tirzepatide injection

Tirzepatide is a novel medication approved by the US Food and Drug Administration (FDA) for treating type 2 diabetes mellitus (T2DM). This medication also demonstrates efficacy in weight loss, leading to its off-label use for obesity treatment. Tirzepatide is a dual agonist for the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors. The drug leads to significantly improved glycemic control and weight reduction in patients with T2DM, maximizing benefits similar to GLP-1 medications such as semaglutide.

Tirzepatide is currently utilized as a second-line diabetes medication akin to GLP-1 drugs, such as semaglutide, and is administered once weekly via subcutaneous injection with incremental dosage adjustments. Tirzepatide is not approved for the treatment of type 1 diabetes mellitus (T1DM) and has not undergone studies in patients with pancreatitis. The most commonly reported adverse effects of the drug are gastrointestinal, including nausea, vomiting, and diarrhea. This activity provides an overview of the indications, mechanism of action, adverse effects, contraindications, and important considerations for using tirzepatide. This activity also aids clinicians in gaining proficiency in administering tirzepatide and managing T2DM in patients, thereby enhancing overall outcomes in patient care and safety.

Objectives:

• Identify appropriate candidates for tirzepatide therapy based on their clinical profile and treatment goals.
• Assess patient response to tirzepatide therapy by regularly monitoring glycemic control and weight changes.
• Select optimal combination therapies or alternative treatment options for patients with complex medical histories or treatment-resistant diabetes.
• Collaborate with interdisciplinary healthcare teams to coordinate care transitions and follow-up appointments to facilitate continuity of tirzepatide therapy and monitor long-term outcomes.

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Indications

FDA-Approved Indications

Tirzepatide is a novel medication approved by the US Food and Drug Administration (FDA) in May 2022 for treating type 2 diabetes mellitus (T2DM). Tirzepatide is a synthetic polypeptide and dual agonist for the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors. Therefore, the drug leads to significantly improved glycemic control and weight reduction in patients with T2DM, maximizing benefits similar to GLP-1 medications such as semaglutide.[1]

Tirzepatide is currently utilized as a second-line diabetes medication akin to GLP-1 drugs, such as semaglutide, and is administered once weekly via subcutaneous (SQ) injection with incremental dosage adjustments.[2]

Current clinical data demonstrated that tirzepatide is superior to placebo in improving hemoglobin A1c (HbA1c) levels. The SURPASS-5 clinical trial showed a -2.11% reduction in HbA1c levels at 5 mg per week dosing, compared to -0.86% with a placebo. At the highest dose of 15 mg per week, tirzepatide led to a -2.34% reduction in HbA1c. This was demonstrated over 40 weeks. A weight reduction of 5.4 kg was seen with 5 mg of tirzepatide dosing, and a 10.5 kg reduction was observed with 15 mg dosing. This dose-dependent correlation with weight loss is similar to semaglutide—a common GLP-1 medication utilized for weight loss management.[3]

The results of the SURPASS trials demonstrate that tirzepatide yields clinically significant improvements in glycemic control and weight loss when compared with other GLP-1 receptor agonists (semaglutide and dulaglutide), insulin degludec, and insulin glargine. Consequently, the American Diabetes Association (ADA) categorizes tirzepatide as a highly effective therapy for achieving glycemic control and weight loss.[4][5]

Comparatively, tirzepatide works similarly to GLP-1 medications but with greater efficacy. Given the weight loss properties and lack of liver toxicity,[6] it is likely to have an indirect role in the treatment of nonalcoholic fatty liver disease. However, further research is needed before the use is approved for metabolic dysfunction-associated steatotic liver disease.[7]

Off-Label Uses

Tirzepatide is not approved for the treatment of type 1 diabetes mellitus (T1DM) and has not undergone studies in patients with pancreatitis. Tirzepatide can also demonstrate efficacy in weight loss, leading to its off-label use for obesity treatment.

Mechanism of Action

Tirzepatide is a synthetic polypeptide dual agonist for GLP-1 and GIP. Tirzepatide, “twincretin,” exhibits distinct characteristics from GLP-1 receptor agonists.[8] The medication comprises 39 amino acids and is an analog of the gastric inhibitory polypeptide. Functionally, tirzepatide stimulates insulin release from the pancreas and reduces hyperglycemia. In addition, tirzepatide also increases the levels of adiponectin.

The dual agonism ability decreases hyperglycemia significantly more than GLP-1 agonist agents and reduces the patient’s appetite.[9] Among patients without diabetes, administering tirzepatide 5 to 15 mg once weekly for managing obesity led to remarkable reductions in body weight, ranging from 16.5% to 22.4% over 72 weeks. Post hoc analyses of fasting biomarkers indicated that tirzepatide exhibited more significant improvements in markers of insulin sensitivity and β-cell function.[10]

Pharmacokinetics

Absorption: Tirzepatide has a bioavailability of approximately 80%. The time it takes to reach peak serum levels can range from 8 to 72 hours.

