When a patient can no longer swallow oral medicines, continuous subcutaneous infusion via a syringe driver becomes the standard route for symptom control in the last days of life. The pharmacist's role — checking compatibility, advising on dilution and stability, and flagging combinations that should never be mixed — is one of the most clinically consequential tasks in community palliative care.

What is a syringe driver?

A syringe driver (most commonly the McKinley T34 in NHS settings) delivers medicines continuously over 24 hours through a subcutaneous needle. It is used when oral, transdermal or rectal routes are no longer appropriate — typically in the last days of life, but also during severe nausea or bowel obstruction earlier in the illness trajectory.

District nurses set up and monitor the device, but the choice of medicines, their compatibility in combination, and the diluent used are pharmacy decisions.

Common two-drug and three-drug combinations

The most frequently prescribed syringe driver combinations in UK palliative care, according to published compatibility databases, are:

Diamorphine, once the first-line opioid for syringe drivers, remains compatible with a wider range of co-administered drugs than morphine sulphate, largely because of its high solubility. However, morphine sulphate has become the default in many NHS trusts following periodic diamorphine supply shortages.

Combinations to avoid

Certain drugs are known to cause precipitation, crystallisation or pH-driven incompatibility when mixed:

• Cyclizine is problematic in combination with most opioids at higher concentrations. It precipitates with morphine above approximately 20 mg/mL and is unreliable with haloperidol. Where cyclizine is needed, many palliative care teams now switch to levomepromazine as the antiemetic.
• Dexamethasone is alkaline and should generally not be mixed with other drugs in a syringe driver. If a corticosteroid is needed, it is usually given as a separate subcutaneous bolus injection.
• Diclofenac and ketorolac (NSAIDs) have limited compatibility data and are typically administered via a separate syringe driver if continuous infusion is required.

What the pharmacist checks

Before endorsing a syringe driver prescription, the pharmacist should verify:

1. Drug-drug compatibility — using the Palliative Care Formulary, palliativedrugs.com Syringe Driver Survey Database, or the trust's own compatibility chart. Published evidence is graded: "compatible" means tested and stable for 24 hours; "caution" means limited data; "incompatible" means do not mix.

1. Diluent — water for injection is the standard diluent for most combinations. Sodium chloride 0.9% is preferred for some drugs (e.g. granisetron, octreotide) but causes precipitation with cyclizine. Getting the diluent wrong is a common error.

1. Total volume — the McKinley T34 typically uses a total volume of 17–23 mL over 24 hours. If multiple drugs at high doses push the volume beyond the syringe capacity, a second driver may be needed.

1. Concentration limits — some drugs have maximum recommended concentrations for subcutaneous use. Morphine, for example, should ideally not exceed 40 mg/mL to avoid site reactions, though specialist palliative care teams may use higher concentrations with close monitoring.

1. Stability duration — most combinations are stable for 24 hours at room temperature, but some (particularly those containing metoclopramide or ketamine) may degrade faster. The pharmacist confirms that the prepared syringe will last the intended infusion period.

The community pharmacy role

Most syringe driver prescriptions are written by GP practices or specialist palliative care teams and dispensed by community pharmacies. The community pharmacist's responsibilities include:

• Ensuring adequate stock of injectable formulations, particularly opioids, midazolam and hyoscine butylbromide — these are anticipatory medicines that should be available without delay.
• Checking that the prescribed combination is compatible and flagging concerns to the prescriber before the district nurse collects the medicines.
• Advising on storage requirements — most injectable palliative care medicines are stored at room temperature, but some (e.g. octreotide) require refrigeration.
• Supporting carers with information about what the syringe driver does, what to expect, and when to contact the district nurse.

Community pharmacists who want to develop expertise in this area can access the PharmSee jobs board to explore specialist palliative care roles, or use the salary tool to compare palliative care pharmacist pay with other specialties.

Key resources

The two most widely used compatibility references in UK practice are the Palliative Care Formulary (PCF, published by palliativedrugs.com) and the Syringe Driver Survey Database (SDSD), which collates real-world compatibility reports from palliative care services across the UK. Many NHS trusts maintain local compatibility charts based on these sources, adapted for their formulary.

NICE guideline NG31 (Care of dying adults in the last days of life) recommends that anticipatory prescribing should include medicines for pain, breathlessness, nausea, vomiting, agitation and respiratory secretions — all of which may need to be delivered via syringe driver.

Limitations of compatibility data

Compatibility evidence is observational, not from randomised trials. Most data comes from visual inspection (no precipitate at 24 hours) rather than chemical assay. A combination marked "compatible" in one database may carry a "caution" flag in another if testing conditions differed. When in doubt, the safest approach is to use a second syringe driver rather than risk an untested combination.

For pharmacists looking to explore palliative care career pathways, the PharmSee pharmacy directory can help identify community pharmacies that serve hospice catchment areas across England.