CLINICAL NUTRITION W90) 9: 29-30 C Longman Group UK Ltd 1990
0261-5614/90/OLW-OO29/S10.00
Flocculation of Fat Emulsions in Total Parenteral Feeding Mixtures by Heparin
0. L.Johnson, C. Washington, S. S. Davis and K. Schaupp*
Department of Pharmaceutical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK. *Leopold &
Co., Hafnerstrasse 36, A-8055 Graz, Austria (Reprint requests to C.W.)
There has recently been concern expressed about the incompatibility of parenteral fat emulsions and heparin in TPN mictures [ 1, 21. The incompatibility results in the production of emulsion aggregates or flocculates in the presence of heparin. The reports also suggest that the flocculation is the result of interactions between cal- cium ions, the fat emulsion and heparin, since floccula- tion only occurred when both calcium and heparin were present. The flocculates formed in the mixtures within a few minutes, and a cream layer was visible by eye within l-2 min.
We have measured the surface charge and floccula- tion of ‘Intralipid 200,,’ in the presence of calcium and sodium in an attempt to understand the nature of the flocculation. Heparin sodium 5000IU/ml (Multiparin, batch no 86105272) and ‘Intralipid 200,’ (Kabivitrum, batch no. 69643) were obtained from the hospital phar- macy, Queen’s Medical Centre, Nottingham. Calcium chloride and sodium chloride were B.D.H. Analar grade, and were used as received.
Mixtures of ‘Intralipid 200,’ (10ml) and calcium or sodium chloride solution (10 ml) containing heparin (5 I.U. ml--l) were prepared and their flocculation observed visually. The final electrolyte concentrations were: calcium chloride 0-20mM, sodium chloride O- 500 mM. One hour after mixing, the particle size of the aggregates was determined by dilution into distilled water followed by droplet size analysis (2600 diffraction sizer, Malvern Instruments, UK). Surface (zeta) poten- tials at 25°C were measured using a Zetasizer II (Mal- vern Instruments, UK) fitted with a PC3 narrow-bore cell.
Table la shows the zeta potential of ‘Intralipid 200,’
in the presence of calcium and heparin, and the particle size after 1 h. ‘Intralipid 20°0’ had a zeta potential of
- 38.2 mV in the absence of calcium, in agreement with previous observations [3]. This decreases with increas- ing calcium concentration, the point of zero charge occurring between 2 and 5mM. Flocculation was observed visually for all mixtures containing calcium, and this is confirmed by the particle size data.
Table 1 b shows the zeta potential and particle size of
‘Intralipid 20 O(,’ in the presence of sodium and heparin.
The charge was slowly neutralised as sodium was
added, but a point of zero charge was not reached in the concentration range studied (O-500 mM). Flocculation was not detected visually or by particle size analysis in any of the mixtures containing sodium and heparin.
The zeta potential measurements indicated that a low concentration of calcium ions (1 mM) brought about a large reduction in the stabilising zeta potential (from
-38 mV to - 4mV) on the Intralipid droplets. A further increase in the concentration of calcium ions resulted in the reversal of the surface charge. This is in agreement with data reported previously [3]. Notwith- standing the reduction in charge, ‘Intralipid 2Oqi’
would normally be expected to flocculate only slowly (over several hours to days) in the presence of calcium of the concentration range used here.
When the emulsion charge was reduced below - 5 mV (i.e. was made more positive) in the presence of heparin, a negatively charged polyectrolyte, the fioccu- lation rate increased dramatically, leading to visually
Table 1 Effect of electrolytes on zeta potential and heparin- induced flocculation of ‘Intralipid 200,’
(a) Calcium
Zeta potential Ca. cont. d90”, (pm)* (mv)
(mM) (n=4) (n=5) Flocculation
0 1.28f0.02 -38.2+0.1 _
1 5.54iO.08 -4.5+0.1 +
2 8.65 f 0.48 -3.5f0.2 +
5 9.26 f 0.85 +1.6f0.4 +
10 6.60f0.11 +4.6+0.3 +
20 7.50f0.37 +4.1 f0.5 +
(b) Sodium
Zeta potential
Na cont. d90°, (I@* (mv)
(M) (n=4) (n= 5) Flocculation
0 1.20 f 0.02 -35.5f 1.2 _
10 1.21 f0.02 -30.5fl.O _
50 1.21 f0.02 - 17.5 f 5.0 _
100 1.22io.02 -1O.lfl.O -
500 1.26iO.02 -15.111.0 -
*90°, of the droplets had a diameter less than this value.
29
30 FLOCCULATION OF FAT EMULSIONS IN TOTAL PARENTERAL FEEDING MIXTURES BY HBPARIN observable separation within minutes. We propose that
this is due to heparin acting as a bridging flocculant between oil droplets; that is, when the oil droplet charge falls below approximately - 5 mV, heparin can interact with the positively charged sites on the droplet surface caused by calcium binding. Since heparin inter- acts with neutral or positive droplets, its effect is to accelerate flocculation which would occur slowly in the presence of calcium alone. This acceleration effect is considerable since separation is observed in minutes in- stead of hours.
In conclusion, we have demonstrated that heparin is responsible for flocculation of fat emulsions when the electrolyte composition of these materials causes the surface charge on the oil droplets to be near zero or
positive. We suggest that the addition of heparin to such mixtures is strongly contraindicated.
REFERENCES
[l] Rattenbury J M, Taylor C J, Ganapathy S. Lipid deposition in parenteral nutrition lines. Lancet 1988; i:
701
[2] Rauff I’, Von Kreis R, Schmidt E, Pfahl H, Gunther 0.
Incompatibility between fat emulsion and calcium plus heparin in parenteral nutrition of premature babies.
Lancet 1988; i: 700
[3] Davis S S. The stability of fat emulsions for intravenous administration. In: Johnson I D A, Advances in clinical nutrition, Proc. 2nd. Int. Symp., 1982,213-239, MTP Press Ltd, Lancaster