# 59 - Other medicines

# Other medicines

Drug treatment of psychiatric symptoms in the context of other conditions 
CHAPTER 10
Lithium around the time of bariatric surgery
The continued use of lithium throughout the perioperative phases of bariatric surgery 
requires particularly close monitoring. The following guidance is based on available 
case reports and expert opinion.40
■
■Monitor lithium plasma levels preoperatively and perform a scale-­based clinical 
assessment of mood.
■
■Educate the patient preoperatively on the importance of drinking 2.5–3 litres of fluid 
per day (including liquid meal replacement).
■
■Postoperatively assess for toxicity by monitoring lithium plasma levels and renal 
function weekly for 6  weeks (as fluid intake gradually increases), 2-­weekly for 
6  months and monthly thereafter. Resume usual lithium monitoring 1 ­year post-­
bariatric surgery.
■
■If plasma levels increase by >25% or approach 1.2mmol/L consider decreasing the 
lithium dose.
■
■Withhold lithium if signs of toxicity are present and review the dose.
■
■To prevent dehydration, counsel the patient to alert their physician or psychiatrist in 
case of any changes in food or fluid intake or severe vomiting.
■
■Monitor mental state periodically, using formal rating scales if possible.
Other medicines
Table 10.19 summarises the use of other medicines in bariatric surgery.
Table 10.19  Miscellaneous agents in bariatric surgery.
Medication
Summary of evidence and considerations
Antimuscarinics
No data available on absorption after bariatric surgery
Benzodiazepines43–46
Bioavailability probably unaffected, shorter time to peak concentration
Lisdexamfetamine47
A single-­dose case–control study found no significant differences in lisdexamfetamine 
and active metabolite d-­amfetamine following RYGB compared to non-­surgical controls.
Due to potential for inter­individual differences, monitor for adverse effects and loss of 
efficacy.
Methadone48
Substantial increase in bioavailability after sleeve gastrectomy in one case report, possibly 
related increased rate of gastric emptying; consider plasma level and QT monitoring
Methylphenidate49,50
Conflicting limited data; one case report of reduced treatment efficacy after RYGB that 
resolved after switching to transdermal patch suggesting reduced oral bioavailability; 
another reported signs of toxicity
Modafinil
No data available on absorption after bariatric surgery
Orexin antagonists
No data available on absorption after bariatric surgery
Pregabalin17
Increased levels shortly after surgery and decreased values in the long term post-­surgery; 
monitor for adverse effects and loss of efficacy
Solriamfetol
No data available on absorption after bariatric surgery
Zolpidem
In an in vitro model found to have non-­significant lower dissolution after RYGB.32
Food delays the onset of effect; take on an empty stomach.51
RYGB, Roux-­en-­Y gastric bypass.