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Randomized Controlled Trial Assessing Dermal Bioequivalence of Two Doxepin Hydrochloride Creams in Healthy Volunteers

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What is this study about?

The trial involves healthy volunteers and does not focus on any disease. Two skin creams containing the medication doxepin hydrochloride are being compared. One cream is the test product with a lower amount of the drug, and the other is a reference cream with a higher amount. Both creams are applied to the skin in a topical manner, meaning they are placed on the surface of the skin.

The purpose of the study is to find the optimal dose for a later study and to determine whether the test cream works the same way as the reference cream, a concept known as bioequivalence.

Participants will have each cream applied to a small area of skin. A tiny device using open flow microperfusion will gently collect fluid from just beneath the skin surface to measure how much medication reaches the skin over time. These measurements, called pharmacokinetic data, show the drug’s concentration at different times after application. The study lasts for about a day of monitoring after each application, with a short visit schedule for the volunteers.

1 initial study visit

you arrive at the study center and are given a study identification number.

a brief medical review is performed to confirm that you are a healthy volunteer and that no medical condition is being investigated.

2 randomization and assignment of cream

you are randomly assigned to receive either the test cream (containing 400 mg of doxepin hydrochloride) or the comparator cream (containing 550 mg of doxepin hydrochloride).

the assignment is concealed from you, and the study staff prepares the appropriate cream for the next step.

3 application of the assigned cream

the study staff cleans a small area of skin on your forearm and measures the exact amount of cream required.

the cream is applied once to the designated skin area and gently rubbed in as instructed.

4 insertion of dermal open flow microperfusion probe

a tiny probe used for dermal open flow microperfusion (dofm) is inserted into the skin at the site where the cream was applied.

the probe allows continuous collection of fluid from the skin to measure the drug concentration over time.

5 sampling period

the probe remains in place for 24 hours.

fluid samples are collected at several time points (for example, at 0, 1, 2, 4, 8, 12 and 24 hours) to create a concentration‑time curve.

you may be asked to remain at the center or to return for scheduled sample collections, depending on the study protocol.

6 removal of the probe and final skin check

after the 24‑hour sampling period, the probe is carefully removed.

the skin area is examined for any irritation or other adverse events.

7 follow‑up visit

you attend a final visit where the study staff asks about any side effects you may have experienced.

any remaining cream is removed and the skin is inspected again.

the study is concluded for you after this assessment.

Who Can Join the Study?

  • Be between 18 and 65 years old when you sign the consent form.
  • Be a healthy volunteer, which means you do not have any ongoing medical problems, you do not smoke, and you are not taking medicines that are not allowed for the study.
  • Your body‑mass index (BMI) must be between 18 and 30. BMI is a number that compares your weight to your height to see if you are in a normal range.
  • You can be a man or a woman who is not pregnant and not breastfeeding. Women who could become pregnant must use reliable birth‑control methods for at least four weeks before the second study visit.
  • You must be able to sign a written informed consent and agree to follow the study’s rules and restrictions.

Who Cannot Join the Study?

  • Allergy (hypersensitivity) to the study medicine or any similar product, including doxepin hydrochloride, will keep you from joining.
  • If a breath test shows alcohol in your system, you cannot take part.
  • A positive urine test for illegal drugs will exclude you.
  • If routine lab tests (blood or urine) show abnormal results that the doctor thinks are important, you cannot participate.
  • A blood test (serology) that shows you have hepatitis B or hepatitis C will exclude you; a confirmatory test is used to decide.
  • A positive HIV test (blood test for human immunodeficiency virus) will exclude you; a confirmatory test is used to decide.
  • Any abnormal findings during the physical exam or vital signs (such as blood pressure, heart rate, temperature) that the doctor considers significant will keep you out.
  • If the measurement of water loss through the skin (TEWL) on the thigh is higher than 20 g/m²·h, you cannot join.
  • People who smoke, vape, use e‑cigarettes, or any nicotine product must have not smoked for at least 6 months and must stay smoke‑free during the study; otherwise they are excluded.
  • A history of drug or alcohol abuse within the past year will exclude you.
  • If the investigator believes any reason would make it unsafe for you to join, you will be excluded.
  • Having a heart, lung, liver, kidney, digestive, hormone, blood, nerve, or inherited blood disorder that could change how the drug is absorbed, processed, or removed, or that could pose a risk, will exclude you.
  • Tattoos, broken skin, damaged skin, or scarring at the areas where the study medicine will be applied will keep you out.
  • If you are prone to thick raised scars (keloid or hypertrophic scars) or have a known wound‑healing problem, you cannot participate.
  • A history of severe allergies to medicines, foods, plaster, or a severe anaphylactic (life‑threatening) reaction will exclude you.
  • If you are not willing to avoid strong sun, steam baths, sauna, swimming, or heavy exercise for 14 days after the treatment, you cannot join.
  • Very heavy hair on the planned application sites that could affect the test will exclude you.
  • If you are not willing to stop shaving or using skin‑care products on the application sites for at least 5 days before the treatment, you cannot participate.
  • If you are not willing to avoid alcohol on the day you leave the clinic after the treatment and not drive that day, you will be excluded.
  • Having a fear of needles (needle phobia) will keep you out.
  • Having a higher risk of blood clots (thrombosis), such as a personal or close family history of deep vein thrombosis, will exclude you.
  • Any current serious illness, especially a psychiatric (mental health) disorder, that the investigator thinks could affect your safety or the study results will exclude you.
  • Recent or repeated problems with automatic body functions (autonomic dysfunction) like fainting or fast heartbeats, as judged by the doctor, will keep you out.
  • Having known clotting disorders (thrombophilia), active cancer, large varicose veins with inflammation (phlebitis), glaucoma, enlarged prostate causing urinary problems, recent major surgery or trauma will exclude you.
  • If you are not willing to stop taking any medicines (including vitamins and herbal supplements) except certain hormonal contraceptives or hormone therapy for at least 7 days (or five drug half‑lives) before dosing and until the study ends, you cannot join.
  • Use of monoamine oxidase (MAO) inhibitors—specific medicines such as isocarboxazid, phenelzine, or tranylcypromine—within 2 weeks before screening will exclude you.
  • Being enrolled in another clinical trial or having taken part in one where a new drug or device was used within 30 days before signing consent will keep you out.
  • If an electrocardiogram (12‑lead ECG) shows important heart abnormalities, you cannot participate.

Where you can join this trial?

Verified and Recommended Sites

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Verified Sites

Site Name City Country Status
Medical University Of Graz Graz Austria

Other Sites

No sites found in this category

Want to learn more about this study or check if you can participate? Contact us.

Trial status

Country Status Recruitment Start
Austria Austria
Not yet recruiting
20.07.2026

Trial locations

Doxepin hydrochloride (reference cream) is a topical cream that contains the medication doxepin hydrochloride. In this trial it is used as the standard or “comparator” product against which the new cream is measured. Participants apply the cream to their skin, and researchers collect tiny samples of fluid from the skin using a technique called dermal open flow microperfusion (dOFM). This helps them see how much of the drug gets into the skin from the reference cream, providing a baseline for comparison.

Doxepin hydrochloride (test cream) is another topical cream that also contains doxepin hydrochloride, but it is the new formulation being evaluated. It is applied in the same way as the reference cream, and the same dOFM method is used to collect skin fluid samples. By comparing the amount of drug that reaches the skin from the test cream with the amount from the reference cream, the study can determine whether the new cream works in a similar way and is bio‑equivalent.

Trial ID:
2026-526078-18-00
Protocol code:
FDA03A2
Trial Phase:
Human Pharmacology (Phase I) – Bioequivalence Study

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