Peoples Drug Stores Inc. reported a 100 percent increase in sales and profits in its second fiscal quarter ended April 11, compared with the same period a year ago.

The drug chain's second-quarter profits totaled $1,030,000 (27 cents a share), exceeding the $939,000 profit (25 cents) a year ago. Second-quarter sales were more than $140 million, compared with $127.7 million in 1980.

The company was particularly pleased with the second-quarter sales gains this year, which were achieved without the benefit of the Easter selling season, which fell in the third fiscal quarter; last year it was in the second.

Profits for the first six months of the 1981 fiscal year increased 15 percent to $347.3 million from $297 million for the same period a year ago.

Peoples Drug operates in 14 states and the District of Columbia.

In other reports:

Universal Security Instruments Inc. said its profits for the 1981 fiscal year, ending March 31, totaled $664,047 (42 cents), compared with a loss of $267,358 (17 cents) the previous year. Sales for the Owings Mills, Md., firm nearly doubled, rising from $7.9 million in fiscal 1980 to $13.6 million in the most recent fiscal year. The company produces security systems for homes and automobiles and a line of communications and telephone accessories, including several cordless telephones.

Sales for the fourth fiscal quarter ended March 31 totaled $4.1 million, up 70 percent over the total for the same period a year ago.