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8. CONVERTIBLE PROMISSORY NOTES (Details) (USD $)
12 Months Ended
Dec. 31, 2013
Balance at beginning of period $ 318,658us-gaap_ConvertibleDebt
January 2013 Notes, face value 550,000opxa_DebtIssuedJanuary2013NotesFaceValue
Discount on beneficial conversion feature of January 2013 Notes at issuance (120,009)opxa_DebtIssuedDiscountOnBeneficialConversionFeatureOfJanuary2013NotesAtIssuance
Discount on fair value of Series J warrant liability at issuance (165,820)opxa_DebtIssuedDiscountOnFairValueOfSeriesJWarrantLiabilityAtIssuance
Repayment of January 23, 2013 Notes (450,000)us-gaap_RepaymentsOfConvertibleDebt
Unamortized discount closed to loss on debt extinguishment 1,949,003opxa_UnamortizedDiscountClosedToLossOnDebtExtinguishment
Amortization of debt discount to interest expense through December 31, 2013 1,473,168opxa_AmortizationOfDebtDiscountToInterestExpense
Balance at December 31, 2013 0us-gaap_ConvertibleDebt
Conversion 1  
Conversion of Notes common stock (100,000)us-gaap_ConversionOfStockAmountIssued1
/ us-gaap_DebtInstrumentAxis
= opxa_Conversion1Member
[1]
Conversion 2  
Conversion of Notes common stock (900,000)us-gaap_ConversionOfStockAmountIssued1
/ us-gaap_DebtInstrumentAxis
= opxa_Conversion2Member
[2]
Conversion 3  
Conversion of Notes common stock $ (2,555,000)us-gaap_ConversionOfStockAmountIssued1
/ us-gaap_DebtInstrumentAxis
= opxa_Conversion3Member
[2]
[1] Conversion of January 23, 2013 Notes into common stock
[2] Conversion of July 25, 2012 Notes into common stock