I'm just pasting this because I took a look at it. Every patient is different etc. I'd ignore the start dosage and increases etc. Your doc modified it for good reason.
Primidone — The AAN guidelines concluded that primidone, up to 750 mg/day, is effective for the treatment of limb tremor associated with ET [2,13]. This conclusion is supported by the findings of systematic reviews and four well-designed, prospective, randomized controlled clinical trials that evaluated primidone for the treatment of ET [9,14]. In these studies, tremor magnitude was reduced by approximately 50 percent as measured by accelerometry, and clinical rating scales also improved by approximately 50 percent, an effect similar to treatment with propranolol. The mean dose of primidone, available from three of these studies, was approximately 480 mg/day.
There are also some data to suggest that primidone may be effective for vocal tremor. A retrospective series reported improvement in vocal symptoms in 14 of 26 patients (54 percent) [26]. Of note, this study used categorical, subjective vocal outcomes and did not have a control group.
Side effects from primidone are typically more severe at treatment initiation, and they may include sedation, drowsiness, fatigue, depression, nausea, vomiting, ataxia, malaise, dizziness, unsteadiness, confusion, vertigo, and an acute toxic reaction [2]. In an open-label study, transient acute side effects occurred in 8 of 22 patients (36 percent) assigned to primidone [6]. Primidone tolerability was not improved in a well-designed trial by use of a very low initial dose (7.5 mg/day) and slow titration (increasing by 7.5 mg/day for 20 days) [27]. Primidone may be better tolerated in patients with epilepsy in whom hepatic enzymes have been induced by the previous administration of phenobarbital or other anticonvulsant drugs [28]. Nevertheless, stopping primidone because of adverse effects is not necessarily a contraindication to trying it again for ET; significant adverse effects may not recur if rechallenged with the medication, particularly if the rechallenge starting dose is low and the rate of increase is slow.
The mechanism of action of primidone in ET is unknown; it is converted to phenylethylmalonamide and phenobarbital, but neither of these agents alone appears to have a significant effect on tremor [7,29].
Primidone should be started at 25 mg (one-half of the available 50 mg tablet) once daily before sleep and should be titrated up carefully over several weeks as tolerated and according to therapeutic response. One suggested regimen is to increase in 25 mg increments every three to four days to 250 mg at night, according to response and side effects (mainly sedation). Titration can be even slower for older adult patients. The medication should be withdrawn if there is no benefit using 250 mg each night. If there is a partial response at 250 mg nightly, the titration can continue to 500 mg nightly [30,31]. Coadministration of a beta blocker and primidone (see 'Propranolol plus primidone' above) may provide useful additive therapeutic benefits.
I do have a link I can PM you if you are interested which talks about essential tremors and all the relevant studies etc. It links out to a lot of info.
