A serious shortage of metformin modified-release (XR) 500mg tablets has led to recommendations for patients with type 2 diabetes to be have their medication substituted by a pharmacists.

The TGA has issued a Serious Shortage Medicine Substitution Notice allowing pharmacists to substitute alternative options of immediate-release metformin 500mg or metformin modified-release 1000 mg tablets, without the prior approval of the doctor.

The TGA advises that any metformin substitution by pharmacists must be done with the full informed consent of the patient, with their doctor being informed of the substitution as soon as possible.

“Please refer patients to their doctor or diabetes nurse educator if substitution is not appropriate or where alternative treatments other than substitution may be more appropriate (e.g. alternative strengths, fixed-dose combination products or therapeutic alternatives),” the TGA advises.

Patients who are switched should be told to undertake more frequent blood glucose monitoring, be aware of more frequent dosing intervals and to see their doctor if they have any concerns about their glycaemic control. They should also be warned about a possible increase in gastrointestinal adverse events with a switch to immediate-release metformin

Doctors are also advised to be aware of the shortage when prescribing metformin.

“If based on your professional and clinical assessment, a change to metformin treatment is deemed appropriate, discuss the changes and counsel your patient on possible adverse effects (e.g. gastrointestinal tolerability),” the TGA advises.

The substitution notice applies until 31 July 2020.