Razzouk will help guide the development and management of Memphis, Tenn.-based Paradigm Capital Partners. Founded in 1999, Paradigm has funded such companies as dotLogix, Vention and FirstDoor.com.
Razzouk was previously PlanetRx's chief executive before transferring those duties to Michael Beindorff in April.
PlanetRx spokesman Dennis Joyce said Razzouk's departure would not affect the online drug store, noting that Beindorff had already taken over the company's strategic direction and day-to-day operations.
"It really is business as usual," Joyce told CNET News.com late yesterday. "We're going to continue to move forward and continue to drive the business."
Joyce said he did not know the reasons for Razzouk's departure, saying only that he did not think it was associated with the downturn in PlanetRx's fortunes.
The resignation is the latest in a spate of bad news for the South San Francisco, Calif.-based company, which recently missed second-quarter revenue forecasts and laid off 70 employees in June.
The company received a badly needed $50 million cash infusion last month, although analysts say its outlook remains shaky unless it finds a long-term strategic partner.
PlanetRx paid Razzouk $160,000 in salary last year and a $160,000 bonus. The company also paid him $22,000 in relocation expenses.
As of April 28, Razzouk owned 2 million shares of PlanetRx stock, a 3.9 percent stake in the company, according to a document filed with Securities and Exchange Commission.
Included in those shares were options for 300,000 shares in the company. However, the exercise price for those options was $5.50, well above today's close. PlanetRx stock has not traded above $5 since early April.
Assuming a 10 percent annual appreciation in the price of PlanetRx, Razzouk's options would have been worth $2,629,675.
PlanetRx shares closed up 6 cents at 94 cents at the end of regular trading yesterday, well below their 52-week high of $36.50.
PlanetRx is backed by Benchmark Capital and Sequoia Capital, each of which owned a 10.2 percent stake in the company as of April. The company competes against Amazon.com-aligned Drugstore.com and CVS.com, the online arm of giant offline pharmacy CVS.
Reuters contributed to this report.