I take my girls/boy to the vet to get dewormed every six months. Just as a precaution. But I did buy some over the counter dewormer for one of my moms cats, because they are inside/outside and cats can get worms so easily.

The package directions read:
for kittens 8 weeks and older use one capsule. Sprinkle directly on food. Repeat dosage the following day.

For older cats use one capsule for every 2 1/2 pounds of body weight. ( her cat is 10 pounds and it equals 4 capsules). repeat following day. At 30 day intrevals, repeart the 2 day dosage as followed above to prevent reinfestation. And the brand is Hartz advanced care once-a-month wormer. I got it at winn dixie for about 3 dollars. I hope this helps.