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Q: I am a pharmacist in Argentina. I am often requested to prepare a cream containing 15% phenylalanine, apparently used for repigmentation of the skin. The concentration exceeds the solubility limit. Should I prepare a suspension and then mix it with the base cream? Or can I dissolve it with something else?
A: Phenylalanine is only sparingly soluble in water. The product will be a suspension. If you choose to use a vanishing cream (oil in water) or a cold cream (water in oil) as the vehicle, refer to the label to determine the levigating agent to employ. Usually, glycerin or propylene glycol is present in the vehicle and will therefore be compatible if used as the levigating agent. Phenylalanine powder is crystalline. Comminuting (grinding) the powders in a ceramic or Wedgwood mortar before incorporating them into the vehicle, making a paste with the chosen levigating agent, and then using geometric dilution technique to incorporate the paste into the vehicle should produce an elegant compound.
References found used phenylalanine 10% to 15% to treat various skin conditions, including vitiligo. In one reference, the administration of phenylalanine (Phe) combined with ultraviolet A (UVA) exposure was found to be effective in treating vitiligo. Twenty-one patients with vitiligo were divided into 2 groups. In both groups, the patients were treated with oral LPhe in a dose of 100 mg/kg of body weight and with UVA exposure. In one group, a cream containing 10% L-Phe was applied to the vitiliginous areas. The best results occurred in that group. No side effects were found in either group (Antoniou C, et al. Int J Dermatol. 1989;28(8):545-547).
Mr. Erickson is director of professional affairs at Gallipot Inc.
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