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PENG 2006 R.White Drug Nutrient Interactions Pharmacological, Physical and Pharmacokinetic Rebecca White Lead Pharmacist; Surgery, GI & Nutrition John.

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Presentation on theme: "PENG 2006 R.White Drug Nutrient Interactions Pharmacological, Physical and Pharmacokinetic Rebecca White Lead Pharmacist; Surgery, GI & Nutrition John."— Presentation transcript:

1 PENG 2006 R.White Drug Nutrient Interactions Pharmacological, Physical and Pharmacokinetic Rebecca White Lead Pharmacist; Surgery, GI & Nutrition John Radcliffe Hospital, Oxford

2 PENG 2006 R.White Nutrition and Drugs Identifying the Issues Drug effects on nutritional intake Drug effects on nutrient metabolism Nutrient effects on drug metabolism Drug administration via enteral feeding tubes –Practical administration Equipment, formulation choice –Physical Interactions –Pharmacokinetics interactions –Legal considerations

3 PENG 2006 R.White Drug administration via enteral feeding tubes… …a multidisciplinary problem The Dietitian…wants to ensure the patient is receiving the full volume of feed prescribed The Pharmacist…wants to make sure the drugs are administered safely and at effective doses The Doctor…wants the drug to work and doesnt want to have to replace the tube The Nurse…has to administer the medicine and feed without harming the patient or themselves The Patient…needs their feed and their medication and may need to be independent

4 PENG 2006 R.White Side Effects of Drugs Influence on Nutrient Intake Reduced Gastric Emptying –Paralysing Agents, Anticholinergics, Opiates Increased Gastric Emptying –Metoclopramide, Erythromycin, Cisapride Anorexia Taste disturbance

5 PENG 2006 R.White Drug Effects on Nutrient Metabolism

6 PENG 2006 R.White Folate Folic acid is involved in DNA synthesis Deficiency causes: –Megaloblastic anaemia –Diarrhoea Folate metabolism DihydrofolateFolic Acid Tetrahydrofolate Dihydrofolate reductase (DHFR)

7 PENG 2006 R.White Folate Deficiency DHFR Inhibitors Methotrexate Trimetrexate Pentamidine Proguanil Pyrimethamine Trimethoprim Triamterene Impaired Absorption or Utilisation Alcohol Metformin Nitrofurantoin O.C.P Phenobarbitone Phenytoin (Carl, 1992) Primidone Sulphasalazine (Pironi, 1988)

8 PENG 2006 R.White Thiamine (Vitamin B1) Deficiency causes Beri Beri –Lactic acidosis, cardiovascular, cerebral and peripheral neurological impairment Drugs associated with thiamine deficiency –Frusemide (Seligmann et al, 1991)

9 PENG 2006 R.White Pyridoxine Co-factor for the transaminases and for decarboxylation of amino acids Deficiency causes: –Peripheral neuropathy –Dermatitis and rough skin –Irritability –Hypochromic anaemia –Glossitis

10 PENG 2006 R.White Pyridoxine Deficiency Isoniazid Phenelzine Penicillamine Oral contraceptive pill Hydralazine Phenytoin Theophylline (Delport et al, 1988)

11 PENG 2006 R.White Effect of Nutrition on Drug Pharmacokinetics Malnutrition –Low plasma proteins Altered protein binding Increased volume of distribution –Reduced hepatic enzyme function Nutrition composition

12 PENG 2006 R.White Drug Administration via Feeding Tubes

13 PENG 2006 R.White Before administering a drug via a feeding tube…...things to consider Is this drug needed at all? Can I administer it via any other route? Does it come in a suitable formulation for administering down a tube? If not, can I crush the tablet/open capsule? Does it interact with the enteral feed? Is the drug absorbed from where it is being delivered to?

14 PENG 2006 R.White Choice of formulation Solution Syrup Suspension Soluble tablet Effervescent tablet Dispersible tablet

15 PENG 2006 R.White

16 Factors Affecting Drug & Formulation Tube Blockage GI side effects Pharmacokinetics

17 PENG 2006 R.White Tube Blockage Bore size of Tube Feed related –Inadequate flushing –Warm water flushes –Pancreatic enzyme locking (Sriram, 1997) Drug related –Medication significant cause of tube blockage (Marcuard & Stegall, 1990) –Inappropriate formulations Physical Interactions –Sucralfate (Aggozzine et al, 1983) Aluminium binds to protein to form insoluble complex (bezoar). –High electrolyte containing solutions

18 PENG 2006 R.White


20 GI Side effects GI Side effects (Edes, 1990) Not all liquids are suitable –Osmolality (Dickerson & Melnik, 1988) –pH –Viscosity –Sorbitol Content (Greenwood, 1989) Kay-Cee-L liquid Baclofen liquid

21 PENG 2006 R.White Pharmacokinetics Changing between formulations of the same drug –Bioavailability –Dosing Frequency Exit point of feeding tube –Site of absorption of drug –Significant for Phenytoin (Rodman et al, 1998) and Ketoconazole (Adams, 1994)

22 PENG 2006 R.White Drug Interactions Phenytoin (Bauer, 1982; Summers & Grant,1989) –Enteral feed reduces drug absorption by 75% Theophylline (Gal &Layson, 1986) –Interaction poorly defined and very variable Warfarin (Petretich, 1990) –Binds to protein in enteral feed. Be aware of variable vitamin K intake

23 PENG 2006 R.White Ciprofloxacin (Mueller et al, 1994) –Binds to divalent ions. Absorption reduced by 30%. Peak levels reduced by up to 50% Tetracyclines –Absorption reduced by 70-80% in the presence of milk or dairy products –Stop feed 1 hour before and after feed? Rifampicin –Absorption reduced by food –Give during break in feed to maximise absorption Drug Interactions

24 PENG 2006 R.White Practical Solutions Simplify drug choice to once daily preparations with long half lives Document feeding and drug regimen accurately Avoid frequent changes in feeding regimen and drug regimen Stabilise regimen at earliest opportunity

25 PENG 2006 R.White Clinical Monitoring Very little information relating to clinical significance of interactions No data for most drugs Clear monitoring parameters

26 PENG 2006 R.White Information Available Available from

27 PENG 2006 R.White Summary Broad range of complex interactions Range of clinical outcomes Requires multidisciplinary input Correct identification of issues Use of correct formulation Practical application of pharmaceutical and clinical skills

28 PENG 2006 R.White References White.R, Ashworth.A. (2000) How drug therapy can affect, threaten and compromise nutritional status. Journal of Human Nutrition and Dietetics 13(2):119- 129 Adams.D (1994) Administration of drugs through a jejunostomy tube. Br.J. Int.Care 4:10-17 Thompson.F.C, Naysmith.M.R, Lindsay.A (2000) Managing drug therapy in patients receiving enteral and parenteral nutrition. Hospital Pharmacist 7(6):155-164 Boullata.J.I, Armenti.V.T (2004) Handbook of drug- nutrient interactions. Humana Press, NJ, USA BPNG Handbook of Drug Administration via Enteral Feeding Tubes (2006), Pharmaceutical Press, (in press)

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