuade applicants that they need to delay their patent filings until they have more data to verify the proposed indications for the claimed compounds, especially when they may have read their competitors’ patent applications which may suffer from the deficiencies noted above.

There is a delicate balance, bound to be case-specific, and hence pointers in a general article like this may not easily translate into actions on a given invention. Drafters should carefully analyse the data vis-à-vis the desired claim scope and also the impact on the client of the act of filing the application. Submitting successive updated patent applications in the priority year as new data accumulates is, again, a means to mitigate some of the above-identified problems.

Selection Inventions

The EPO standards for determining whether an amendment to an application goes beyond the content of the application as filed are relatively strict compared to other patent offices around the world.

Standing back from this “added matter” examination at the EPO, drafters should appreciate another side of this coin: the EPO allows selection inventions, in that proposed amended definitions that would add matter if presented during prosecution constitute new definitions if made the subject of a later filed patent application.

One aspect where this is important is when making selections of a number of parameters where several values or ranges are disclosed for each parameter in the application.

The EPO uses its infamous “selection from two-lists” principle when it comes to assessing both novelty and added matter. Whilst it is permissible to amend an application to specify a single entity from a list of possibilities, amending to specify a combination of entities for two different variables is often not allowed, when that particular combination is not disclosed.

If during prosecution an applicant wishes to amend the claims of an application by “selecting from two lists”, it should be considered whether instead of hazarding such an amendment, a new patent application should be filed with this limitation. An amendment which constitutes selecting from two lists and infringes the EPO requirements regarding added matter will most likely be found to be novel over the earlier application when viewed as prior art. If there is an unexpected advantage not derivable from the earlier application, there is a good case that a later “selection” application will be held to be inventive over the earlier application as well.

Of course, if the amendment is filed before a later application then, as the EPO register is open to public inspection, filing of the amendment will constitute a public disclosure of the subject matter and hence prejudice an attempt to protect that “added matter” in the later application.

When drafting, it is therefore necessary to consider which approach would be preferred. One option is to draft the application in such a way that there is basis for all combinations of all features. Alternatively, the drafter may wish to purposefully not specify certain combinations so that these can be protected in a later application as a selection invention, with a later filing date thereby extending the patent lifetime for the narrower combination.

This approach is commonly seen in the pharmaceutical field, where a first filing may not specifically disclose the lead compound (often as it is not yet known) but broadly encompasses it in the claims. As lead compounds have advantageous properties (which are often unpredictable based on their structure), a later filing directed specifically towards the lead compound (or a narrowly defined family of compounds) can be held as new and inventive.

Drafters can decide at the time of filing whether to leave opportunities for later selection filings. As with many decisions, it must be taken there and then.


Many issues relating to clarity are straight-forward and obvious to drafters, without any need for specific knowledge of the field. However, there are a number of occasions where unexpected clarity objections could arise which originate from particular “quirks” in the technical field of the invention.

For example, when providing measurements in an application, it is important to state how these measurements were taken. This applies not only to the specific description of the invention, but also for the general statements of invention, which may be used as basis for a claim during prosecution.

For certain measurements, for example when measuring particles having a size in the nanometre range, the recorded value can depend on the method used to obtain the measurement. Where this is known within the art, it can be argued that by just stating a measurement, the value is unclear, as this does not provide the reader with sufficient information to clearly identify whether a particle has the specified sizes.

Drafters should check all key parameters and include relevant measurement guidance on filing.

Executive Summary

  • Although the drafters’ view of the best wording may change over time, it is important to make sure the original wording is retained when successively revising the specification of an application. Add to the original wording, don’t delete any of it, and keep track of the nature of and date of revisions.
  • File when you have enough data. This may sound like a desideratum, but ask whether the data you have is convincing enough to lead to the conclusion that you want it to lead to. If in doubt, file further applications as new data becomes available.
  • Understand how the patent world (particularly in Europe) deals with selection inventions and decide how to cover (or specifically NOT cover) combinations. Try to gain an understanding of the field from the client and assess the risk of competition in filing for patent protection based on novel combinations not specifically disclosed in your application.
  • Be aware of using parameters when defining the invention. It is recommended to check the meaning and terms and vocabulary used, rather than just relying on the wording used by the inventor. If it is envisaged that parameters could be vital to defining the invention, then show how they parameters can be / are measured.

We hope these few pointers are helpful to all involved in securing valid patent protection for inventions.


Our articles are for general information only. They should not be considered specific legal advice, which is available upon request. All information in our articles is considered to be accurate at the date of publishing.


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