Vials and pens: what changes in your log

Which GLP-1 medicines come in vials

Vials are the exception rather than the rule. In the current US labels they belong to tirzepatide alone; the other injectable GLP-1 medicines are pens or prefilled syringes, some single-dose and some holding several doses. The table summarises section 3 and section 16 of each label.

Four presentations of tirzepatide

• Single-dose pen: prefilled, one dose of 0.5 mL, used once. Sold in cartons of 4 ^[1].
• Single-dose vial: one dose of 0.5 mL, drawn up with a syringe. Sold as 1 or 4 vials ^[1].
• Multi-dose vial: 2.4 mL, enough for four weekly doses of 0.6 mL each, drawn up with a new syringe each time ^[1].
• Single-patient-use KwikPen: 2.4 mL for four weekly doses, plus extra volume for priming the device ^[1].
• Each comes in six strengths, from 2.5 mg to 15 mg per dose, and the labels describe the solution as clear and colourless to slightly yellow ^[1][2].

Same milligrams, different millilitres

This is the detail that matters most for a log. In single-dose pens and vials, each dose is in 0.5 mL. In multi-dose vials and KwikPens, each dose is in 0.6 mL, and the concentration per mL is lower. For example, the label lists 2.5 mg per 0.5 mL for single-dose products and 2.5 mg per 0.6 mL, or 4.17 mg/mL, for the multi-dose vial ^[1].

So a volume written down for one presentation does not carry over to another. If you switch, the label asks your prescriber to make sure you are trained for the new presentation and to point you to its Instructions for Use ^[1][2]. Your pharmacist can confirm what volume your own prescription corresponds to.

What vials need that pens do not

A pen has its own needle system. A vial does not, so the labels ask people using Zepbound® or Mounjaro® vials to use a syringe suited to the dose, giving a 1 mL syringe that can measure 0.5 mL or 0.6 mL as an example, and to take a fresh syringe and needle for each injection ^[1][2].

The multi-dose formulation also contains extra ingredients. According to section 11, single-dose products contain sodium chloride, sodium phosphate and water, while each multi-dose dose also contains benzyl alcohol, glycerin and phenol ^[1]. If you have had a reaction to any ingredient, that is worth raising before a switch.

Storage rules differ

• Single-dose pens and vials: kept in the fridge; if needed, each can be out of the fridge at up to 30°C (86°F) for a total of 21 days, then discarded ^[1][2].
• Unopened multi-dose vials and KwikPens: kept in the fridge until the expiry date; if kept at room temperature up to 30°C, discarded after 30 days ^[1][2].
• Opened multi-dose vials and KwikPens: kept in the carton in the fridge or at room temperature up to 30°C, and discarded at whichever limit comes first: 30 days in total out of the fridge, 30 days since the first dose was drawn, or the fourth weekly dose. Leftover medicine does not extend this ^[1][2].
• All presentations: not frozen, and kept in the carton away from heat and light ^[1][2].

Compounded vials: what the FDA says

Compounded semaglutide and tirzepatide are not FDA-approved, and they may be dispensed as multi-dose vials for self-injection. The FDA’s page on unapproved GLP-1 drugs, last updated on 1 October 2026, addresses these vials directly ^[9]:

• A multi-dose vial of a sterile medicine is generally used within 28 days of first use because contamination risk rises after that; the FDA advises discarding it then, even if medicine remains and even if the compounder’s instructions allow longer ^[9].
• A new, sterile needle and syringe for every dose, since reuse can contaminate the vial ^[9].
• Reports of adverse events, some requiring hospital care, that may be linked to dosing errors with compounded semaglutide: patients measuring the wrong amount and, in some cases, professionals miscalculating it ^[9].
• Products that arrive warm or without enough cooling should not be used ^[9].

Sharing and self-injection

• The labels say a KwikPen must never be shared, even with a new pen needle, because of the risk of passing on blood-borne infections ^[1][2]. The Ozempic® pen and Wegovy® FlexTouch® labels carry the same warning ^[3][4]. For vials the same logic applies: a new syringe and needle every time.
• The KwikPen is not recommended for self-injection by people with visual impairment, and the Mounjaro® label adds that it is not recommended for self-injection by children ^[1][2]. The Wegovy® label says the same about FlexTouch® and visual impairment ^[3].
• Single-dose pens, vials and syringes have their own training needs; which suits you is your prescriber’s call.

What to write down for each presentation

• Every dose: date, time, injection site and the dose in mg as prescribed.
• The presentation: single-dose pen, single-dose vial, multi-dose vial or KwikPen, so the volume makes sense later.
• For single-dose products kept out of the fridge: the date each came out, to track the 21-day limit ^[1].
• For multi-dose vials and KwikPens: the date of first use and how many of the four doses have been taken ^[1].
• For any vial or pen: the lot number and expiry date from the label, which are needed if a product is recalled or a problem is reported.
• Any change of presentation, with the date you were trained on the new one.

Ozempic®, Wegovy®, Saxenda® and Victoza® are registered trademarks of Novo Nordisk A/S. Mounjaro®, Zepbound® and Trulicity® are registered trademarks of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Novo Nordisk or Eli Lilly and Company.

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