Compounding Hotline: Your Compounding Questions Answered

Q. Would you be able to help us with providing a stable formulation of phenol 7.5% injectable solution for intrathecal instillation? We have a pain specialist who would like to use this for nerve blockade.

A. Phenol USP, or carbolic acid, (mw 94.11; d 1.071) occurs as colorless or faintly pink or yellow deliquescent crystals or more commonly as crystalline masses (fused crystals) because of its deliquescent nature. Fused crystals must be melted (preferably in a fume hood) to weigh the required quantities for compounding. Phenol USP is soluble in water, and miscible with ethanol, ether, and glycerin. It congeals at 41°C and melts at 43°C. It is incompatible with alkaline salts and nonionic surfactants. Precautions should be taken when handling phenol USP because it is corrosive and can cause toxic symptoms when absorbed through the skin or when the vapor is inhaled.

Phenol 7% in water was injected to block pain of trigeminal neuralgia. Phenol injection recently was reported to have successfully blocked refractory pain from metastatic cancer involvement of the abdominal wall (Restrepo-Garces CE, Asenjo JF, Gomez CM, et al. Subcostal transversus abdominus plane phenol injection for abdominal wall cancer pain [published online April 8, 2013]. Pain Pract.

It is important to compound this preparation using strict aseptic technique (see USP <797>).

Suggested ingredients:

• Phenol crystals...................................2.10 g
• Ethanol 95% ......................................1.00 mL
• Sterile water for injection USP .........20.00 mL

Supplies:

• Empty sterile vials: 30 mL
• Syringes: 30 mL, 5 mL, 3 mL
• Sterile 0.22 micron filter (stable in phenol, eg, Acrodisc syringe filter with PTFE membrane)
• Needles: 18 ga, 20 ga
• Glass beaker

Suggested procedure:

• Weigh 2.1 gm phenol, place into the beaker.
• Add 1.0 mL Ethanol 95% to (1) and allow phenol to dissolve.
• Add 29 mL sterile water for injection (SWFI) to (2) with stirring.
• Pass mL Ethanol 95% through the filter to wet it, then flush with 5 mL SWFI.
• Draw phenol mixture in (3) into 30 mL syringe,add filter from (4),and add 20 ga needle.
• Prepare 30 mL empty sterile vial: wipe stopper with alcohol; insert 20 ga needle as air vent.
• Inject phenol solution into vial in (6). Remove needles and seal as desired.
• Label.

Precautions: Phenol is corrosive; steps 1 to 3 could be performed in a fume hood and the process moved into the cleanroom at step 4.

No claims are made as to the uses, safety, efficacy, or bioavailability of this preparation; the formulation is for information purposes only.

Mr. Erikson is director of professional affairs and director of professional services at Gallipot, a Fagron company.