Is Oral Vitamin B12 as Effective as Intramuscular Injection?

Clinical Question

Can vitamin B12 deficiency be treated orally?

Evidence-Based Answer

In patients with vitaminB12 deficiency, two oral regimens have been shown to achieve neurologic and hematologic response in the short term. Effective dosages were (1) 2,000 mcg daily or (2) 1,000 mcg daily for 10 days, then weekly and monthly.

Practice Pointers

Vitamin B12 deficiency causes macrocytic anemia, fatigue, loss of appetite, and mood disturbances. It also can cause serious neurologic and neuropsychiatric illness such as paresthesias, ataxia, and memory loss. The process of vitamin B12 absorption can be impaired at the level of the stomach, where intrinsic factor is produced, or at the level of the terminal ileum, where intrinsic factor bound to vitamin B12 is absorbed. Medications such as metformin (Glucophage) or antacids also can impair absorption. A small amount of vitamin B12 is absorbed by passive diffusion without intrinsic factor.

Traditionally, vitamin B12 replacement has been administered intramuscularly because absorption through the gastrointestinal tract is deficient. However, this route is less convenient for patients than oral medication and may not be covered by health insurance. Because a small amount of vitamin B12 is absorbed by passive diffusion, megadoses of oral vitamin B12 medication have been used as a cost-saving and more comfortable alternative to intramuscular B12 administration.1

Vidal-Alaball and colleagues searched for randomized controlled trials comparing oral with intramuscular administration of vitamin B12. They found two trials with a total of 93 patients who were followed for between 90 days and four months. All patients had vitamin B12 deficiency, defined as vitamin B12 level less than 244 pg per mL (180 pmol per L). Some patients had conditions that cause malabsorption from the gut, but no patients with inflammatory bowel disease or celiac disease were included in either study. One study used a daily oral dosage of 2,000 mcg, and the other an oral dosage of 1,000 mcg daily for 10 days, then weekly for four weeks, then monthly for life. In both studies, high-dose oral B12 was as effective as intramuscular injection at achieving neurologic and hematologic response.

Vitamin B12 is available over the counter in the form of tablets (100, 500, 1,000, or 5,000 mcg) and lozenges (50, 100, 250, or 500 mcg).

Anticholinergic Drugs for Overactive Bladder

Clinical Question

Which anticholinergic drug regimen is most effective for overactive bladder?

Evidence-Based Answer

Tolterodine (Detrol) is as effective as immediate-release oxybutynin (Ditropan) and causes less dry mouth. A dose of 1 mg tolterodine twice daily is as effective as higher dosages of tolterodine. Extended-release preparations have less risk of dry mouth but are more expensive.

Practice Pointers

Overactive bladder syndrome is characterized by the sensation of urgency to urinate, sometimes with involuntary leakage (urge incontinence), with no metabolic, mechanic or neurologic cause. Most patients also have frequency and nocturia. It is thought to be caused by an overactive detrusor muscle surrounding the bladder. Overactive bladder syndrome can cause significant discomfort and is more common in older persons.

Options for treatment include nonpharmacologic approaches such as adjusting urine output to 1 to 1.5 L daily, urge-suppression training, bladder retraining, and prompted voiding. Drug treatments include oxybutynin, tolterodine, propantheline (Pro-banthine), dicyclomine (Bentyl), and tricyclic antidepressants.1

In a 2002 Cochrane review,2 Hay-Smith and colleagues determined that, compared with placebo, anticholinergic medications produce a statistically significant improvement in symptoms. To determine which anticholinergic medication regimen is most effective, Hay-Smith and colleagues searched for randomized controlled trials that compared anticholinergic drugs in adults with overactive bladder symptoms.

The two most studied drugs were oxybutynin and tolterodine. In studies comparing the abilities of tolterodine and oxybutynin in reducing leakage episodes and micturitions, the two drugs were similar in effect. However, patients receiving tolterodine were less likely to withdraw because of adverse events (7 versus 12 percent, respectively) and had one half to one third the risk of dry mouth. In addition, 1 mg of tolterodine twice daily was as effective as the more standard dosage of 2 mg twice daily and caused fewer adverse effects. Limited data showed extended-release preparations were equally as effective as immediate-release preparations with fewer adverse effects.

Tolterodine and oxybutynin are available in the following forms: tolterodine immediate-release, 1- and 2-mg capsules; tolterodine extended-release, 2- and 4-mg capsules; oxybutynin immediate-release, 5-mg tablets and 5-mg (5-mL) syrup; oxybutynin extended-release, 5-mg tablets and a transdermal patch that delivers 3.9 mg daily.