Failure to thrive is defined by the Institute of Medicine as "weight loss of more than 5%, decreased appetite, poor nutrition, and physical inactivity, often associated with dehydration, depression, immune dysfunction, and low cholesterol" [1]. It is not a single disease or medical condition. Rather, it is a multidimensional problem that requires a multidisciplinary approach for its treatment. The four chief characteristics of geriatric failure to thrive are impaired physical function, malnutrition, depression, and cognitive impairment [2]. Failure to thrive is commonly used as a nonspecific diagnosis when a patient loses weight due to an unknown cause. After the diagnosis is made, it stimulates further assessment and interventions. Each of the domains of geriatric failure to thrive should be evaluated to determine areas in which the elder is having difficulty.

When developing a treatment plan for patients with geriatric failure to thrive, it is important to take a holistic and interdisciplinary approach in order to address all of the domains of geriatric failure to thrive [2]. Input from medical specialists, nursing staff, social workers, and physical, speech, and occupational therapists should be considered. Treatment efforts addressing only the physical effects of geriatric failure to thrive will most likely not achieve the desired results. For patients with both acute and chronic illnesses, acute infections and conditions should be resolved before a longer term plan is implemented.

Correction of vitamin and nutritional deficits is necessary to reverse malnutrition. As such, collaboration with a dietician and a speech therapist is essential when caring for patients with failure to thrive. The speech therapist can determine the consistency of food best suited for the patient's needs and can recommend modifications to the established diet. The patient may require thickened liquids, puréed diet, mechanical soft diet, or other variation. Some patients will benefit from a restorative dining program, as supervision, encouragement, and socialization may increase food intake.

Discontinuation of restricted diets is an appropriate step for the patient with malnourishment. Therapeutic and restrictive diets do not promote adequate energy intake and should be thoroughly reviewed for each patient [3]. For example, the American Dietetic Association recommends a liberalized diet approach for nursing home residents [4]. A dietician should assess patients' food preferences and determine if oral nutritional supplements would be appropriate and accepted by the patient. The most common approach is to provide liquid nutritional supplements, shakes, and puddings between meals, with the goal of increasing calorie consumption. Geriatric patients may eat most of their calories at breakfast, which should be accommodated. It is important to provide high-calorie, fortified foods when the patient's appetite is greatest [2].

The consequences of vitamin D deficiency include muscle weakness, body sway, osteomalacia, and a tendency for falls and fractures [5]. Many elderly persons are not exposed to enough sunlight each day for adequate vitamin D synthesis. Supplementation with 800 IU of vitamin D daily is recommended and has been shown to reduce falls [6,7].

Vitamin B12 deficiency occurs due to inadequate dietary intake or impaired absorption. It may be associated with neurologic symptoms such as tingling of extremities, fatigue, irritability, depression, weakened concentration, and impaired memory [8]. It is fairly common in the elderly population due to decreased or absent intrinsic factor secondary to atrophic gastritis, achlorhydria, or previous gastric surgery. Deficiency may also be caused by medication side effects, such as those associated with the prolonged use of proton pump inhibitors. Vitamin B12 deficiency is traditionally treated by injectable cobalamin but is also effectively addressed with an oral supplement 1–2 grams daily.

Psychiatric symptoms associated with dementia, such as anxiety or agitation, may cause an increased energy demand. Psychiatric symptoms such as pacing, hyperactivity, repetitive behaviors, insomnia, and mania all can lead to weight loss. These symptoms should be effectively managed. Referral to a psychiatrist or psychologist is recommended in cases of continued weight loss, treatment failures, and additional behavioral problems.

Potential underlying causes of unintentional weight loss should be fully assessed and treated prior to initiating pharmacotherapy for geriatric failure to thrive. Each patient should be evaluated on an individual basis prior to prescribing an appetite stimulant. The medications commonly used and discussed in the following section are not approved by the U.S. Food and Drug Administration (FDA) for appetite stimulation in patients with failure to thrive.

Mirtazapine is an atypical antidepressant with noradrenergic and specific serotonergic effects. It is indicated for major depressive disorder in the elderly; the starting geriatric dose is 7.5 mg at bedtime [15]. This can be increased to a maximum of 45 mg, if necessary. Mirtazapine's antihistamine-like effects are more pronounced at the 15 mg daily dosage. Mirtazapine has been studied for treatment of depression, anxiety, and anorexia nervosa with depression, with weight gain as a secondary endpoint. The weight gain usually occurs early in therapy. It has not been shown to be effective for weight gain in nondepressed individuals. Its sedating effects can be useful for patients with sleep disturbances or anxiety.

Megestrol acetate is a synthetic progestin and antineoplastic agent product, originally used for patients with cancer. Its use for weight loss in geriatric patients without cancer or AIDS is considered off label [15]. In small studies, megestrol has been effective at increasing appetite in certain geriatric patients at higher doses, although the actual impact on weight gain appears slight and side effects are common [17,18,19,20]. It has the potential to increase hypercoagulability, leading to thromboembolism. In addition, megestrol has glucocorticoid-like activity, which can potentially cause adrenal insufficiency and worsening of diabetes. New-onset diabetes and exacerbation of pre-existing diabetes have been reported with long-term use [15]. A case report associated megestrol acetate to two cases of osteoporosis; higher dosages of megestrol are associated with decreased bone density and may be associated with bone loss and fractures [21].