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How to avoid dosing errors

Study documents a need for greater dosing precision

Cheryl Guttman Krader

Posted: Sunday, September 1, 2019

Intracameral injection of cefuroxime at the end of the case has become standard practice in the UK for preventing endophthalmitis after cataract surgery, but dosing errors are relatively common, according to a study presented at the 2019 annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) in Vancouver, Canada.

The recommended dose of cefuroxime for prophylaxis of postoperative endophthalmitis after cataract surgery is 1mg/0.1mL. In the study, the actual dose administered was determined in a series of 26 patients by comparing the pre- and post-injection volumes in the syringe. Two surgeons at Moorfields Eye Centre, Bedford Hospital, Bedford, UK, performed all of the operations, and a 1mL insulin syringe was used for the intracameral injection in all cases.

In the study, the mean pre-injection volume was 0.36±0.11mL, the mean post-injection volume was 0.24±0.11mL and the mean injected volume was 0.12±0.02ml, exceeding the standard dose by 20%. Dosing errors occurred in six cases (23%), reported Simrun Singh Virdee MBBS.

“The occurrence of dosing errors with intracameral cefuroxime should not be disregarded because underdosing might increase susceptibility to postoperative infection, while overdosing can increase the risk of drug-related toxicity,” said Dr Virdee.

“Because the intracameral injection is performed without direct visualisation of the syringe, we recommend that surgeons check the syringe pre- and post-injection to ensure that the correct dose was administered. Although it seems to be an obvious step, we believe it is something that it is not being done routinely.”

Dosing errors included three cases of overdosing and three cases of initial underdosing. In the cases of overdosing, there was accidental loss of the antibiotic prior to injection that necessitated repriming the syringe and led to excess injection. In the cases of underdosing, the error was identified when the post-injection volume was measured, allowing immediate correction.

Dr Virdee noted that the average 20% excess administered dose of cefuroxime recorded in the study is below the toxic range. He reported that no cefuroxime-related toxicity was observed in the series. Nevertheless, concern about safety in cases of overdosing is justified considering that even a standard dose has been reported to cause retinal toxicity, Dr Virdee said.

He suggested that a graduated pre-made syringe providing tactile feedback could help overcome the potential for cefuroxime dosing errors that can occur with current preparation methods that involve loading the syringe with exactly 0.1mL or with extra volume to allow for accidental loss.

Simrun Singh Virdee: simvirdee@aol.com