Flea and Tick Cat Squeeze-on. Kills Fleas and Ticks and Repels Mosquitoes. Kills Fleas and Ticks and Repels Mosquitoes. Sentry PurrScriptions Plus topical flea and tick prevention for cats kills fleas, ticks and chewing lice for up to 30 days. Sentry PurrScriptions Plus is a vet-quality formula flea treatment that contains the active ingredient fipronil. PurrScriptions for cats also kills deer ticks that may transmit Lyme disease. For best results, apply flea & tick treatment for cats directly to dry skin on your cat's back-between the shoulder blades-on a monthly basis.