versão impressa ISSN 0256-9574
SAMJ, S. Afr. med. j. vol.99 no.3 Cape Town mar. 2009
Pitfalls of administering drugs via nasogastric tubes
Eric Decloedt; Gary Maartens
Crushing tablets and opening capsules before administration via nasogastric or enteral feeding tubes is a widespread practice. A survey of nursing homes in the UK reported that more than 80% crush tablets on at least a weekly basis, and 40% of nurses crush tablets on every drug round.1 In hospitals in Queensland, Australia, 104 different drugs were recorded as being altered at the bedside, with 84% of the drugs altered on a daily basis;2 tablet crushing accounted for 75% of alterations.2 However, data on the safety and efficacy of administering crushed tablets or opened capsules are limited. Patients may be harmed if the bioavailability of drugs is either impaired, resulting in reduced efficacy, or enhanced, resulting in toxicity. Mechanical failure of nasogastric tubes may also occur as a consequence of administering drugs. Finally, there are important medico-legal implications of administering altered oral drug formulations.
This article highlights the problems associated with administering drugs via nasogastric or enteral feeding tubes, and suggests ways of improving the safety of this practice.
Enteric-coated tablets protect the active ingredient against degradation by gastric acid, and crushing these tablets will reduce the bioavailability of the drug. For example, omeprazole is a lipophilic weak base that is unstable at a low pH and is formulated in a gelatin capsule containing small entericcoated granules that release the drug at a pH of >6.3 Crushing these granules will expose omeprazole to the acidic gastric contents, reducing its half-life to less than 10 minutes at a pH of <4.3 Some formulations, such as nitrates, may be sugar-or film-coated to protect against light and should therefore be administered immediately after being crushed.
Erratic drug concentrations may be caused by crushing controlled-release drug formulations. Decreased bioavailability of a sustained-release formulation of theophylline, which is likely to reduce efficacy, was observed when it was crushed and administered via nasogastric tube.4 Enhanced bioavailability of a crushed sustained-release formulation of nifedipine has been demonstrated,5 which is likely to increase toxicity, graphically illustrated by a case report of fatal cardiac arrest after a patient received crushed sustained-release nifedipine.6
Drug-enteral feed interaction
Flushing crushed tablets down the nasogastric tube with enteral feeds is a common nursing practice that may cause sub-therapeutic concentrations if the administered drug binds to the feed. Serum concentrations of phenytoin are reduced by 72% when it is administered with enteral feeds.7 Phenytoin binds strongly to serum proteins, and it is thought that the decreased absorption of this drug when it is given with enteral feeds may be caused by binding to proteins in the feed. The bioavailability of crushed ciprofloxacin is also markedly reduced when it is co-administered with enteral feed,8 probably owing to ciprofloxacin binding to divalent cations.9 Enteral feeds should be withheld for 2 hours before and after administering drugs known to interact with feeds.
Mechanics of crushing - interactions and hypersensitivity
Crushing different medications in the same receptacle should be avoided owing to possible drug interactions. For example, the bioavailability of tetracycline is decreased when it is crushed together with iron supplements because of formation of poorly soluble tetracycline-iron chelates.10
It is important to clean the pestle and mortar properly before crushing tablets for the next patient to prevent hypersensitivity reactions, which may be triggered after exposure to a small amount of the drug allergen.
Binding to the nasogastric tube
Nasogastric tubes are made of polyvinyl chloride, and certain drugs (e.g. phenytoin11 and carbamazepine suspensions,12 and levothyroxine13 and amiodarone tablets14) have been shown to bind to the wall of the nasogastric tube. Diluting the administered drug and irrigating afterwards with water, sodium chloride or dextrose will decrease binding to the tube.12
Administering crushed medication via a nasogastric tube may occlude the tube. Bulk-forming laxatives, such as ispaghula, form a semi-solid mass that may occlude the tube.9 Cholestyramine, a bile acid sequestrant, and crushed gelatin-coated capsules, such as omeprazole, may also occlude nasogastric tubes.15 Various approaches have been used to clear blocked tubes, but there is no evidence that any of these are more effective than flushing with water.15
Rate of gastric emptying
Gastric emptying may be delayed in critically ill or postoperative patients who require nasogastric tubes. Delayed gastric emptying will reduce the bioavailability of drugs that are either crushed and administered via nasogastric tube or taken orally. Paracetamol16 and atenolol17 were demonstrated to have significantly reduced bioavailability when administered as crushed formulations via nasogastric tube postoperatively compared with intact tablets preoperatively.
Drugs are registered to be administered as particular formulations, and altering the formulation before administration renders their use off-label. Consequently the manufacturer will assume no responsibility for any harm caused to the patient by crushing tablets.1 To minimise liability, the reasons why dose modification needed to be made should be clearly documented. Ideally evidence-based practice should be followed, but there are data supporting the safety of only very few drugs (e.g. antituberculosis drugs,18,19 fluconazole,20 linezolid21 and moxifloxacin22). Importantly, nursing staff should not administer crushed tablets without authorisation, which is the responsibility of the prescriber. Despite the fact that unauthorised crushing of tablets exposes nursing staff to litigation, a study looking at medication errors in psychiatric inpatients found that unauthorised crushing was the commonest error encountered.23 More worrying is the fact that 9.8% of nurses surveyed in nursing homes in the UK would not seek advice before crushing tablets.1
Guidelines for safer practices
Table I lists safer practices for administering drugs to patients with nasogastric or enteral feeding tubes.
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16. Elfant AB, Levine SM, Peikin SR, et al. Bioavailability of medication delivered via nasogastric tube is decreased in the immediate postoperative period. Am J Surg 1995; 169(4): 430-432. [ Links ]
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19. Felton CP. Tips for administering TB medication to children and adults who are unable to swallow pills. Jan 2005. http://www.vdh.virginia.gov/epidemiology/DiseasePrevention/Programs/Tuberculosis/blast/January2005.htm#Tips (accessed 22 October 2008). [ Links ]
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21. Beringer P, Nguyen M, Hoem N, et al. Absolute bioavailability and pharmacokinetics of linezolid in hospitalized patients given enteral feedings. Antimicrob Agents Chemother 2005; 49(9): 3676-3681. [ Links ]
22. Burkhardt O, Stass H, Thuss U, Borner K, Welte T. Effects of enteral feeding on the oral bioavailability of moxifloxacin in healthy volunteers. Clin Pharmacokinet 2005; 44(9): 969-976. [ Links ]
23. Haw C, Stubbs J, Dickens G. An observational study of medication administration errors in old-age psychiatric inpatients. Int J Qual Health Care 2007; 19(4): 210-216. [ Links ]
Eric Decloedt is a registrar in Clinical Pharmacology in the Department of Medicine, University of Cape Town. Gary Maartens heads the Division of Clinical Pharmacology in the same department.
Corresponding author: G Maartens (firstname.lastname@example.org)