Pfizer’s new Paxlovid tablets are shown here at La Clinica Fruitvale Village in Oakland, Calif. on March 3, 2022. COVID-19 antiviral pills Paxlovid and molnupiravir are becoming increasingly available now that supply has vastly improved since the rollout began in January.

COVID-19 antiviral pills, Paxlovid and molnupiravir, are becoming increasingly available nationwide and in the Bay Area now that supply has improved since the rollout began in January. Here’s a guide to getting them.

Pfizer’s Paxlovid is many doctors’ first choice because it performed better than Merck’s molnupiravir in clinical trials, reducing severe disease and death by 90%, compared with 50% for molnupiravir. You need a positive test result, either by PCR or home antigen test, to obtain a prescription to either drug. The pills must be started within the first five days of symptom onset.

Both pills work by stopping virus replication in the body’s cells.

If you have a regular health care provider, like a primary care physician, it’s generally advised to contact them first after you test positive and ask if you’re a good candidate.

If you don’t have a regular doctor or health insurance, you can check the federal government’s website to find locations for Test to Treat sites — where you can get tested and, if positive and eligible, get a prescription on the spot. The same website also includes locations of pharmacies that have the drugs, so if you get a prescription from your own doctor, they can send it there for you to pick up. Many CVS, Safeway and Walgreens pharmacies now have supplies of Paxlovid or molnupiravir. Testing and the pills are free.

The federal website does not always include up-to-date inventory on how many courses are available at each location. This website, run by an engineer in Washington state — who created the tool to help his wife find Evusheld, the preventive injection for immunocompromised people — is a helpful tool to search drug availability by state and county.

Here’s what Bay Area health departments have announced recently:

• San Francisco: Antiviral pills should be available at all CVS, Safeway and Walgreens locations, though demand may be high and supplies might go quickly. Test to Treat sites include Mission Wellness Pharmacy, four Carbon Health clinics and Northeast Medical Services. More locations are listed here.

• Contra Costa County has set up a phone advice line that residents can call after they test positive, where an advice nurse can connect you with a doctor who can potentially write a prescription for antiviral pills. The number, which is open 24 hours a day, is 1-877-661-6230.

• San Mateo County has opened a drive-through Test to Treat site at the College of San Mateo.

• Marin County has opened Test to Treat sites at Marin Community Clinics in San Rafael, and are opening three more Carbon Health clinics in Novato, San Rafael and Mill Valley.

Paxlovid may interact harmfully with other drugs, so if you take certain common medications, including some statins or immunosuppressants, you may have to pause or adjust them while taking Paxlovid. The prescriber should review your current medications before prescribing Paxlovid. Many doctors use the University of Liverpool drug interaction tool to help determine how to handle drug interactions.

Not everyone is eligible for Paxlovid or molnupiravir. The drugs are authorized for people who are 12 and older, weigh at least 88 pounds, have mild-to-moderate symptoms, and have underlying conditions that put them at higher risk of progressing to severe disease. Those include diabetes; cancer; chronic heart, lung or kidney disease, obesity; older age; being immunocompromised; being a current or former smoker; and many other conditions. The full list of conditions that the U.S Centers for Disease Control considers higher risk are here.

Catherine Ho (she/her) is a San Francisco Chronicle staff writer. Email: cho@sfchronicle.com Twitter: @Cat_Ho

Catherine Ho covers health care at The San Francisco Chronicle. Before joining the paper in 2017, she worked at The Washington Post, the Los Angeles Times and the Daily Journal, writing about business, politics, lobbying and legal affairs. She's a Bay Area native and alum of UC Berkeley and the Daily Californian.