When applying for a Marketing Authorisation (MA) for a new medicine, previously known as a Product Licence, the manufacturer has to clearly set out how they intend the product to be used. The MA specifies which medical conditions the product can be used to treat and how the medication should be taken, including dosage and formulation. This is done on the basis of clinical trials conducted and the evidence base for that product. Prescribing or using that product in any way other than that specified in the MA is classed as unlicensed use.

Of course there are a variety of reasons why a prescriber might wish a product to be used off-licence - also known as 'off-label'. There are a huge number of medicines that have not undergone clinical trials in children and so these medicines are not licensed for children. There may also be cases where a medicine has been shown to be an effective treatment for a medical condition that is not covered under the MA. There may also be physical reasons why a particular product is not suitable for a patient - perhaps they have a percutaneous endoscopic gastrostomy (PEG) tube fitted or they have dysphagia and can't swallow solid dosage forms.

Where an appropriate licensed product is not available a clinical decision is made by the prescriber in order to provide treatment for their patient. Depending on the nature of the intended unlicensed use there will be a number of considerations for the prescriber, patient and pharmacist.

In all cases of unlicensed use the prescriber and dispensing pharmacist legally share clinical responsibility for the safety and efficacy of the treatment. The key concerns for the pharmacist would be the safety and stability of the medicine. Where a medicine is used for an unlicensed indication it is likely to remain in its original form and so stability and pharmacokinetics should be unaltered. The issue here is whether the drug itself can be safely used in that patient.

However, where a medicine is altered from its original form, for example by crushing and dissolving in water, its stability also comes into question. Will the drug remain chemically stable? Will the pharmacokinetic profile be altered? Will this affect plasma concentrations of the drug? How will this affect the patient's treatment? Crushing tablets, or opening capsules, therefore raises numerous questions over the safety and efficacy of a medicine.