GlaxoSmithKline has sold half its stake in Aspen Pharmacare Holdings for about 10.5bn rand (£570m, €798m, $846m) following a long investment in the South African firm.

The sale of 28.2 million ordinary shares in Aspen Pharma was conducted through a placing at a discount to the market price as the UK's largest drugmaker reorganises its business.

GSK's stock was trading 0.61% lower at 10.37am in London while Aspen's stock was down 2.96% at 12.21pm in Johannesburg.

Shares in GSK have gained some 11.8% so far this year while Aspen's stock has shed some 3%.

GSK, in a 13 March statement, said it has sold the Aspen shares at 372 rand apiece compared to 12 March's closing price of 406.5 rand. The sale was handled by Citi and UBS.

GSK said that the funds raised from the transaction "will be used for general corporate purposes".

The British firm said: "Following settlement of the sale, GSK will hold 28.2 million ordinary shares in Aspen, representing approximately 6.2% of the issued share capital. GSK has undertaken not to dispose of any further shares in Aspen for a period of 180 days following completion, subject to certain limited exceptions.

"...The net profit on disposal will not be included in core operating profit and core EPS in 2015 and it is expected that GSK will no longer account for Aspen as an associate going forward.

Simon Dingemans, GSK's chief financial officer, said in a separate statement that the disposal affords GSK the flexibility to invest in new opportunities in the wake of a last year's $20bn-plus asset swap deal with Switzerland's Novartis.

Dingemans commented: "As we continue to reshape the Group around our core franchises and drive the benefits from the Novartis transaction, optimizing our financial flexibility to invest behind these priorities is key.

"As a result we have decided now is the right time to realise further value from this successful relationship. We continue to believe in the strategy of Aspen and we remain committed to working together in the future."

In November 2013, GSK sold another similar sized tranche of Aspen stock for 250 rand a share.