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Q: Methenamine oral suspension is not available. Do you have a formulation?
A: Commercially produced “mandelamine suspension” formerly contained mandelamine, 250 or 500 mg per teaspoonful, along with flavors, propylparaben, saccharin sodium, sesame oil, and thixcin. Thixcin is a rheology-adjusting agent, imparting thixotropy to the preparation. (You might recall the preparation was thicker than good white enamel paint.)
Methenamine is hydrolyzed in acid urine to ammonia and formaldehyde. The latter is bacteriocidal; resistance does not occur. Formulations for extemporaneous preparation of the suspension are not readily available. Some incompatibilities occur. Below is a formulation suggestion.
Methenamine Mandelate Oral Suspension
Methenamine mandelate, qs 1% Methocel gel 50% Syrup (cherry flavor), qs ad 100%
1. Calculate amounts of material needed for the preparation.*
2. Weigh/measure ingredients for preparation accurately.
3. Crush tablets in a ceramic or Wedgewood mortar with the pestle to a fine, uniform consistency. If bulk active pharmaceutical ingredient is used, reduce to fine, uniform consistency using the same method.
4. Wet the powder with a small amount of the Methocel with trituration to make a smooth paste.
5. Continue adding Methocel liquid to the mixture until all combined.
6. Transfer mixture to a conical graduate.
7. Using 4 to 5 aliquots of the syrup and a flexible spatula, wash the remaining material in the mortar/pestle into the conical graduate.
8. Add sufficient syrup to the mixture to bring to desired final volume.
9. Stir well, transfer to amber oval Rx bottle, label, dispense.
(For labels, consider “Shake well” and “Refrigerate.”) Beyond-use date (BUD): 14 days, refrigerated.
*No information is available regarding compatibility of the drug with SyrSpend SF, but it is reasonable to use SyrSpend SF for the vehicle in place of Methocel and syrup. In this case, the mandatory BUD is 14 days, refrigerated.
Mr. Erickson is director of professional affairs at Gallipot Inc.