Distribution: The mean steady-state volume of distribution (Vd) of tirzepatide is approximately 10.3 L. Tirzepatide is highly bound to plasma albumin (99%).

Metabolism: When injected, the peptide structure undergoes proteolytic cleavage. In addition, the C20 fatty diacid composition undergoes β-oxidation and amide hydrolysis. Being a modified polypeptide, tirzepatide undergoes metabolism into individual amino acids in various tissues, including the liver.[6]

Elimination: Tirzepatide has a half-life of 5 days, facilitating weekly dosing, and is cleared in urine and feces as metabolites.[11]

Administration

Available Dosage Forms and Strengths

Tirzepatide is administered via the SQ route and is not yet available in an oral form.

Tirzepatide dosages are available in strengths of 2.5 mg/0.5 mL, 5 mg/0.5 mL, 7.5 mg/0.5 mL, 10 mg/0.5 mL, 12.5 mg/0.5 mL, and 15 mg/0.5 mL.

Adult Dosage

Standard dosing is once weekly; prescribed doses can be increased on follow-up visits based on efficacy, as defined by HbA1c levels, body weight, and adverse effects. The patient’s ability to tolerate adverse effects plays a significant role in dosing titration.

The initial dosage of tirzepatide for treatment initiation is 2.5 mg administered SQ once weekly, with the primary goal of initiation rather than glycemic control. After 4 weeks, increase to 5 mg SQ once weekly. For additional glycemic control, escalate the dosage by 2.5 mg after at least 4 weeks on the current dose. The maximum tirzepatide dosage is 15 mg SQ once weekly. If a tirzepatide dose is missed, it should be administered within 4 days (96 hours) if feasible; otherwise, skip the missed dose and return to the regular once-weekly schedule.

Specific Patient Population 

Hepatic impairment: According to the manufacturer’s product information, no dosage adjustment of tirzepatide is suggested for patients with hepatic impairment.

Renal impairment: No dosage adjustment of tirzepatide is suggested for patients with hepatic impairment. However, tirzepatide is associated with gastrointestinal adverse drug reactions, including nausea, vomiting, and diarrhea, leading to dehydration, which may cause acute kidney injury. Use with caution in patients prone to dehydration.

Pregnancy considerations: Available information on tirzepatide use in pregnant women is inadequate to evaluate for a drug-related risk of congenital disabilities and adverse maternal or fetal outcomes. Exposure to the mother and fetus is associated with poorly controlled diabetes in pregnancy. Animal reproduction studies have shown higher occurrences of external, visceral, and skeletal malformations when exposed to tirzepatide. Potential risks exist to the fetus if ingested during pregnancy. Hence, tirzepatide should only be prescribed to pregnant patients of childbearing age when the benefits outweigh the potential risks and after a thorough discussion of the teratogenic effects. Clinicians should also discuss the decreased efficacy of oral contraceptives and offer non-oral methods for at least 4 weeks after beginning tirzepatide.

Breastfeeding considerations: No information exists on tirzepatide in animal or human milk or its effects on the breastfed infant. Clinicians should consider the developmental and health benefits of breastfeeding, the mother’s need for tirzepatide, and the potential adverse impacts on the breastfed infant. Tirzepatide is a large molecule with high molecular weight. Accordingly, the milk concentration is likely less, and absorption is unlikely because it is presumably partially destroyed in the infant’s gastrointestinal tract. Therefore, until more clinical data are available, tirzepatide should be used cautiously during breastfeeding, especially in newborn or preterm infants.[12]

Pediatric patients: Tirzepatide has not been established as safe and effective for pediatric patients.

Older patients: For older patients, in a collective analysis of 7 clinical trials, 30.1% were aged 65 or older, with 4.1% aged 75 or older. While safety and efficacy were comparable to younger counterparts, acknowledging heightened sensitivity in older patients remains crucial.

Adverse Effects

Based on available data, most users do not experience significant adverse drug reactions. The primary adverse effects are gastrointestinal-related, but other side effects have also been infrequently reported. Decreased appetite is frequently reported, though this is a potential contributory etiology of intentional weight loss. The adverse drug reactions according to the System Organ Class (SOC) are listed below.

Gastrointestinal: Decreased appetite is often reported. Nausea and diarrhea may occur in up to 10% of patients, in addition to some infrequent reports of vomiting and acid reflux. Constipation has also been reported in some users.[1]

Cardiovascular: Sinus tachycardia is reported but may be blunted by concurrent medication use.[13]

Renal: Infrequent cases of acute kidney injury have been reported, likely secondary to dehydration from gastrointestinal losses. These may occur in healthy and preexisting chronic renal disease patients. Monitoring for signs of dehydration is likely to prevent renal injury.

Dermatologic: Hypersensitivity reactions have been infrequently reported at the injection site. The prevalence is similar to those reported by patients using GLP-1 agonists. Such events should be discussed with a clinician and may warrant medication discontinuation.