b12 pills or injection Vitamin monthly. Oral B12 vs. B12 Injections:

Not sure how long it will last

In some cases, if symptoms are severe and clearly related to the medication, discontinuation may be considered, though this decision should always be made in consultation with your prescribing clinician

Although the serum MMA concentration reflects an intracellular cobalamin deficiency, other causes of elevated MMA must be considered, such as renal failure, reduced plasma volume reduction, and abnormalities in hepatic methyl-malonyl CoA mutase activity [15,47]

A vitamin B12 injection is generally very safe and has no side effects including administration in higher doses

That is the right mental model for reasoning about supply and frequency