Concentration confusion

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PDL has issued guidance on the difference between milligrams and millilitres – especially regarding doses for children during the cold season, as well as methadone

“The colder weather sees a predictable increase in the prescribing of prednisolone oral liquid for children,” observes PDL in a practice update.

“Often these prescriptions are written by after-hours or hospital-based doctors and many will be handwritten.

“As dosages are typically based on the child’s weight, the prescribed dose is frequently written in milliGRAMS instead of milliLITRES.”

PDL says that the seasonal increase in prescribing of this medicine has historically led to more reports of this error to PDL, because the dose in milligrams has been mistakenly translated into millilitres.

“This can lead to the patient receiving a dose of prednisolone five times prescribed because of the concentration of the available products,” it says.

It gives a case scenario in which an 11-month-old was prescribed prednisolone 10mg daily for three days.

In this case, the directions were inadvertently recorded as 10ml, and dispensed with this dose.

“The infant was given the higher dose by the parents and shortly afterwards started displaying symptoms of discomfort and agitation,” says PDL.

“The parents took the child to the local hospital where a doctor identified the incorrect dose. The doctor reassured the parents that there was no risk of long-term harm to the child and informed the pharmacy of the error.

“The pharmacist contacted the parents to apologise and ascertain the child’s state of health.

“The parents were understandably upset with the pharmacist and sought reassurance that this sort of error would not occur in the future.”

PDL says that while there was no harm to the patient in this particular case, the likelihood of a formal complaint is higher when an error involves a child.

This isn’t the only concentration error the organisation receives reports about.

“Other reports to PDL involving similar errors with misinterpretation of doses in millGRAMS rather than milliLITRES include antibiotic mixtures, especially amoxicillin +/- clavulanic acid and omeprazole mixtures that are compounded for young children with reflux,” it says.

It offers a second case scenario, in which a prescription for omeprazole suspension 5mg/ml with a dose of 5mg bd was ordered by a paediatrician for a two-month-old child.

“The medicine was correctly prepared however the dose was misinterpreted and labelled as 5ml bd,” PDL notes.

“The child was given the higher dose on two occasions before the parent contacted the pharmacy concerned that it was difficult to administer this volume to the infant.”

The error was then identified, and again, the child suffered no harm from the higher dose.

A third area where concentration confusion reigns is methadone liqud, PDL warns.

“Once again, the dose is prescribed in milliGRAMS and measured in milliLITRES,” it says, outlining a third case scenario.

“Several factors have been identified as a cause of this error including familiarity of the client, an assumption of the dose based on repetition of preparation, distraction by clients and others at the time of measuring the dose, multiple clients receiving the medicine daily and the involvement of locums or other pharmacists less familiar with the process.

“The product is 5mg/ml and there is potential for consequences from a dose FIVE times that prescribed, especially given the nature of the drug.”

In the experience of PDL’s professional officers, resolving such a situation can be difficult as pharmacies do not always have the best current contact details for patients receiving methadone.

“In a situation when the client is unable to be contacted other actions may be warranted such as requesting the police to conduct a welfare check on the client,” PDL warns.

“Take steps to minimise the risk of errors in medicines being prescribed by milligram, including use of a shelf tags or laminates where prednisolone liquids are stored, and reminding staff to check the dose in mgs and mls,” it says.

“Other actions could be including a warning message in the dispense system’s drug file for these medicines.”

PDL encourages its members to contact it on 1300 854 838 if this topic raises any concerns. PDL membership includes 24/7 access to speak with a Professional Officer for immediate advice and incident support, Australia wide. This includes leaving a comment or question for Professional Officers via PDL’s blog at

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