Medication Overview

Orlistat, sold under the brand names Alli and Xenical, is a medication designed to treat obesity. It works by inhibiting the absorption of fats from the human diet, thereby reducing caloric intake. Orlistat is typically prescribed for individuals with a body mass index (BMI) exceeding 30, or a BMI over 27 with associated risk factors such as hypertension, diabetes, or hyperlipidemia.

Mechanism of Action

Orlistat functions by inhibiting pancreatic and gastric lipases, enzymes that break down triglycerides in the intestine. When the activity of these enzymes is blocked, triglycerides from the diet are not hydrolyzed into absorbable free fatty acids and monoglycerides, thereby allowing about 30% of dietary fat to be excreted undigested. This results in reduced caloric intake from fats.

Dosage and Administration

The standard dosage of Orlistat is 120 mg taken three times a day with each main meal containing fat. It should be taken during or up to one hour after the meal. If a meal is missed or contains no fat, the dose should be skipped. The over-the-counter version, Alli, is generally given at a lower dose of 60 mg. It is advisable to follow a nutritionally balanced, reduced-calorie diet containing approximately 30% of calories from fat.

Pharmacokinetics Details

Orlistat is minimally absorbed into the systemic circulation, which limits its systemic effects. After oral administration, its absorption is very poor, with minimal systemic bioavailability. Orlistat is mostly excreted unchanged in feces, with 97% of the drug eliminated this way within 3-5 days post-ingestion. The minimal amount absorbed is metabolized in the liver to inactive metabolites, excreted primarily in the bile.

Potential Drug Interactions

Orlistat may interfere with the absorption of fat-soluble vitamins such as A, D, E, and K. Therefore, a multivitamin supplement containing these vitamins is recommended to be taken once a day, at least 2 hours before or after taking Orlistat, such as at bedtime. Orlistat can also reduce the absorption of certain medications, such as cyclosporine and levothyroxine, potentially decreasing their efficacy. It can affect the absorption of amiodarone, an antiarrhythmic medication, so monitoring and dose adjustments may be necessary.

Contraindications of Use

Orlistat is contraindicated in patients with chronic malabsorption syndrome or cholestasis. It should not be used by individuals with a history of hypersensitivity to Orlistat or its components. Additionally, it is not recommended for use during pregnancy, as weight loss may harm an unborn baby, or in children under 12 years of age. Breastfeeding mothers should consult with healthcare providers before using Orlistat.

Common Side Effects

Common side effects of Orlistat are primarily gastrointestinal and include oily spotting on undergarments, flatus with discharge, urgent bowel movements, and fatty or oily stool. These symptoms are typically due to the unabsorbed fat that remains in the gastrointestinal tract. Additionally, diarrhea and abdominal pain may occur. These side effects tend to decrease with continued use and adherence to a low-fat diet.

Serious Adverse Effects

While rare, serious adverse effects of Orlistat can include severe liver injury. Symptoms of liver damage include itching, yellowing of the skin or eyes, dark urine, loss of appetite, or light-colored stool. Pancreatitis, kidney stones, and oxalate kidney injury are also potential risks but are less commonly reported. Seek immediate medical attention if any severe side effects are observed.

Monitoring and Follow-Up

Regular monitoring is advised while on Orlistat therapy, including assessments of weight, BMI, and dietary adherence. Periodic laboratory tests may be performed to check for fat-soluble vitamin levels, hepatic function, and renal function. Healthcare providers should monitor patients for any signs of allergic reactions, as well as adherence to the concurrent intake of a multivitamin supplement.

Special Populations Considerations

Special consideration should be given to elderly patients, as they may have increased sensitivity to the drug’s effects. Dosage adjustments may not be necessary in patients with renal impairment, but caution is advised. Orlistat’s safety and efficacy in pediatric patients under 12 years of age have not been established, and it should be used cautiously in adolescents aged 12 to 16 years. Usage during pregnancy is not recommended due to potential risks to fetal development.

Dietary Recommendations

Patients taking Orlistat should adhere to a nutritionally balanced, reduced-calorie diet. The diet should contain approximately 30% of calories from fat, with an even distribution of protein and carbohydrates. The intake of fat, carbohydrates, and proteins should be spread over three main meals. High-fat meals may exacerbate gastrointestinal side effects, therefore, it is important to avoid consuming more than 30% of calories from fat per meal.