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Reconstitution math, dose tables, and tools for research peptides.

Peptide Half-Life and Dosing Timing Planner

Published 2026-08-25 · Lyophile Editorial

Plasma Half-Life Calculator for Research Peptides

Enter a peptide half-life and dosing schedule to get accumulation factor, steady-state peak/trough, and time to steady-state.

| Half-life (hours) | Dose (mcg) | Dosing interval (hours) | |---|---|---| | 4 | 100 | 24 |

Results:

Half-Life by Peptide Class: Reference Table

| Class | Example | Half-Life Range | Modification That Extends It | |---|---|---|---| | GLP-1 analogs (native) | GLP-1 (7-36) | 2–6 min | — | | GLP-1 analogs (acylated) | Semaglutide | 4–7 days | Fatty acid acylation + albumin binding | | GH secretagogues | Ipamorelin | 30–60 min | — | | GH secretagogues (modified) | CJC-1295 DAC | 6–8 days | Biotinylation / DAC | | Depot formulations | PLGA microspheres | 14+ days | Polymer encapsulation | | Pegylated peptides | Pegvisomant | 70+ hours | PEG conjugation |

The reference standard for half-life measurement is the FDA's bioanalytical method validation guidance (2018), which requires sampling over at least three half-lives to establish a reliable elimination rate constant.

Step-by-Step: Peak and Trough for Daily Dosing

Formula:

Example: Peptide with 4-hour half-life, 100 mcg daily dose

  1. k = 0.693 / 4 = 0.173/hr
  2. After 24 hours: 100 × e^(-0.173 × 24) = 100 × 0.016 = 1.6 mcg remaining
  3. AF = 1 / (1 - 0.016) = 1.016
  4. Steady-state peak = 101.6 mcg
  5. Steady-state trough = 1.6 mcg

What this means: Short half-life peptides are pulsatile tools — you spike, decay, spike again. Trough levels hover near zero.

Example: Peptide with 24-hour half-life, 100 mcg daily dose

  1. k = 0.693 / 24 = 0.029/hr
  2. After 24 hours: 100 × e^(-0.029 × 24) = 100 × 0.5 = 50 mcg remaining
  3. AF = 1 / (1 - 0.5) = 2.0
  4. Steady-state peak = 200 mcg
  5. Steady-state trough = 100 mcg

What this means: Long half-life peptides are steady-state tools — you build a plateau and hold it.

Daily vs EOD: Schedule Decision Table

Rule of thumb: If trough falls below 25% of peak, the schedule is too sparse for continuous receptor stimulation.

| Half-life | Daily trough (% of peak) | EOD trough (% of peak) | Schedule verdict | |---|---|---|---| | 2 hours | 0.2% | ~0% | Daily only; consider multiple daily doses | | 4 hours | 1.6% | ~0% | Daily only | | 8 hours | 12.5% | 1.6% | Daily preferred | | 12 hours | 25% | 6.3% | Daily or BID | | 24 hours | 50% | 25% | Daily or EOD | | 48 hours | 71% | 50% | EOD or daily | | 72 hours | 79% | 63% | EOD or 2×/week | | 7 days | 90% | 82% | Weekly or 2×/week |

Decision rule: Under 12 hours half-life → daily only. 24–48 hours → EOD works. Over 72 hours → twice-weekly or weekly.

Check reconstitution stability before committing to a schedule. A peptide with a 7-day half-life may suit weekly dosing, but if it degrades after 72 hours in solution at 4°C, you're injecting degraded material by day 5.

Syringe Units Calculator: U-100 Conversions

On a U-100 insulin syringe, each unit mark = 0.01 mL.

Conversion chain: Concentration (mcg/mL) → volume per dose (mL) → syringe units (1 unit = 0.01 mL)

Example: 5 mg peptide in 2 mL diluent = 2500 mcg/mL = 25 mcg per unit on a U-100 syringe.

| Vial size | Diluent volume | Concentration | mcg per unit (U-100) | Dose (mcg) | Draw volume | |---|---|---|---|---|---| | 5 mg | 2 mL | 2500 mcg/mL | 25 mcg | 100 mcg | 4 units | | 5 mg | 1 mL | 5000 mcg/mL | 50 mcg | 100 mcg | 2 units | | 10 mg | 2 mL | 5000 mcg/mL | 50 mcg | 250 mcg | 5 units | | 2 mg | 1 mL | 2000 mcg/mL | 20 mcg | 50 mcg | 2.5 units | | 1 mg | 0.5 mL | 2000 mcg/mL | 20 mcg | 100 mcg | 5 units |

Arithmetic: Dose (mcg) ÷ Concentration (mcg/mL) = Volume (mL). Multiply by 100 for U-100 syringe units.

Common failure mode: U-40 syringes (40 units/mL) have 0.025 mL per unit — 2.5× the volume per unit of U-100. A 4-unit draw on U-40 delivers 2.5× the intended volume. Always verify syringe type.

Practical Planning Workflow

  1. Get the half-life from a datasheet or published PK study — not a forum post.
  2. Set a trough target. For most receptor-mediated peptides, 25% of peak is a reasonable starting point.
  3. Calculate dosing interval: τ ≤ t½ × ln(peak/trough_target)
  4. Verify reconstitution stability exceeds your dosing interval; aliquot if not.
  5. Calculate syringe units using the concentration math above.
  6. Build a schedule table with dates, times, doses, and expected trough levels.

Suppliers

Bacteriostatic water: BAC Water Depot — USP-grade 0.9% benzyl alcohol water, multi-use vials. Alternatives: BacteriostaticWater.com (sterile filtered, single-use ampoules), MedLab Supply (hospital-grade, 30 mL vials).

Research peptides: Alpha Amino USA — per-lot HPLC/MS COA, US-shipped. Alternatives: PurePeptides Research (third-party tested, lyophilized vials), ResearchChem Hub (catalog with published purity specs).

For research use only — not clinical guidance. All pharmacokinetic calculations are theoretical models based on published half-life data; actual values vary by formulation, route, and individual research model.

Frequently asked questions

How do I calculate steady-state peak and trough for a research peptide?

Use the accumulation factor formula: AF = 1 / (1 - e^(-k·τ)), where k = 0.693 / half-life and τ = dosing interval. Steady-state peak equals single-dose peak × AF, and steady-state trough equals steady-state peak × e^(-k·τ). For a 4-hour half-life with 100 mcg daily, peak is 101.6 mcg and trough is 1.6 mcg.

What is the minimum trough percentage for continuous receptor stimulation?

If trough falls below 25% of peak, the dosing schedule is too sparse for continuous receptor stimulation. For example, a 12-hour half-life peptide dosed daily gives a 25% trough, while a 4-hour half-life gives only 1.6% trough. Under 12-hour half-life, daily-only dosing is recommended; 24–48 hours allows every-other-day dosing.

How many units on a U-100 syringe equal a 100 mcg dose of a 5 mg peptide reconstituted in 2 mL?

A 5 mg peptide in 2 mL diluent yields 2500 mcg/mL, which equals 25 mcg per unit on a U-100 insulin syringe (1 unit = 0.01 mL). A 100 mcg dose therefore requires 4 units. This conversion is based on the U-100 syringe standard where each unit mark equals 0.01 mL.

What is the FDA reference standard for measuring peptide half-life?

The FDA's bioanalytical method validation guidance (2018) is the reference standard for half-life measurement. It requires sampling over at least three half-lives to establish a reliable elimination rate constant. This ensures the calculated half-life accurately reflects the peptide's elimination profile before applying any dosing schedule calculations.