<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2006-09-13</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001355015</issuerCik>
        <issuerName>TENBY PHARMA INC</issuerName>
        <issuerTradingSymbol>NONE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001376439</rptOwnerCik>
            <rptOwnerName>Avalon Ventures VI LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>888 PROSPECT STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 320</rptOwnerStreet2>
            <rptOwnerCity>LA JOLLA</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92037</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1020650</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Series A Convertible Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>38274</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Due to certain limitations in the Certificate of Designations for the Series A Convertible Preferred Stock, the shares of Series A Convertible Preferred Stock listed in Table 2 are not currently convertible into the underlying shares of Common Stock listed in Table 2, absent an express waiver of such limitations by the holders of record of such shares of Series A Convertible Preferred Stock, which waiver would in no event be effective earlier than 61 days following the date on which it is given to the issuer.</footnote>
        <footnote id="F2">Not applicable.</footnote>
        <footnote id="F3">Subject to the limitations on conversion referenced in Footnote 2, the shares of Series A Convertible Preferred Stock are convertible into shares of Common Stock at a ratio of 1 to 1.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Avalon Ventures VI, L.P. By:  Avalon Ventures GP, LLC Its:  General Partner /s/ Kevin J. Kinsella</signatureName>
        <signatureDate>2006-09-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
