Page 1148 - Small Animal Clinical Nutrition 5th Edition

1196 Small Animal Clinical Nutrition

neys may change the rate of urinary elimination. Likewise,
Table 69-1. Factors affecting the disposition of drugs that can
VetBooks.ir be influenced by foods. changes in functional morphology or pathology due to specific
nutrient deficiencies or excesses can affect drug clearance.
Absorption
GI transit time
GI luminal environment GENERAL EFFECTS OF FOOD AND
Enterocyte function DRUG INTERACTIONS
Electrochemical gradient across the GI mucosa
pH gradient across the GI mucosa
Distribution Ameliorating Potential Adverse Effects
Drug-binding proteins
Blood cells that bind or metabolize drugs The composition and volume of food consumed can modify the
Metabolism degree of GI irritation caused by concurrently administered oral
Site of metabolism
Organ drugs. Enteral and parenteral fluid intake can augment drug
Tissue absorption and distribution and protect against renal damage
Cell type induced by nephrotoxic agents. Supplementation with specific
Cell organelle
Biotransformation pathways nutrients may prevent deficiencies secondary to adverse drug
Phase I oxidative vs. phase II conjugative pathways effects on nutrient absorption and metabolism.
Cofactors required for metabolism
Vitamins Potentiating Drug Action
Minerals
Reducing agents Specific nutrients can increase drug effects by facilitating GI
Non-nutrient enzyme inducers absorption, improving drug distribution or decreasing drug
Phytochemicals
Synthetic contaminants metabolism and excretion. Furthermore, some nutrients may be
Preservatives necessary for optimal drug effects (e.g., arginine for nitric oxide
Excretion production, cysteine for nitroglycerin action and carnitine for
Route of excretion
Biliary optimal activity of cardiac glycosides).
Fecal
Mammary Impaired Drug Action
Pulmonary
Renal Impaired drug action is the adverse effect most often consid-
Salivary ered when evaluating nutrient-drug interactions that impair
Sweat therapeutic efficacy. These adverse effects may result from
Electrochemical gradient across mucosa of excretory organs
Rate of excretion decreased drug absorption, inadequate amounts of the drug
reaching the site of action, or nutrient interference with the
drug’s action. Drug action may be impaired for variable periods
of time after food composition and feeding behavior are altered,
if target cell receptor numbers or affinity are suppressed or
Table 69-2. Selected factors that can determine the effects of
nutrients on drug absorption. long-lived biotransforming enzyme systems have been induced.
Factors Examples Adverse Side Effects
Physiochemical properties Lipophilic or hydrophilic
of drugs Pathologic reactions to nutrient-induced changes in drug dis-
Drug formulation Tablet, capsule or liquid tribution and metabolism can be of greater immediate conse-
Meal type Volume, temperature,
moisture quence than loss of disease control following impaired drug
Drug dose Amount and concentration action. Drug metabolism and excretion routes may be altered,
Route of administration By mouth, gastric tube, etc. resulting in accumulation of toxic quantities of the agent itself
Order of administration Pre- vs. postprandial
Time interval between food Phase of digestion or the products of its biotransformation. This phenomenon is
and drug administration similar in principle to adverse interactions between concurrent-
Owner/patient compliance Mixing drugs and food for ly administered drugs, but may be more difficult to identify
ease of administration
because mental recollection and written records of nutrient
intake are not usually as complete as for administration of phar-
maceutical agents.
alter pharmacokinetics and apparent drug effectiveness.

Indirect Physiologic Effects EFFECTS OF NUTRIENTS
The rate of drug elimination is also affected by changes in ON DRUG ABSORPTION
blood flow and drug delivery to the principal organs of metab-
olism for that particular agent.Thus, postprandial alterations in General Observations
blood flow to the liver may affect drug clearance from the por- The absorption of orally administered drugs may be: 1)
tal and systemic circulation, and altered blood flow to the kid- decreased, 2) delayed, 3) unaffected or 4) enhanced by the con-