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The University of Southampton
Centre for Clinical and Experimental PsychopharmacologyGAD Research

Evaluating duloxetine treatments with CO2

Using the 7.5% carbon dioxide challenge as a predictor of responses to anxiety treatments.

What is the aim of the research?

If there was a ‘model’ of GAD, (that is, a way of temporarily producing some of the symptoms of GAD,) it could be used to increase understanding of the condition and of the response to treatment, and possibly also discover new and potentially more effective treatments. We have been developing a model of GAD, using the inhalation of air enriched with 7.5% carbon dioxide (CO2) for 20 minutes. In volunteers this temporarily makes some people feel anxious and tense and reduces feelings of being relaxed and happy. It also temporarily increases blood pressure and heart rate as well as alters attention and emotion processing, which is commonly reported in anxious patients. The effects of CO2 are different from the inhalation of normal room air and we believe this model could be used to explore how treatments work in GAD.

Can I take part in the research?

You should have a diagnosis of GAD and/or depression and not currently be taking any medication for this, the exception being if you have been on a medication for 4 weeks or more which has not improved your symptoms.

You should be generally healthy, have no history of or current asthma, migraine, seizures, renal or hepatic impairment or glaucoma,. Your alcohol intake should not be more than recommended guidelines; 28 units per week (males), or 21 units per week (female). You should not smoke more than 6 cigarettes per day. Females should be using adequate methods of contraception and should not be pregnant or breast feeding, or be considering becoming pregnant.

You should either not currently be taking any medication for GAD/depression OR you should have been on a treatment for GAD/depression for at least 4 weeks that has not managed to improve your symptoms and so you are at the stage where you would usually be advised to stop taking it and to consider switching to an alternative. Participation in the study requires you to be medication free for 2 weeks prior to the research study.

What will I have to do if I am eligible?

1. 10-minute phone call and screening interview: Before entering the research study the researchers will phone to ask some brief questions about your health to check you are fit to take part in the study and to arrange a time for you to attend a 30 minute screening interview. During the screening interview we will ask specific questions about your medical and psychiatric history, to confirm that you are potentially eligible to take part in the study. This will take about 30 minutes, and will be arranged at your convenience. . All information will remain confidential. At this time you will be shown around the lab to make you are familiar with the setting so that if you do decide to continue into the research study you would feel confident about the testing sessions.

2. Attend a baseline 7.5% CO2 inhalation experimental test session:  You will be required to attend a baseline test session of approximately 3 hours. You will remain seated in a comfortable position throughout the testing session. During the testing session, measurements of your blood pressure and heart rate will be periodically taken using six peripheral (i.e. non-invasive) skin-sensors. You will complete some questionnaires to measure how you are feeling. Before you agree to participate you will have the opportunity view example emotional pictures. After each inhalation period you will be asked about any thoughts that occurred during the inhalation, and will be asked to complete a 15 minute thought sampling task in which you will be asked to focus your attention on your breathing and a current worry/concern. Finally you will be asked to complete a short 5 minute computerized facial expression classification task. Please remember that you are free to withdraw from the study at any time.

3. Take duloxetine daily for 4 weeks: Following completion of the baseline test session you will then receive a 4 week course of duloxetine (at a dose licenced for treating GAD and depression). The dose will start at 30 mg for 3 days and will increase to 60mg per day if no side effects are reported.

4. Attend a repeat 7.5% CO2 inhalation experimental test session: This is an exact repeat of the original baseline test session described above.

Will there be any risk to me as a participant?

Side effects of gas inhalations: Carbon dioxide inhalation may cause feelings of anxiety or unpleasantness. Other effects that may occur include racing of heart, dizziness, pins and needles, and breathlessness. Some people also experience a mild headache afterwards.

People experience and describe the effects of inhaling 7.5% CO2 gas in different ways, and there is no way of knowing in advance how you will respond. Some people do not notice it at all, and some experience more marked anxiety. Most people will notice some effects, and if you do not like these effects you can ask to stop. These feelings should be short-lived (typically resolving within a couple of minutes) and would not cause any lasting harm.

Any effects of the gas inhalation are temporary and typically resolve within a minute after inhalation. At the end of the study session you will remain in the testing room until you feel that any effects of the gas have worn off. We will contact you the day after the study day to check that you are healthy and well.

Side effects of duloxetine treatment: Duloxetine is a serotonin-noradrenaline reuptake inhibitor that is licensed in the UK for treating depression and GAD. Duloxetine has been associated with a range of different side effects; the most commonly reported side effects are nausea, dizziness and fatigue although there are occasional reports of dry mouth, constipation and insomnia or drowsiness. These side-effects are usually well tolerated by most individuals and if occur tend to last for only a few days. The research team will speak with you over the phone twice a week to briefly discuss this and any queries you may have.

How do I get more information?

If you are interested in taking part in this study, please complete the contact form and you will be contacted by someone from our research team. If you are not sure whether you are eligible for the study, but still want to take part, have a look at our ‘diagnostic criteria’ page. If you are still not sure, let us know through the contact form 

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