By Tiisetso Motsoeneng JOHANNESBURG (Reuters) - Aspen Pharmacare is to sell the rights to market a blood clot drug in the United States to rival Mylan Inc for up to $300 million, it said on Wednesday, a move that would help Africa's top generic drugmaker pay down debt. Mylan will pay an initial $225 million and the rest would be held by a third party until payment is due on meeting certain conditions. Aspen would retain all the rights to sell the thrombosis drug elsewhere in the world. The sale, prompted by Aspen's lack of sales representation in the United States, forms part of wider review of its portfolio to improve returns, Deputy Chief Executive Gus Attridge said. Shares in Aspen were up 4.3 percent at 336.92 rand by 1344 GMT, outpacing an almost 1 percent fall in the blue-chip JSE Top-40 index. Aspen, which also on Wednesday reported a rise in full-year profits which missed growth forecasts, acquired the drugs from GlaxoSmithKline last year as part of an aggressive push into overseas markets. Last year it spent around 20 billion rand on acquisitions including buying a Merck & Co. Inc plant in the Netherlands and a Nestle drugs and infant nutrition plant in Mexico. But the spending has increased its borrowings to around nearly 30 billion rand, putting its net debt to EBITDA ratio at around 3.3 times -- above the company's stated target of less than three times. Attridge said the company's strong cash flow, as well as the sale of underperforming assets and marketing rights, would help push the debt-to-EBITDA multiple back down. Aspen reported an almost one-third rise to 10.16 rand in headline earnings per share in the year to end June, missing a consensus estimate of 10.71 rand in a Reuters poll of 12 analysts, as a weak home market weighed. Headline EPS, the most widely watched profit measure in South Africa, strips out certain one-off items. Sales jumped 51 percent to 31.4 billion rand ($2.87 billion) with sales from its South Africa business flat while acquisitions resulted in revenue more than tripling in Europe and Latin America. Domestic rival Adcock Ingram posted a hefty nine-month loss of 179.5 cents a share last month, compared with a profit of 271.7 cents a year earlier due to restructuring writedowns and as a weaker rand currency pushed up imported raw materials costs that regulated price increases are often not sufficient to fully recover. Adcock makes virtually all of its profits in a heavily regulated home market where a weak economy and high personal debt has stunted consumer spending. (1 US dollar = 10.9535 South African rand)