Pharm/dosing/half life

[kensaundersva]

I am looking for some clarity on dosing and half life of a med. I understand the therapeutic level, toxic level and the desire to stay in the therapeutic range. Is there a formula that addresses when to expect to dose a patient? For example (and simplicity sake), if a med is 1000 mg (half life 6 hrs) Q4-6H and they are dosed at 0800 on Monday, at what time can we (a nurse) expect to administer the med on Tuesday morning? This was an exact sample from the class. Is it that we are trying to keep the full 1000 mg in the therapeutic range? Do I want to dose just before the half life? Thanks.

[Here.I.Stand, BSN, RN]

Hmmm, it's hard to say without knowing what drug we're talking about. Something that is dosed "q 4-6 hrs" I tend to think as a prn med, and nurses tend to think more in terms of effect/assessment of the pt than the actual pharmacokinetics.

We do consider peak and duration when dosing especially for things like insulin where you can't gauge effectiveness based on subjective assessments. Also for pain meds when we have both an order for IV and PO meds prn, because with narcotics especially you don't want the two meds to peak at the same time; or you might want them to peak at PT time because pain can also peak during PT.

Pharmacists do often time/dose meds based on drug levels, the pt's renal labs, etc. Usually each dose is ordered as a one-time per protocol.

Not sure if that answers your question, but that's how I've seen it work in practice.