Woke up 3 times; waking up every 2 hours at night; I started this batch the same time I took the Pfizer COVID vaccine; I am wondering if they interacted; Frequent urinations; couldn't make it to the toilet; Couldn't even wipe myself with toilet paper; had pee all over myself; was bent over just trying to get myself back to bed; Extreme pain in lower right back; This is a spontaneous report based on the information received by Pfizer from Pharmaceutical (Mfr. Control No: 2021PRN00103). A contactable 63-year-old female consumer (patient) reported that she received losartan potassium from an unknown date in 2019 at a dose of 25 mg, 2x/day for high blood pressure. On an unspecified date in Mar2021, about last week (relative to 15Mar2021), the patient re-started treatment with Losartan potassium 25 MG at 25 mg, orally, 2x/day for high blood pressure. On an unspecified date in Mar2021, the same time she started this batch of Losartan potassium, the patient received the first dose of BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE; Solution for injection; Lot number: unknown) via an unspecified route of administration on an unknown date in Mar2021 (at 63-year-old), as dose 1, singlefor COVID-19 immunization. The patient's medical history included hypertension from an unknown date and unknown if ongoing, rubber sensitivity from an unknown date and unknown if ongoing A latex allergy, blindness from an unknown date and unknown if ongoing Legally blind, retinitis pigmentosa from an unknown date and unknown if ongoing, blood potassium decreased from an unknown date and unknown if ongoing, vertigo from an unknown date and unknown if ongoing and migraine from an unknown date and unknown if ongoing. The patient's concomitant medications included metformin taken for an unspecified indication, start and stop date were not reported; hydroxyzine embonate (Vistaril) taken for an unspecified indication, start and stop date were not reported; meclizine taken for an unspecified indication, start and stop date were not reported; fenofibrate taken for an unspecified indication, start and stop date were not reported; topiramate taken for an unspecified indication, start and stop date were not reported; vitamin d3 taken for an unspecified indication, start and stop date were not reported; fish oil taken for an unspecified indication, start and stop date were not reported and vitamin b complex (Super B Complex) taken for an unspecified indication, start and stop date were not reported. On an unspecified date in Mar2021, after the 12th dose after resuming use of Losartan potassium and after receiving the COVID vaccine, the patient experienced frequent urination and could not make it to the toilet. She had to get up and run to the toilet every 2 hours. Due to this, she had an accident and went through lots of laundry. After taking the 15th tablet of Losartan potassium, she also experienced extreme pain in her lower right back and had to use naproxen, which she felt she should not have done. She also used tramadol and Tylenol (acetaminophen) for the back pain. She could not even wipe herself with toilet paper and had pee all over herself, and she was "bent over just trying to get back in bed". On 12Mar2021, (relative to 15Mar2021) and after her 13th pill, treatment with Losartan potassium was withdrawn and the frequent urinations and back pain resolved immediately. On 15Mar2021, after not taking the product for 2 days, she re-started treatment with Losartan, and the symptoms (presumed frequent urination and back pain) came right back that same night. The patient wondered if the Losartan potassium and COVID vaccine interacted. The patient called the pharmacist and asked if there was a diuretic in the medication. Her doctor told her to stop the Solco (Losartan potassium). The first night she felt good, she slept, and had no frequent urination. Based on that, the doctor said it was not a UTI (urinary tract infection). She stayed off the product for 2 nights. The day she re-started the product, she woke up 3 times that night and had extreme back pain. She called the nurse and the doctor wrote back to stop the Solco (Losartan potassium). The patient withdrew treatment on an unspecified date in Mar2021, started treatment with Cozaar (Losartan potassium), and had no issues since. As of 24Mar2021, the status of any additional COVID doses was not reported. No additional information was provided. The outcome of all the events was unknown.  No follow-up attempts wer possible; information about lot/batch number could not be obtained.