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Use and practice implications of modified-release medicines

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Extended nurse prescribing will make a significant difference to practice across the country, and should benefit both health care professionals and patients. It is therefore vital that nurses understand the particular issues regarding the prescription of modified-release drugs and transdermal strong opioids to ensure safe prescribing and administration.


VOL: 101, ISSUE: 50, PAGE NO: 21

Andrew Dickman, MSc, MRPharmS, is specialist principal pharmacist, palliative care team, Whiston Hospital, Merseyside

Tina Carney, PGCE, BSc, NP, RGN, works in partnership development at Astra Zeneca

Extended nurse prescribing will make a significant difference to practice across the country, and should benefit both health care professionals and patients. It is therefore vital that nurses understand the particular issues regarding the prescription of modified-release drugs and transdermal strong opioids to ensure safe prescribing and administration.

Many prescribers may assume that there are sufficient safeguards to prevent any potential for inaccuracy or confusion in prescribing. However, this is not always the case, and it is a matter for specific concern in the area of modified-release controlled drug preparations.

Modified formulations
Modified-release drugs have complex formulations that can offer an advantage over standard medication for some patients.

They may be prescribed in order to (National Prescribing Centre, 2000):

- Reduce the dosing frequency and to improve patient compliance;

- Reduce fluctuations (peaks and troughs) in drug plasma concentrations and therefore concentration-related side-effects or improve effectiveness;

- Control the site of drug delivery in the gastrointestinal tract.

Modified-release drugs are particularly difficult to standardise, given their complex formulations. For example, the therapeutic effect of several modified-release morphine sulphate preparations are comparable but the technology by which the active ingredient is released, absorbed and distributed may vary between products. Thus, wide variations in some pharmacokinetic parameters may exist between different modified-release preparations of the same drug (NPC and NHS Executive, 1998)

It is perhaps best to consider each modified-release preparation as unique, rather than considering different brands of the same drug as interchangeable. Indeed, the Medicines and Healthcare products Regulatory Agency (MHRA) recommends that all modified-release preparations should be prescribed by their brand name (NPC and NHSE, 1998).

Accurate prescribing
Until recently all prescriptions for Schedule 2 controlled drugs had to be written in the prescriber’s own handwriting, but since November 2005 computer-generated prescriptions have been allowed (NPC, 2005). The basic elements required on these prescriptions still include:

- Signature and date;

- Name and address of patient;

- Dose to be administered (‘as directed’ or ‘when required’ is not acceptable);

- Dosage form;

- Strength of preparation, where appropriate;

- Total quantity in words and figures of the preparation or dosage units.

These requirements are helpful in preventing prescription misuse or fraud. However, they may not always prevent dispensing error or confusion. For example, based on the above guidelines it is possible to write a prescription simply for ‘morphine sulphate s/r capsules’, without specifying further details. More than one preparation could be dispensed from such a prescription, and it seems unwise to allow this potential for confusion or misunderstanding to continue.

Generic prescribing is widely accepted as best practice for the majority of pharmaceutical products. It is good clinical practice to use the generic names of drugs if all the available formulations are equivalent and interchangeable. There are, however, recognised exceptions.

Diltiazem, for example, is available in various modified-release formulations, the therapeutic effects of which may differ to some degree. For this reason it is recommended that diltiazem is prescribed in brand form rather than generically (Mehta et al, 2005).

Branded prescribing in a few specific cases can be both safer and more cost-effective than generic prescribing. The potential safety benefit lies in the reduction of dispensing or administration confusion, and cost savings may also result by minimising the chance of errors, thereby reducing health professional time, cost of wasted incorrect medicines and of issuing new prescriptions for the correct product. This does not take into account the potential costs of rectifying prescribing or dispensing errors that lead to patient harm or even death.

Practice implications
A report by the chief pharmaceutical officer (DoH, 2003) supports this argument. It suggests that oral sustained-release opioids should be prescribed by brand name to avoid ambiguity. Special care needs to be taken with opioid analgesics, given their narrow therapeutic margin and the variety of doses and formulations available. There are many potential causes of prescribing and dispensing errors, including dose calculation mistakes, drug name confusion, use of abbreviations and availability of different formulations. Using brand names for those opioid analgesics that pose a particular risk, such as modified-release and transdermal products, is a useful way to limit potential problems. The following examples illustrate the current scope for confusion:

- Morphine sulphate: When a prescription for modified-release morphine is written, only the form of the product needs to be specified. In practice, this means that writing ‘morphine sulphate s/r tablets’ is acceptable. However, there are two brands that could fill that prescription: MST Continus and Morphgesic SR (Mehta et al, 2005).

- Fentanyl: Similarly, with a prescription for ‘transdermal fentanyl’, two forms are currently available - Durogesic (a gel-filled reservoir patch) and Durogesic D-Trans (a matrix patch) (Mehta et al, 2005). Thus, a generic prescription for fentanyl could result in patients receiving a product other than that intended by the prescriber. There are unlikely to be clinically significant differences in bioavailability between the two types of patch. However, the patches have a different physical appearance, which may confuse patients. An additional factor with fentanyl is that some patients are advised by their doctors to cut their matrix patches to obtain the desired dose. With a generic prescription, they may on some occasions be dispensed reservoir patches and may try to cut them, not realising that this is not advisable with reservoir patches.

Modified-release preparations should only be used where there is a clear clinical advantage over conventional-release preparations. In such cases it is particularly important to prescribe by brand name as there is concern over the clinical implications of switching between inequivalent preparations.

- This article has been double-blind peer-reviewed.

For related articles on this subject and links to relevant websites see

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