Welcome to another installment of This Week at FDA, your weekly source for updates – big and small – on FDA, drug and medical device regulation, and what we're reading from around the web. This week, FDA published several guidance documents relating to drug-drug interaction studies, nonclinical evaluation of immunotoxicity, interstitial cystitis and its Q-submission program, and the agency announced it will allow another type of in-person, face-to-face meeting with drugmakers.