Rectal Suspension

The active ingredient in the rectal suspension enema, a disposable (60 mL) unit, is mesalamine, also known as 5-aminosalicylic acid. Each rectal suspension enema unit contains 4 g of mesalamine. In addition to mesalamine, the preparation contains the inactive ingredients carbomer 934P, edetate disodium, potassium acetate, potassium met- 

Each rectal suspension enema unit contains 4 g of mesalamine. In addition to mesalamine, the preparation contains the inactive ingredients carbomer 934P, edetate 

Under continuous stirring, add potassium bicarbonate and metformin hydrochloride to purified water and dissolve to get a clear solution. 

Add hydrochloric acid solution as a dilute solution (approximately 1 molar) to the mixture of the previous step. This results in carbon dioxide gas formation (effervescent gas). 

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Henderson, L.M. Johnson, C.E. Berardi, R.R. Stability of mesalamine in rectal suspension diluted with distilled water. Am.J.Hosp.Pharm., 1994, 51, 2955-2957... 

Mesalamine (5-aminosalicylic acid asacol, others) is a salicylate that is used for its local effects in the treatment of inflammatory bowel disease (see Chapter 38). It currently is available as a suppository and rectal suspension enema (rowasa) for treatment of mild-to-moderate proctosigmoiditis Cl rectal suppository (canasa, others) for the treatment of distal ulcerative colitis, proctosigmoiditis, or proctitis. Oral formulations and controlled-release capsule that deliver drug to the lower intestine are efficacious in treatment of inflammatory bowel disease, in particular ulcerative colitis. Sulfasalazine (salicylazosulfapyridine azulfidine) contains mesalamine linked covalently to sulfapyridine (see Chapter 38) it is absorbed poorly after oral administration, but it is cleaved to its active components by bacteria in the colon. The drug is of benefit in the treatment of inflammatory bowel disease, principally because of the local actions of mesalamine. 

The pH of a beclometasone rectal suspension with carbomer as viscosity enhancer has been adjusted to 5-6. That pH is lower than usual for a carbomer hydrogel and is chosen as a compromise for two aspects the viscosity of the carbomer hydrogel and the stability of beclometasone dipropionate. The same pH is chosen for the beclometasone and mesalazine rectal suspension of Table 11.16. As an additional benefit mesalazine is less soluble at pH 5.5 and hence more stable than at a higher pH. To protect the dissolved fraction of mesalazine against oxidation sodium metabisulfite is added. Adequate storage conditions are important to obtain a reasonable shelf life protected from light and in the refrigerator. 

Some suspensions have such a limited stability, that they have to be prepared just before use. An example is an enema with budesonide, where the active substance is incorporated in a dispersible tablet, that has to be added to a solution for rectal suspension. Here again, correct instruction of the user or caregiver is important. 

T, tablet C, capsule C-SR, controlled- or sustained-release I, injection L, liquid solution, elixir, or suspension LC, liquid concentrate, R, rectal suppository. 

C-ll, C-lll, C-IV, controlled substance schedule 2, 3, and 4, respectively cap, capsule chew tab, chewable tablet CINV, chemotherapy-induced nausea and vomiting liquid, oral syrup, concentrate, or suspension OTC, nonprescription Rx, prescription supp, rectal suppository tab, tablet. 

The design of vaginal, rectal, and nasal irritation studies is less formalized, but follows the same basic pattern as the primary dermal irritation test. The rabbit is the preferred species for vaginal and rectal irritation studies, but the monkey and dog have also been used for these (Eckstein et al., 1969). Both the rabbit and rat have commonly seen use for nasal irritation evaluations. Defined quantities (typically 1.0 ml) of test solutions or suspensions are instilled into the orifice in question. For the vagina or rectum inert bungs are usually installed immediately thereafter to continue exposure for a defined period of time (usually the same period of hours as future human exposure). The orifice is then flushed clean, and 24 h after exposure it is examined and evaluated (graded) for irritation using the scale in Table 11.1. 

Rectal Avoids problems of stability in gastrointestinal tract No first-pass metabolism Useful if oral administration is not possible Unpopular Inconvenient Erratic absorption Irritation Suppositories, enemas (solutions, suspensions, emulsions), foams, ointments, creams... 

Suspension The usual dosage of mesalamine suspension enema in 60 mL units is 1 rectal instillation (4 g) once a day, preferably at bedtime, and retained for approximately 8 hours. While the effect may be seen within 3 to 21 days, the usual course of therapy is 3 to 6 weeks depending on symptoms and sigmoidoscopic findings. 

Rectal Mesalamine administered rectally as a suspension enema is poorly absorbed from the colon and is excreted principally in the feces during subsequent bowel movements. At steady state, approximately 10% to 30% of the daily 4 g dose can be recovered in cumulative 24-hour urine collections. 

Drugs are administrated by intravenous routes or ex-travascular routes including oral, sublingual, subcutaneous, intramuscular, rectal (by enema or suppository), and transdermal. Available dosage forms include suspensions, immediate-release capsules or tablets, sustained-release capsules or tablets, and enteric-coated capsules or tablets that resist dissolution in the acidic pfi of the stomach. 

Enema are solution, suspension or emulsion (oil/water type) of medicament intended for rectal administration. 

Oral 25, 50 mg capsules 75 mg sustained-release capsules 25 mg/5 mL suspension Rectal 50 mg suppositories Ketoprofen (generic, Orudis)... 

Oral Asacol 400 mg delayed-release tablets Pentasa 250 mg controlled-release capsules Rectal Rowasa 4 g/60 mL suspension Canasa 500, 1000 mg suppositories Methylprednisolone (Medrol Enpack)... 

Enemas These are available as solutions (aqueous or oily) as well as suspensions for rectal administration of drugs for cleaning, diagnostic, or therapeutic effect. Lotions These are available as solutions and suspensions to be applied topically without friction. They may either contain humectant, so that moisture is retained on the skin after application, or alcohol, which evaporates quickly imparting a cooling sensation to the skin. 

Solutions, suspensions, or retention enemas represent rectal dosage forms with very limited application. 

Included in the FDA Inactive Ingredients Guide (dental preparations inhalations IM, IV, and SC injections nasal and ophthalmic preparations oral capsules, solutions, suspensions, syrups, and tablets rectal, topical, and transdermal preparations). Included in the Canadian List of Acceptable Non-medicinal Ingredients. Included in nonparenteral and parenteral medicines licensed in the UK. 

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