Rectal formulation available

Some opioids are available in rectal formulations, and administration via this route avoids the first-pass effect. If liver metabolism is sufficiently impaired, administration via this route would theoretically cause less of an increase in peak opioid levels. 

Bisacodyl is available in tablet and suppository formulations for the treatment of acute and chronic constipation. It also is used in conjunction with PEG solutions for colonic cleansing prior to colonoscopy. It induces a bowel movement within 6-10 hours when given orally and 30-60 minutes when taken rectally. It has minimal systemic absorption and appears to be safe for acute and long-term use. Phenolphthalein, another agent in this class, was removed from the market owing to concerns about possible cardiac toxicity. 

Acetylsalicylic acid is usually given by oral administration (0.5-8 g/day) for pain and inflammation and for antiplatelet therapy (75-100 mg/day). It is also available in rectal and topical formulations and as a soluble lysine derivative for intravenous or intramuscular application. Acetylsalicylic acid is often used in multi-drug preparations. The main side-effects are gastrointestinal disorders. Use in children is limited due to the risk of Reye s syndrome (Waldmann et al., 1982). The lithium, magnesium, calcium, and aluminium salts of acetylsalicylic acid are used in some special preparations. 

Tramadol is available as drops, capsules, and sustained-release formulations for oral use, suppositories for rectal use, and solution for intramuscular, intravenous, and subcutaneous injection. After oral administration, tramadol is rapidly and almost completely absorbed. Sustained-release tablets release the active ingredient over a period of 12 h, reach peak concentrations after 4.9 h, and have a bioavailability of 87 to 95% compared with capsules. One 100-mg dose given to healthy volunteers resulted in plasma levels of 375 ng/ml at 1.5 h.55 Tramadol is 20% bound to plasma protein and it is rapidly distributed in the body it is mainly metabolized by O- and A-demethylation forming glucuronides and sulfates that are excreted by the kidney. 

Standard tablets are taken twice a day, but with higher doses a three or four times a day regimen may be necessary. Rectal and liquid formulations are available, but there is no i.v. preparation. 

Artemisinin is an antimalarial constituent isolated from Qinghao. It is a sesquiterpene lactone with an endoper-oxide bridge, structurally distinct from other classes of antimalarial agents. Several derivatives of the original compound have proved effective in the treatment of Plasmodium falciparum malaria and are currently available in a variety of formulations artesunate (intravenous, rectal, oral), artelinate (oral), artemisinin (intravenous, rectal, oral), dihydroartemisinin (oral), artemether (intravenous, oral, rectal), and artemotil (intravenous). Artemisinic acid (qinghao acid), the precursor of artemisin, is present in the plant in a concentration up to 10 times that of artemisinin. Several semisjmthetic derivatives have been developed from dihydroartemisinin (1). 

Thahdomide is slowly and variably absorbed after rectal administration (19). The mean availability of several formulations relative to oral administration was less than 40%. 

Sumatriptan is available as fUm-coated tablets, as prefilled syringes for self-administered subcutaneous injection, as intranasal spray, and in a formulation for rectal... 

Morphine is available for oral, rectal, and parenteral administration. Oral formulations include immediate and controlled release tablets, as well as oral solution regular strength and concentrate. Parenterally, it can be administered subcutaneously, intramuscularly, intravenously, or by continuous infusion. It is a drug of abuse and can be nasally insufflated. 

Historically, rectal or intravenous paraldehyde has been used for refractory GCSE. Although effective, it is extremely difficult to administer, is associated with serious adverse effects (e.g., hypotension, tachycardia, pulmonary edema, and polyethylene emboli), and is no longer manufactured in the United States. The only available formulation currently licensed is an enteral product that is difficult to obtain in a timely manner. If a rectal dose is given, it should be diluted 1 1 in vegetable oil and given every 20 minutes as needed via a rubber catheter."... 

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. 

Clearly, the formulation chosen for particular drugs is not random. Furthermore, the degree to which it is critical varies from drug to drug. For example, hydrocortisone is available for at least seven routes of administration, as tablets, several creams and ointments, intraocular solutions, suppositories, intra-rectal foams, injections, and eardrops. Even newer drugs, with fewer indications than hydrocortisone, seek greater market acceptability by providing a variety of alternative formulations (e.g. sumatriptan is available as an injection, intranasal spray, suppository, and tablets). 

Methadone is a potent synthetic opioid analgesic, structurally unrelated to any of the opium-derived alkaloids. It is a highly lipophilic, basic drug (pKa 9.2) available as a hydrochloride powder formulation that can be reconstituted for oral, rectal, or parenteral administration. Methadone was developed in Germany in 1942 as a synthetic substitute for morphine, and has been approved and widely employed for opioid detoxification maintenance as well as acute and chronic pain management. 

Hydromorphone is a potent semi-synthetic opioid analgesic that is available in oral, rectal, and parenteral formulations for control of moderate to severe pain. 

---