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Part II Nutrition Assessment, Consequences, and Implications

TABLE 17.6 Common Genetic Variants in Phase I Drug Metabolizing Enzymes Gene

Selected Medication Substrates CYP2D6

Amitriptyline, atomoxetine, carvedilol, chlorpheniramine, chlorpromazine, citalopram, clomipramine, clozapine, codeine, debrisoquine, desipramine, dextromethorphan, doxepin, flecainide, fluoxetine, fluvoxamine, gefitinib, haloperidol, imipramine, maprotiline, metoprolol, mexiletine, mianserin, morphine, nortriptyline, paroxetine, risperidone, tamoxifen, thioridazine, timolol, tolterodine, tramadol

CYP2C19

Lansoprazole, omeprazole, pantoprazole, rabeprazole, phenytoin, phenobarbitone, amitriptyline, carisoprodol, clopidogrel, citalopram, clomipramine, cyclophosphamide, hexobarbital, imipramine, indomethacin, nelfinavir, nilutamide, primidone, progesterone, proguanil, propranolol, teniposide, warfarin

CYP2C9 CYP3A4

Irbesartan, losartan, phenytoin, cyclophosphamide, tamoxifen, fluvastatin, celecoxib, diclofenac, ibuprofen, meloxicam, naproxen, glibenclamide, glimepiride, glipizide, tolbutamide, warfarin

Clarithromycin, erythromycin, telithromycin, quinidine, alprazolam, diazepam, midazolam, triazolam, cyclosporine, tacrolimus, indinavir, nelfinavir, ritonavir, saquinavir, cisapride, astemizole, chlorpheniramine, terfenadine, amlodipine, diltiazem, felodipine, lercanidipine, nifedipine, nisoldipine, nitrendipine, verapamil, atorvastatin, cerivastatin, lovastatin, simvastatin, estradiol, hydrocortisone, progesterone, testosterone, alfentanil, aprepitant, aripiprazole, buspirone, caffeine/ergotamine, caffeine, cilostazol, cocaine, codeine, dapsone, dextromethorphan, docetaxel, domperidone, eplerenone, fentanyl, finasteride, imatinib, haloperidol, irinotecan, LAAM, lidocaine, methadone, nateglinide, ondansetron, pimozide, propranolol, quetiapine, quinine, risperidone, salmeterol, sildenafil, sirolimus, tamoxifen, taxol, terfenadine, trazodone, vincristine, zaleplon, ziprasidone, zolpidem

CYP3A5 CYP2B-6

Broad overlap with CYP3A4

Bupropion, cyclophosphamide, diazepam, efavirenz, ifosfamide, ketamine, methadone, MDMA, meperidine, mephenytoin, midazolam, nevirapine, nicotine, propofol, selegiline, tamoxifen

Source: Adapted with permission from Pinto N, Dolan M. Clinically relevant genetic variations in drug metabolizing enzymes. Current Drug Metabolism. 2011;2(5):487-497.

Medication and Enteral Nutrition Interactions

Continuous enteral feeding may be an effective method of providing nutrients to older adults who are unable to swallow or eat adequately, depending on the wishes of the person and signed advance directives. However, use of the feeding tube to administer medication can cause problems. When liquid medications are mixed with enteral feeding formulas, incompatibilities may occur. Types of physical incompatibility include granu- lation, gel formation, and separation of the enteral product, frequently resulting in clogged feeding tubes and interruption of the nutrition delivery to these indi- viduals. Examples of drugs that can cause granulation and gel formation are ciprofloxacin (Cipro) suspension,

chlorpromazine (Thorazine) concentrate, ferrous sulfate elixir, guaifenesin (Robitussin), and metoclopr- amide (Reglan) syrup (31).

Emulsion breakage also commonly occurs when acidic pharmaceutical syrups are added to enteral for- mulas. This reaction is more common in enteral formu- las with intact protein and is less common with hydrolyzed protein or free amino acids (32). Most compatibility studies of medication and enteral products have focused on the drug’s effect on the integrity of the enteral product. More important is the effect of the enteral product on the bioavailability of the drug. This area requires much more research, as the placement of feeding tubes is becoming a more common practice. Bioavailability problems are common with phenytoin (Dilantin) suspension and