PN formulations

Question 1

Dextrose solutions are acidic, with a pH ranging from 3.5 to 6.5, and vary in osmolarity depending upon their concentration. Higher dextrose concentrations (range from 2.5% to 70%) are generally reserved for central venous administration bcuz of propensity to cause thrombophlebitis in peripheral veins.

Answer 1

Another CHO energy substrate used less frequently is glycerol, a sugar alcohol which provides 4.3kcal/g. Glycerol, or glycerin, is contained in certain pre-mixed PN formulations marketed for peripheral administration.

Question 2

Specialty formulations for use in renal failure are composed primarily of essential a.a. However, this offers no significant advantage over standard a.a. Therefore indications for this formulation is limited and standard formulation in reduced amt is usually prescribed.

Answer 2

Modified a.a formulations designed for use in hepatic encephalopathy contain increased amt of branched-chain a.a (BCAA) and decreased amt of aromatic a.a (AAA) compared with standard PN a.a formulation. However, indications for these formulations are very limited. NB. altered metabolism in pt w/ hepatic failure can result in high serum ratio of AAA to BCAA. Thus, causing an increased transport to the brain, where they serve as precursors for transmitters that responsible for altered mental status.

Question 3

Glutamine is an a.a known to be conditionally essential during periods od metabolic stress. Crystalline a.a formulations do not contain glutamine. However because of stability and compatibility limitations, there’s no IV form of glutamine commercially available for admixtures in PN solutions.

Answer 3

1. IVFE using 50:50 mix of soybean oil and safflower oil contains 1/2 as much omega-6 fatty acid (linoleic acid) as IVFE using 100% soybean oil.
2. Carnitine is necessary for proper transport and metabolism of LCFA. Therefore IV form of L-carnitine must be added for pt with carnitine deficiency. NB: MCT (medium chain trigglycerides) transport into mitochondria is carnitine independent.

Question 4

When IVFE is given in the piggyback fashion, what is the recommended hang time from the CDC and why?

Answer 4

1. Maximum of 12hrs.
2. Prevent the support of bacterial and fungal growth (if contaminated). NB: Faster infusion rates (over 4-6hrs), this may predisposed susceptible pts to hypertriglyceridemia

Question 5

When PN is administered via a peripheral line (not a PICC), osmolarity should be

Answer 5

Advantages of TNA system are:

1. Less risk of contamination during administration.
2. Inhibited or slower bacterial growth if contamination does occur compared to separate IVFE.
3. Fat clearance may be better when IVFE is administered over >12 hrs.
4. Dextrose and venous access tolerance may be better in some situations.

Question 6

Disadvantages of TNA system are:

1. Admixed IVFE less stable, more prone to separation of lipid components.
2. Formulations are more sensitive to destabilization w/ certain electrolytes concentrations.
3. Formulations are more sensitive to destabilization w/ low conc of dextrose and a.a.
4. Lower pH a.a formulations may destabilized the IVFE-portion of admixture.

Answer 6

Disadvantages cont’d

5. Formulation may be unstable when the final concentration of IVFE is low.
6. Difficult to visualize precipitate or particular material in the opaque admixture.
7. Certain medications are incompatible with the IVFE portion of the admixture.
8. Catheter occlusion more common w/ daily IVFE.
9. Less stable over time than dextrose-a.a PN formulations w/ separate IVFE.

Question 7

Stability: the stability of PN formulations refers to the degradation of nutritional components that changes its original characteristics. It may also refer to the ability of the PN additives including medication, to maintain their chemical integrity and pharmacological activity.

Answer 7

Compatibility: compatibility issues with PN formulations generally involves the formulation of precipitates. These precipitates may be solid, such as crystalline matter, or liquids, such as phase separation of oil and water in a TNA.

Question 8

Since Calcium phosphate is a major compatibility concern with PN formulation, the factors that influence Ca and P compatibility in PN formulation are:

1. A.a concentration and composition
2. Ca and P content
3. Ca salt form
4. Dextrose concentration
5. pH of formulation
6. Temperature of formulation
7. Order of mixing additives

Answer 8

Factors explained

1. Lowering the pH of the PN admixture lowers the likelihood that Ca and P will precipitate. This method is important in compounding pediatric PN formulations where relatively large doses of Ca and P are routinely required to optimize bone formation in neonatal and pediatric populations.
2. Increase concentration of Ca or P, increases the chances that precipitation would occur.

Question 9

Factors explained cont’d:
3. Ca salt form. Ca gluconate and gluceptate are generally less dissociated forms of Ca than the chloride salts. Therefore, there’s less free calcium available to form complexes with P.

Answer 9

Factors explained cont’d
4. A.a products composition (ie, pH or phosphorus content); the lower the pH, the less chance of precipitation. E.g, L-cysteine a semi-essential a.a in premature infants, when added to pediatric PN formulation decreases the pH and thus reduces precipitation.