Unclassified Interactions

Effects of Nutritional Status on Drugs
The presence of nutritional abnormalities may have an effect on drugs. Drug
dosages may need adjustment based on actual body weight for some drugs. Other
drugs may need to be dosed differently in obese, normal, and underweight patients,
based on actual, ideal, or an adjusted body weight corrected for lean body mass.
Somatic protein status may affect the dosing of medications that bind to somatic
protein.
Effects of Drugs on Nutritional Status
The converse effect may also be observed. Some drugs will have an effect on a
patient’s nutritional status. The mechanisms for these effects are varied and are
usually due to drug side effects. Medications may have direct effects on the gastrointestinal
tract (GIT), which can affect food ingestion. Nonsteroidal antiinflammatory
agents, commonly used to treat arthritis, including aspirin, can cause irritation
of the upper gastrointestinal mucosa and even cause ulcers. This can depress appetite
and produce weight loss. Chemotherapeutic agents used to treat cancer can affect
rapidly growing tissues, particularly the lining of the GIT. Nausea is a common side
effect and will interfere with eating. Some patients develop oral and esophageal
lesions that cause pain upon chewing and swallowing (odynophagia), which limits
oral intake. Antibiotics can suppress commensal bacteria, and this may result in
overgrowth of other organisms such as Candida albicans. Overgrowth in the GIT
may produce malabsorption and, subsequently, diarrhea. Overgrowth in the mouth
may result in candidiasis or thrush, which can reduce oral intake. Drug-related
dysgeusia may result in alteration of taste perceptions and avoidance of certain foods.
Many drugs reduce salivation and cause dryness of the mucus membranes. This may
also inhibit oral intake. Nausea, vomiting, diarrhea, and constipation are ubiquitous
side effects associated with most medications and even with placebo medications.
Again, oral intake of food may be reduced due to these effects.
Some drugs have a direct effect on digestion. Orlistat (Xenical®) interferes with
the digestion and subsequent absorption of fat intentionally to enhance weight loss.
Pancreatic enzymes enhance digestion for patients with limited amounts of digestive
enzymes. Several types of drugs interfere with hydrochloric acid production, but
none have demonstrated a significant effect on macronutrient absorption. Increasing
the gastric pH may affect absorption of weakly acidic drugs, as well as iron and
vitamin B12. Intrinsic factor requires an acidic pH to bind with vitamin B12. Without
the acidic pH, B12 deficiency can have an irreversible effect on brain function if
prolonged without treatment.
Some drugs have a direct effect on appetite. The amphetamines and their derivatives
were long used for weight loss. Unfortunately, side effects and transient results
for most patients have limited their usefulness. Sibutramine (Meridia®) has both an
appetite suppressing effect and a mild antidepressant effect and is approved by the
Food and Drug Administration (FDA) for weight loss. These drugs are discussed in
more detail in the Chapter 11, Obesity and Appetite Drugs, and Chapter 7, Gastrointestinal
and Metabolic Disorders and Drugs.
Dronabinol (Marinol®), also known as THC (from tetrahydracannabinols), the
active principle in cannabis, is also used as an appetite stimulant. Oxandrolone
(Oxandrin®) is an anabolic steroid approved for weight gain. Megesterol (Megace®),
a progestin used to treat certain types of cancer, is also indicated to enhance appetite.
Cyproheptadine (Periactin®) has been used to enhance appetite, although this is an
off-label use and not an FDA-approved indication.
Besides drugs specifically indicated to effect changes in appetite, some drugs may
affect appetite as a side effect. Several antidepressants have been observed to consistently
increase or decrease appetite. When these drugs are prescribed, their relative
side-effect profiles in relation to weight change may make one or another a preferred
agent for an individual who would benefit from an increase or decrease in weight.