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9. RELATED PARTY TRANSACTIONS (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Balance at December 31, 2012 $ 0opxa_RelatedPartyConvertibleDebtNet $ 58,105opxa_RelatedPartyConvertibleDebtNet
January 2013 Notes, face value 0us-gaap_ProceedsFromRelatedPartyDebt 100,000us-gaap_ProceedsFromRelatedPartyDebt
Discount on beneficial conversion feature of January 2013 Notes at issuance   (21,820)us-gaap_DebtInstrumentConvertibleBeneficialConversionFeature
Discount on fair value of Series J warrant liability at issuance   (30,149)opxa_DiscountOnFairValueOfSeriesJWarrantLiabilityAtIssuance
Repayment of January 23, 2013 Notes   (100,000)opxa_RepaymentOfJanuaryNotes
Conversion of July 25, 2012 Notes into common stock   (630,000)us-gaap_DebtConversionOriginalDebtAmount1
Unamortized debt discount closed to loss on debt extinguishment   483,678opxa_ExtinguishmentOfDebtNetOfUnamortizedDebtDiscountInExchangeForCommonStock
Amortization of debt discount to interest expense through December 31, 2013   140,186opxa_AmortizationOfDebtDiscountToInterestExpenseRelatedParty
Balance at December 31, 2013   $ 0opxa_RelatedPartyConvertibleDebtNet