^^^Alex, the indicated/recommended dose for butalbital is 50-100mg, however, it is probably a good idea to stick w/ 50mg on the first go if combining w/ an opioid--which is of course also a CNS depressant. However, since the OP indicated he/she is intending to use a smaller amount of hydrocodone than usual I figured 50mg-100mg would be adequate, although I suggest still starting with one pill (or 50 mg of butalbital). While I do NOT recommend this to anyone, I have taken close to triple my normal dose of butalbital (my normal dose is typically 250-300mg) along with buprenorphine with very little adversity (see below).
However, with that said; I have only used butalbital in combination with a mixed agonist/antagonist/high affinity opioid (buprenorphine) & not a full agonist like hydrocodone--conversely however, bupe is known to be sensitive to overdose & even death when mixing with benzodiazepines, and even though barbiturates have a different GABAergic mode of action one would assume the same synergy would apply barbs & opiates. My recommendation to the OPer is to start w/ 50mg-100mg with no more than 10mg of hydrocodone at a time (since it seems the OPer is pretty much opioid naive). Remember! if you aren't feeling much, you can always stack additional barbs if you don't feel any potentiation around 15-25 minutes after dosing seeing as though butalbital has a relatively quick onset, even though it is an intermediate/longer acting barb (if you wait more than 30 minutes, you might as well wait at least an additional 4 hours before redosing butalbital, at least in my experience staking beyond 30 minutes becomes cumulatively less effective). Anyway, i'd recommend dosing both at the same time, and/or taking the butalbital ~10 minutes prior to dosing your hydrocodone. Then redosing butalbital around ~15 minutes after taking hydrocodone if needed; and do not use anymore than 100 mg of butalbital MAXIMUM per dose (or 300 mg per 4 hours, and even THAT is a higher end dose) if you end up having to stack. But of course this is assuming you still have the same tolerance to barbiturates & opioids.
And again Alex:
I have read this over & over how barbiturate toxicity does not increase w/ physical and psychological tolerance to recreational effects. But I haven't noticed this whatsoever. I have taken 1300mg at once, & experienced no extreme adverse side effects other than ataxia & slurred speech. I've never noticed any sort of amnesia, or blackouts, or EXTREME ataxia like I have experienced w/ high doses of benzodiazepines or even carisoprodol (Soma, name brand). Although, with short acting barbs like secobarbital I'm sure one would experience these adverse effects. Either way, i'm sure our posts are irrelevant since this thread was posted some ~2 years ago & the OPer has probably long but ran out of his hydro & butalbital and/or is using higher doses anyway.