Misuse of liquid phosphate laxatives
used for bowel preps
From the July 12, 2000 issue
FDA ADVISE-ERR
Editor's note: FDA ADVISE-ERR is a new error prevention
feature provided by FDA's Office of Post-marketing Drug Risk
Assessment (OPDRA). An active medication error prevention
effort is underway at OPDRA. Pharmacist Jerry Phillips heads
the Medication Error Program, which is staffed with other
pharmacists and support personnel. Among their many duties,
program staff reviews medication error reports sent to the
USP-ISMP Medication Errors Reporting Program and MEDWATCH,
evaluates causality, and trends the data to provide feedback
to others at FDA. ISMP is cooperating with OPDRA to facilitate
widespread communication of medication error issues under
scrutiny at FDA. The first of these reports appears below.
FDA and ISMP encourage you to share this information with
all who may benefit.
Phosphate intoxication from misuse of oral and rectal solutions
of sodium phosphates has been the subject of many reports1-5.
FDA, USP and ISMP recently learned of the death of a hospitalized,
frail woman who was prescribed "one and one-half bottles"
of FLEET PHOSPHO-SODA (2.4 g monobasic sodium phosphate
and 0.9 g dibasic sodium phosphate/5 ml) orally with a repeat
dose in preparation for a colonoscopy. The order was received
in a small hospital after the pharmacy closed for the evening.
A nursing supervisor entered the pharmacy and obtained three
bottles of the product. The first dose was given at 6 p.m.
followed by another dose at 8 p.m. After a night of pain,
anxiety, respiratory difficulty, and several episodes of cardiac
arrest, the patient expired. When hospital staff reviewed
the event, phosphate overdose was suspected. Before Fleet
Phospho-soda was administered, the patient's calcium and phosphorous
levels were 8.8 (n=8.5-10.5 mg/dL) and 1.5 mg/dL (n=2.5-4.5
mg/dL), respectively. When the patient arrested, her calcium
and phosphorous levels were 6.2 and 27.7, respectively. The
patient was also in metabolic acidosis with a pH of 7.03!
Fleet Phospho-soda is commercially available in 45 and 90
mL bottles. The pharmacy stocked only 90 mL bottles, but the
physician had expected that the smaller bottles would be used.
There also have been several accidental phosphate enema overdoses
in children. For example, a 5-month-old child was hospitalized
after his mother gave him an entire adult sodium phosphates
enema.
Prior actions taken by FDA to reduce similar adverse events
include requiring the following warning and direction statements
in the official labeling of Fleet Phospho-soda: "Since Fleet
Phospho-soda is available in two sizes, prescribe by volumes.
Do not prescribe by the 'bottle' as serious side effects from
overdosage may occur." Statements also note that exceeding
the recommended dose can be harmful. To reduce the risk of
overdoses, FDA has also limited the size of the OTC oral preparation
to 90 mL or less. Fleet withdrew a 240 mL container from the
market in 1998. Practitioner efforts also are needed to further
reduce the risk of accidents when the drug is prescribed ambiguously.
Consider stocking only 45 mL bottles at your practice site.
If phosphate-containing laxatives are used for bowel preps,
please educate practitioners about the need to always communicate
the volume prescribed. If possible, build maximum dose warnings
in your computer system or use preprinted orders that clearly
communicate the appropriate dose by volume, not "bottles."
ISMP note: If 24-hour pharmacy service is not possible,
medical, pharmacy and nursing staff should work together to
design a stringent formulary of medications accessible outside
the pharmacy, with due consideration given to the safety of
each product and quantity. ISMP would be happy to provide
advice in designing such a system, which would work even in
small rural hospitals. References for this article appear
on the ISMP web site.
References
1. Rohack JJ et al. Hyperphosphatemia and hypocalcemic coma
associated with phosphate enema. South Med J 1985;78:1241-2
2. Filho AJP et al. Severe hyperphosphatemia induced by a
phosphate-containing oral laxative. Ann Pharmacother 1996;30:141-3
3. Pitcher DE et al. Fatal hypocalcemic, hyperphosphatemic,
metabolic acidosis following sequential sodium phosphate-based
enema administration. Gastrointest Endosc 1997;46:266-8
4. Kirschbaum B. The acidosis of exogenous phosphate intoxication.
Arch Int Med 1998;158:405-8
5. Orias M et al. Extreme hyperphosphatemia and acute renal
failure after a phosphorous-containing bowel regimen. Am J
Nephrol 1999;19:60-63
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