A nasogastric tube and four formulations that should not be crushed
Mr Doug Harris is 71 and was admitted 10 days ago with a left hemisphere stroke. He now has a fine-bore nasogastric tube in situ, is tolerating feed and is transferring to a rehabilitation unit tomorrow. His discharge medicines are oxycodone controlled-release 10 mg twice daily, sodium valproate modified-release 500 mg twice daily, metformin XR 1000 mg each evening, aspirin 100 mg enteric-coated daily and paracetamol 1 g four times daily as required. His eGFR is 58 mL/min/1.73 m2 and his swallow has not been reassessed. The rehabilitation unit has asked for the medicines to be dispensed as tablets for the nurses to administer down the tube.
1. Which of these formulations must not be crushed or opened for administration through this tube? Explain the pharmaceutical reason and the clinical consequence for each.
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| Medicine | Why it cannot be crushed | Consequence |
|---|---|---|
| Oxycodone CR 10 mg | The tablet is built on a hydrophilic polymer matrix (or wax matrix) that slowly erodes over 12 hours | Crushing releases the entire 20 mg dose within minutes. In an elderly, largely opioid-naive stroke patient that is a potentially fatal dose-dumping event - profound sedation and respiratory depression |
| Sodium valproate MR 500 mg | Modified-release (coated/matrix) design smooths absorption over 12 hours | Crushing produces a rapid peak: sedation, ataxia, tremor, nausea, and loss of seizure cover later in the dosing interval |
| Metformin XR 1000 mg | Swelling polymer matrix that also makes a bulky, sticky residue | Loss of the extended profile with more gastrointestinal upset, and the swollen residue readily blocks a fine-bore tube |
| Aspirin 100 mg enteric-coated | The coat is designed to resist gastric acid and dissolve in the duodenum | Least dangerous of the four - the coat's gastric-protection purpose is partly bypassed by tube delivery - but crushing still risks gastric irritation and tube blockage. An immediate-release product is preferable |
Paracetamol 1 g is an ordinary immediate-release tablet and is not a formulation problem.
The general principle: crushing a modified-release or enteric-coated product converts a controlled delivery system into an uncontrolled one. This is a change to an unapproved dose form and the pharmacist shares accountability for it, so it should be a documented, prescriber-endorsed decision rather than an instruction to nursing staff.
2. Propose an interim regimen for analgesia and seizure cover that can go down the tube today. Show your dose conversion reasoning and what you would monitor.
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Analgesia
- Current oxycodone exposure: CR 10 mg twice daily = 20 mg per day.
- Controlled-release to immediate-release by the same route is a 1:1 conversion of total daily dose. Use oxycodone oral liquid 5 mg/5 mL: 2.5-5 mg (2.5-5 mL) every 4-6 hours as needed, or 5 mg every 6 hours regularly with the same dose for breakthrough.
- He is opioid-naive and elderly, so start at the low end and reassess with a pain score. Monitor sedation score, respiratory rate, bowel function and nausea; have naloxone accessible and ensure laxatives are charted.
Epilepsy cover
- Current valproate exposure: MR 500 mg twice daily = 1000 mg per day.
- Switch to sodium valproate oral liquid 200 mg/5 mL at the same total daily dose, initially divided into two or three doses (for example 12.5 mL twice daily, or 10 mL mane, 7.5 mL midi and 7.5 mL nocte).
- The MR-to-immediate-release switch alters the absorption profile, so measure a trough valproate level 3-5 days after the change and watch for sedation, tremor and vomiting.
- Important interaction: aspirin displaces valproate from albumin and inhibits its glucuronidation, raising the free fraction. With aspirin on board I would watch more closely for valproate toxicity and discuss with the prescriber whether the aspirin is still indicated.
Also: the liquid is alkaline and unpalatable - give it diluted and flush well afterwards. Document the conversions and the monitoring plan in the discharge summary so the rehabilitation unit continues them.
3. The nursing staff ask for general rules on giving medicines down the tube. What do you tell them, and what else needs to be organised before discharge?
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Administration rules
- Give one medicine at a time; never mix several crushed tablets or liquids together.
- Flush with 15-30 mL of water before, between and after doses. Flushing is what prevents tube blockage and drug-drug interaction within the tube.
- Do not add medicines directly to the enteral feed container, and consider pausing the feed briefly around doses.
- Use a designated crushing device or mortar and pestle, crush and disperse in water immediately before use, and use an oral syringe for liquids.
- Confirm tube position and tube type - fine-bore tubes block easily, which is another reason to prefer liquid formulations.
- Remember that the tube bypasses the mouth, so oral hygiene and mouth care still matter.
Before discharge
- Obtain a speech pathology swallow assessment - the tube may be short-term and the whole problem may resolve.
- Get prescriber authorisation for each formulation change; do not let nursing staff make the decision at the bedside.
- Update the medication chart and the discharge summary with the new products, doses, timing and monitoring (opioid sedation score, valproate level).
- Counsel the family on what each medicine is for and what to do if a dose is missed.
- Give the rehabilitation unit a written administration plan, and a contact number for the pharmacy.